JP2000058964A - Quantum-well structured optical semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the semiconductor laser element, which can improve slope efficiency and decrease threshold. SOLUTION: This quantum-well structured optical semiconductor element is formed by a III-V group compound semiconductor, which has a quantum barrier layer 106b and a quantum-well layer 106a formed by the V-group elements of two or more kinds including III-group elements and nitrogen. This quantum-barrier layer 106b is formed of the III-group element and the V-group elements, including the III-group elements and two or more kinds of the V-group elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device having a long wavelength band. In particular, optical fiber communication for delivering high-speed data to homes, so-called FTTH (Fiber To
The Home), and a long-wavelength band semiconductor laser device required for low threshold current and low drive current characteristics under a high temperature environment, which is used for communication between boards of a computer, so-called optical interconnection.

[0002]

2. Description of the Related Art As a light source of an optical communication system or an optical interconnection using an optical fiber, an InGaAsP-based long wavelength band semiconductor laser device formed on an InP substrate has been conventionally developed. However, in this semiconductor laser device, a band discontinuity difference (an energy gap difference) for electrons between the active layer and the cladding layer.
Since ΔEc is as small as about 100 meV, there is a problem that electrons cannot be sufficiently confined in the active layer during high-temperature operation, and so-called carrier overflow occurs. Due to this, as the above semiconductor laser device,
Only a temperature characteristic of about 50K was obtained.

For this reason, when the above-mentioned semiconductor laser device is used at a severe environmental temperature, a high operating current at a high temperature requires a high output of a drive circuit. As a result, the circuit configuration becomes very complicated, and a device for cooling the laser element is required, which causes problems such as an increase in the size of the optical communication device and an increase in power consumption.

In order to improve the above-mentioned problem of temperature characteristics,
A semiconductor laser device using InGaAlAs as an active layer on an InP substrate;
Although a semiconductor laser device using nAsP has been developed, a practically sufficient one has not yet been obtained.

On the other hand, in order to improve the above temperature characteristics,
A semiconductor laser device in which a quantum well layer is formed of GaInNAs on a GaAs substrate has been proposed (JP-A-8-195522). In this semiconductor laser device:
3 to 1.7 μm long wavelength band light can be oscillated, and
A temperature characteristic of about K can be expected. Note that the quantum barrier layer having the quantum well structure is made of an (Al) GaAs layer or InGaP
It has a multi-layer structure of layers and GaAs layers (Examples 4 to 6 of JP-A-8-195522).

Hereinafter, the relationship between the structure and the physical properties of the GaInNAs-based semiconductor laser device will be described in more detail.

FIG. 7 shows the relationship between the composition of In and N and the lattice constant or band gap of a GaInNAs-based material. As can be seen from this figure, in a GaInNAs-based mixed crystal obtained by adding nitrogen to a GaInAs material, the lattice constant becomes smaller than the lattice constant of GaInAs and gradually approaches the lattice constant of GaAs according to the amount of addition. (It changes in the direction of lattice matching with GaAs). Also,
Due to the effect of the large energy gap Boeing on nitrogen, the energy level at the band edge of the conduction band becomes A →
B → C and the energy level at the band edge of the valence band is D →
By changing from E to F, the band gap Eg
Becomes smaller.

From the above, the energy gap of GaAs is 1.42 by using a GaInNAs-based material and appropriately selecting the composition of indium and nitrogen therein.
It can be seen that a material that oscillates in an energy gap smaller than eV (λ: 873 μm), that is, a long wavelength band of 1.3 to 1.7 μm, and that is lattice-matched on a GaAs substrate is obtained.

In the case of a GaInNAs-based material, Ga
Since an As substrate can be used, an AlGaAs layer having a larger band gap than the InP cladding layer used in the conventional element structure can be used for the cladding layer.
For this reason, the band discontinuity difference can be made large, and it can be expected that a laser device having a temperature characteristic of about 150 K can be obtained.

