JPH08316585A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE: To obtain a semiconductor light emitting element in which the uniformity is enhanced in the injection of holes into an active layer of multiple quantum well structure. CONSTITUTION: Holes are injected uniformly into the entire MQW active layer 4 from a p-clad layer 8 by providing a tensile strain layer 5 between the MQW active layer 4, comprising an alternating laminate of compressive strain barrier layer and tensile strain well layer, and the p-clad layer 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device such as a semiconductor laser device or a light emitting diode having an active layer of a multiple quantum well structure in which a plurality of well layers and a plurality of barrier layers are alternately laminated.

[0002]

2. Description of the Related Art Recently, a semiconductor laser device having an active layer having a multiple quantum well structure has been developed for the purpose of reducing the oscillation threshold current, improving the temperature characteristics, and shortening the oscillation wavelength. In particular, for improving the luminous efficiency and reducing the operating current, for example, 14th IE ³ Intl. Semiconductor Laser Con
f. W3.5, p.206, Hiroyama et al. reported a semiconductor laser device having an active layer with a strain-compensated multiple quantum well structure.

FIG. 11: An active layer (hereinafter referred to as MQ) having a strain-compensated multiple quantum well structure of a main part in a conventional semiconductor laser device.
FIG. 3 is an energy band diagram of a W active layer). Figure 11
As shown in, the MQW active layer 4 is formed by alternately stacking four barrier layers 41 and three well layers 42. Outside the barrier layers 41 on both sides, an n-clad layer 3 and a p-clad layer 7 are provided via a light guide layer 43, respectively.

The barrier layer 41 has a band gap larger than that of the well layer 42. The lattice constant of the barrier layer 41 is set to be larger than the lattice constant of the substrate, and the well layer 42 is
Has a lattice constant smaller than that of the substrate. As a result, the barrier layer 41 has compressive strain with respect to the substrate, and the well layer 42 has tensile strain with respect to the substrate. FIG.
1, the compressive strain is indicated by "/" and the tensile strain is indicated by "x"
Indicated by

FIG. 12 is a detailed energy band diagram of the valence band of the MQW active layer 4 in the semiconductor laser device of FIG. In FIG. 12, HH indicates the level of heavy holes, and LH indicates the level of light holes. Heavy holes have a larger effective mass and smaller mobility than light holes. here,
Energy bands of heavy holes and light holes will be described with reference to FIGS. 13 to 15.

FIG. 13 is a diagram showing an energy band structure of a semiconductor layer having no strain, FIG. 14 is a diagram showing an energy band structure of a semiconductor layer having a tensile strain, and FIG. 15 is an energy band structure of a semiconductor layer having a compressive strain. FIG. Here, the unstrained semiconductor layer means a semiconductor layer lattice-matched with the substrate. 13 to 15, the horizontal axis represents the wave number k.

As shown in FIG. 13, in the unstrained semiconductor layer, the top of the heavy hole energy band hh coincides with the top of the light hole energy band lh. On the other hand, as shown in FIG. 14, in the semiconductor layer having tensile strain, the peak of the light hole energy band lh is higher than the peak of the heavy hole energy band hh.
Therefore, the ground state of the holes is a light hole. Also,
As shown in FIG. 15, in the semiconductor layer having compressive strain, the energy band hh of heavy holes is higher than the energy band lh of light holes. Therefore, the ground state of holes is a heavy hole.

Referring again to FIG. 12, since the barrier layer 41 has compressive strain, the level HH of heavy holes is higher in energy than the level of light holes, and the ground state of holes is heavy holes. Becomes On the other hand, since the well layer 42 has tensile strain, the light hole level LH is at a position where the energy is higher than that of the heavy hole level, and the ground state of the holes is a light hole. The energy of heavy holes is 10 to 20 meV lower than the energy of light holes. In such an MQW active layer 4, a heavy hole continuous level (continuous state) HC starts at a position having a higher energy than a light hole continuous level (continuous state) LC. Further, the light guide layers 43 in contact with the barrier layers 41 on both sides are lattice-matched with the substrate, that is, there is no strain.

