JPH07105567B2 - Transverse current injection type quantum well semiconductor laser device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a III-V group compound semiconductor, and more specifically, to a lateral current injection quantum well (QW) type semiconductor laser device.

(Prior Art) As a crystal growth method for manufacturing a semiconductor laser device, a molecular beam epitaxy (MBE) method is used.
In recent years, attention has been paid, and recently, the MBE method has made it possible to control the thickness of the epitaxial layer with high accuracy of the order of a single molecule. For this reason, quantum wells (Quantum Wel) with extremely thin layers, which were difficult to fabricate by liquid phase epitaxy (LPE), etc.
An l: QW) type semiconductor laser is manufactured by the MBE method. The QW type semiconductor laser has a quantum well structure in which quantum well layers (200 Å or less) and barrier layers, which are thinner than the active layer (several hundred Å or more) in the conventional double hetero structure semiconductor laser, are alternately stacked. Two-dimensionally confining the carriers injected into the quantum well layer of the quantum well structure makes it possible to lower the threshold current as compared with the semiconductor laser of the double hetero structure, and the temperature characteristics Has the advantage that

In order to improve the characteristics of the QW semiconductor laser, it is necessary to two-dimensionally confine the carriers injected into the quantum well layer of the quantum well structure in this thin quantum well layer.
For that purpose, the barrier layers sandwiching the quantum well layer in the quantum well structure may be thickened, and the bandgap of the barrier layer may be widened to surely confine the carriers in the quantum well layer.
In a quantum well type semiconductor laser, carriers are usually injected from the direction perpendicular to the quantum well layer. The carrier injection efficiency is reduced. For this reason,
The thickness of the barrier layer and the forbidden band width in the quantum well structure can be determined in consideration of the efficiency of carrier injection into the quantum well layer and the two-dimensional constraint efficiency of carriers in the quantum well layer. Proposed (WTTsang, Appl.Phys.Lett.39,
786 (1981)). As described above, in the semiconductor laser in which carriers are injected in the direction perpendicular to the quantum well layer, there is a limit to improving the oscillation characteristics. Therefore, a lateral current injection type quantum well semiconductor laser, for example, a multiple quantum well lateral junction shown in FIG.
e Junction Stripe: MQW-TJS) type semiconductor laser has been proposed (YJ Yang et al., Appl. Phys. Lett. 49, 835 (198).
6)).

The semiconductor laser consists of a Cr-doped GaAs semi-insulating substrate 51 with Si
A quantum well structure 53 sandwiched between a doped (1 × 10 ¹⁷ cm ⁻³ ) Al _0.65 Ga _0.35 As clad layer 52 and a similar Si-doped (1 × 10 ¹⁷ cm ⁻³ ) Al _0.65 Ga _0.35 As clad layer 54 is formed. It is provided. The quantum well structure 53 is made of Si-doped (2 × 1
0 ¹⁸ cm ^-3 ) GaAs quantum well layer and 150 Å thick Si-doped (1 ×
10 ¹⁷ cm ^-3 ) Al _0.65 Ga _0.35 As barrier layers are alternately laminated.

In the semiconductor laser device, for example, Zn as an impurity is partially diffused in the vertical direction of the semiconductor laminated structure to form ap ⁺ region 56, and then the diffused Zn is annealed to be diffused again in the horizontal direction to form ap ⁻ region. 57 are formed and carriers are horizontally injected into the quantum well layer 53 of the multiple quantum well structure.

Recently, the LCI-MQW (Lateral Curr) shown in FIG.
An en injection-multiple quantum well) type semiconductor laser device has also been proposed (A. Furuya et al., Appl. Phys. Lett.
49,134 (1987). The semiconductor laser device is made of Cr-doped GaAs.
A non-doped GaAs buffer layer 62 and a superlattice buffer layer 63 are sequentially laminated on a semi-insulating substrate 61, and a pair of high resistance Al _0.45 Ga _0.55 As clad layers 64 are formed on the superlattice buffer layer 63.
A multiple quantum well structure 65 sandwiched between and 66 is provided. The multiple quantum well structure 65 has a structure in which Si-doped (1 × 10 ¹⁷ / cm ⁻³ ) GaAs quantum well layers with a thickness of 80 Å and undoped Al _0.3 Ga _0.7 As barrier layers with a thickness of 120 Å are alternately laminated. ing. The semiconductor laser device includes a semiconductor layered structure having a double hetero structure and an n region formed by diffusion of Si as an impurity.
67 and the p region 68 by diffusion of Zn as an impurity,
Carriers are horizontally injected into the quantum well layer of the quantum well structure 65 so as to sandwich the stripe region.

