JP2004247563A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device which is suitable for a light-emitting element emitting blue light or green light by providing a semiconductor layer having desired indium composition. <P>SOLUTION: On a board 11 consisting of sapphire, respective layers including an active layer 17 are laminated via a low temperature buffer layer 12 and a base layer 13. The active layer 17 has a quantum well structure consisting of AlGaInN mixed crystal as the whole, and the indium composition of a well layer is ≥14 % e.g. The base layer 13 consists of GaInN mixed crystal, and a grid constant difference thereof with the well layer of the active layer 17 is within 1 %. Compared with a buffer layer consisting of conventional GaN, the grid constant of the base layer 13 is close to the grid contact of the active layer 17, and indium is easily fetched without generating a defect to the active layer 17 in the growth of crystal. Further, distortion to be introduced to the active layer 17 is reduced, and Stark effect hardly comes to appear. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor device having a semiconductor layer made of a nitride III-V compound semiconductor, and more particularly to a semiconductor device such as a semiconductor laser containing indium (In) in a light emitting layer.
[0002]
[Prior art]
AlGaInN mixed crystal, which is a nitride III-V compound semiconductor, is a semiconductor material of direct transition and has a feature of having a band gap energy ranging from an ultraviolet region to a red region, and has a wavelength range corresponding to this energy. Applications to light-emitting elements are being promoted. Actually, a semiconductor laser that emits ultraviolet light or blue light, a light emitting diode that emits ultraviolet light, blue light or green light, and the like have been realized by using this material system. These devices generally have a heterojunction composed of semiconductor layers having different compositions, and the light emitting layer contains indium.
[0003]
FIG. 5 shows an example of the structure of a conventional semiconductor laser. In this semiconductor laser, an n-side contact layer made of n-type GaN is formed on a c-plane of a substrate 111 made of sapphire via, for example, a first buffer layer 112 made of GaN grown at a low temperature and a second buffer layer 113 made of GaN. 114, n-type cladding layer 115 made of n-type AlGaN mixed crystal, n-type guide layer 116 made of n-type GaInN mixed crystal, active layer (light emitting layer) 117 made of AlGaInN mixed crystal, p-type made of p-type GaInN mixed crystal A guide layer 118, a desorption preventing layer 119 made of AlGaN mixed crystal, a p-type clad layer 120 made of p-type AlGaN, and a p-side contact layer 121 made of p-type GaN are provided on a part of the p-type guide layer 118. It has a configuration stacked in this order. A p-side electrode 122 is provided on the p-side contact layer 121, and an n-side electrode 123 is provided on the n-side contact layer 114. Note that the desorption preventing layer 119 is for preventing indium from being desorbed from the active layer 117 and for preventing injection current from overflowing.
[0004]
Such a semiconductor laser is generally manufactured by growing each layer on a substrate by using a vapor deposition method. At this time, AlN, GaN, and InN, which are raw materials, have different lattice constants, and the lattice constant in a free-standing state (free-standing) increases in the order of AlN, GaN, and InN. There is a risk. This distortion extends to the active layer and causes the following two problems during crystal growth.
[0005]
One is the so-called compositional effect, in which when growing an active layer, the lattice constant of the active layer (the value in the free-standing state of the design value) becomes equal to the lattice constant of each layer below the active layer. If they are different, it is difficult to obtain an active layer having an indium composition as designed. This is because when indium is taken in the active layer, a compressive strain is generated, but when indium is not taken in, the energy due to the strain in the active layer becomes small and the active layer becomes more stable. For example, when a GaInN mixed crystal layer is formed after a GaN layer is formed on a sapphire substrate, GaInN mixed crystal has a larger lattice constant than GaN, so that indium is less likely to be taken in (for example, See Non-Patent Document 1.)
[0006]
The other is a piezoelectric effect caused by strain generated in the active layer (for example, see Non-Patent Document 2). In particular, the AlGaInN mixed crystal has a high ionic bonding property, so that the piezoelectric effect tends to appear.
[0007]
Further, another cause of distortion in the active layer is a difference in thermal expansion coefficient between layers including the substrate. The distortion caused by the difference in thermal expansion coefficient becomes more remarkable as the difference between the temperature at the time of crystal growth and room temperature is larger.