FIG. 8 shows an example of the structure of a semiconductor laser device having a single quantum well structure using a GaInNAs-based material (the 58th Annual Meeting of the Japan Society of Applied Physics).
2p-ZC-4 October 1997). This semiconductor laser device has an n-type GaAs lower cladding layer 704 and an n-type GaAs lower optical waveguide layer 70 on an n-type GaAs substrate 700.
5 (thickness: 140 nm), GaInNAs quantum well layer 7
06 (thickness: 7 nm), p-type GaAs upper optical waveguide layer 7
07 (thickness: 140 nm), a p-type AlGaAs upper cladding layer 708, and a p-type GaAs cap layer 718 are formed in this order. Note that an n-side electrode 720 and a p-side electrode 722 are provided on the back surface of the substrate 700 and on the cap layer 718, respectively.

The GaInNAs quantum well layer 706 having a thickness of 7 nm has a strain of 1.0% with respect to the GaAs substrate. In the above structure, when the resonator length is 800 μm,
A laser device having a threshold value of about 103 mA and an oscillation wavelength of about 1.3 μm is obtained.

[0012]

In the semiconductor laser device disclosed in Japanese Patent Application Laid-Open No. 8-195522, the quantum well structure constituting the active region has GaIn as a quantum well layer.
An NAs layer is used, and (Al) Ga is used as a quantum barrier layer.
A multilayer structure of an As layer or an InGaP layer and a GaAs layer is used. However, in such a quantum well structure, there is a problem that sufficiently good device characteristics cannot be obtained.

The main cause of the above problem is that a good hetero interface is formed between a nitrogen-containing layer such as a GaInNAs layer and a nitrogen-free layer such as an (Al) GaAs layer. It is thought to be difficult.

III- containing nitrogen and group V elements other than nitrogen
Group V compound semiconductor (hereinafter abbreviated as N-based semiconductor) material has high mixing instability as one characteristic, that is, a property of easily separating phases. In the case of forming a laser device having a GaInNAs-based quantum well structure, conventionally, an N-based semiconductor layer for forming a quantum well layer is formed on a nitrogen-free compound semiconductor layer called an (Al) GaAs quantum barrier layer. Or (Al) GaAs on N-based semiconductor
It is necessary to grow a quantum barrier layer by s or the like. During the growth, particularly in the early stage of the growth, when forming a semiconductor layer containing no nitrogen on a semiconductor layer containing nitrogen due to the above-described instability of the N-based semiconductor, only As is supplied as a group V element. Localization of nitrogen on the surface tends to cause phase separation, making it difficult to form a favorable hetero interface. Furthermore, since it is difficult to form an N-based semiconductor having a uniform composition on a compound semiconductor containing no nitrogen, a transition layer is formed due to a transition in the composition near the interface, and an interface having a steep composition can be obtained. There is another problem.

[0015] In addition to the above-mentioned mixing instability, the N-based semiconductor material has a high nitrogen dependency on the energy gap. That is, the value of the energy gap of the N-based semiconductor material is strongly affected by the concentration of nitrogen. For example, even if the indium mixed crystal ratio changes by 0.01, the energy gap of the N-based semiconductor material changes only by about 0.01 eV and about 0.007% in lattice constant. However, when the nitrogen mixed crystal ratio changes only by 0.01, the energy gap of the N-based semiconductor changes by about 0.15 eV and the lattice constant changes by about 0.21%. This is because Boeing such as energy gap for nitrogen content of N-based semiconductor is
Because it is very large. From this, when a quantum well structure is formed of a layer containing nitrogen and a layer containing no nitrogen, a quantum well layer having a structure with a steep energy gap is obtained unless a steep switching of the nitrogen source is performed. I can't.

In the case where a layer containing nitrogen and a layer containing no nitrogen are continuously grown, the substrate temperature must be changed during the growth. More specifically, GaInAsN
When growing a well layer, low-temperature growth of about 500 ° C. is required to increase the amount of nitrogen taken in. On the other hand, when growing a Ga (Al) As barrier layer, a high temperature condition of about 700 ° C. is required to improve the crystallinity. As described above, when switching from the growth of the GaInAsN quantum well layer to the growth of the Ga (Al) As quantum barrier layer, the substrate temperature must be changed. At this point, an element having a high vapor pressure on the surface of the quantum well layer is re-evaporated, or residual impurities such as C, O, or moisture remaining in the growth chamber are adsorbed on the surface of the quantum well layer. As a result, the crystallinity at the interface of the quantum well layer deteriorates,
Furthermore, phase separation or clustering is likely to occur due to a change in the surface state of the quantum well layer. As a result, it becomes difficult to form a hetero interface having good crystallinity and sharpness.