(Problems to be Solved by the Invention) In each of the semiconductor laser devices shown in FIGS. 3 and 4, the oscillation wavelength is shifted to the short wavelength side with respect to the set wavelength. It is considered that this is because the laminated structure of the quantum well layer and the barrier layer of a certain quantum well structure is destroyed. The semiconductor laser device shown in FIG. 3 has a high temperature of 900 ° C. when diffusing Zn, which is an impurity, and the semiconductor laser device shown in FIG. 4 has a high temperature of 850 ° C. when diffusing Si, which is an impurity. Therefore, the mutual diffusion of the quantum well layer and the barrier layer in the quantum well structure is considered to be the cause of the destruction of the quantum well structure.
Therefore, if the temperature at the time of diffusing the impurities is lowered, the quantum well structure is prevented from being destroyed, but it takes a long time to diffuse the impurities, and the production efficiency of the semiconductor laser device is lowered. Also,
Since it is very difficult to control the diffusion region in the horizontal direction at the time of impurity diffusion, the quantum well structure may be destroyed by the diffusion of a large amount of impurities in the oscillation region.

By destroying the quantum well structure in this way, the third
Each of the semiconductor laser devices shown in FIGS. 4 and 5 has a drawback that the threshold current becomes high, and the semiconductor laser device shown in FIG. 4 does not continuously oscillate at room temperature.

The present invention solves the above-mentioned conventional problems. The object of the present invention is that since a step such as impurity diffusion is not necessary, continuous oscillation is possible at room temperature with a low threshold current, and further manufacturing is easy. It is intended to provide a semiconductor laser device of a lateral current injection type quantum well.

(Means for Solving the Problem) The lateral current injection type quantum well semiconductor laser device of the present invention is
As a semiconductor growth surface, a III-V group compound having a (n11) A surface (where n is an integer, A is a group III element surface) having a Miller index and a surface having a different Miller index provided adjacent to the surface A semiconductor substrate and a quantum well structure formed by growing a semiconductor layer using an amphoteric element as a dopant on each semiconductor growth surface of the semiconductor substrate, and having different conductivity types of the semiconductor layer on each semiconductor growth surface; , Which achieves the above-mentioned object.

(Function) When a group III-V compound semiconductor layer is grown on a (100) substrate by a molecular beam epitaxy (MBE) method, a group IV amphoteric element such as Si is usually added to
It is used as a type dopant, and in this case, the amphoteric element functions as a donor. However, when the semiconductor growth surface is the (n11) A surface (where n is an integer and A is a group III element surface), the lattice point of the group V element is IV than the lattice point of the group III element.
It is easy to be replaced by a group amphoteric element. Therefore, on the semiconductor growth surface, the group IV element is replaced with a group IV amphoteric element, and the group IV amphoteric element functions as a p-type dopant (acceptor). To do.

Therefore, as shown in Fig. 1, the Miller index is (n11)
A semiconductor growth surface 11 having an A surface (where n is an integer, A is a group III element surface) and a semiconductor growth surface 12 having a Miller index different from the Miller index of the semiconductor growth surface 11 are arranged adjacent to each other. The semiconductor substrate 10 of the III-V group compound thus prepared is used, and a III-V group compound semiconductor using a group IV amphoteric element as a dopant is formed on each semiconductor growth surface 11 and 12 of the substrate 10.
When grown simultaneously by the E method, the semiconductor layer 21 laminated on the (n11) A semiconductor growth surface 11 becomes p-type and the semiconductor layer 22 laminated on the other semiconductor growth surface 12 becomes n-type. As a result, a pn junction surface 23 is formed between them.

Therefore, on each semiconductor growth surface 11 and 12 of the semiconductor substrate 10, a cladding layer, a quantum well structure in which a quantum well layer and a barrier layer are alternately transferred by a III-V compound semiconductor, and a cladding layer are sequentially formed by MBE. The pn junction is formed in the quantum well structure by the method. Further, laser oscillation occurs in the p-type region, that is, in the quantum well active layer 21a on the (n11) A plane due to the difference in diffusion length of electrons and holes.

When the (n11) A plane is the (111) A plane, the optical transition is increased as compared with the (100) plane, so that various laser activities can be improved.

(Example) Hereinafter, the present invention will be described with reference to Examples.