[0008]
Conventionally, an InGaN buffer layer is formed on a silicon (Si) substrate, and a GaN layer is further formed thereon, so that a difference in lattice constant and a difference in thermal expansion coefficient between the silicon substrate and the GaN layer are reduced. Proposals have been made to alleviate this (for example, see Patent Document 1).
[0009]
[Non-patent document 1]
S. S. Pereira, 6 others, Physical Review B. (USA), November 2001, Vol. 64, No. 20, 205311.
[Non-patent document 2]
Tetsuya Takeuchi, 6 others, Japanese Journal of Applied Physics (Jpn. J. Appl. Phys.), 1997, Vol. 36, p. L382-p. L385
[Patent Document 1]
JP 2001-93834 A
[0010]
[Problems to be solved by the invention]
In order to obtain an element that emits blue light or green light using an AlGaInN mixed crystal, it is necessary to increase the indium composition of the active layer to some extent. However, conventionally, as shown in FIG. 5, since the second buffer layer 113 made of GaN having a lattice constant relatively smaller than that of the GaInN mixed crystal was used, the above-described process was performed during the crystal growth of the active layer 117. Such a composition-introducing effect and a piezoelectric effect occur, and it is difficult to obtain the active layer 117 having a desired indium composition.
[0011]
In order to prevent a decrease in the indium composition due to the composition incorporation effect, it is necessary that a lattice defect occurs in the active layer itself and a part of the strain is alleviated. However, lattice defects generated in the active layer are undesirable because they cause a reduction in luminous efficiency and a shortened life of the device.
[0012]
When the above-described piezoelectric effect occurs, a built-in potential is induced. As a result, the Stark effect occurs, reducing the probability of radiative recombination of the injected carriers, causing a decrease in the luminous efficiency of the device or an increase in the threshold value of the semiconductor laser.
[0013]
Furthermore, when the injected carrier density increases, the carriers are redistributed so as to cancel the electric field generated by the Stark effect, and the wavelength of the light emitted from the active layer is shortened. In particular, when applied as a light source of a display device, if an attempt is made to increase the light output, the wavelength of the light emitted from the active layer is shortened, which may cause a deterioration in display quality.
[0014]
In addition, another problem due to the Stark effect is that the energy difference between the quantum levels is smaller than when no electric field is applied. The light emitted from the light source has a longer wavelength. FIG. 6 is an experimental result showing that the oscillation wavelength is increased by the Stark effect. _0.05 N barrier layer and GaIn _0.15 N-well layer and GaIn _0.05 The relationship between the peak energy of the photoluminescence (PL) spectrum and the well width from the active layer having the quantum well structure formed by laminating the barrier layer made of N and the well width is determined in the case of weak excitation (excitation power density of 10 W). / Cm ² ) And strong excitation (expressed by the peak energy of the stimulated emission light spectrum, and the excitation power density corresponds to a threshold power density shown in FIG. 7 described later). Here, the well width refers to the thickness of only the well layer (thickness in the stacking direction) and does not include the thickness of the barrier layer (thickness in the stacking direction). As can be seen from FIG. 6, as the well width increases, the difference in peak energy between the case of weak excitation and the case of strong excitation increases. This is considered to be due to the fact that the Stark effect becomes remarkable as the well width increases.
[0015]
FIG. 7 shows the correspondence between the threshold power density at which stimulated emission occurs and the well width for the same sample as in FIG. The feature is that the threshold power density increases nonlinearly with respect to the well width. This is considered to be due to the fact that the carrier recombination probability is reduced by the Stark effect, in addition to the fact that the carrier density is inversely reduced with the increase of the well width.
[0016]
The present invention has been made in view of such a problem, and an object of the present invention is to provide a semiconductor element that includes a semiconductor layer having a desired indium composition and is suitable for a light-emitting element that emits blue light or green light. .