As described above, when a quantum well structure is formed by a layer containing nitrogen and a layer not containing nitrogen, the ratio of non-radiative recombination at the interface between the quantum well layer and the quantum barrier layer increases, and Due to the reduction of the quantum effect, the threshold value increases and the slope efficiency decreases. For this reason, as shown in FIG. 9, the slope efficiency of the current-optical characteristics at room temperature is lower than that of the ordinary real refractive index structure despite the fact that the structure has a small loss inside the resonator, that is, a so-called real refractive index structure. In the case of (非常 0.4 W / A), only a very low value of 0.16 W / A can be obtained.

Furthermore, despite the characteristic that the temperature characteristics are good, the drive current at the time of high-temperature operation is increased due to poor slope efficiency, and the circuit configuration becomes complicated. As a result of performing a reliability test on the above-described semiconductor laser device, it was found that the device life was only about 5000 hours.

As described above, according to the prior art, a semiconductor having good device characteristics due to an increase in threshold and a decrease in slope efficiency due to an increase in non-radiative recombination at an interface and a reduction in quantum effect. No laser element was obtained.

The present invention has been made in view of the above circumstances. It is an object of the present invention to improve the crystallinity at the interface between a quantum well layer and a quantum barrier layer and optimize the band structure. It is still another object of the present invention to provide a quantum well structure optical semiconductor device having a high slope efficiency and a low threshold with improved design flexibility.

[0021]

SUMMARY OF THE INVENTION A quantum well structure optical semiconductor device according to the present invention has a quantum barrier layer and a quantum well layer formed of two or more group V elements containing a group III element and nitrogen. What is claimed is: 1. A quantum well structure optical semiconductor device comprising a group III-V compound semiconductor having an active region, wherein said quantum barrier layer comprises at least two types of V including a group III element and nitrogen.
It is formed of a group III element, thereby achieving the above object.

In one embodiment, the group III element is A
l, Ga, In and Tl.
The group element is selected from the group including As, P and Sb in addition to the nitrogen.

In one embodiment, the value of the lattice constant of the quantum well layer is larger than the value of the lattice constant of the quantum barrier layer.

In one embodiment, the crystal structures of the quantum well layer and the quantum barrier layer have strain, and the strain stress of the quantum well layer and the strain stress of the quantum barrier layer are equal in magnitude and That direction is the opposite direction.

In one embodiment, the composition of the group V element included in the quantum well layer is the same as the composition of the group V element included in the quantum barrier layer.

In one embodiment, an optical waveguide layer for propagating light from the active region is further provided on at least one of the upper and lower sides of the active region, and the optical waveguide layer is formed of III.
It is formed by a group V element and two or more group V elements including nitrogen.

In one embodiment, the energy gap of the optical waveguide layer changes stepwise or continuously.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Referring to FIGS. 1A and 1B, a buried semiconductor laser according to a first embodiment of a quantum well structure optical semiconductor device according to the present invention will be described. The element will be described.

As shown in FIG. 1A, this semiconductor laser device includes a p-type GaAs substrate 100 and a p-type GaAs substrate.
s buffer layer 102, p-type Al _0.3 Ga _0.7 As lower cladding layer 104, and quantum well structure 106 (active region)
And an n-type Al _0.3 Ga _0.7 As first upper cladding layer 10
8, current confinement structure 110, and n-type Al _0.3 Ga _0.7 As
A second upper cladding layer 116 and an n-type GaAs cap layer 118 are provided.