Therefore, mainly heavy holes are injected into the MQW active layer 4 from the p-clad layer 7 through the optical guide layer 43. In this case, since the heavy holes have a large effective mass and a low mobility, many holes are easily injected into the well layer 42 on the p-cladding layer 7 side in the MQW active layer 4. The Proceedings of the Japan Society of Applied Physics 93 Spring National Convention 31
p-C-6, p. 1088 and 31p-C-8,
p. As reported in 1089, it is known that a carrier having a smaller effective mass and a higher mobility is more likely to be uniformly injected into the MQW active layer.

When the barrier layer of the MQW active layer is strain-free, the energy level of heavy holes and the energy level of light holes match, as shown in FIG. In this case, since the density of states of heavy holes is higher than that of light holes, heavier holes are injected into the MQW active layer from the p-clad layer than light holes. Also in this case, many holes are easily injected into the well layer on the p-cladding layer side in the MQW active layer.

[0011]

The above MQW active layer 4
In the above, many holes are injected into the well layer 42 on the p-clad layer 7 side, and it becomes difficult to uniformly inject holes into the entire MQW active layer 4. As a result, the threshold current and operating current of the semiconductor laser device increase. When holes are nonuniformly injected into the MQW active layer 4, the recombination time of carriers becomes long and the relaxation time becomes long.
Here, the relaxation time is the time from when the current supplied to the semiconductor laser element is turned off until the emitted laser light is actually turned off. When the relaxation time increases, it becomes difficult to perform high speed modulation of the semiconductor laser device.

An object of the present invention is to provide a semiconductor light emitting device capable of uniformly injecting holes into the entire active layer having a strain compensation multiple quantum well structure.

[0013]

A semiconductor light emitting device according to the present invention has a multi-quantum well structure in which a plurality of well layers and a plurality of barrier layers having or without compressive strain are alternately laminated. In a semiconductor light emitting device in which an active layer is arranged between an n-type clad layer and a p-type clad layer, a band gap smaller than that of the p-type clad layer and a tensile strength are provided between the p-type clad layer and the active layer. A tensile strain layer having strain is provided.

In particular, it is preferable that the energy of the ground state of holes in the tensile strained layer is approximately equal to the energy of the continuous state of light holes in the active layer or lower than the energy of the continuous state of light holes in the active layer. .

Further, a plurality of barrier layers having a multiple quantum well structure may have compressive strain. Further, a plurality of well layers having a multiple quantum well structure may have tensile strain. Further, each of the plurality of barrier layers is formed by stacking a layer having compressive strain and a layer having tensile strain, and the energy of holes in the layer having compressive strain is higher than the energy of holes in the layer having tensile strain. High is preferred.

[0016]

In the semiconductor light emitting device according to the present invention, a tensile strain layer having a band gap smaller than that of the p-type clad layer and a tensile strain is provided between the active layer and the p-type clad layer. In this tensile strain layer, the level of light holes is higher than that of heavy holes, and the ground state of holes is light. Therefore, p
The holes injected from the mold cladding layer are mainly light holes in the tensile strain layer, and the light holes are injected into the active layer.

At this time, the light holes have a smaller effective mass in the thickness direction of the active layer and a higher mobility than the heavy holes. Therefore, most of the light holes injected into the active layer are not relaxed to heavy holes, but remain light holes and are easily injected uniformly into all well layers in the active layer. As a result, the threshold current and operating current of the semiconductor light emitting device are reduced. Also, the relaxation time is shortened, and high-speed modulation of the semiconductor light emitting device becomes possible.

In particular, when the energy of the ground state of holes in the tensile strained layer is approximately equal to the energy of the continuous state of light holes in the active layer or lower than the energy of the continuous state of light holes in the active layer. , More holes are injected into the active layer as light holes.

When a plurality of barrier layers having a multiple quantum well structure have compressive strain, the level of heavy holes is higher than that of light holes in the barrier layers having compressive strain. It is located at a high position, and the ground state of holes is a heavy hole. In such an active layer, the continuous state having the highest energy is the continuous level of heavy holes. In this case, the effect of improving the uniformity of the injection of holes into the active layer becomes greater.

Further, when a plurality of well layers of the multiple quantum well structure have tensile strain, in the well layer having tensile strain, the position of light holes has a higher energy than the level of heavy holes. And the ground state of the holes is light holes. Also in this case, the effect of improving the uniformity of the injection of holes into the active layer becomes greater.