[0017]
[Means for Solving the Problems]
A semiconductor device according to the present invention includes a substrate, and is provided on one surface side of the substrate and includes at least gallium (Ga) and indium (In) among Group 3B elements and at least nitrogen (N) among Group 5B elements. A semiconductor layer made of a nitride III-V compound semiconductor, and a nitride III containing at least gallium (Ga) and indium (In) of the group 3B element and at least nitrogen (N) of the group 5B element It is made of a group V compound semiconductor, has a lattice constant difference of 1% or less from the semiconductor layer, and has an underlayer provided between the semiconductor layer and the substrate.
[0018]
In the semiconductor device according to the present invention, the underlayer is a nitride III-V compound semiconductor containing at least gallium (Ga) and indium (In) of the group 3B element and at least nitrogen (N) of the group 5B element. And the difference in lattice constant from the semiconductor layer is within 1%, so that the indium composition of the semiconductor layer can be easily controlled to a desired value in the manufacturing process.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
[First Embodiment]
FIG. 1 shows a sectional structure of a semiconductor laser according to a first embodiment of the present invention. This semiconductor laser has, for example, an SCH (Separate Definition-Heterostructure) structure, and has an n-side contact layer 14, an n-type cladding layer 15, and an n-type layer on a substrate 11 via a low-temperature buffer layer 12 and a base layer 13. It has a configuration in which a guide layer 16, an active layer (light emitting layer) 17, a p-type guide layer 18, a barrier layer 19, a p-type clad layer 20, and a p-side contact layer 21 are stacked in this order. The substrate 11 is made of, for example, sapphire having a thickness of 80 μm, and a low-temperature buffer layer 12 is formed on the c-plane of the substrate 11.
[0021]
The low-temperature buffer layer 12 is, for example, a buffer layer having a thickness of 20 nm to 30 nm and grown at a relatively low temperature of 450 ° C. to 550 ° C. The low-temperature buffer layer 12 is made of, for example, a nitride-based III-V semiconductor containing at least gallium (Ga) and indium (In) of a group 3B element and at least nitrogen (N) of a group 5B element. ing. In particular, it is preferable to be constituted by an undoped GaInN mixed crystal to which no impurity is added. This is because if the low-temperature buffer layer 12 is made of GaN like the conventional first buffer layer 112 shown in FIG. 5, the lattice constant is determined at that stage, and the effect of the present invention is hardly expected. The material of the low-temperature buffer layer 12 is not limited to the GaInN mixed crystal, but may be, for example, a quaternary AlGaInN mixed crystal.
[0022]
The underlayer 13 is provided, for example, on the substrate 11 with the low-temperature buffer layer 12 interposed therebetween, and at least gallium (Ga) and indium (In) of the group 3B element and at least nitrogen (N) of the group 5B element. And a nitride III-V compound semiconductor containing: Specifically, it is preferable to use, for example, an undoped GaInN mixed crystal to which no impurity is added. Details of the underlayer 13 will be described later.
[0023]
The n-side contact layer 14 has a thickness of, for example, 2 μm, and is made of n-type GaN to which silicon (Si) is added as an n-type impurity.
[0024]
The n-type cladding layer 15 has a thickness of, for example, 1.4 μm, is made of an n-type AlGaN mixed crystal to which silicon is added as an n-type impurity, and has an aluminum composition of 6.5%. The n-type cladding layer 15 may be an AlGaN mixed crystal / GaN superlattice.
[0025]
The n-type guide layer 16 has a thickness of, for example, 0.1 μm, and is made of an n-type GaInN mixed crystal to which silicon is added as an n-type impurity.
[0026]
The active layer 17 is composed of, for example, AlGaInN mixed crystal as a whole, and has a multiple quantum well structure in which barrier layers and well layers are alternately stacked. The indium composition of the well layer of the active layer 17 needs to be large to some extent in order to constitute an element that emits blue or green light. For example, when the oscillation wavelength is longer than 440 nm, the active layer The indium composition of the seventeenth well layer is preferably set to 14% or more. Specifically, when the oscillation wavelength is 460 nm, the active layer 17 is made of, for example, AlGa. _0.95 In _0.05 A 6 nm-thick barrier layer made of N mixed crystal, and AlGa _0.82 In _0.18 It has a multiple quantum well structure in which well layers each having a thickness of 3 nm made of N mixed crystal are alternately stacked, and the number of wells is three. Here, the active layer 17 corresponds to the “semiconductor layer” in the present invention.