As shown in FIG. 2 (a), the semiconductor laser device of the present invention has a tilted (111) A plane (A is a Group III element plane) semiconductor growth surface 31a, and an upper side of the semiconductor growth surface 31a and It has a Cr-doped semi-insulating GaAs substrate 31 having (100) planes of semiconductor growth surfaces 31b and 31b continuous on the lower side.

On the semiconductor growth surfaces 31a and 31b of the Cr-doped semi-insulating GaAs substrate 31, a 1 μm thick non-doped high resistance GaAs buffer layer 32 and a 1 μm thick non-doped high resistance Al _0.6 Ga _0.4 A
A current blocking layer 33 and a Si (1 × 10 ¹⁸ cm ⁻³ ) doped Al _0.45 Ga _0.55 As clad layer 34 having a thickness of 2 μm are sequentially laminated. Then, on the clad layer 34, as schematically shown in FIG. 2 (b), five layers of GaAs quantum well layers each having a thickness of 150 Å are formed between six layers of Al _0.3 Ga _0.7 As barrier layers having a thickness of 150 Å. Si (1 × 10 ¹⁸ cm ^-3 ) -doped multi-quantum well structure 35, sandwiched between
Si (1 × 10 ¹⁸ cm ^-3 ) -doped Al _0.45 Ga _0.55 As with a thickness of 2 μm
The cladding layers 36 are sequentially laminated, and 1 μm thick Si (3 × 10 ¹⁸ cm ⁻³ ) except for the upper regions of the lower semiconductor growth surfaces 31 a and 31 b of the cladding layer 36 on the substrate 31.
A doped GaAs contact layer 37 is laminated. these
Si-doped Al _0.45 Ga _0.55 As clad layer 34, quantum well structure 35,
Si-doped Al _0.45 Ga _0.55 As clad layer 36, and Si-doped G
The aAs contact layer 37 is p-type in the region above the semiconductor growth surface 31a of the substrate 31 and n-type in the region above the semiconductor growth surface 31b.
A pn junction surface is formed above the junction portion of. Then, in the region adjacent to the upper side of the semiconductor growth surface 31a of the pn junction surface, the GaAs sandwiched by the Al _0.3 Ga _0.7 As barrier layers.
The quantum well layer becomes the active region.

A current block layer 38 is laminated on the junction portion of the Si-doped GaAs contact layer 37 and on the Si-doped GaAs contact layer 37 on the uppermost semiconductor growth surface 31b. An AuGe / Ni n-type electrode 39 is provided on the contact layer 37 on the lower semiconductor growth surface 31b of the substrate 31,
Au / AuZn p-type electrode on the semiconductor growth surface 31a of the substrate 31
40 are provided.

The semiconductor laser device of the present invention having such a structure is manufactured as follows. First, a stripe mask in the [011] direction was formed on a (100) Cr-doped semi-insulating GaAs substrate,
Etching was performed using a sulfuric acid-based etchant, and as shown in FIG. 2, the inclined (111) A plane (A is a group III element plane) of the semiconductor growth surface 31a and the semiconductor growth surface 31a above and below the semiconductor growth surface 31a, respectively. A continuous (100) plane of semiconductor growth surface 31b and
Cr-doped semi-insulating GaA on the forward mesa sloping surface formed with 31b
s The substrate 31 is molded.

Then, at the same time on each semiconductor growth surface 31a and 31b of the substrate 31, a growth temperature of 700 ° C. is used by the MBE method to obtain a thickness of 1 μm.
Non-doped high resistance GaAs buffer layer 32, 1 μm thick non-doped high resistance Al _0.6 Ga _0.4 As current blocking layer 33, thickness 2
A μm Si (1 × 10 ¹⁸ cm ⁻³ ) doped Al _0.45 Ga _0.55 As cladding layer 34 is sequentially grown. Then, on the clad layer 34, Si (1) in which 5 layers of GaAs quantum well layers each having a thickness of 100 Å are sandwiched between 6 layers of Al _0.3 Ga _0.7 As barrier layers having a thickness of 150 Å
× 10 ¹⁸ cm ^-3 ) Doped multiple quantum well structure 35, 2 μm thick S
i (1 × 10 ¹⁸ cm ^-3 ) doped Al _0.45 Ga _0.55 As clad layer 36,
A Si (3 × 10 ¹⁸ cm ⁻³ ) -doped GaAs contact layer 37 having a thickness of 1 μm is sequentially and continuously grown. As a result, the Si-doped Al _0.45 Ga _0.55 As clad layer 34, the Si-doped quantum well structure 35, and the laminated structure part of the Si-doped Al _0.45 Ga _0.55 As clad layer 36 and the Si-doped GaAs contact layer 37 are The region above the semiconductor growth surface 31a of the substrate 31 is p-type, and the region above the semiconductor growth surface 31b is n-type, and p-type is present above the junction between the semiconductor growth faces 31a and 31b.
A -n junction surface is formed.