In particular, when a plurality of well layers having a multiple quantum well structure have a tensile strain and a plurality of barrier layers have a compressive strain, it is possible to improve the uniformity of hole injection into the active layer. It gets particularly large.

When each of the plurality of barrier layers is composed of a layer having compressive strain and a layer having tensile strain, relaxation of light holes into heavy holes in the active layer is suppressed. As a result, the non-uniformity of hole injection into the active layer is further improved.

[0023]

FIG. 1 is a sectional view showing the structure of an AlGaInP based semiconductor laser device having a buried ridge structure according to the first embodiment of the present invention.

In FIG. 1, the n-GaAs substrate 1 has a crystal growth plane whose plane orientation is tilted by 9 ° from the (100) plane in the [011] direction. n-Ga on n-GaAs substrate 1
N-buffer layer 2 made of _0.51 In _0.49 P, n- (Al
_An n-clad layer 3 made of _0.7 Ga _0.3 ) _0.51 In _0.49 P and an MQW active layer 4 are sequentially formed. MQ
The W active layer 4 is formed of (Al _0.5 Ga _0.5 ) _0.51 In _0.49 P on the optical guide layer 43 (Al _0.5 Ga _0.5 ) _0.45 I.
n _0.55 P, four layers of compressive strain barrier layers 41 and Ga
Three tensile strain well layers 42 made of _0.6 In _0.4 P are alternately laminated.

On the MQW active layer 4, (Al _0.5 Ga
_0.5 ) _0.56 In _0.44 P tensile strain layer 5, (Al
_The optical guide layer 6 and the multiple quantum barrier layer 7 made of _0.57 Ga _0.43 ) _0.51 In _0.49 P are sequentially formed. Multiquantum barrier layer 7, Ga _0.51 In _0.49 wells 10 layers of P layer 71 and _{(Al 0.7 Ga 0.3) 0.51 In} 0.49 barrier layer 72 of 10 layers of P are laminated alternately. The multiple quantum barrier layer 7 is provided to improve temperature characteristics.

On the multiple quantum barrier layer 7, p- (Al _0.7
A p-clad layer 8 made of Ga _0.3 ) _0.51 In _0.49 P is formed. The upper region of the p-clad layer 8 is formed in a stripe-shaped ridge portion by mesa etching or the like. The width of the ridge portion is 5 μm. p-cladding layer 8
On the ridge portion of p-Ga _0.51 In _0.49 P
The contact layer 9 is formed.

On both sides of the p-clad layer 8, n-GaA is formed.
The n-current blocking layer 10 made of s is formed, and p is formed on the p-contact layer 9 and the n-current blocking layer 10.
A p-cap layer 11 made of -GaAs is formed. An n-electrode 12 is formed on the lower surface of the n-GaAs substrate 1, and a p-electrode 13 is formed on the upper surface of the p-cap layer 11.

Table 1 shows the material and film thickness of each layer in the semiconductor laser device of FIG.

[0029]

[Table 1]

In this semiconductor laser device, n-Ga
The layers 2 to 11 on the As substrate 1 are formed by MOCVD (metalorganic chemical vapor deposition) or the like. FIG. 2 shows an energy band diagram of the main part of the semiconductor laser device of FIG. In FIG. 2, "/" represents compressive strain, and "x" represents tensile strain.

As shown in FIG. 2, the compressive strain barrier layer 41 has a band gap larger than that of the tensile strain well layer 42. The light guide layer 43 has a band gap having the same size as the compressive strain barrier layer 41. The lattice constant of the compressive strain barrier layer 41 is set to be larger than the lattice constant of the n-GaAs substrate 1. Thereby, the compressive strain barrier layer 41 is n-GaAs.
The substrate 1 has compressive strain. The lattice constant of the tensile strain well layer 42 is set smaller than the lattice constant of the n-GaAs substrate 1. Thereby, the tensile strained well layer 42 is n
-Has tensile strain with respect to the GaAs substrate 1.

