JP3561105B2 - P-type semiconductor film and semiconductor device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a p-type semiconductor film used for, for example, a semiconductor laser or a light-emitting diode, and a semiconductor device having a p-type layer.
[0002]
[Prior art]
At present, nitride compound semiconductors such as GaN have attracted attention as a material for blue light emitting diodes and semiconductor lasers, and blue light emitting diodes have been realized in some parts, and semiconductor lasers are about to be realized. Such an element has a so-called double hetero structure in which a light emitting layer is sandwiched between a pair of materials having different conductivity types such as p-type and n-type. Note that the energy gap of the p-type and n-type materials is larger than that of the light emitting layer. However, when the p-type nitride compound semiconductor layer is formed, as described in JP-A-2-257679 and JP-A-5-183189, metalorganic vapor phase epitaxy ( After the film is formed by the MOCVD method or the like, a process such as electron beam irradiation or thermal annealing must be performed. Such a process generates defects such as nitrogen vacancies that are unique to the nitride compound semiconductor. For this reason, although a p-type nitride compound semiconductor layer was realized, the p-type carrier concentration could not be increased yet, and the element resistance including the contact resistance of the electrodes could not be reduced.
[0003]
[Problems to be solved by the invention]
As described above, the conventional manufacturing process of the p-type compound semiconductor layer includes a process that causes a phenomenon contrary to the purpose, and it is difficult to form a p-type nitride compound semiconductor layer having a high carrier concentration. could not.
Therefore, an object of the present invention is to provide a p-type semiconductor film having a high carrier concentration and a semiconductor element having the same.
[0004]
[Means for Solving the Problems]
According to the present invention, an acceptor impurity for imparting p-type conductivity to a semiconductor film is provided.Selected from the group consisting of, titanium, iron, and nickelAnd acceptor impurities to compensate for residual donors.Consisting of a compound semiconductor represented by the following chemical formulaA p-type semiconductor film is provided.
B _x In _y Al _z Ga _(1-xyz) N (0 ≦ x, y, z ≦ 1)
[0005]
Further, according to the present invention, an acceptor impurity for imparting p-type conductivity is provided.Selected from the group consisting of, titanium, iron and nickelAnd acceptor impurities to compensate for residual donors.And a p-type semiconductor layer comprising a compound semiconductor represented by the following chemical formula:A semiconductor device is provided.
B _x In _y Al _z Ga _(1-xyz) N (0 ≦ x, y, z ≦ 1)
Furthermore, according to the present invention, a substrate, an n-type cladding layer, a p-type cladding layer, and an active layer provided between the n-type cladding layer and the p-type cladding layer, wherein the n-type cladding layer, The p-type cladding layer and the active layer are made of a compound semiconductor represented by the following chemical formula, and the p-type cladding layer is made of an acceptor impurity for imparting p-type conductivity and titanium, iron and nickel. There is provided a semiconductor laser containing an acceptor impurity for compensating for a residual donor selected from the group.
B _x In _y Al _z Ga _(1-xyz) N (0 ≦ x, y, z ≦ 1)
According to still another aspect of the present invention, the n-type cladding layer includes a substrate, an n-type cladding layer, a p-type cladding layer, and a light-emitting layer provided between the n-type cladding layer and the p-type cladding layer. , The p-type cladding layer, and the light-emitting layer are made of a compound semiconductor represented by the following chemical formula, and the p-type cladding layer is formed of an acceptor impurity for imparting p-type conductivity and titanium, iron, and nickel. There is provided a light emitting diode comprising an acceptor impurity for compensating for a residual donor selected from the group consisting of:
B _x In _y Al _z Ga _(1-xyz) N (0 ≦ x, y, z ≦ 1)
[0006]
The present inventors have earnestly studied the reason why a p-type nitride compound semiconductor having a high carrier concentration could not be manufactured, and have obtained the following knowledge. That is, the nitride compound semiconductor should originally exhibit p-type conduction only by adding Mg (magnesium) having an acceptor property as a dopant. However, first, since the nitride semiconductor easily generates nitrogen vacancies and Ga in interstitial positions, the residual donor concentration in the p-type semiconductor layer is high. Second, the acceptor level of Mg in the nitride semiconductor is significantly deeper than the generally accepted acceptor level in the semiconductor. Due to these two phenomena, it was not possible to form a nitride compound semiconductor having a high carrier concentration only by adding Mg.
[0007]
Therefore, by adding an impurity which is not usually involved in p-type conversion or an acceptor impurity together with Mg, a donor due to the generated nitrogen vacancies can be compensated. That is, it is possible to remove a factor that hinders the addition of Mg to provide p-type crystal, thereby realizing a p-type crystal with a high carrier concentration using Mg.
[0008]
As an impurity for compensating for a residual impurity and realizing a crystal with a high carrier concentration or an acceptor impurity, an impurity deep in energy is preferably used. By using such impurities, the capture cross section can be increased, and a large amount of the remaining donor can be compensated with a small amount of addition.
[0009]
When Si is further added to the p-type layer in addition to the acceptor impurity for compensating the residual donor, the diffusion of Mg can be suppressed and the ease of etching can be increased. Further, Si also has an effect of suppressing the inhibition of acceptor formation due to the binding of Mg to hydrogen or oxygen.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Example 1)
FIG. 1 shows a cross-sectional structure of a semiconductor laser 100 according to the present embodiment. The semiconductor laser 100 has a p-type SiC substrate 101, and a GaN buffer layer 102 having a thickness of 10 nm is formed on the SiC substrate 101 to reduce lattice mismatch. Further, on the GaN buffer layer 102, a p-type GaN layer 103 (2 μm), a p-type AlGaN layer 104 (500 nm), an InGaN active layer 105 (100 nm), an n-type AlGaN layer 106 (500 nm), and an n-type GaN The layers 107 (300 nm) are sequentially stacked. Each layer is given p-type or n-type conductivity by intentionally adding impurities. Specifically, the impurities added to the p-type GaN 103 layer and the p-type AlGaN layer 104 are Mg and C (carbon), and the impurity added to the n-type AlGaN layer 106 and the n-type GaN layer 107 is Si. Among such impurities, C in the p-type layers 103 and 104 forms a deep acceptor level, thereby compensating for a residual donor and helping to increase the carrier concentration by Mg forming a relatively shallow acceptor level. .
[0011]
On the n-type GaN layer 107, SiO₂  A Ti / Au laminated electrode 111 striped with a width of 10 μm by the film 110 is formed, and a similar Ti / Au laminated electrode 111 is formed on the back surface of the p-type SiC substrate 101 with the same thickness. I have.
[0012]
Hereinafter, a method for manufacturing the semiconductor laser 100 will be described in order.
The semiconductor laser 100 was manufactured by using a vapor phase growth method using a well-known metal organic chemical vapor deposition method (MOCVD method). The raw materials used were trimethylgallium (TMG), trimethylaluminum (TMA), trimethylindium (TMI) and biscyclopentadienyl magnesium (Cp) as organic metal raw materials.₂  Mg), and ammonia, silane and propane as gas raw materials. Hydrogen and nitrogen were used as carrier gases.
[0013]
First, after treating the SiC substrate 101 by organic cleaning and acid cleaning, the SiC substrate was placed in a reaction chamber of a MOCVD apparatus and mounted on a susceptor heated by high frequency. Next, a natural oxide film formed on the surface of the SiC substrate 101 was removed by performing gas phase etching at 1200 ° C. for about 10 minutes while flowing hydrogen at a flow rate of 20 liters / minute at normal pressure.
[0014]
In forming the semiconductor layer on the substrate, first, the temperature of the SiC substrate 101 was lowered to 800 ° C., and hydrogen, nitrogen, ammonia, and TMG were flowed for about 5 minutes to form the GaN buffer layer 102. The flow rates of hydrogen, nitrogen and ammonia were all 5 liter / min, and the flow rate of TMG was 30 cc / min.