The quantum well structure 106 of the semiconductor laser device according to the present invention has an undoped Ga _0.80 In _0.20 N _0.022 As _0.978 quantum well active layer 1 as shown in FIG.
06a and undoped Ga _0.98 In _0.02 N _0.024 As
_{It has a} three-period laminated structure with the _0.976 quantum barrier layer 106b. The quantum well active layer 106a is formed on the GaAs substrate 1
It has a compressive strain of 1.0% with respect to 00 and has a thickness of about 60 nm. The quantum well active layer 106a has an energy gap of about 0.886 eV and a lattice constant of about 5.7.
10 °. On the other hand, the quantum barrier layer 106b is made of GaAs.
Having a tensile strain of 0.25% with respect to the substrate 100,
It has a thickness of about 120 nm. The quantum barrier layer 106b has an energy gap of about 1.03 eV and a lattice constant of 5.667 °.

The current confinement structure 110 is provided on both sides of a mesa structure 109 composed of the lower cladding layer 104, the quantum well structure 106, and the first upper cladding layer 108. The current confinement structure 110 includes an n-type InGaP layer 112 lattice-matched to the GaAs substrate 100, a p-type InGaP layer 113, and an n-type InGaP layer 114.

The p-side electrode 120 is provided on the back surface of the substrate 100.
Is formed, and an n-side electrode 122 is formed on the n-type GaAs cap layer 118.

Hereinafter, the manufacturing process of the semiconductor laser device will be described.

In this manufacturing process, a solid raw material such as gallium, indium and aluminum is used as a raw material of the group III element, and a solid raw material such as arsenic and ammonia are used as the raw material of the group V element. Note that silicon is used as a source of an n-type impurity, and beryllium is used as a source of a p-type impurity.

First, at a substrate temperature of 650 ° C., a p-type GaAs substrate 100 is formed by MBE (Molecular Beam Epitaxy).
On top, a p-type GaAs buffer layer 10 having a thickness of about 0.3 μm
2 and a p-type Al _0.3 Ga _0.7 As lower cladding layer 104 having a thickness of about 1.0 μm are sequentially formed.

Subsequently, in order to prevent arsenic escape, the substrate temperature is lowered to about 500 ° C. which is the optimum growth temperature of the GaInNAs layer while irradiating arsenic flux, and undoped Ga _0.80 In _0.20 N
_0.022 As _0.978 quantum well active layer 106a and undoped Ga _0.98 In _0.02 N _0.024 As _0.976 quantum barrier layer 106b
Are stacked three times to form the quantum well structure 106.

Thereafter, the substrate temperature was raised to 650 ° C. while supplying arsenic flux and ammonia, which are the raw materials of the group V element.
After the temperature was increased to about 1.0 μm, the n-type Al _0.3 Ga _0.7
An As first upper cladding layer 108 and an n-type GaAs protective layer (not shown in FIG. 1A) are formed.

Subsequently, a dielectric mask made of a striped SiN film is formed by n-type GaAs by a normal photolithography process.
It is formed on the s protective layer. Next, in a wet etching process, the lower cladding layer 104, the quantum well structure 106,
The first upper cladding layer 108 and the n-type GaAs protective layer are selectively etched to form a 1.5 μm wide mesa structure 109.
To form

Further, the mesa structure 1 is selectively grown by MOCVD using a dielectric mask.
09 on the exposed surface of the buffer layer 102 on both sides of the n-type InGaP
Layer 112 (thickness: about 0.6 μm), p-type InGaP layer 1
13 (thickness: about 1 μm) and n-type InGaP layer 114
(Thickness: about 1 μm). n-type InGaP layer 112, p-type InGaP layer 113, and n-type InGaP
The layer 114 forms a current confinement structure 110 for confining light in the lateral direction and confining current.

Subsequently, after removing the dielectric mask, the n-type Al _0.3 Ga _0.7 As second upper cladding layer 116 and the n-type GaAs are formed on the mesa structure 109 and the current confinement structure 110 by MBE. The cap layer 118 is formed sequentially.

Finally, a p-side electrode 120 and an n-side electrode 122 are formed on the back surface of the substrate 100 and the upper surface of the cap layer 118, respectively. Thus, a buried type semiconductor laser device is obtained.

