JP4553457B2 - III-V compound semiconductor device having pn junction - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a group III-V compound semiconductor device that can be used for light emitting diodes, laser diodes, solar cells, and the like, such as GaN-based compound semiconductors, AlGaAs-based compound semiconductors, and InAlGaP-based compound semiconductors. More specifically, it has a pn junction of a photoelectric conversion element such as a semiconductor light-emitting element or a solar cell that prevents dopants from interdiffusion through a pn junction and each semiconductor layer has low resistance and excellent device characteristics. The present invention relates to a III-V compound semiconductor device.
[0002]
[Prior art]
Group III-V compound semiconductors are, for example, compound semiconductors such as AlGaAs, InAlGaP, GaP, and GaN, light emitting diodes (LEDs) ranging from infrared to ultraviolet, semiconductor light emitting devices such as laser diodes (LD), Is used in thin film solar cells and the like, and is used in various fields. The semiconductor light emitting device has a double hetero structure in which, for example, an n-type layer and a p-type layer are joined, or an active layer is sandwiched between the n-type layer and the p-type layer, and a forward voltage is applied to the pn junction. Light is emitted by injecting holes into the junction and recombining electrons and holes.
[0003]
Therefore, it is preferable that the n-type layer and the p-type layer have a higher carrier concentration, so that current can be easily injected, and a large current can be injected at a low operating voltage. However, in actual devices, the AlGaAs-based and InAlGaP-based compounds described above can obtain only about 10 ¹⁹ to 2 × 10 ²⁰ cm ^{−3 for} the n-type layer and about 1 × 10 ¹⁸ cm ^{−3 for the} p-type layer. For example, it becomes smaller than the carrier concentration in a single layer of only the n-type layer.
In addition, GaN-based compounds that have recently been developed as blue light-emitting elements have a lower carrier concentration.
[0004]
In addition, when a double heterostructure is used in the above-described LED or LD, depending on the element, if the dopant diffuses into the active layer, it is not preferable because the crystallinity of the active layer is reduced or light is emitted due to impurity levels. There is an example in which the device is configured by reducing the carrier concentration of at least the n-type layer or p-type layer close to the active layer as much as possible, and the series resistance is further increased.
[0005]
[Problems to be solved by the invention]
As described above, when a device having a pn junction is used as compared with a device having a single conductivity type and no impurity concentration gradient, each carrier concentration decreases, and the operating voltage of a semiconductor light emitting element increases. In addition, the luminous efficiency of the solar cell is reduced, and the photoelectric conversion efficiency of the solar cell is reduced. Further, as described above, if the carrier concentration of the n-type layer or p-type layer sandwiching the active layer is lowered in order to minimize the diffusion of the dopant into the active layer, the operating voltage is further increased and the luminous efficiency is reduced. There's a problem. These problems have become serious problems with the recent spread of battery-powered portable devices such as mobile phones, and the demand for electronic components with even lower power consumption.
[0006]
The present invention has been made to solve such a problem. Even in a device in which a pn junction is formed, the carrier concentration of the n-type layer and the p-type layer is maintained high, and the n-type layer in contact with the active layer is provided. There is provided a III-V group compound semiconductor device having a pn junction that can suppress the diffusion of impurities into the active layer without reducing the carrier concentration of the p-type layer and that operates with low resistance and high efficiency. For the purpose.
[0007]
Another object of the present invention is to provide a semiconductor light emitting device such as an LED or an LD that emits light with high efficiency at a low voltage with a high carrier concentration in the n-type layer and the p-type layer.
[0008]
[Means for Solving the Problems]
The III-V compound semiconductor device having a pn junction according to the present invention includes an n-type layer made of a III-V compound semiconductor and a p-type layer made of a III-V compound semiconductor , sandwiching an undoped active layer. In the semiconductor device in which a pn junction is formed, the n-type layer has a donor-acceptor complex containing an n-type dopant and a p-type dopant acting as a donor , and the p-type layer is An acceptor-donor composite containing a p-type dopant and an n-type dopant has a pn junction formed by acting as an acceptor .