[0015]
Thereafter, the temperature of the SiC substrate 101 is raised and maintained at 1100 ° C., and hydrogen and nitrogen are used as carrier gases, ammonia and propane are used as gas materials, and TMG and Cp are used as organometallic materials.₂  The p-type GaN layer 103 was formed by flowing Mg for about 30 minutes. The flow rate of the carrier gas was set to 5 liter / min, and the flow rate of the organic metal raw material was set to 30 cc / min. The flow rates of ammonia and propane were 5 liter / min and 10 cc / min, respectively. Subsequently, TMA at a flow rate of 100 cc / min was added to these gases and the p-type AlGaN layer 104 was formed by flowing the gases for about 8 minutes.
[0016]
In forming the InGaN active layer 105, the temperature of the SiC substrate 101 was lowered and maintained at 800 ° C., and nitrogen (10 liter / min), ammonia (5 liter / min), TMG (30 cc / min), and TMI (200 cc / min) ) Was run for about 10 minutes.
[0017]
Thereafter, the temperature of the SiC substrate 101 is again raised and maintained at 1100 ° C., and hydrogen and nitrogen as carrier gases, TMG and TMA as organometallic raw materials, and ammonia and silane as gas raw materials are flowed for about 8 minutes to form n-type AlGaN. The layer 106 was formed. The flow rate of the carrier gas was 5 liters / minute, and the flow rates of TMG and TMA were 30 cc / minute and 100 cc / minute, respectively. The flow rates of ammonia and silane were 5 liter / min and 1 cc / min, respectively. Subsequently, the supply of TMA was stopped, and the remaining gas was allowed to flow for about 1 hour to form the n-type GaN layer 107. Thereafter, the wafer was cooled to room temperature while flowing only nitrogen at a flow rate of 10 L / min, and the growth wafer was taken out of the reaction chamber.
[0018]
Next, SiO 2 is formed on the n-type GaN layer 107 by using a well-known thermal CVD method or the like.₂  After forming the film 110 to a thickness of 0.5 μm,₂  A hole having a width of 10 μm was formed by applying a photoetching process or the like to the film. Further, a Ti film having a thickness of 50 nm and an Au film having a thickness of 3 μm were sequentially formed thereon by a well-known vacuum deposition method or the like, thereby forming a Ti / Au laminated electrode 111. A Ti / Au laminated electrode having the same thickness was formed on the back surface of the SiC substrate 101.
[0019]
In such an element, C is approximately 1 × 10 in the p-type GaN layer 103 and the p-type AlGaN layer 104.¹⁷cm^-3It is contained at a concentration of. This is because the carrier concentration approximately matches the undoped GaN film. The Mg concentration is about 5 × 10 5 in the p-type GaN layer 103.¹⁹cm^-3In the p-type AlGaN layer 104, about 3 × 10¹⁹cm^-3It is.
[0020]
In the example described above, the carbon concentration in the p-type layer is set to the above value, but the carbon concentration is not limited to this. Since the residual donor concentration varies depending on the crystal growth conditions, the concentration for compensating for the residual donor concentration can be appropriately determined according to the growth conditions. However, in order to compensate for the residual donor concentration and not to be a hindrance to the p-type crystal, the carbon concentration is 1 × 10¹⁶cm^-3More than 1 × 10¹⁹cm^-3Must be less than or equal to 1 × 10¹⁸cm^-3It is desirable that:
[0021]
The wafer thus fabricated was cleaved to a size of 350 μm × 500 μm to obtain a laser diode chip. This chip oscillated continuously at room temperature at 420 nm, depending on the In composition in the active layer, and oscillated at 420 nm when the average composition ratio of In was about 8%.
(Example 2)
FIG. 2 shows a sectional structure of another semiconductor laser 200 of the present invention. The semiconductor laser 200 has a spinel substrate 201, on which an AlN buffer layer 202 is formed with a thickness of 50 nm. Further, on the buffer layer 202, an n-type GaN layer 203 (4 μm), an n-type AlGaN layer 204 (500 nm), an InGaN active layer 205 (100 nm), a p-type AlGaN layer 206 (500 nm), and a p-type GaN layer 207 (300 nm) are sequentially formed. Each layer is given p-type or n-type conductivity by intentionally adding impurities. Specifically, the impurities added to p-type AlGaN layer 206 and p-type GaN layer 207 are Mg and Cd (cadmium), and the impurities added to n-type GaN layer 203 and n-type AlGaN layer 204 are Si (silicon). It is. Among such impurities, Cd in the p-type layers 206 and 207 functions to compensate for the residual donor.
[0022]
On the p-type GaN layer 207, SiO₂  A Ti / Au laminated electrode 210 striped with a width of 10 μm by the film 211 is formed. The Ti / Au laminated electrode 210 has a laminated structure of a Ti film having a thickness of 50 nm and an Au film having a thickness of 3 μm. Are also formed on the n-type GaN layer 203 exposing.
[0023]
The semiconductor laser 200 was manufactured by the same MOCVD method as in the above (Example 1), and dimethylcadmium (DMCd) was used as a raw material of Cd added to the p-type layer. If the Cd concentration in the p-type layer is too high, carriers are trapped in the p-type region, light emission occurs in this region, and the injection into the active layer may not be performed sufficiently. Therefore, the Cd concentration is 1 × 10¹⁸cm^-3It is desirable that: However, if the concentration is too low, the effect of adding Cd does not appear, so that 1 × 10^Fifteencm^-3The above concentration is required. Preferably 1 × 10¹⁶cm^-3More than 1 × 10¹⁷cm^-3When it was below, the carrier concentration of the p-type crystal had a maximum region.
[0024]
The spinel used as a substrate in this embodiment has a lower cleavage current and conductivity than SiC, and thus has a threshold current about 20% higher than that in the case of the first embodiment. However, since spinel does not have a penetrating defect peculiar to the SiC substrate, it was possible to increase the output by about 30%.
(Example 3)
FIG. 3 shows a cross-sectional structure of the light emitting diode 300 according to the present embodiment. The light emitting diode 300 has a sapphire substrate 301, and on the sapphire substrate 301, a GaN buffer layer 302 (20 nm), an n-type GaN layer 303 (4 μm), an InGaN light-emitting layer 304 (100 nm), and a p-type AlGaN layer 305 (300 nm) and a p-type GaN layer 306 (500 nm) are sequentially laminated. Each layer is given p-type or n-type conductivity by intentionally adding an impurity. Specifically, the impurities added to the p-type AlGaN layer 305 and the p-type GaN layer 306 are Mg and Fe (iron), and the impurity added to the n-type GaN layer 303 is Si. Of these, Fe in the p-type layers 305 and 306 functions to compensate for residual donors. Since the level of Fe is very deep, it is sufficient that a small amount of Fe is contained in the p-type layer.^Thirteencm^-3More than 1 × 10¹⁶cm^-3It is desirable that:
[0025]
On the p-type GaN layer 306, a Ni / Au stacked electrode 310 having a stacked structure of a Ni film having a thickness of 20 nm and an Au film having a thickness of 1 μm is formed. On the n-type GaN layer 303 whose upper surface has been removed by etching to expose the surface, a Ti / Au laminated structure 311 composed of a laminated structure of a 50 nm thick Ti film and a 2 μm Au film is formed. Have been.
[0026]
The stacked structure of the nitride compound semiconductor in the light emitting diode of this example was manufactured by the same MOCVD method as in the above (Example 1). The growth thickness of each layer was controlled by the growth time, and then measured by a scanning electron microscope (SEM). Note that Fe, which is an impurity for compensating for the residual donor, was introduced into the crystal by ion implantation after the p-type AlGaN layer 305 and the p-type GaN layer 306 were epitaxially grown. In addition, Zn (zinc) and Si were introduced into the InGaN light emitting layer 304 as luminescent centers, and dimethyl zinc (DMZn) and silane were used as raw materials.
[0027]
After forming the stacked structure in this manner, a part of the p-type GaN layer 306, the p-type AlGaN layer 305, and a part of the InGaN light emitting layer 304 are removed by dry etching using chlorine gas, and the n-type GaN layer is removed. 303 was exposed, and an n-type electrode 311 was formed on the n-type GaN layer 303. This wafer was scribed to a size of 350 μm square, placed on a stem, bonded and molded to obtain a light emitting diode lamp. This lamp emitted light at a wavelength of 450 nm and showed an output of about 3 mW at a forward current of 20 mA.