On the other hand, it has a band gap larger than that of the compressive strain barrier layer 41. Further, the light guide layer 6 has a band gap having a size substantially equal to the tensile strain 5. The lattice constant of the tensile strained layer 5 is set smaller than that of the n-GaAs substrate 1. Thereby, the tensile strained layer 5 is n
-Has tensile strain with respect to the GaAs substrate 1.

3 and 4 are more detailed energy band diagrams of the valence band of the MQW active layer 4 in the semiconductor laser device of FIG. 3 and 4, HH
Indicates the level of heavy holes, and LH indicates the level of light holes.

In FIG. 3, in the compressive strain barrier layer 41, the level HH of heavy holes is higher in energy than the level LH of light holes, and the ground state of holes is heavy holes. On the other hand, in the tensile strained well layer 42, the light hole level L
Since H is at a position where the energy is higher than the level HH of a heavy hole, the ground state of the hole is a light hole.

In such an MQW active layer 4, as shown in FIG. 4, the energy of the heavy hole continuous level (continuous state) HC is lower than the energy of the light hole continuous level (continuous state) LC. Start at a high position.

On the other hand, in the tensile strained layer 5, the light hole level LH is higher in energy than the heavy hole level HH, and the ground state of the holes is a light hole. In the present embodiment, the tensile strained layer 5 is set so that the energy of the light hole level LH, which is the ground state of the tensile strained layer 5, is substantially equal to the energy of the light hole continuous level LC of the MQW active layer 4. The composition of is set.

Therefore, the holes injected from the p-cladding layer 8 become mainly light holes in the tensile strain layer 5, and the light holes are injected into the MQW active layer 4. At this time, the time τ required for the light holes to pass through the MQW active layer 4 is about 100 psec (picosecond). MQ
After the light holes are injected into the W active layer 4, it takes a time longer than the above time τ to relax the light holes into the heavy holes.

Therefore, a considerable part of the light holes injected into the MQW active layer 4 remains as light holes without being relaxed to heavy holes. Light holes have a smaller effective mass in the thickness direction of the MQW active layer 4 and higher mobility than heavy holes. Therefore, holes are likely to be uniformly injected into all the tensile strain well layers 42 in the MQW active layer 4. As a result, the threshold current and operating current of the semiconductor laser device are reduced. Also, the relaxation time is shortened, and high-speed modulation of the semiconductor laser device becomes possible.

In the example shown in FIG. 3, the tensile strain well layer 42
Of the heavy hole of the compressive strain barrier layer 41 has a higher energy level than the heavy hole level HH of the compressive strain barrier layer 41. However, as shown in FIG. HH
May be at an energy position between the heavy hole level HH and the light hole level LH of the compressive strain barrier layer 41.

Further, as shown in FIG. 6, the heavy hole level HH of the tensile strain well layer 42 may be lower in energy than the light hole level LH of the compressive strain barrier layer 41. . Note that, as shown in FIG. 7, the tensile strained layer 5 is pulled so that the energy of the hole level LH in the ground state is lower than the energy of the light hole continuous level LC of the MQW active layer 4. The composition of the strained layer 5 may be set.

Further, as shown in FIG. 8, the MQW active layer 4
Of the compressive strain barrier layer 41 of (Al _0.5 Ga _0.5 ) _0.45 In
_A compressive strained layer 41a made of _0.55 P and (Al _0.5 Ga
_0.5) may be constituted by a laminated structure of the tensile strain layer 41b made of _{0. 56} In _0.44. In this case, the tensile strain layer 41b
The energy at the top of the valence band of is lower than the energy at the top of the valence band of the compression strained layer 41a. According to this structure, it is possible to further suppress the relaxation of light holes into heavy holes in the MQW active layer 4. As a result, MQW
It is possible to further improve the non-uniformity of the injection of holes into the active layer 4.

In the example of FIG. 8, the compressive strain layer 41a of the compressive strain barrier layer 41 is provided on the n-cladding layer side, and the tensile strain layer 41b is provided on the p-cladding layer side. The tensile strain layer 41b of the compressive strain barrier layer 41 may be provided on the n-cladding layer side, and the compressive strain layer 41a may be provided on the p-cladding layer side.