[0009]
Having a pn junction here means not only when the n-type layer and the p-type layer are directly joined, but also when the undoped layer is sandwiched between the n-type layer and the p-type layer as in the double hetero structure of the light-emitting element. This also includes the structure.
[0010]
By adopting this structure, a donor-acceptor complex such as Si—Mg—Si (III-V compound constituent elements are omitted) is formed in the n-type layer, and is formed by a chemical bond due to mutual strong attraction. A donor that becomes stable in mass and does not diffuse due to heat or electric field can be realized. Similarly, in this state, a stable acceptor can be realized by forming, for example, an Mg—Si—Mg acceptor-donor complex in the p-type layer. As a result, the phenomenon that the dopant diffuses or evaporates to the outside due to the temperature during the growth of the semiconductor layer, the subsequent annealing, the temperature rise during the operation, or the application of voltage is suppressed. Further, since the shared energy due to the interaction between the donor and the acceptor is strong, the level of the donor and the acceptor becomes shallow, and the activation energy becomes small, so that the carrier concentration is further increased. As a result, it is possible to obtain a semiconductor layer having a highly stable dopant with a carrier concentration that is two to three times higher than that of the conventional structure and one digit or more higher than that of the p-type layer. become.
[0011]
The group III-V compound semiconductor is made of a GaN-based compound, and the n-type layer includes n-type dopant Si more than p-type dopant Mg, and n-state in a state where Si-N-Mg-N-Si is bonded. The p-type layer is formed such that Mg as the p-type dopant is more than the n-type dopant Si, and acts as the p-type dopant in a state where Mg—N—Si—N—Mg is bonded. This is particularly preferable because a strong bonding force between the n-type dopant and the p-type dopant can be obtained and thermal diffusion can be suppressed.
[0012]
The atomic concentration ratio between the n-type dopant and the p-type dopant in the n-type layer, or the atomic concentration ratio between the p-type dopant and the n-type dopant in the p-type layer is 1.3: 1 to 3: 1, respectively. It is preferable to obtain a large carrier concentration.
[0013]
If the laminated structure of the n-type layer and the p-type layer is a light-emitting layer forming part that sandwiches the active layer between the n-type clad layer and the p-type clad layer, the double heterojunction high-brightness LED or LD is low. It can be obtained at the operating voltage. In particular, by using a GaN-based compound semiconductor capable of emitting blue light, it has been difficult to increase the carrier concentration of the p-type layer, and the operating voltage is high. In addition, the n-type layer can also increase the carrier concentration, and the effect becomes more remarkable.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, a group III-V compound semiconductor device having a pn junction according to the present invention will be described with reference to the drawings. A group III-V compound semiconductor device having a pn junction according to the present invention comprises a group III-V compound semiconductor, for example, a GaN compound semiconductor, as shown in FIG. A pn junction is formed by laminating an n-type layer (clad layer) 3 and a p-type layer (clad layer) 5 made of a III-V compound semiconductor, for example, a GaN compound semiconductor (shown in FIG. 1). In this example, an active layer 4 made of an undoped InGaN-based compound semiconductor is interposed between the n-type layer 3 and the p-type layer 5). In the present invention, the n-type layer 3 contains not only an n-type dopant such as Si but also a p-type dopant such as Mg, and the p-type layer 5 also includes, for example, Mg. It is characterized by containing not only a p-type dopant but also an n-type dopant such as Si.
[0015]
The n-type layer 3 is formed by doping a group III-V compound such as GaN with an n-type dopant, for example, Si and a p-type dopant, for example, Mg. That is, when Si is doped more than Mg, it is formed into an n-type. For example, as shown in FIG. 2, the bonding model indicates that Si and Mg enter Si at the adjacent Ga position of GaN. It enters in a bonded state of -Mg-N-Si and acts as an n-type dopant of Si in a stable state. In this way, Si and Mg have a structure bonded through N, but they are electrically positive and negative, and they are attracted to each other by Coulomb attractive force, which is very stable. In this state, Si more than Mg in quantity acts as a donor.