[0028]
In this embodiment, Fe was added to the p-type layer as an impurity for compensating for the residual donor. However, the same effect can be obtained by adding a small amount of Zn to the p-type layers 305 and 306 as an emission center. Can be However, since the energy level of Zn is shallower than that of iron, the concentration of Zn is 1 × 10¹⁴cm^-3More than 1 × 10¹⁷cm^-3It is desirable to make the following.
(Example 4)
FIG. 4 shows a cross-sectional structure of the light emitting diode 400 according to the present embodiment. The light emitting diode 400 has an n-type SiC substrate 401, on which an n-type GaN layer 402 (1 μm), an InGaN light-emitting layer 403 (100 nm), a p-type AlGaN layer 404 (300 nm), And a p-type GaN layer 405 (500 nm) are sequentially formed. Each layer is given p-type or n-type conductivity by intentionally adding an impurity. Specifically, the impurities added to p-type AlGaN layer 404 and p-type GaN layer 405 are Mg and Ti (titanium), and the impurity added to n-type GaN layer 402 is Si. Of these, Ti in the p-type layers 404 and 405 functions to compensate for the residual donor. Note that this Ti was introduced into the p-type layers 404 and 405 by vapor deposition and thermal diffusion after film growth.
[0029]
On the p-type GaN layer 405, a Ti / Au laminated electrode 410 having a laminated structure of a 50 nm thick Ti film and a 2 μm Au film is formed. A similar Ti / Au laminated electrode 410 is also formed on the back surface of the n-type SiC substrate 401.
[0030]
The light emitting diode 400 was manufactured by a gas source MBE method using ammonia gas. The group 3 evaporation crucible contained Ga (gallium) metal, In (indium) metal, and Al (aluminum) metal, and each was heated to a predetermined temperature. The heating temperature of Ga metal was 1050 ° C., In metal was heated to 750 ° C., and Al metal was heated to 1060 ° C. The gas was introduced by using a cracking gas cell filled with aluminum fibers therein, heated to 500 ° C., and supplied at a rate of 5 cc / min by directly blowing the gas onto the substrate.
[0031]
First, the SiC substrate 401 was subjected to organic cleaning and acid cleaning, and the cleaned substrate was mounted on a heatable susceptor and introduced into the reaction chamber. After that, the SiC substrate 401 is heated at 900 ° C. for 30 minutes, and then the semiconductor layer is formed on the substrate while maintaining the temperature at 650 ° C.
[0032]
In film formation, while supplying ammonia gas from the cracking gas cell, first, the Ga and Si shutters were opened to form an n-type GaN layer 402 having a film thickness of 1 μm at a film formation rate of about 0.5 μm / hour. Next, the In and Ga shutters were opened to form the InGaN light emitting layer 403, the Al, Ga and Mg shutters were opened, the AlGaN layer 404 was opened, and the Ga and Mg shutters were opened to form the GaN layer 405 sequentially.
[0033]
After forming these films, the supply of ammonia gas was stopped, and then a 300-nm-thick Ti film was formed on the GaN layer 405 in the reaction chamber by sputtering or the like. Thereafter, the temperature was raised to 1000 ° C., and the AlGaN layer 404 and the GaN layer 405 were made p-type by diffusing Ti into the AlGaN layer 74 and the GaN layer 405. At this time, the diffusion amount of Ti into AlGaN layer 404 and GaN layer 405 can be controlled by the thickness of the Ti film and the temperature of the heat treatment. Since the level of Ti is very deep, it is sufficient that Ti is contained in a small amount in the Mg-doped GaN-based semiconductor. Specifically, the Ti concentration in the p-type layer is 1 × 10^Thirteencm^-3More than 1 × 10¹⁶cm^-3It is desirable that:
[0034]
In the light emitting diode 70 thus manufactured, the light emission intensity was improved as compared with the case where Ti was not added to the p-type layers 404 and 405, and the light output was about 5 mW at the light emission wavelength of 430 nm. .
(Example 5)
FIG. 5 shows a cross-sectional structure of a ZnSe-based semiconductor laser 500 according to the present embodiment. Even with ZnSe-based materials, it is difficult to realize a p-type high-carrier-concentration crystal, and Se vacancies can be considered as an inhibitory factor. The semiconductor laser 500 has a GaAs substrate 501, on which a GaAs buffer layer 502, an n-type ZnSe layer 503, a CdZnSe active layer 504, and a p-type ZnSe layer 505 are sequentially formed. . Each layer can be formed by using a well-known MOCVD method, and the n-type ZnSe layer 503 and the p-type ZnSe layer 505 are imparted with respective conductivity by intentionally adding impurities. Specifically, the impurity added to the n-type ZnSe layer 503 is Cl, and the impurities added to the p-type ZnSe layer 505 are nitrogen (N) and arsenic (As). Among them, As in the p-type layer 505 functions to compensate for the residual donor.
[0035]
In the ZnSe-based semiconductor layer, the residual donor concentration is 2 × 10¹⁶cm^-3Therefore, the concentration of As added to the p-type layer 505 is 1 × 10^Fifteencm^-3More than 1 × 10¹⁷cm^-3It is desirable that: At this time, the p-type layer 505 is 2 × 10¹⁸cm^-3It has a carrier concentration of about and oscillated at a wavelength of 500 nm.
[0036]
In the above-described example, As is used as the impurity for compensating the residual donor. However, O (oxygen), P (phosphorus), Ti, Ni (nickel), or the like may be used. The preferred concentration of the impurities mentioned here differs depending on the type thereof. For example, in the case of O and P, 1 × 10^Fifteencm^-3More than 1 × 10¹⁷And preferably 1 × 10 5 in the case of Ti and Ni.¹⁴cm^-3More than 1 × 10¹⁷cm^-3The following is preferred. When added in such a concentration range, the same effect as described above can be obtained.
(Example 6)
FIG. 6 shows a cross-sectional structure of an electronic device (MOSFET) 600 made of 4H silicon carbide (SiC) according to the present embodiment. In the illustrated electronic device 600, two p-type layers 602 are formed in an n-type SiC substrate 601 by ion implantation so as to be separated from each other, and a source and drain electrode 605 is provided on the p-type layer 602. Further, a gate electrode 604 is formed on an area between the two p-type layers 602 with an oxide film 603 interposed therebetween.
[0037]
Nitrogen as a donor impurity is very easily taken into SiC and has a very high activation rate, so that nitrogen is present in the crystal as a residual donor. Due to this, it is difficult to produce a p-type high carrier concentration crystal. When imparting p-type conductivity to the SiC layer, Al or B (boron) is usually used as an acceptor impurity. However, by simultaneously adding an impurity selected from In, Ga, Sc, and the like, residual impurities are added. A p-type crystal with a high carrier concentration can be formed by compensating for the donor. In addition, as these concentrations, 1 × 10¹⁴cm^-35 × 10 or more¹⁶cm^-3It is desirable that:
[0038]
The impurity for compensating the residual donor as described above can be added to the p-type layer simultaneously with the acceptor impurity by, for example, ion implantation. Usually, when implanting impurities into SiC, heat treatment at a temperature of about 1500 ° C. or more is required after implantation at a temperature of about 1000 ° C., but such a high-temperature heat treatment is not required depending on the kind of impurities. There are also things. In that case, it is possible to first implant Al or B at a high temperature to perform a heat treatment, and then reduce the temperature to about 600 ° C. to implant an impurity such as In.
[0039]
Further, B as an acceptor impurity may diffuse outward during a high-temperature heat treatment. To suppress this, B is doped with an impurity for compensating for residual donors such as In, Ga, and Sc on the surface before the heat treatment. It is effective to perform vapor deposition and then heat treatment. Further, even when oxygen or hydrogen as the third impurity is implanted at a concentration approximately two orders of magnitude lower than that of B, outward diffusion can be suppressed.