FIG. 9 shows Zn in the second embodiment of the present invention.
It is sectional drawing which shows the structure of Se type | system | group semiconductor laser element. In FIG. 9, on the n-GaAs substrate 21, n-GaAs
Consisting of consisting n- first Bafffa layer 22, n-ZnSe n- second buffer layer _{23, n-Mg 0.4 Zn 0.6} S
N-clad layer 24 made of _0.3 Se _0.7 , and MQ
The W active layer 25 is sequentially formed. MQW active layer 25
Is formed by alternately stacking five compressive strain barrier layers made of Mg _0.3 Zn _0.7 S _0.1 Se _0.9 and four tensile strain well layers made of ZnS _0.2 Se _0.8 .

Mg _0.3 Zn is formed on the MQW active layer 25.
_0.7 S _0.3 Se _0.7 tensile strain layer 26 and p-
A p-clad layer 27 made of Mg _0.4 Zn _0.6 S _0.3 Se _0.7 is sequentially formed. The upper region of the p-clad layer 27 is a striped ridge portion.

On the ridge portion of the p-clad layer 27, p
A p-contact layer 28 made of -ZnSe is formed,
SiO ₂ films 29 are formed on both sides of the ridge portion of the p-clad layer 27 and the p-contact layer 28. n-
An n electrode 30 is formed on the lower surface of the GaAs substrate 21, and p-
The p electrode 3 is formed on the contact layer 28 and the SiO ₂ layer 29.
1 is formed.

Table 2 shows the material and film thickness of each layer in the semiconductor laser device of FIG.

[0047]

[Table 2]

In the semiconductor laser device of the second embodiment, since the tensile strain layer 26 is provided between the MQW active layer 25 and the p-clad layer 27, it is the same as the semiconductor laser device of the first embodiment. Similarly, holes are likely to be uniformly injected into the entire MQW active layer 25. As a result, the threshold current and operating current of the semiconductor laser device are reduced. In addition, the relaxation time of the semiconductor laser device becomes long, and high speed modulation becomes possible.

FIG. 10 shows G in the third embodiment of the present invention.
It is sectional drawing which shows the structure of an aN type light emitting diode. FIG.
At 0, sapphire (Al₂O₃) On the substrate 51,
GaN buffer layer 52, n-GaN layer 53, n-Al
_0.42Ga_0.48In_0.1An n-clad layer 54 of N,
And the MQW active layer 55 are sequentially formed. MQW
The active layer 55 is made of Al_0.35Ga_0.53In_0.128 consisting of N
Layer compressive strain barrier layer and Al_0.2Ga _0.87 consisting of N
The tensile strained well layers are alternately laminated.

Al _0.36 Ga is formed on the MQW active layer 55.
Tensile strain layer 56 made of _0.6 In _0.04 N, p-Al _0.42
A p-clad layer 57 made of Ga _0.48 In _0.1 N and a p-GaN contact layer 58 are sequentially formed.
The region from the p-GaN contact layer 58 to the upper region of the n-GaN layer 53 is etched, the n-electrode 59 is formed on the upper surface of the n-GaN layer 53, and the p-GaN contact layer 58 is formed.
A p-electrode 60 is formed on the upper surface of the.

Table 3 shows the material and film thickness of each layer in the light emitting diode of FIG.

[0052]

[Table 3]

In the light emitting diode of the third embodiment, a tensile strain layer 56 is provided between the MQW active layer 55 and the p-clad layer 57. Therefore, holes are likely to be uniformly injected into the entire MQW active layer 5. As a result, the operating current of the light emitting diode is reduced, and high speed modulation becomes possible.

In the semiconductor laser device of the first embodiment, the optical guide layer 43 is provided between the n-clad layer 3 and the compressive strain barrier layer 41 on the n-clad layer 3 side in the MQW active layer 4. Although provided, the light guide layer 43 may not be provided.

The present invention can also be applied to the case where the barrier layer in the MQW active layer is strain-free, and also in the case where the well layer in the MQW active layer has compressive strain or is strain-free. Can be applied. Also in this case, holes are likely to be uniformly injected into the entire MQW active layer.

[0056]

As described above, according to the present invention, the tensile strain having a band gap smaller than that of the p-type clad layer and a tensile strain between the active layer of the multiple quantum well structure and the p-type clad layer. Since the layer is provided, light holes are mainly injected from the p-type cladding layer into the active layer. Therefore, it becomes easy to uniformly inject holes into the entire active layer,
The threshold current and operating current of the semiconductor light emitting device are reduced, and high speed modulation is possible.