[0016]
The model shown in FIG. 2 is an example in which two Si are doped in a relationship of Si: Mg = 2: 1 in which one Mg and N are bonded through N. It is not necessarily doped in the relationship of: 1. However, since the interaction as described above works between Si and Mg, even if Si and Mg do not enter the adjacent Ga positions, and they enter each other, they are coulombs between them. Maintains a mutually stable structure due to attractive force, acts as if the mass has tripled locally, becomes very difficult to diffuse even when the temperature rises, and acts as a donor due to the fact that Si is more than Mg To do.
[0017]
For example, FIGS. 3A to 3C show the state of this doping in a two-dimensional manner with a tetracoordinate compound in which a donor can possibly enter (a III-V compound becomes a tetracoordinate compound). It is preferable that (donor) :( acceptor) is contained in a ratio of 3: 1 to 1.3: 1 as shown in the modeled example in FIG. That is, FIG. 3 (a) shows an example (Si: Mg = 3: 1) in which two donors (for example, Si) and one acceptor (for example, Mg) are combined and one acceptor is included. Is an example that exists throughout. If donors increase more than this, the repulsive force between donors will become large and it will be considered that it is the upper limit about solubility. Further, the example shown in FIG. 3B is an example in which the above-described combination of two donors and one acceptor is present in the entire element (Si: Mg = 2: 1), and is the most energy stable. State. FIG. 3C shows an example in which one pair of two donors and one acceptor and two pairs each having one donor and one acceptor exist (Si: Mg = 1.3: 1). This corresponds to the minimum example of acting as a donor. In FIG. 3, white circles represent elements constituting the compound, black circles represent acceptors (Mg), and white circles surrounded by black circles represent donors (Si).
[0018]
The n-type dopant is not limited to the above-mentioned Si, but may be oxygen, and an element having a small atomic number is preferable as much as possible. However, other group IV elements or group VI elements may be used. When O is used as the n-type dopant, O enters the N position of GaN. Therefore, Mg and O enter adjacent Ga and N, respectively, resulting in a stronger bond of O—Mg—O. Further, as the p-type dopant, a group II element such as Zn or a group IV element such as C can be used in addition to the above-mentioned Mg.
[0019]
In order to dope both Si and Mg, for example, when growing by metal organic chemical vapor deposition (MOCVD), together with trimethylgallium (TMG) and ammonia (NH ₃ ) which are reaction gases for GaN growth, It is obtained by introducing silane (SiH ₄ ) and cyclopentadienyl magnesium (Cp ₂ Mg) in a ratio of about 2: 1. If the amount of Si is too large, Si is easy to move and diffuses to the p-type layer side as in the case of doping Si alone, and the thin film crystal is distorted as a lattice penetration type. The conductivity becomes worse. In addition, since the bond between Si and Mg described above may be decomposed and fluctuated if the temperature of annealing after film formation is too high, it is necessary not to increase the temperature during annealing. .
[0020]
Contrary to the n-type layer 3, the p-type layer 5 is formed by doping a III-V group compound such as GaN with a large amount of Mg as a p-type dopant and a small amount of Si as an n-type dopant. That is, it is formed in a p-type by doping Mg more than Si, for example, in a structure in which Si and Mg in the bond model shown in FIG. 2 are reversed, and Mg and Si enter the Ga position of GaN. As in the case of the n-type, the Mg—N—Si—N—Mg is bonded, and Mg acts as a p-type dopant in a stable state. As in the case of the n-type as described above, the p-type dopant is entered in the model shown in FIG. 3, and only the donor and the adapter are reversed, and Mg: Si = (1.3-3) ) It is preferable to dope so as to be 1.
[0021]
In order to grow the p-type layer 5 doped with both Mg and Si, in the case of the MOCVD method, while introducing the same gas as in the case of the n-type layer 3 described above, cyclopentadienyl magnesium (Cp ₂ Mg ) Is introduced at a ratio more than twice that of silane (SiH ₄ ). That is, since Mg is easier to evaporate than Si, in order to dope the ratio of Mg: Si to about 2: 1, it is necessary to introduce Mg dopant gas more than twice as much as Si dopant gas. As described above, the ratio of Mg and Si to be finally doped is set to Mg: Si = (1.3 to 3): 1, which prevents thermal diffusion of Mg and a deep acceptor. It is preferable from the viewpoint of preventing the formation. In this case, since Mg easily evaporates, care must be taken not to raise the annealing temperature to 900 ° C. or higher.