[0027]
The p-type guide layer 18 has a thickness of, for example, 0.1 μm, and is made of p-type GaN to which magnesium (Mg) is added as a p-type impurity.
[0028]
The desorption preventing layer 19 is for preventing indium from being desorbed from the active layer 17 and for suppressing an overflow of the injection current. The desorption preventing layer 19 is provided on, for example, a part of the p-type guide layer 18 and is made of AlGaN mixed crystal, and has a thickness of, for example, 10 nm.
[0029]
The p-type cladding layer 20 has a thickness of, for example, 0.5 μm, is made of a p-type AlGaN mixed crystal to which magnesium is added as a p-type impurity, and has an aluminum composition of 6.0%. Note that, as the p-type cladding layer 20, an AlGaN mixed crystal / GaN superlattice may be used.
[0030]
The p-side contact layer 21 has a thickness of, for example, 0.1 μm, and is made of p-type GaN to which magnesium is added as a p-type impurity.
[0031]
On the p-side contact layer 21, a p-side electrode 22 is formed. The p-side electrode 22 has, for example, a structure in which palladium (Pd), platinum (Pt), and aluminum (Al) are sequentially stacked from the p-side contact layer 21 side. Connected. The p-side electrode 22 is also extended in a band shape so as to constrict the current, and a region of the active layer 17 corresponding to the p-side electrode 22 is a light emitting region. On the other hand, an n-side electrode 23 is formed on the n-side contact layer 14. The n-side electrode 23 has, for example, a structure in which titanium (Ti) and aluminum are sequentially laminated and alloyed by heat treatment, and is electrically connected to the n-side contact layer 14.
[0032]
In this semiconductor laser, for example, a pair of side faces facing each other in the length direction of the p-side electrode 22 are resonator end faces, and a pair of reflecting mirror films (not shown) are formed on the pair of resonator end faces, respectively. I have. The reflectance of one of the pair of reflecting mirror films is adjusted so as to decrease the reflectance, and the other of the reflecting mirror films is adjusted to increase the reflectance. As a result, light generated in the active layer 17 reciprocates between a pair of reflecting mirror films and is amplified, and is emitted from one of the reflecting mirror films as a laser beam.
[0033]
Next, the underlayer 13 in the present embodiment will be described in detail. First, it is preferable that the lattice constant of the underlayer 13 be as close as possible to the lattice constant of the active layer 17. This is because the strain introduced into the active layer 17 during crystal growth can be reduced. Specifically, it is preferable that the difference in lattice constant between the underlayer 13 and the active layer 17 be within 1%. The reason is that, in a semiconductor laser having an active layer of a strained quantum well structure formed on a sapphire substrate and having an oscillation wavelength of 405 nm, a practical level characteristic is obtained when the lattice constant difference between the underlayer and the active layer is within the above range. This is because the effect of reducing the distortion of the active layer 17 is considered to be most exhibited within the above range. Here, the "lattice constant of the active layer 17" refers to the lattice constant of the well layer when the active layer 17 has a quantum well structure, and when the active layer 17 is a bulk type having one thick layer. It refers to the lattice constant of the thick layer.
[0034]
The lower limit of the lattice constant of the underlayer 13 is preferably equal to or greater than the lattice constant of GaN, specifically, equal to or greater than the lattice constant of the conventional second buffer layer 113 made of GaN shown in FIG. By doing so, the lattice constant of the active layer 17 becomes closer to that of the conventional second buffer layer 113 (see FIG. 5) made of GaN, so that the compressive strain introduced into the active layer 17 during crystal growth is increased. This is because the effect of the present invention that the upper limit value of becomes smaller can be obtained.