In the above configuration, the quantum well active layer 10
The lattice constant A _{well of} 6a is set to be larger than the lattice constant A _barrier of the quantum barrier layer 106b. Thereby, as shown in FIG. 7, a structure for confining electrons and holes in the quantum well layer can be formed.

According to the present embodiment, the quantum well active layer 10
6a and the quantum barrier layer 106b are both formed of a semiconductor containing nitrogen. Therefore, when a semiconductor containing nitrogen is formed on a compound semiconductor containing no nitrogen, or when a semiconductor layer is formed in the reverse order, an interface between the layers (an interface between the quantum well layer and the quantum barrier layer) is formed. ) Can prevent crystallinity deterioration due to phase separation or clustering. As a result, a heterointerface having good crystallinity and sharpness can be formed, and a quantum well structure having a sharp change in energy gap can be obtained.

Since the quantum well active layer 106a and the quantum barrier layer 106b have the same constituent elements, the growth temperature during the formation of the quantum well structure can be kept constant. For this reason, the growth of the quantum well active layer 106a prevents the quantum barrier layer 10 from growing.
When switching to the growth of 6b, there is no need to provide a waiting time to reach the optimum growth temperature, and it is possible to prevent the adsorption of impurities at those interfaces or the deterioration of crystallinity due to the re-evaporation of the constituent elements.

FIG. 2 shows evaluation results obtained by calculating the satellite wells of the X-ray diffraction pattern by the two-crystal method for the quantum well structure according to the present embodiment. It can be confirmed that, in the structure of the present invention, the sharpness of the composition at the interface F between the quantum well layer and the quantum barrier layer is improved as compared with the conventional structure. By improving the crystallinity at the interface and the steepness of the composition of the interface, non-luminous components can be reduced and luminous efficiency can be improved, and the oscillation threshold value is reduced to about 92 mA, which is about 10% lower than the conventional one. . According to the present invention, it is possible to obtain a semiconductor laser device having good characteristics such that the slope efficiency shows a value of 0.25 W / A.

Further, Ga (Al) As is used as a quantum barrier layer.
According to the present invention, a barrier layer having a smaller energy gap can be formed as compared with the above-described conventional example using a layer. Thereby, even when the quantum well layer is made thick, the band discontinuity difference between the quantum well layer and the quantum barrier layer can be reduced so that the level of the quantum well level becomes one. As a result, it is also possible to suppress a jump in the oscillation wavelength due to a change in the oscillation level, which occurs when a large number of levels exist in the quantum well.

Further, InGaAs is used for forming the quantum well structure.
Using an N-based material has the following advantages over using a GaAsN-based material. GaAsN-based materials are
In order to obtain the same band gap as that of the InGaAsN-based material, it is necessary to increase the mixed crystal ratio of nitrogen (see FIG. 7). When the nitrogen mixed crystal ratio is high, layer separation and clustering are likely to occur, and it is difficult to obtain a good crystal structure. On the other hand, in the case of an InGaAsN-based material, such a problem can be avoided. Furthermore, G
Even when a semiconductor film needs to be formed thick because it does not lattice match with the aAs substrate, it is possible to use InG rather than GaAsN-based materials.
It is preferable to form a quantum well structure using an aAsN-based material.

In the above description, the MBE is used for forming the semiconductor layer.
Although the growth method is used, another growth method, for example, an MOCVD (metal organic chemical vapor deposition) method may be used.

(Second Embodiment) A buried type semiconductor laser device according to a second embodiment of the quantum well structure optical semiconductor device according to the present invention will be described below with reference to FIGS. 3 (a) and 3 (b). Will be described. The semiconductor laser device of the present embodiment differs from the first embodiment in the configuration of the quantum well structure, and the other elements are the same.

As shown in FIG. 3A, this semiconductor laser device comprises a p-type GaAs substrate 100 and a p-type GaAs substrate.
s buffer layer 102, p-type Al _0.3 Ga _0.7 As lower cladding layer 104, quantum well structure 206, n-type Al
_0.3 Ga _0.7 As first upper cladding layer 108, current confinement structure 110, n-type Al _0.3 Ga _0.7 As second upper cladding layer 116, n-type GaAs cap layer 118,
It has.