[0022]
In order to manufacture the LED shown in FIG. 1, the buffer layer 2 is deposited on the sapphire (Al ₂ O ₃ ) substrate 1 at a low temperature of about 400 to 600 ° C. at a temperature of about 0.01 to 2 μm, and then 600 to 1000. The above-described n-type layer 3 that becomes a cladding layer at a high temperature of about 1 ° C. has a thickness of about 1 to 5 μm and a material whose band gap energy is smaller than that of the cladding layer, for example, an active layer 4 made of an InGaN-based compound semiconductor is 0.05 to 0.05. A pn junction is formed by sequentially laminating the p-type layer 5 of about 0.3 μm and about 0.2 to 1 μm. For simplicity, the n-type layer 3 and the p-type layer 5 are made of GaN. However, in order to increase the bandgap energy, the n-type layer 3 and the p-type layer 5 are made of an AlGaN compound or an AlGaN compound semiconductor layer is provided on the active layer 4 side. It can also be composed of a composite layer with a GaN layer or the like.
[0023]
Then, Ni and Au are deposited on the surface by vacuum deposition or the like, and sintered at about 400 to 700 ° C., thereby forming a current diffusion layer 7 that is conductive and transmits light to a thickness of about 2 to 100 nm. Thereafter, a resist film or the like is provided on the surface of the current diffusion layer 7 for patterning, and the current diffusion layer 7 and part of the semiconductor layers 3 to 5 are etched by reactive ion etching using chlorine gas or the like to form an n-type layer. 3 is exposed, Ti and Al are formed by vacuum deposition or the like, and the n-side electrode 9 is formed by sintering, and the p-side electrode 8 is formed by laminating Ti and Au on the current diffusion layer 7, respectively. By forming each and forming a chip, the LED chip shown in FIG. 1 having a double hetero structure in which the active layer 4 is sandwiched between the n-type layer 3 and the p-type layer 5 is obtained.
[0024]
According to the present invention, the n-type layer 3 and the p-type layer 5 are not only doped with a single dopant of n-type dopant (donor) or p-type dopant (acceptor), respectively, but also have a main conductivity type dopant. However, the dopant of the opposite conductivity type is simultaneously doped with about half of the main dopant. For this reason, in the compound semiconductor, the donor and the acceptor are bonded by a strong attractive force between each other, and maintain a very stable state that is difficult to move with respect to heat and an electric field, and act as a donor or an acceptor. As a result, it is possible to maintain a high concentration of donors and acceptors without interdiffusion even when the temperature of the semiconductor layer is increased during growth or after annealing. Can be realized. In particular, the carrier concentration of the n-type layer was conventionally considered to reach a saturation state at about 10 ¹⁹ to 10 ²⁰ cm ^-3 , but according to the present invention, the carrier concentration is about 6 × 10 ²⁰ cm ^-3. A concentration was obtained, and a carrier concentration of about 2 to 3 times was obtained. Regarding the p-type layer, a carrier concentration of about 2 to 3 × 10 ²⁰ cm ^-3 was obtained, although the limit of about 10 ¹⁸ cm ^-3 was conventionally limited.
[0025]
Furthermore, the coexistence of the donor and the acceptor makes the shared energy strong, so that the level of the donor and acceptor becomes shallow, and as a result, more carriers are activated and mobility is increased, resulting in less dopant. The resistance can be further reduced. As a result, the internal quantum efficiency is further improved, and a large light output can be obtained when the light emitting device is used.