[0035]
The upper limit of the lattice constant of the underlayer 13 is preferably equal to or less than the lattice constant of the active layer 17 in the free standing state. If the lattice constant of the underlayer 13 significantly exceeds the lattice constant of the active layer 17 in the free standing state, the active layer 17 may be subject to tensile strain. However, even if the lattice constant in the free standing state of the active layer 17 is slightly exceeded, the effect of the present invention can be obtained as long as the lattice constant difference from the active layer 17 is within 1% as described above. In particular, if the lattice constant of the underlayer 13 is made equal to the lattice constant of the active layer 17 in the free standing state, the compressive strain introduced into the active layer 17 during crystal growth becomes zero, and the greatest effect can be expected.
[0036]
The thickness of the underlayer 13 is preferably, for example, not less than 1.5 μm and not more than 4 μm. If the thickness is smaller than 1.5 μm, the crystallinity of the active layer 17 may decrease due to the state of the interface, and if the thickness is larger than 4 μm, the substrate 11 may be cracked due to a difference in thermal expansion coefficient. .
[0037]
The growth temperature of the underlayer 13 is preferably higher than the growth temperature of the low-temperature buffer layer 12, for example, 600 ° C. or more and 800 ° C. or less.
[0038]
This semiconductor laser can be manufactured, for example, as follows.
[0039]
First, a substrate 11 of, for example, sapphire having a thickness of about 430 μm is prepared, and a low-temperature buffer layer 12, a base layer 13, an n-side contact layer 14, an n-type cladding layer are formed on, for example, a c-plane of the substrate 11 by, for example, MOCVD. 15, an n-type guide layer 16, an active layer 17, a p-type guide layer 18, a desorption preventing layer 19, a p-type clad layer 20, and a p-side contact layer 21 are sequentially grown.
[0040]
Specifically, first, the low-temperature buffer layer 12 made of, for example, undoped GaInN mixed crystal is grown on the substrate 11 at a temperature of, for example, about 450 ° C. to 550 ° C. Next, for example, the temperature of the substrate 11 is raised to 600 ° C. or more and 800 ° C. or less, and on the low-temperature buffer layer 12, an underlayer 13 made of mixed GaInN, an n-side contact layer 14 made of n-type GaN, and an n-type AlGaN An n-type clad layer 15 made of a mixed crystal and an n-type guide layer 16 made of an n-type GaInN mixed crystal are sequentially grown. Subsequently, for example, AlGa _0.95 In _0.05 Barrier layer made of N mixed crystal and AlGa _0.82 In _0.18 The active layer 17 is formed by alternately growing well layers made of N mixed crystal. Here, since the underlayer 13 is made of a GaInN mixed crystal and the lattice constant difference with the active layer 17 is within 1%, the underlayer 13 is compared with the conventional second buffer layer 113 made of GaN (see FIG. 5). The lattice constant of 13 becomes close to the lattice constant of active layer 17, and indium is easily taken in without causing defects in active layer 17 during crystal growth. Further, the distortion introduced into the active layer 17 is reduced, and the Stark effect is less likely to be exhibited.
[0041]
After that, for example, on the active layer 17, a p-type guide layer 18 made of a p-type GaInN mixed crystal, a desorption preventing layer 19 made of an AlGaN mixed crystal, a p-type clad layer 20 made of a p-type AlGaN mixed crystal, and p A p-side contact layer 21 of type GaN is sequentially grown.
[0042]
When MOCVD is performed, the source gas of gallium is, for example, trimethylgallium ((CH ₃ ) ₃ Ga) or triethylgallium ((C ₂ H ₅ ) ₃ Ga), as a source gas of aluminum, for example, trimethylaluminum ((CH ₃ ) ₃ Al) and indium as a source gas, for example, trimethylindium ((CH ₃ ) ₃ In), for example, ammonia (NH) ₃ ) Are used. As the silicon source gas, for example, monosilane (SiH ₄ ), And, for example, bismethylcyclopentadienyl magnesium ((C ₅ H ₅ ) ₂ Mg).
[0043]
After growing the p-side contact layer 21, for example, a mask (not shown) made of a resist is selectively formed on the p-side contact layer 21. Next, using this mask, the p-side contact layer 21, the p-type cladding layer 20, the desorption preventing layer 19, the p-type guide layer 18, the active layer 17, the n-type guide layer 16, the n-type clad layer 15, and the n-side A part of the contact layer 14 is sequentially etched to expose the n-side contact layer 14 on the surface. Subsequently, for example, titanium and aluminum are sequentially deposited to form the n-side electrode 23, and a heat treatment is performed to alloy the n-side electrode 23. After the heat treatment, p-side electrode 22 is formed by sequentially depositing, for example, palladium, platinum and gold.