In addition, the quantum well structure 3 above the semiconductor growth surface 31a
In the region adjacent to the pn junction surface in 5, the GaAs quantum well layer is
_The GaAs quantum well layer sandwiched by _0.3 Ga _0.7 As barrier layers becomes the active region.

Next, each pn junction part of the Si-doped GaAs contact layer 37 and the Si-doped GaAs contact layer 37 on the uppermost semiconductor growth surface 31b are etched by photolithography and NH ₄ OH-based etchant. Then, an insulating film of SiNx is formed on the etched portion by the plasma CVD method, and the current block layer 38 is formed by using the photolithography method and the selective etchant of SiNx (mixed solution of HF and NH ₄ F).

Then, an n-type electrode 39 of AuGe / Ni is vapor-deposited on the n-type portion of the contact layer 37, that is, on the contact layer 37 located above the lower semiconductor growth surface 31b. An Au / AuZn p-type electrode 40 is vapor-deposited on the p-type portion, that is, on the contact layer 37 in the region above the semiconductor growth surface 31a.

After that, the substrate 31 is adjusted to have a thickness of 150 μm.
The lateral current injection type quantum well semiconductor laser device of the present invention can be easily manufactured by polishing the back surface of 1 and then dividing it into chips.

In the obtained semiconductor laser device, the region adjacent to the pn junction face in the quantum well structure 35 in the region above the semiconductor growth surface 31a becomes the active region 35a, and laser light is oscillated from the active region 35a. For example, in the lateral current injection type quantum well semiconductor laser device shown in FIG. 2 (a) having a cavity length of 250 μm, laser light could be continuously oscillated at room temperature with a low threshold current of 10 mA.

(Effects of the Invention) In the lateral current injection type quantum well semiconductor laser device of the present invention, the quantum well structure in which the quantum well layers are sandwiched by the barrier layers is thus formed by the growth of the semiconductor layer once by the MBE method. Moreover, since different conductivity types are formed in the quantum well layer of the quantum well structure, the impurity diffusion step, the annealing step, etc. are unnecessary, and the process steps are simplified and the conventional method is used. The quantum well structure can be easily manufactured without being destroyed by being exposed to high temperature, and it has good oscillation characteristics that it can continuously oscillate at room temperature with low threshold current of lateral current injection type, and has high quantum efficiency. The high-performance semiconductor laser device thus obtained can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view of a semiconductor laser device of the present invention, FIG. 2 (a) is a sectional view showing an example of a semiconductor laser device of the present invention, and FIG. 2 (b) is a schematic diagram for explaining a quantum well structure. ，
3 and 4 are sectional views showing an example of a conventional semiconductor laser device. 10 ... Semiconductor substrate, 11, 12 ... Semiconductor growth surface, 21 ... P-type semiconductor layer, 22 ... N-type semiconductor layer, 31 ... Cr-doped semi-insulating GaAs substrate, 3
2… Non-doped high resistance GaAs buffer layer, 33… Non-doped high resistance Al _0.6 Ga _0.4 As current blocking layer, 34… Si-doped Al _0.45 G
a _0.55 As clad layer, 35… Si-doped multiple quantum well structure, 35a
… Active region, 36… Si-doped Al _0.45 Ga _0.55 As cladding layer, 37
… Si-doped GaAs contact layer, 38… SiNx current blocking layer,
39 ... n type electrode, 40 ... p type electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Hosoda 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Co., Ltd. (72) Tororou Hayakawa 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Incorporated (56) References JP 62-265787 (JP, A)

Claims (1)

[Claims] 1. A semiconductor growth surface has a Miller index of (n1
1) A III-V compound semiconductor substrate having an A plane (where n is an integer, A is a III group element plane) and a plane having a different Miller index provided adjacent to the plane, and each of the semiconductor substrates. A lateral current injection type quantum well having a quantum well structure in which a semiconductor layer using an amphoteric element as a dopant is grown on a semiconductor growth surface of the semiconductor layer, and the conductivity type of the semiconductor layer on each semiconductor growth surface is different. Semiconductor laser device.