[0026]
As described above, conventionally, for example, GaN-based compounds have been studied to further increase the carrier concentration for the p-type layer, but for the n-type layer, the carrier concentration is sufficient, Although the mobility due to the entry has hardly been a problem, according to the present invention, the diffusion of the n-type layer is prevented, the mobility is improved, and the n-type layer has a very low resistance. In the case of a device having a junction, the effect is particularly remarkable. In addition, according to the present invention, since the thermal diffusion of the dopant can be prevented, the active layer is conventionally used from the viewpoint of avoiding a decrease in luminous efficiency due to the dopant diffusing into the active layer and reducing the crystallinity of the active layer. In some cases, the carrier concentration of the cladding layer in contact with the substrate is very small, but even in such a case, the entire n-type layer and p-type layer can be formed with a high carrier concentration. A large current can be obtained at a much lower operating voltage, and a highly efficient light-emitting element can be obtained.
[0027]
In the above example, the LED is an example, but even in the case of the LD, only the semiconductor layer stack structure is slightly different, and in addition to the main dopant in the n-type layer and the p-type layer, other conductive type dopants are added. By doping so as to be slightly reduced, a semiconductor laser having a low operating voltage and a large output can be obtained. Furthermore, it is needless to say that the present invention can be similarly applied to a device in which an n-type layer and a p-type layer are stacked so as to form a pn junction, such as a solar battery.
[0028]
Furthermore, in the above-mentioned example, it was an example of a GaN-based compound semiconductor. However, with a GaN-based compound, it is difficult to obtain a semiconductor layer with a high carrier concentration, the operating voltage tends to be high due to the large band gap energy, etc. However, other AlGaAs compounds, AlGaInP compounds, GaP compounds, etc. can increase the carrier concentration, and can reduce the impurity level to increase the electron mobility. The device efficiency such as luminous efficiency is improved and the operating voltage can be lowered, which is particularly effective when used for a battery-driven portable device.
[0029]
In the above-described example, each semiconductor layer is grown by the MOCVD method. However, it can be similarly grown by the molecular beam epitaxy (MBE) method. In this case, a compound semiconductor layer having a composite dopant (cluster in which a donor and an acceptor are bonded) is obtained by reacting and growing on the substrate by directly irradiating each metal instead of a reactive gas. Note that plasma nitrogen is used as a raw material of N.
[0030]
【The invention's effect】
According to the present invention, since both the n-type layer and the p-type layer of the III-V group compound semiconductor having a pn junction have high-concentration donors and acceptors and the impurity levels thereof can be shallow, Excellent characteristics, such as high concentration, high mobility, stable thermal and electric field, little change with time, excellent light emitting efficiency of semiconductor light emitting devices and solar cells with excellent photoelectric conversion efficiency A group III-V compound semiconductor device having a pn junction can be obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an LED chip which is an embodiment of a compound semiconductor device of the present invention.
2 is a diagram showing a modeled state of doping of the n-type layer of FIG.
FIG. 3 is a diagram showing the doped state of the present invention modeled with a tetracoordinate compound.
[Explanation of symbols]
3 n-type layer 5 p-type layer

Claims (4)

A semiconductor device in which a pn junction is formed by laminating an n-type layer made of a III-V compound semiconductor and a p-type layer made of a III-V compound semiconductor with an undoped active layer interposed therebetween , In the n-type layer , a donor-acceptor composite containing an n-type dopant and a p-type dopant acts as a donor , and the p-type layer is an acceptor-donor composite containing a p-type dopant and an n-type dopant. III-V compound semiconductor device having a pn junction in which an object acts as an acceptor . The group III-V compound semiconductor is made of a GaN-based compound, and the n-type layer includes n-type dopant Si more than p-type dopant Mg, and n-state in a state where Si-N-Mg-N-Si is bonded. 2. The p-type layer acts as a p-type dopant in a state in which Mg as a p-type dopant contains more Mg than an n-type dopant, and Mg—N—Si—N—Mg is bonded. The semiconductor device described.   3. The semiconductor device according to claim 1, wherein an atomic concentration ratio of the n-type dopant to the p-type dopant in the n-type layer is 1.3: 1 to 3: 1.   4. The semiconductor device according to claim 1, wherein an atomic concentration ratio of the p-type dopant to the n-type dopant in the p-type layer is 1.3: 1 to 3: 1.

Images