(Example 7)
FIG. 7 is a sectional view of a semiconductor laser 700 according to the present embodiment. The semiconductor laser 700 has an n-type SiC substrate 701, and an AlN buffer layer 702 having a thickness of 5 nm is formed on the SiC substrate 701 to reduce lattice mismatch. Further, on the AlN buffer layer 702, an n-type GaN layer 703 (2 μm), an n-type AlGaN layer 704 (500 nm), an InGaN active layer 705 (10 nm), a p-type AlGaN layer 706 (500 nm), and a p-type GaN layer 707 (300 nm) are sequentially formed. Each layer is given p-type or n-type conductivity by intentionally adding an impurity. Specifically, the impurity added to the n-type GaN layer 703 and the n-type AlGaN layer 704 is Si, and the impurities added to the p-type AlGaN layer 706 and the p-type GaN layer 707 are Mg, C, and Zn. Among them, C added to the p-type layers 706 and 707 is an impurity for compensating for the residual donor. Note that Zn added simultaneously to the p-type layer is also an acceptor impurity, and therefore the same effect as when other impurities such as C are added can be expected. However, even when Zn was added simultaneously with Mg, a p-type GaN-based crystal was not obtained, and the effect shown by the present invention was not observed. This is probably because the impurity level of Zn is shallower than other impurities.
[0040]
On the p-type GaN layer 707, SiO₂  A Ni / Au stacked electrode 711 striped by the film 710 with a width of 10 μm is formed as an ohmic electrode. The Ni / Au stacked electrode 711 has a stacked structure of a Ni film having a thickness of 200 nm and an Au film having a thickness of 2 μm. Similar electrodes are formed on the back surface of the n-type SiC substrate 701.
[0041]
This semiconductor laser 700 was manufactured using the same raw materials and equipment as in Example 1 described above. Note that dimethyl zinc was used as a raw material of Zn added to the p-type layer. The wafer thus fabricated was cleaved to a size of 350 μm × 500 μm to obtain a laser diode chip. This chip oscillated continuously at room temperature at a wavelength of 410 nm and a current value of 50 mA, depending on the In composition in the active layer.
(Example 8)
FIG. 8 shows a cross-sectional structure of a semiconductor laser 800 according to this embodiment. The semiconductor laser 800 has a sapphire substrate 801 having a c-plane as a main surface, and a GaN buffer layer 802 having a thickness of 50 nm is formed on the sapphire substrate 801. On the GaN buffer layer 802, an n-type GaN contact layer 803 (2 μm), an n-type AlGaN cladding layer 804 (500 nm), an InGaN active layer 805 (50 nm), a p-type AlGaN cladding layer 806 (500 nm), and a p-type GaN contact layers 807 (300 nm) are sequentially formed. In each layer, p-type or n-type conductivity is imparted by intentionally adding impurities. Specifically, the impurity added to the n-type GaN layer 803 and the n-type AlGaN cladding layer 804 is Si, and the impurities added to the p-type AlGaN layer 806 and the p-type GaN layer 807 are Mg, Si, and C. Among these impurities, C added to the p-type layers 806 and 807 functions to compensate for the residual donor.
[0042]
On the p-type GaN layer 807, SiO₂  A Ni / Au laminated electrode 811 striped by the film 810 with a width of 10 μm is formed. A Ti / Au stacked electrode 812 having the same thickness as that of the Ni / Au stacked electrode 811 is also formed on the n-type GaN layer 803 whose upper surface is removed by etching to expose the surface.
[0043]
Hereinafter, a method of manufacturing the semiconductor laser 800 will be described in order.
The semiconductor laser 800 was manufactured by using a vapor phase growth method using a well-known MOCVD method. Organic metal raw materials include TMG, TMA, TMI and Cp₂  Mg, and ammonia, SiH₄  And C₃  H₈  Was used. Hydrogen and nitrogen were used as carrier gases.
[0044]
The organometallic raw material is not limited to those described above, and for example, triethylgallium (TEG) having an ethyl group bonded thereto instead of the methyl group can be used. Furthermore, Cp₂  It is also possible to use methyl biscyclopentadienyl magnesium or the like instead of Mg.
[0045]
Among the organometallic raw materials described above, SiH₄  And C₃  H₈  When these two gases are simultaneously used, Si and C can be simultaneously introduced into the p-type layer. It should be noted that, besides using two kinds of raw materials, hexamethyldisilane ((CH₃  )₆  Si₂  ), It is possible to add Si and C simultaneously into the p-type layer.
[0046]
First, after treating the sapphire substrate 801 by organic cleaning and acid cleaning, the sapphire substrate was placed in a reaction chamber of a MOCVD apparatus and mounted on a susceptor heated by high frequency. Next, a natural oxide film formed on the surface of the sapphire substrate 801 was removed by performing gas phase etching at a temperature of 1200 ° C. for about 10 minutes while flowing hydrogen at a flow rate of 20 liters / minute at normal pressure. .
[0047]
In forming a semiconductor film on the substrate, first, the sapphire substrate 801 was cooled to 550 ° C., and hydrogen, nitrogen, ammonia, and TMG were allowed to flow for about 4 minutes to form a GaN buffer layer 802. The flow rates of hydrogen, nitrogen, ammonia, and TMG were 15 liter / min, 5 liter / min, 10 liter / min, and 30 cc / min, respectively. Thereafter, the supply of TMG was stopped, and the temperature was increased to 1100 ° C. over 12 minutes.
[0048]
Subsequently, the sapphire substrate 801 is kept at 1100 ° C., and hydrogen (15 liter / min), nitrogen (5 liter / min), ammonia (10 liter / min), TMG (100 cc / min), and SiH₄  By flowing (8 cc / min) for about 60 minutes, an n-type GaN layer 803 was formed. Note that SiH₄  Was used after being diluted to 10 ppm with hydrogen. Subsequently, TMA at a flow rate of 50 cc / min was added to these raw materials and flowed for about 10 minutes to form an n-type AlGaN layer 804.
[0049]
Next, the temperature of the sapphire substrate 801 is lowered and maintained at 800 ° C., and nitrogen (20 l / min), ammonia (10 l / min), TMG (30 cc / min), and TMI (200 cc / min) are flowed for about 10 minutes. Thus, an InGaN active layer 805 was formed.
[0050]
Thereafter, the temperature of the sapphire substrate 801 is raised and maintained again at 1100 ° C., and nitrogen (20 l / min), ammonia (10 l / min), TMG (30 cc / min), TMA (100 cc / min), Cp₂  Mg (150cc / min), SiH₄  (1 cc / min), and C₃  H₈  (0.2 cc / min) for about 10 minutes to form a p-type AlGaN layer 806. Subsequently, the supply of TMA was stopped, and the remaining source gas was allowed to flow for about 10 minutes to form the p-type GaN layer 807.
[0051]
Si added to the p-type layers 806 and 807 has an effect of suppressing the diffusion of Mg. Further, by adding Si in this manner, the crystal can be easily etched. Note that when Mg is bonded to hydrogen or oxygen, it is prevented from becoming an acceptor. However, by adding Si, such an undesired bond can be suppressed. However, since Si in the GaN-based semiconductor itself acts as a donor, if excessively added, p-type conversion may be inhibited. Specifically, the concentration of Si in the p-type layer is 6 × 10¹⁶cm^-3More than 2 × 10¹⁹cm^-3It is desirable that: On the other hand, since carbon needs to simultaneously compensate for Si and residual donor added simultaneously, its concentration is 1 × 10¹⁶cm^-3It is preferable that it is above.
[0052]
Thereafter, the mixture was cooled to 350 ° C. while flowing ammonia (10 l / min) and nitrogen (20 l / min). Further, only the supply of ammonia was stopped, and then cooled to room temperature, and the wafer was taken out of the reaction chamber.
[0053]
Next, the SiO 2 is formed on the p-type GaN layer 807 by using a well-known thermal CVD method or the like.₂  The film 810 was formed with a thickness of 0.5 μm, and subjected to a photoetching process or the like to form a striped structure with a width of 150 μm. SiO₂  By removing the p-type GaN layer 807 from which the film 810 has been removed together with the p-type AlGaN layer 806, the InGaN active layer 805, and the n-type AlGaN layer 804 by etching using chlorine gas or the like, the n-type GaN layer 803 is removed. Surface was exposed.