The quantum well structure 206 of the present embodiment is similar to that of FIG.
As shown in (b), undoped Ga _0.90 In _0.10
N _0.027 As _0.973 quantum well active layer 206a and undoped Ga _0.96 In _0.04 N _0.022 As _0.978 quantum barrier layer 206
b) to have a six-cycle laminated structure.

The quantum well active layer 206a has a compressive strain of 0.25% with respect to the GaAs substrate 100,
m thickness. The quantum well active layer 206a has an energy gap of about 0.885 eV and a lattice constant of about 5.667 °. On the other hand, the quantum barrier layer 206b
It has a tensile strain of 0.14% with respect to the aAs substrate 100 and has a thickness of about 220 nm. Quantum barrier layer 206b
Has an energy gap of about 1.03 eV and a lattice constant of 5.645 °.

Hereinafter, the manufacturing process of the semiconductor laser device of this embodiment will be described.

In the manufacturing process of this embodiment, a solid raw material such as gallium, indium and aluminum is used as a raw material of the group III element, and a raw material such as arsine (AsH ₃ ) or phosphine (PH ₃ ) is used as a raw material of the group V element. Use hydride and ammonia. Note that hydrogen selenide (H ₂ Se) is used as a raw material of the n-type impurity, and diethyl zinc (DEZ) is used as a raw material of the p-type impurity.

First, gas source molecular beam epitaxy (G
P-type Ga at a substrate temperature of 500 ° C. by the SMBE method.
On an As substrate 100, a p-type GaAs buffer layer 102 having a thickness of about 0.3 μm and a p-type Al _0.3 Ga
_{And a 0.7} As lower cladding layer 104 are sequentially formed. p
-Type GaAs buffer layer 102 and p-type Al _0.3 Ga
_{The 0.7} As lower cladding layer 104 is a p-type GaAs substrate 1
00 and lattice match.

Subsequently, on the lower cladding layer 104, an undoped Ga _0.90 In _0.10 N _0.027 As _0.973 quantum well active layer 206a and an undoped Ga _0.96 In _0.04 N _0.022 A
and s _{0. 978} quantum barrier layer 206 b, to form a. The quantum well structure 206 is formed by laminating the quantum well active layer 206a and the quantum barrier layer 206b for six periods so as to compensate for the distorted stress of each layer. Thereafter, an n-type Al _{0.3 having a} thickness of 1.0 μm is formed.
A Ga _0.7 As first upper cladding layer 108 is formed.

Subsequently, a dielectric mask made of a stripe-shaped SiN film is formed on the first upper cladding layer 108 by a usual photolithography process. In the wet etching process, the lower cladding layer 104 and the quantum well structure 20 are exposed so that a part of the surface of the buffer layer 102 is exposed.
6 and the first upper cladding layer 108 are selectively etched to form a mesa structure 109 having a width of 1.5 μm.

Further, the mesa structure 1 is selectively grown by MOCVD using a dielectric mask.
09 on the exposed surface of the buffer layer 102 on both sides of the n-type InGaP
Layer 112, p-type InGaP layer 113, and n-type InGa
P layers 114 are formed sequentially. n-type InGaP layer 112,
p-type InGaP layer 113 and n-type InGaP layer 114
As a result, a current confinement structure 110 for confining light in the lateral direction and confining the current is formed.

Subsequently, after removing the dielectric mask, the n-type Al _0.3 Ga _0.7 As second upper cladding layer 116 and the n-type GaAs are formed on the mesa structure 109 and the current confinement structure 110 by the GSMBE method. The cap layer 118 is formed sequentially.

Finally, a p-side electrode 120 and an n-side electrode 122 are formed on the back surface of the substrate 100 and the upper surface of the cap layer 118, respectively. Thus, a buried type semiconductor laser device is obtained.