Particularly, when the ground state energy of holes in the tensile strained layer is substantially equal to or lower than the energy of continuous states of light holes in the active layer or lower than the energy of continuous states of light holes in the active layer. Since more holes are injected into the active layer as light holes, the uniformity of injection of holes into the active layer is further increased.

Further, when the plurality of barrier layers of the multiple quantum well structure have compressive strain, the effect of improving the non-uniformity of injection of holes into the active layer becomes greater. Further, even when a plurality of well layers of the multiple quantum well structure have tensile strain, the effect of improving the uniformity of hole injection into the active layer becomes greater.

When each of the barrier layers is composed of a layer having compressive strain and a layer having tensile strain, relaxation of light holes into heavy holes in the active layer is further suppressed. Therefore, holes are more uniformly injected into the entire active layer.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of an AlGaInP-based semiconductor laser device having a buried ridge structure according to a first embodiment of the present invention.

FIG. 2 is an energy band diagram of a main part of the semiconductor laser device of FIG.

3 is mainly MQ in the semiconductor laser device of FIG.
It is a detailed energy band figure of the valence band of a W active layer.

4 is mainly MQ in the semiconductor laser device of FIG.
It is a detailed energy band figure of the valence band of a W active layer.

5 is mainly MQ in the semiconductor laser device of FIG.
It is an energy band figure which shows the other example of the valence band of a W active layer.

6 is mainly MQ in the semiconductor laser device of FIG.
It is an energy band figure which shows the further another example of the valence band of a W active layer.

FIG. 7 is an energy band diagram showing another configuration example of the semiconductor laser device of the first embodiment.

FIG. 8 is an energy band diagram showing still another configuration example of the semiconductor laser device of the first embodiment.

FIG. 9 is a sectional view showing the structure of a ZnSe based semiconductor laser device according to a second embodiment of the present invention.

FIG. 10 is a sectional view showing the structure of a GaN-based light emitting diode according to a third embodiment of the present invention.

FIG. 11 is an energy band diagram of a main part of a conventional semiconductor laser device.

FIG. 12 is a detailed energy band diagram of a valence band of the MQW active layer in the conventional semiconductor laser device.

FIG. 13 is a conceptual diagram showing an energy band structure of a strain-free semiconductor layer.

FIG. 14 is a conceptual diagram showing an energy band structure of a semiconductor layer having tensile strain.

FIG. 15 is a conceptual diagram showing an energy band structure of a semiconductor layer having compressive strain.

[Explanation of symbols]

 1 n-GaAs substrate 3,24,54 n-clad layer 4,25,55 MQW active layer 5,26,56 tensile strain layer 8,27,57 p-clad layer 41 compressive strain barrier layer 42 tensile strain well layer HH Heavy hole level LH Light hole level LC Light hole continuous level HC Heavy hole continuous level

Claims (5)

[Claims] 1. An active layer having a multi-quantum well structure in which a plurality of well layers and a plurality of barrier layers having or without compressive strain are alternately laminated to form an n-type clad layer and a p-type clad layer. In the semiconductor light emitting device arranged between the p-type clad layer and the active layer,
A semiconductor light emitting device comprising a tensile strain layer having a band gap smaller than that of a mold cladding layer and having tensile strain. 2. The ground state energy of holes in the tensile strained layer is substantially equal to or lower than the energy of continuous states of light holes in the active layer, or lower than the energy of continuous states of light holes in the active layer. The semiconductor light emitting device according to claim 1, wherein: 3. The barrier layer of the multi-quantum well structure has a compressive strain.
The semiconductor light-emitting device as described above. 4. The semiconductor light emitting device according to claim 1, 2 or 3, wherein the plurality of well layers of the multiple quantum well structure have tensile strain. 5. Each of the plurality of barrier layers is formed by laminating a layer having compressive strain and a layer having tensile strain, and the hole energy of the layer having compressive strain is the same as that of the layer having tensile strain. It is higher than energy, The semiconductor light emitting element of Claim 1, 2, 3 or 4 characterized by the above-mentioned.