[0054]
SiO formed on p-type GaN layer 807₂  A hole having a width of 10 μm was formed in the film 810 by a photoetching process or the like. A Ni / Au laminated electrode 811 was formed by sequentially forming a 50 nm thick Ni film and a 3 μm Au film in this hole by a well-known vacuum deposition method or the like. Further, on the n-type GaN layer 803, a Ti / Au laminated electrode was formed by sequentially laminating a 50 nm-thick Ti film and a 3 μm Au film.
[0055]
In addition, as the electrode, an alloy or a laminated structure of Pt, Pd, In, Mg, Ti, or the like and the above-described Ni or Au on the P-type layer can also be used. Further, on the n-type layer, an alloy or a laminated structure of Si or Cr and the above-described Ti or Au may be formed.
[0056]
The wafer thus fabricated was cleaved to a size of 350 μm × 500 μm to obtain a laser diode chip. This chip has a current density of 5 kA / cm, depending on the In composition in the active layer.²  , A continuous oscillation at room temperature was performed at a wavelength of 420 nm and an output of 5 mW.
[0057]
In the above-described example, C is used as the impurity for compensating the residual donor, but Cd, Ti, Ni, and Fe can be used (Zn can be included in addition to these impurities). These can be introduced during crystal growth using an organic metal raw material such as dimethylcadmium. Alternatively, the above-described metal film may be formed on the crystal surface after growth by using a method such as sputtering, and then the film may be heated to diffuse and introduce impurities into the crystal. Furthermore, these materials can be introduced by ion implantation after crystal growth. Since it is known that crystallinity is disturbed when ion implantation is performed, it is preferable to perform heat treatment after implantation.
[0058]
The preferred concentrations of the impurities mentioned here differ depending on the type. For example, in the case of Cd, 1 × 10^Fifteencm^-3More than 1 × 10¹⁸cm^-3Or less, and in the case of Ti and Fe, 1 × 10^Thirteencm^-3More than 1 × 10¹⁶cm^-3It is desirable that: In the case of Ni, 1 × 10^Thirteencm^-34 × 10 or more¹⁶cm^-3It is desirable that: If any of the impurities is added at a concentration exceeding the upper limit, the activation of Mg to the acceptor may be hindered. On the other hand, when the impurity concentration is below the lower limit, the effect of compensating for the residual donor is reduced. It is difficult to obtain.
[0059]
In this embodiment, the crystal growth is performed by using the MOCVD method. However, a material beam transport method using a molecular beam epitaxy method (MBE method) or a chlorine gas can be used. However, it is not surprising that raw materials must be selected in each case.
[0060]
In this embodiment, a GaN-based semiconductor has been described as a III-V compound semiconductor, but the present invention is not limited to this. B_x  In_y  Al_z  Ga_(1-xyz)  Any compound semiconductor represented by N (0 ≦ x, y, z ≦ 1) can be used. In a semiconductor such as GaAs or InGaP, the Si concentration in the p-type layer is 5 × 10¹⁸cm^-3It was necessary to be above. In this case, since the acceptor level of Mg was shallow, p-type conversion was not completely inhibited at such a Si concentration.
[0061]
Further, in the above-described example, GaN was used as the buffer layer, but the present invention is not limited to this._x  Al_y  In_z  Any compound semiconductor represented by N (x + y + z = 1) can be used.
(Example 9)
FIG. 9 shows a cross-sectional view of the semiconductor laser 900 of the present embodiment. The semiconductor laser 900 has a p-type SiC substrate 901, and a GaN buffer layer 902 having a thickness of 10 nm is formed on the SiC substrate 901 to reduce lattice mismatch. Further, on the GaN buffer layer 902, a multiple quantum well (MQW) structure having a p-type GaN layer 903 (2 μm), a p-type AlGaN layer 904 (500 nm), a well layer having a thickness of 20 nm and a barrier layer having a thickness of 40 nm. InGaN active layer 905, n-type AlGaN layer 906 (500 nm), and n-type GaN layer 907 (300 nm) are sequentially laminated. All of the GaN-based layers 902, 903, 904, 905, 906 and 907 are doped with Si, and the p-type GaN layer 903 and the p-type AlGaN layer 904 are doped with Mg and C. ing. Of these, C in the p-type layers 903 and 904 functions to compensate for residual donors because they form a deep acceptor level, and to help increase the carrier concentration by Mg that forms a relatively shallow acceptor level.
[0062]
On the n-type GaN layer 907, SiO₂  A Ti / Au laminated electrode 911 striped by the film 910 with a width of 10 μm is formed. The Ti / Au laminated electrode 911 is formed by a laminated structure of a 50 nm thick Ti film and a 2 μm Au film, and a Ti / Au laminated electrode 911 having the same thickness as the Ti / Au laminated electrode 911 is formed on the p-type SiC substrate 901. It is also formed on the back surface.
[0063]
Hereinafter, a method of manufacturing the semiconductor laser 900 will be described in order.
The semiconductor laser 900 was manufactured by using a known MOCVD method. TMG, TMA, TMI and Cp as organic metal raw materials₂  Mg was used, and ammonia, silane and propane were used as gas raw materials. Hydrogen and nitrogen were used as carrier gases.
[0064]
First, after treating the p-type SiC substrate 901 by organic cleaning and acid cleaning, the SiC substrate 901 was placed in a reaction chamber of a MOCVD apparatus and mounted on a susceptor heated by high frequency. Next, a natural oxide film formed on the substrate surface was removed by performing gas phase etching at 1200 ° C. for about 10 minutes while flowing hydrogen at a flow rate of 20 liters / minute at normal pressure.
[0065]
In forming the semiconductor layer on the substrate, first, the temperature of the SiC substrate 901 was lowered to 800 ° C., and hydrogen, nitrogen, ammonia, TMG, and silane were flowed for 5 minutes to form a GaN buffer layer 902. The flow rates of hydrogen, nitrogen and ammonia were all 5 liter / min, the flow rate of TMG was 30 cc / min, and the flow rate of silane was 0.2 cc / min.
[0066]
Thereafter, the temperature of the SiC substrate 901 was raised and maintained at 1100 ° C., and hydrogen and nitrogen were used as carrier gases, ammonia, propane and silane were used as gas materials, and TMG and Cp were used as organometallic materials.₂  The p-type GaN layer 903 was formed by flowing Mg for about 30 minutes. The flow rate of the carrier gas was set to 5 liter / min, and the flow rate of the organic metal raw material was set to 30 cc / min. The flow rates of ammonia, propane and silane were 5 liter / min, 10 cc / min and 0.2 cc / min, respectively. Subsequently, TMA was added to these gases at a flow rate of 100 c / min and flowed for about 8 minutes to form a p-type AlGaN layer 904.
[0067]
Next, the temperature of the SiC substrate 901 is lowered and maintained at 800 ° C., and while flowing nitrogen (10 liters / minute), ammonia (5 liters / minute), TMG (30 cc / minute), and silane (0.2 cc / minute), By switching the flow rate between two types and flowing TMI, an InGaN active layer 905 having a multiple quantum well of 25 periods was formed. The TMI was flowed for 25 cycles, with one cycle of supply at a flow rate of 200 cc / min and one cycle of supply at a flow rate of 50 cc / min for 2 minutes.
[0068]
Subsequently, the temperature of the SiC substrate 901 is again raised and maintained at 1100 ° C., and hydrogen and nitrogen as carrier gases, TMG and TMA as organic metal raw materials, and ammonia and silane as gas raw materials are caused to flow for about 8 minutes to thereby obtain n-type. An AlGaN layer 906 was formed. The flow rate of the carrier gas was set to 5 liter / min, and the flow rates of TMG and TMA were set to 30 cc / min and 100 cc / min, respectively. The flow rates of ammonia and silane were 5 liter / min and 1 cc / min, respectively. Subsequently, the supply of TMA was stopped, and the remaining gas was allowed to flow for about one hour to form an n-type GaN layer 907. Thereafter, the wafer was cooled to room temperature while flowing nitrogen at a flow rate of 10 liter / min, and the growth wafer was taken out of the reaction chamber.