[0044]
After the p-side electrode 22 is formed, the substrate 11 is ground to a thickness of, for example, about 80 μm. After the substrate 11 is ground, it is adjusted to a predetermined size, and a reflection mirror film (not shown) is formed on a pair of resonator end faces facing each other in the length direction of the p-side electrode 22. Thus, the semiconductor laser shown in FIG. 1 is completed.
[0045]
In the semiconductor laser of the present embodiment, when a predetermined voltage is applied between the n-side electrode 23 and the p-side electrode 22, a current is injected into the active layer 17 and light emission is caused by electron-hole recombination. Occur. Here, since the underlayer 13 is made of a GaInN mixed crystal and the lattice constant difference with the active layer 17 is within 1%, the underlayer 13 is compared with the conventional second buffer layer 113 made of GaN (see FIG. 5). The lattice constant of 13 becomes close to the lattice constant of active layer 17, and indium is easily taken in without causing defects in active layer 17 during crystal growth. Therefore, a decrease in the indium composition of the active layer 17 due to the composition incorporation effect is prevented, the luminous efficiency is increased, the threshold value of the semiconductor laser is reduced, and the device life is prolonged. Further, since the distortion introduced into the active layer 17 is reduced and the Stark effect is hardly developed, the luminous efficiency is increased and the threshold value of the semiconductor laser is reduced, so that the slope efficiency is improved. Further, the blue shift of the emission wavelength with respect to the amount of injected current is suppressed.
[0046]
As described above, in the present embodiment, the base layer 13 is formed of GaInN mixed crystal and the lattice constant difference from the active layer 17 is set to be within 1%. Indium can be easily taken in without generating. Therefore, it is possible to prevent a decrease in the indium composition of the active layer 17 due to the composition-introducing effect, and to suppress the manifestation of the Stark effect, thereby increasing the luminous efficiency, reducing the threshold value of the semiconductor laser, improving the slope efficiency, and In addition, suppression of blue shift with respect to the injection current amount of the emission wavelength can be achieved. In addition, since the restriction on the thickness of the active layer 17 is eliminated, the degree of freedom in element design can be increased.
[0047]
These effects are particularly remarkable when the indium composition of the active layer 17 is large to some extent, and therefore are particularly effective for devices that emit blue or green light.
[0048]
[Second embodiment]
FIG. 2 shows a sectional structure of a semiconductor laser according to a second embodiment of the present invention. This semiconductor laser uses a substrate 31 made of GaInN mixed crystal, the underlayer 13 is formed directly on the substrate 31 without providing the low-temperature buffer layer 12, and the n-side electrode 23 is formed on the back surface of the substrate 31. Other than that, it has the same configuration as that of the first embodiment. Therefore, here, the same components are denoted by the same reference numerals, and detailed description of the same portions will be omitted.
[0049]
The substrate 31 is made of, for example, indium chloride (InCl ₃ ), Gallium chloride (GaCl ₃ ) And ammonia (NH ₃ ) As a raw material by a vapor phase growth method. It is preferable that the indium composition of the substrate 31 be substantially the same as the indium composition of the well layer of the active layer 17 (the difference in lattice constant is within 1%). This is because the effect of the present invention that distortion introduced into the active layer 17 during crystal growth is reduced can be further enhanced.
[0050]
This semiconductor laser can be manufactured in the same manner as in the first embodiment, operates in the same manner, and can achieve the same effect.
[0051]
[Third Embodiment]
FIG. 3 shows a sectional structure of a semiconductor laser as a semiconductor device according to a third embodiment of the present invention. This semiconductor laser has the same configuration as that of the first embodiment except that it is a vertical cavity surface emitting laser. Therefore, here, the same components are denoted by the same reference numerals, and detailed description of the same portions will be omitted.