[0069]
Subsequently, SiO 2 is formed on the n-type GaN layer 907 by using a well-known thermal CVD method or the like.₂  A film 910 is formed with a thickness of 0.5 μm,₂  Holes having a width of 10 μm were formed in the film by a photoetching process or the like. Further, a Ti film having a thickness of 50 nm and an Au film having a thickness of 3 μm were sequentially formed thereon by a well-known vacuum deposition method or the like to form a Ti / Au laminated electrode 911. A Ti / Au laminated electrode 911 having the same thickness as this was also formed on the back surface of the p-type SiC substrate 901.
[0070]
In such an element, C is contained in the p-type GaN layer 903 and the p-type AlGaN layer 904 at about 1 × 10¹⁷cm^-3It is contained at a concentration of. This is a value that approximately matches the carrier concentration of the undoped GaN film. In the example described above, the carbon concentration in the p-type layer is set to the above value, but the carbon concentration is not limited to this. Since the residual donor concentration varies depending on the crystal growth conditions, the concentration of the impurity for compensating for the residual donor concentration can be appropriately determined according to the growth conditions.
[0071]
The wafer thus fabricated was cleaved to a size of 350 μm × 500 μm to obtain a laser diode chip. This chip oscillated continuously at room temperature at a wavelength of 420 nm, depending on the In composition in the active layer.
[0072]
In the above-described example, C is used as the impurity for compensating the residual donor, but Cd, Ti, or Fe may be used. These can be introduced during crystal growth using an organic metal raw material such as dimethylcadmium. Alternatively, the above-described metal film may be formed on the crystal surface after growth by using a method such as sputtering, and then the film may be heated to diffuse and introduce impurities into the crystal. Further, these materials can be introduced by ion implantation after crystal growth. Since it is known that crystallinity is disturbed when ion implantation is performed, it is preferable to perform heat treatment after implantation.
[0073]
The preferred concentrations of the impurities mentioned here differ depending on the type. For example, in the case of Cd, 1 × 10^Fifteencm^-3More than 1 × 10¹⁸cm^-3Or less, and in the case of Ti and Fe, 1 × 10^Thirteencm^-3More than 1 × 10¹⁶cm^-3It is desirable that: If any of the impurities is added at a concentration exceeding the upper limit, the activation of Mg to the acceptor may be hindered. On the other hand, when the impurity concentration is below the lower limit, the effect of compensating for the residual donor is reduced. It is difficult to obtain.
[0074]
In this embodiment, a 6H-type substrate is used as the SiC substrate. However, since the energy gap difference between the 6H-type SiC and the GaN-based semiconductor is about 0.5 V, the operating voltage tends to increase. There is. Therefore, it is more preferable to use 4H-type or 2H-type SiC having a small energy gap difference as the substrate.
[0075]
Here, SiC used as the substrate is also a material that is difficult to be etched like the GaN-based semiconductor. Therefore, nitrogen is added to 1 × 10¹⁷cm^-3It is desirable to add above. However, nitrogen is an effective donor impurity in SiC. The residual donor is 2 × 10¹⁶cm^-3It is contained in a concentration of about. It is necessary to realize a p-type SiC crystal having a higher carrier concentration by compensating these donors with acceptor impurities. Particularly at the interface between the p-type layer and the electrode on the substrate surface, the necessity for reducing the operating voltage is high. Examples of the acceptor impurities include Al, Ga, In, Sc, Y, and Ti. The preferable concentration of such an impurity in the p-type layer depends on the type thereof. For example, in the case of Ga or Sc, 1 × 10¹⁷cm^-3It is preferable to set the degree.
(Example 10)
FIG. 10A is a cross-sectional view of the light emitting diode 1000 of the present embodiment. The light emitting diode 1000 has a sapphire substrate 1001, on which a GaN buffer layer 1002 is formed with a thickness of 20 nm. Further, on the buffer layer 1002, an n-type GaN layer 1003 (4 μm), an InGaN light-emitting layer 1004 (100 nm), and a p-type GaN layer 1005 (500 nm) are sequentially stacked. Each layer is given p-type or n-type conductivity by intentionally adding an impurity. Specifically, the impurity added to the p-type GaN layer 1005 is Mg as an acceptor and C for compensating for a residual donor, and the impurity added to the n-type GaN layer 1003 is Si as a donor. In addition, Zn and Si were introduced into the InGaN light emitting layer 1004 as light emission centers.
[0076]
On the p-type GaN layer 1005, a Ni / Au stacked electrode 1010 having a stacked structure of a Ni film having a thickness of 20 nm and an Au film having a thickness of 1 μm is formed. Further, on the n-type GaN layer 1003 whose surface is exposed by removing a layer thereabove by etching, a laminated electrode 1011 of Ti / Au having a laminated structure of a 50 nm thick Ti film and a 2 μm Au film is provided. Is formed.
[0077]
The stacked structure of the nitride compound semiconductor in the light emitting diode of this example was manufactured by the same MOCVD method as in the above (Example 1). The growth thickness of each layer was controlled by the growth time, and then measured by a scanning electron microscope (SEM).
[0078]
After manufacturing the stacked structure in this manner, a part of the p-type GaN layer 1005 and a part of the InGaN active layer 1004 are removed by dry etching using chlorine gas to expose the n-type GaN layer 1003. Then, an n-type electrode 1011 was formed. The wafer was scribed to a size of 350 μm square, placed on a stem, bonded and molded to obtain a light emitting diode lamp. This lamp emitted light at a wavelength of 450 nm and showed an output of about 3 mW at a forward current of 20 mA.
[0079]
When Si is used as the light emission center as in this embodiment, there is a possibility that Si may be accumulated at the interface between the p-type layer and the light-emitting layer, or may be diffused into the p-type layer. When the accumulation or diffusion of Si occurs, a heterobarrier is generated and the n-type inversion of the p-type layer occurs. Therefore, it is desired to avoid such a phenomenon as much as possible. Such a disadvantage can be avoided by increasing the concentration of C added to the p-type layer. Specifically, the carbon concentration in the p-type layer is 8 × 10¹⁷cm^-3It is preferable to make the above.
[0080]
Note that nitrogen vacancies can be cited as a cause of the generation of residual donors in the p-type layer. These vacancies can be filled with As, O, P, and the like, but if these elements are added alone, a reduction in the energy gap and a factor of electrical inactivity will occur. As a result, there is a possibility that the effect of adding the impurity may not be exhibited. Therefore, it is desired that such an element be added simultaneously with C. In addition, residual donors can be compensated by acceptor impurities such as Cd, Fe, Ti, and Ni formed at a deep level. However, these impurities alone cause only electrical inactivity, and therefore it is desirable to add them simultaneously with C.
[0081]
The light emitting diode shown in FIG. 10A can be modified as shown in FIG. In the example shown in FIG. 10A, the p-type GaN layer 1005 in FIG. 10B is divided into two layers, a p-type GaN injection layer 1105 and a p-type contact layer 1106. Here, only Mg was added as an impurity to the injection layer 1105, and Mg and C were added to the contact layer 1106. With such a structure, the resistance of the contact layer can be reduced, so that the operating voltage can be reduced. More specifically, in the structure shown in FIG. 10A, the voltage at a current of 20 mA is 4 V, whereas the structure shown in FIG. 10B reduces the voltage to 3.5 V. I was able to.
[0082]
Further, Si may be added to the contact layer 1106. Si has a function of suppressing the diffusion of Mg and increasing the ease of crystal etching. Since Si is a group IV element, it can be used as an acceptor by substituting it at the nitrogen position. For this purpose, there is a method of growing at a temperature lower than a normal growth temperature. Alternatively, by lowering the nitrogen / group III element supply ratio, the supply of the group III element can be suppressed from being replaced with the group III element position by making the supply of the group III element excessive than the supply of nitrogen. Through such growth, Si can also function as an acceptor.
[0083]
The same effect can be obtained by adding As, P, O, Cd, Fe, Ti or Ni to the contact layer 1106 instead of Si.
(Example 11)
FIG. 11 shows a cross-sectional structure of a semiconductor laser according to this embodiment. The semiconductor laser 1200 has a sapphire substrate 1201 having a c-plane as a main surface. On the sapphire substrate 1201, a GaN buffer layer 1202 (about 50 nm), an undoped GaN layer 1203 (about 2 μm), and an n-type GaN contact Layers 1204 (about 4 μm) are sequentially formed. Further, on the n-type GaN contact layer 1204, an n-type AlGaN cladding layer 1205 (about 0.2 μm), an n-type GaN guide layer 1206 (about 0.1 μm), a well layer having a thickness of 2 nm and a barrier layer having a thickness of 4 nm are provided. InGaN active layer 1207 having a multiple quantum well (MQW) structure, p-type GaN guide layer 1208 (about 0.1 μm), p-type AlGaN cladding layer 1209 (about 0.2 μm), and p-type GaN layer 1210 (about 0.2 μm). 5 μm), an n-type GaN layer 1211 (1 μm), a p-type GaN layer 1212 (about 2 μm), and a high concentration p-type GaN contact layer 1213 (about 0.2 μm).
[0084]
On the p-type GaN contact layer 1213, a 0.5 μm thick SiO₂  A Pt / Ti / Pt / Au stacked electrode 1222 striped to a predetermined width by the film 1220 is formed. This laminated electrode is obtained by sequentially laminating a Pt film having a thickness of about 10 nm, a Ti film having a thickness of about 50 nm, a Pt film having a thickness of about 30 nm, and an Au film having a thickness of about 1 μm. On the n-type GaN contact layer 1204 whose upper surface is removed by etching to expose the surface, a Ti / Au having a laminated structure of a 50 nm thick Ti film and a 0.5 μm Au film is formed. A laminated electrode 1221 is formed.
[0085]
In the illustrated semiconductor laser 1200, Mg, Si, and C are added as impurities to the p-type GaN contact layer 1213 that is required to have particularly low resistance, and C in these compensates for the residual donor. Work. The Mg concentration in the p-type GaN contact layer 1213 is 2 × 10²⁰cm^-3It is preferred that it is about. As described in the above (Embodiment 8), Si has a function of suppressing the diffusion of Mg, and by adding Si, it becomes possible to easily perform crystal etching. However, if Si is excessively added, p-type conversion may be hindered. Therefore, the concentration of Si in the p-type GaN contact layer 1213 is 6 × 10¹⁶cm^-3More than 1 × 10¹⁸cm^-3It is preferably 1 × 10¹⁷cm^-3The following is preferred. On the other hand, the concentration of C is 1 × 10¹⁶cm^-3More than 1 × 10¹⁷cm^-3The following is preferred.
[0086]
Similar impurities are added to the p-type layers other than the p-type GaN contact layer 1213, that is, the p-type GaN guide layer 1208, the p-type AlGaN cladding layer 1209, the p-type GaN layer 1210, and the p-type GaN layer 1212. Is also good. Thereby, the diffusion of Mg can be suppressed and the activation rate can be improved.
[0087]
Hereinafter, a method for manufacturing the semiconductor laser 1200 will be sequentially described.
First, after treating the sapphire substrate 1201 by organic cleaning and acid cleaning, the sapphire substrate 1201 was placed in a reaction chamber of a MOCVD apparatus and mounted on a susceptor heated by high frequency. Next, a natural oxide film formed on the substrate surface was removed by performing gas phase etching at 1100 ° C. for about 10 minutes while flowing hydrogen at a flow rate of 10 liters / minute at normal pressure.
[0088]
In forming the semiconductor layer on the substrate surface, first, the temperature of the sapphire substrate 1201 was lowered to 530 ° C., and hydrogen, nitrogen, ammonia, and TMG were flowed for about 4 minutes to form the GaN buffer layer 1202. The flow rate of each gas was 15 liters / minute of hydrogen, 5 liters / minute of nitrogen, 10 liters / minute of ammonia, and 25 cc / minute of TMG.
[0089]
Next, the sapphire substrate 1201 was heated to 1100 ° C. while flowing hydrogen (15 L / min), nitrogen (5 L / min) and ammonia (10 L / min), and then TMG (100 cc / min) was added to the above-mentioned gas. ) Was added and allowed to flow for 60 minutes to form an undoped GaN layer 1203. Then, an n-type GaN layer 1204 is formed by adding silane (3 cc / min) diluted to 10 ppm with hydrogen and flowing for about 130 minutes, and further adding TMA (50 cc / min) and flowing for about 10 minutes. An n-type AlGaN layer 1205 was formed on the n-type GaN layer 1204. The composition ratio of Al in the n-type AlGaN layer 1205 was 0.15.
[0090]
Subsequently, the sapphire substrate 1201 is maintained at 1100 ° C., and hydrogen (15 l / min), nitrogen (5 l / min), ammonia (10 l / min) and TMG (100 cc / min) are flowed for about 3 minutes. , A GaN guide layer 1206 was formed. Since the guide layer has a function of improving light confinement, a small amount of In may be added to this layer. However, in this case, it is desired to appropriately change the thickness of the guide layer.
[0091]
Thereafter, the temperature of the sapphire substrate 1201 was lowered to 800 ° C. over about 3 minutes while flowing nitrogen (20 L / min) and ammonia (10 L / min). Further, in addition to the above-described gas, TMG (10 cc / min) was flown, and two kinds of flow rates were switched to flow TMI to form an InGaN layer 1207 having a multiple quantum well of 15 periods. In addition, TMI is supplied for about 1 minute at a flow rate of 50 cc / min and supplied for about 30 seconds at a flow rate of 460 cc / min. Shed. The barrier layer in the obtained active layer 1207 has an In content of 5% and a thickness of 4 nm, and the well layer has an In content of 20% and a thickness of 2 nm.
[0092]
In this embodiment, the barrier layer is made of InGaN having an In content of 5%, and the well layer is made of InGaN having an In content of 20%. However, the present invention is not limited to this. In the multiple quantum well structure, since the band gap energy of the barrier layer needs to be larger than that of the well layer, GaN or AlGaN can be used as the barrier layer. In this case, it is necessary to use, for the guide layers 1206 and 1208, a material system having a value smaller than the average refractive index of the active layer. For example, when a GaN layer is used as a barrier layer and an InGaN layer having an In content of 20% is formed with the same thickness as a well layer, InGaN, GaN, and GaN having an In content of less than 10% are used as guide layers. Alternatively, AlGaN can be used. However, it goes without saying that the In content in this case must be smaller than that of the cladding layer.
[0093]
Subsequently, the temperature of the sapphire substrate 1201 was raised to 1100 ° C. in about 3 minutes while flowing nitrogen (20 L / min) and ammonia (10 L / min). The substrate is kept at this temperature and hydrogen (15 l / min), nitrogen (5 l / min), ammonia (10 l / min), TMG (100 cc / min) and Cp₂  By flowing Mg (50 cc / min) for about 3 minutes, a p-type GaN guide layer 1208 was formed. Furthermore, p-type AlGaN cladding layer 1209 was formed by adding TMA (50 cc / min) to these raw materials and flowing them for about 10 minutes. Thereafter, the supply of TMA was stopped, and the remaining gas was allowed to flow for about 15 minutes to form the p-type GaN layer 1210.
[0094]
Next, Cp₂  The supply of Mg was stopped, and silane (3 cc / min) was added to the remaining gas to form an n-type GaN layer 1211. Then, the supply of TMG and silane was stopped, and the temperature of the sapphire substrate was lowered to 350 ° C. Furthermore, the supply of hydrogen and ammonia was stopped at this temperature, and after cooling to room temperature, the growth wafer was taken out of the reaction chamber.
[0095]
Then, the SiO formed by the thermal CVD method₂  Using the film and the photoresist film as masks, Cl₂  A predetermined region of the n-type GaN layer 1211 was removed with a stripe width of 5 μm by etching using gas to expose the surface of the p-type GaN layer 1210.
[0096]
The wafer subjected to this process is returned to the susceptor in the MOCVD apparatus, and heated to 1100 ° C. while flowing hydrogen (15 liters / minute), nitrogen (5 liters / minute), and ammonia (10 liters / minute). did. In addition, TMG (100 cc / min) and Cp₂  The p-type GaN layer 1212 was formed by adding Mg (50 cc / min) and flowing for about 60 minutes.