[0052]
In this semiconductor laser, an n-side contact layer 14 and an n-side distributed Bragg reflection composed of an n-type semiconductor multilayer film are disposed on an upper surface side of a substrate 11 via, for example, a low-temperature buffer layer 12 and an underlayer 13. DBR) layer 45, n-type guide layer 16, active layer 17, p-type guide layer 18, p-side distributed Bragg reflection (DBR) layer 50 composed of a p-type semiconductor multilayer film, for example, SiO ₂ Insulating film 51 and p-side contact layer 21 are laminated in this order.
[0053]
This semiconductor laser can be manufactured substantially in the same manner as in the first embodiment, and the same effect can be obtained since it has the same underlayer 13 as in the first embodiment.
[0054]
As described above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above embodiment, and can be variously modified. For example, in the first embodiment, the case where the substrate 11 made of sapphire is used has been described, but the substrate 11 may be made of silicon carbide (SiC).
[0055]
In the second embodiment, the case where the substrate 31 made of GaInN mixed crystal is used has been described. However, the substrate 31 may be made of GaN.
[0056]
Further, in the third embodiment, the case where the vertical cavity surface emitting laser is formed on the substrate 11 made of sapphire has been described, but a substrate made of GaInN mixed crystal or GaN may be used. In that case, the underlayer 13 can be provided immediately above the substrate as in the second embodiment.
[0057]
In addition, in the above embodiment, the low-temperature buffer layer 12 and the base layer 13 are grown upward from the entire surface of the substrate 11, but as shown in FIG. A seed crystal layer 11A made of a GaInN mixed crystal is formed thereon in a predetermined pattern, and a concave portion 11B is formed in the substrate 11. Then, as shown in FIG. 4B, the GaInN mixed crystal is formed using the seed crystal 11A. The underlying layer 13 may be formed by growing crystals in the lateral direction. In this case, the thickness D of the underlayer 13 is not the distance between the upper surface of the seed crystal layer 11A and the upper surface of the underlayer 13, but the gap D between the underlayer 13 and the substrate 11 and the thickness of the underlayer 13. This is the distance from the upper surface. Also, a low temperature buffer layer is not required.
[0058]
Although a laser having an n-type guide layer and a p-type guide layer has been described as a specific configuration, the present invention can also be applied to a semiconductor laser without these guide layers. The current confinement structure is not limited to the above embodiment. Further, the waveguide system may be either a refractive index waveguide type or a ridge waveguide type. In addition, although the material constituting each layer has been specifically described by way of example, each layer may be made of another nitride-based III-V compound semiconductor.
[0059]
Furthermore, in the above embodiment, the low-temperature buffer layer 12, the underlayer 13, the n-side contact layer 14, the n-type cladding layer 15, the n-type guide layer 16, the active layer 17, the p-type guide layer 18, the desorption preventing layer 19, the case where the p-type cladding layer 20 and the p-side contact layer 21 are formed by the MOCVD method has been described, but an MBE (Molecular Beam Epitaxy) method may be used. In this case, as raw materials, aluminum (Al), gallium (Ga), indium (In), magnesium (Mg), silicon (Si) and ammonia (NH) ₃ ) Can be used. Alternatively, it may be formed by another vapor deposition method such as a hydride vapor deposition method or a halide vapor deposition method.
[0060]
Furthermore, in the above embodiment, the semiconductor laser is described as a specific example of the semiconductor element. However, the present invention includes at least gallium and indium of the group 3B element and at least nitrogen of the group 5B element. The present invention can be widely applied to a semiconductor device including a semiconductor layer made of a nitride III-V compound semiconductor. For example, the invention can be similarly applied to other light-emitting elements such as a light-emitting diode, and furthermore, can be applied to an electronic element such as a transistor.
[0061]
【The invention's effect】
As described above, according to the semiconductor device of the present invention, the underlayer is formed by nitriding containing at least gallium (Ga) and indium (In) of the Group 3B element and at least nitrogen (N) of the Group 5B element. And the lattice constant difference between the semiconductor layer and the semiconductor layer is within 1%, so that the lattice constant of the underlayer is closer to the lattice constant of the semiconductor layer than the conventional buffer layer made of GaN. Thus, indium can be easily taken in without causing defects in the semiconductor layer during crystal growth. Therefore, it is possible to prevent a reduction in the indium composition of the semiconductor layer due to the composition incorporation effect, and to increase the luminous efficiency of the light emitting element, reduce the threshold value of the semiconductor laser, and further increase the life of the element. it can.