[0097]
In this growth process, it is preferable to go through a low-temperature growth process. In the low-temperature growth step, first, the temperature is raised to 550 ° C. over about 3 minutes while flowing nitrogen (about 20 liters / minute) and ammonia (10 liters / minute). Next, the substrate was kept at this temperature, and hydrogen (15 l / min), nitrogen (5 l / min), ammonia (10 l / min), TMG (25 cc / min) and Cp₂  By flowing Mg (50 cc / min) for about 4 minutes, a p-type GaN layer having a thickness of about 50 nm is formed. The GaN layer immediately after being formed here was a polycrystal having c-axis orientation.
[0098]
On the p-type GaN layer 1212 formed as described above, nitrogen (20 l / min), ammonia (10 l / min), TMG (100 cc / min), Cp₂  The p-type GaN contact layer 1213 was formed by flowing Mg (150 cc / min), silane (1 cc / min), and propane (2 cc / min) for 6 minutes. By adding Si and C to the contact layer in this way, the activation rate was improved about three times, and the diffusion of Mg was suppressed as compared with the case where these were not added. Thereafter, the system was cooled to room temperature while flowing only nitrogen at a flow rate of 10 liter / min, and the growth wafer was taken out of the reaction chamber.
[0099]
A 0.5 μm thick SiO 2 is formed on the p-type GaN contact layer 1213 by using a well-known thermal CVD method or the like.₂  A film 1220 is formed, and SiO 2 is formed by a photo etching process or the like.₂  A part of the film was removed. This SiO₂  Using the film 1220 and the resist pattern as a photoetching mask as an etching mask, the upper layer was removed by a reactive ion etching method using a chlorine gas or the like to expose the surface of the n-type GaN layer 1204.
[0100]
On a part of the surface of the n-type GaN layer 1204, a laminated structure of a 50 nm-thick Ti film and a 0.5 μm Au film is formed by using a well-known vacuum deposition method or a sputtering method. The n-side electrode 1221 was formed by performing a heat treatment at 450 ° C. for about 30 seconds.
[0101]
On the other hand, on a substantially entire surface of the p-type GaN layer 1213, a Pt film having a thickness of about 10 nm, a Ti film having a thickness of about 50 nm, a Pt film having a thickness of about 30 nm, and a An Au film was laminated, and a heat treatment was performed in a nitrogen atmosphere at 300 ° C. for about 30 seconds to form a p-side electrode 1222. Here, a laminated structure of Pt / Ti / Pt / Au was used as the p-side electrode, but is not limited to this. For example, Al, Ag, Ni, Cr, Mg, Si, Zn, Be, Ge, In , Pd, and Sn may be used. These metals can be used as a single layer, a laminated structure, or an alloy.
[0102]
On the electrodes 1221 and 1222 formed as described above, a Cr film having a thickness of about 5 nm and an Au film having a thickness of about 1 μm are sequentially laminated in order to enhance the adhesiveness of bonding. Formed. The element operates by bonding with Au or the like.
[0103]
For the device completed up to the electrode formation, the back surface of the sapphire substrate 1201 (the surface opposite to the side on which the device was formed) was polished to a thickness of 60 μm or less, and about 500 μm × 1 mm by line scribe and cleavage from the substrate side. The elements were separated into different sizes. At this time, the end face of the laser was set to the A-plane of the GaN-based material, that is, the (11-20) plane.
[0104]
Thereafter, the surface serving as the laser end surface is coated with SiO 2.₂  Film and TiO₂  By forming a multilayer film with the film, the end face reflectivity of the laser was improved.
The semiconductor laser 1200 thus manufactured has a threshold current density of 3 kA / cm.²  Worked with. The oscillation wavelength depends on the average In composition of the active layer 1207, but can oscillate at a wavelength of 390 to 450 nm.
[0105]
Note that the step structure of this embodiment is manufactured by etching, but can be manufactured by selective growth.
As described above, the present invention has been described by taking a semiconductor element having a specific p-type semiconductor layer as an example. However, the present invention is not limited to this, and in addition to an acceptor impurity for imparting p-type conductivity, A p-type semiconductor film that further includes an acceptor impurity for compensating the donor is within the scope of the present invention.
[0106]
【The invention's effect】
As described in detail above, according to the present invention, a p-type crystal having a high carrier concentration can be realized by allowing a small amount of impurities to exist in the same layer, so that the efficiency of the device can be increased. This leads to an improvement in the reliability of the device, and can be applied to all devices having a p-type semiconductor film, so that its industrial value is large.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an example of a GaN-based semiconductor laser according to the present invention.
FIG. 2 is a sectional view showing another example of the GaN-based semiconductor laser of the present invention.
FIG. 3 is a cross-sectional view illustrating an example of a GaN-based light emitting diode of the present invention.
FIG. 4 is a sectional view showing another example of the GaN-based light emitting diode of the present invention.
FIG. 5 is a sectional view showing an example of a ZnSe-based semiconductor laser according to the present invention.
FIG. 6 is a sectional view showing an example of a MOSFET using 4H SiC of the present invention.
FIG. 7 is a sectional view showing another example of the GaN-based semiconductor laser of the present invention.
FIG. 8 is a sectional view showing another example of the GaN-based semiconductor laser of the present invention.
FIG. 9 is a sectional view showing another example of the GaN-based semiconductor laser of the present invention.
FIG. 10 is a sectional view showing another example of the light emitting diode of the present invention.
FIG. 11 is a sectional view showing another example of the semiconductor laser of the present invention.
[Explanation of symbols]
100 ... Semiconductor laser
101 ... p-type SiC substrate
102: GaN buffer layer
103 ... p-type GaN layer
104: p-type AlGaN layer
105 ... InGaN active layer
106 ... n-type AlGaN layer
107 ... n-type GaN layer
110 ... SiO₂  film
111 ... Ti / Au laminated electrode

Claims (10)

See containing and an acceptor impurity for imparting p-type conductivity to the semiconductor film, titanium, iron, and the acceptor impurity to compensate residual donor selected from the group consisting of nickel, represented by the following chemical formula A p-type semiconductor film comprising a compound semiconductor .
_{B x In y Al z Ga (} 1-xyz) N (0 ≦ x, y, z ≦ 1) The p-type semiconductor film according to claim 1, wherein the acceptor impurity for imparting p-type conductivity is magnesium. An acceptor impurity for imparting p-type conductivity, and an acceptor impurity for compensating for a residual donor selected from the group consisting of titanium, iron and nickel, comprising a compound semiconductor represented by the following chemical formula: A semiconductor element comprising a semiconductor layer .
_{B x In y Al z Ga (} 1-xyz) N (0 ≦ x, y, z ≦ 1) The semiconductor device according to claim 3, wherein the acceptor impurity for imparting p-type conductivity is magnesium. The semiconductor device according to claim 3 , wherein the p-type semiconductor layer further contains silicon . The semiconductor device according to claim 3 , wherein the p-type semiconductor layer is a contact layer . A substrate, an n-type cladding layer, a p-type cladding layer, and an active layer provided between the n-type cladding layer and the p-type cladding layer;
The n-type cladding layer, the p-type cladding layer, and the active layer are made of a compound semiconductor represented by the following chemical formula, and the p-type cladding layer has an acceptor impurity for imparting p-type conductivity, A semiconductor laser containing an acceptor impurity for compensating for a residual donor selected from the group consisting of iron and nickel.
B _x In _y Al _z Ga _(1-x-y-z) N (0 ≦ x, y, z ≦ 1) The semiconductor laser according to claim 7, wherein the p-type cladding layer further contains silicon. A substrate, an n-type cladding layer, a p-type cladding layer, and a light-emitting layer provided between the n-type cladding layer and the p-type cladding layer;
The n-type cladding layer, the p-type cladding layer, and the light emitting layer are made of a compound semiconductor represented by the following chemical formula, and the p-type cladding layer has an acceptor impurity for providing p-type conductivity, A light emitting diode comprising an acceptor impurity for compensating for a residual donor selected from the group consisting of iron and nickel.
B _x In _y Al _z Ga _(1-x-y-z) N (0 ≦ x, y, z ≦ 1) The light emitting diode according to claim 9, wherein the p-type cladding layer further contains silicon.

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