[0062]
In addition, since the strain introduced into the semiconductor layer is reduced, the Stark effect can be suppressed, which also increases the luminous efficiency of the light emitting device, reduces the threshold of the semiconductor laser, and improves the slope efficiency. Further, it is possible to achieve suppression of blue shift with respect to the injection current amount of the emission wavelength. In addition, since the restriction on the thickness of the semiconductor layer is eliminated, the degree of freedom in element design can be increased.
[0063]
These effects are particularly remarkable when the indium composition of the semiconductor layer is large to some extent, and are therefore particularly effective for light-emitting elements that emit blue or green light.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a semiconductor laser according to a first embodiment of the present invention.
FIG. 2 is a sectional view illustrating a configuration of a semiconductor laser according to a second embodiment of the present invention.
FIG. 3 is a sectional view illustrating a configuration of a semiconductor laser according to a third embodiment of the present invention.
FIG. 4 is a sectional view illustrating a modification of the present invention.
FIG. 5 is a cross-sectional view illustrating a configuration of a conventional semiconductor laser.
FIG. 6 is a diagram illustrating an actual example of the Stark effect in the case of weak excitation and the case of strong excitation.
7 is a diagram showing a threshold power density corresponding to the excitation power density in the case of strong excitation shown in FIG.
[Explanation of symbols]
11, 31: substrate, 12: low-temperature buffer layer, 13: base layer, 14: n-side contact layer, 15: n-type cladding layer, 16: n-type guide layer, 17: active layer (semiconductor layer), 18: p Mold guide layer, 19: desorption preventing layer, 20: p-type cladding layer, 21: p-side contact layer, 22: p-side electrode, 23: n-side electrode

Claims (12)

Board and
A nitride-based III-V compound semiconductor provided on one surface side of the substrate and containing at least gallium (Ga) and indium (In) of group 3B elements and at least nitrogen (N) of group 5B elements. A semiconductor layer,
It is made of a nitride III-V compound semiconductor containing at least gallium (Ga) and indium (In) of the group 3B element and at least nitrogen (N) of the group 5B element, and has a lattice constant with the semiconductor layer. A semiconductor element, wherein the difference is within 1%, and comprising a base layer provided between the semiconductor layer and the substrate. 2. The semiconductor device according to claim 1, wherein the semiconductor layer is an active layer, and a composition of indium contained in the active layer is 14% or more. 2. The semiconductor device according to claim 1, wherein said underlayer is made of GaInN mixed crystal. 2. The semiconductor device according to claim 1, wherein the underlayer is provided immediately above the substrate. The semiconductor device according to claim 4, wherein the substrate is made of GaN or GaInN mixed crystal. The underlayer is a nitride-based III-V compound containing at least gallium (Ga) and indium (In) of a group 3B element and at least nitrogen (N) of a group 5B element on the substrate. 2. The semiconductor device according to claim 1, wherein the semiconductor device is provided via a low-temperature buffer layer made of a semiconductor. The substrate, sapphire (Al 2 _{O 3)} or a semiconductor device according to claim 6, characterized in that it is constituted by a silicon carbide (SiC). 7. The semiconductor device according to claim 6, wherein the low-temperature buffer layer is made of GaInN mixed crystal. 2. The semiconductor device according to claim 1, wherein a lattice constant of the underlayer is equal to or larger than a lattice constant of GaN. 2. The semiconductor device according to claim 1, wherein a lattice constant of the underlayer is equal to or smaller than a lattice constant of the semiconductor layer in a free standing state. 2. The semiconductor device according to claim 1, wherein the thickness of the underlayer is 1.5 μm or more and 4 μm or less. 2. The semiconductor device according to claim 1, wherein a growth temperature of the underlayer is not less than 600 ° C. and not more than 800 ° C.

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