In the present embodiment, similarly to the first embodiment, by using a GaInAsN layer for the quantum barrier layer,
The effect of improving the crystallinity of the interface and the steepness of the composition of the interface can be obtained. Further, by reducing the strain stress at the interface between the quantum well active layer and the quantum barrier layer, it is possible to solve the problem of the prior art in which the crystallinity of the interface is degraded due to instability of the interface state due to the strain stress. According to the present embodiment, a quantum well structure having good crystallinity can be obtained without causing phase separation. According to the present embodiment, the oscillation threshold can be reduced by about 15% as compared with the conventional example (about 88 m).
A), Slope efficiency 0.3 W / A, reliability 5000
A semiconductor laser device improved from 20,000 hours to 20,000 hours can be obtained.

(Third Embodiment) Hereinafter, a third embodiment of a quantum well structure optical semiconductor device according to the present invention will be described with reference to FIG.
A ridge-type semiconductor laser device according to the embodiment will be described. In this embodiment, n-type GaAs is used as the substrate.

As shown in FIG. 4, this semiconductor laser device has an n-type GaAs substrate 300, an n-type GaAs buffer layer 302, an n-type Al _0.4 Ga _0.6 As lower cladding layer 304, a quantum well structure 306, and , P-type Al _0.4 G
a _0.6 As upper cladding layer 308, a p-type GaAs cap layer 318, and a SiO ₂ dielectric layer 310. The dielectric layers 310 are provided on both sides of a ridge structure 309 including the lower cladding layer 304, the quantum well structure 306, the upper cladding layer 308, and the cap layer 318. Note that the n-side electrode 32 is
0 is formed, and a p-side electrode 322 is formed on the p-type GaAs cap layer 318 and the dielectric layer 310.

The quantum well structure 306 is made of undoped Ga.
_0.80 In _0.20 N _0.022 As _0.978 Quantum well active layer 306a
And an undoped Ga _0.98 In _0.02 N _0.022 As _0.978 quantum barrier layer 306b.
The quantum well active layer 306a has a compressive strain of 1.0% with respect to the GaAs substrate 300, and has a thickness of about 60 nm. The quantum well active layer 306a has an energy gap of about 0.886 eV and a lattice constant of about 5.710 °. On the other hand, the quantum barrier layer 306b is formed on the GaAs substrate 30.
It has a tensile strain of 0.25% with respect to
It has a thickness of nm. The quantum barrier layer 106b has an energy gap of about 1.07 eV and a lattice constant of 5.63.
9Å.

Hereinafter, the manufacturing process of the above-described semiconductor laser device will be described.

In this manufacturing process, the same raw materials as in the first embodiment are used as the raw materials for the group III elements such as gallium, indium and aluminum, and the group V elements such as arsenic and nitrogen.

First, an n-type GaAs buffer layer 302 having a thickness of about 0.2 μm is formed on an n-type GaAs substrate 300 at a substrate temperature of 700 ° C. (optimum growth temperature of the GaAs layer) by MBE (Molecular Beam Epitaxy). And an n-type Al _0.4 Ga _0.6 As lower cladding layer 304 having a thickness of about 1.0 μm.

Subsequently, in order to improve the rate of incorporation of nitrogen into the GaInNAs film, the substrate temperature was lowered to about 500 ° C. in an atmosphere of arsenic flux and ammonia, and undoped Ga was deposited on the lower cladding layer 304. _0.80 I
An n _0.20 N _0.022 As _0.978 quantum well active layer 306a and an undoped Ga _0.98 In _0.02 N _0.022 As _0.978 quantum barrier layer 306b are formed. The quantum well structure 3 is formed by stacking the quantum well active layer 306a and the quantum barrier layer 306b for three periods.
06 is formed.

Thereafter, the substrate temperature was raised to about 700 ° C. in an atmosphere of arsenic flux and ammonia,
A 1.0 μm thick p-type Al _0.4 Ga _0.6 As upper cladding layer 308 and a p-type GaAs cap layer 318 are formed.

Subsequently, by a usual photolithography process, 3
A stripe-shaped resist pattern having a width of μm is formed on the cap layer 318. Next, the cap layer 318 and the upper clad layer 308 having a certain thickness are selectively etched by a wet etching process.
A ridge structure 309 having a width of μm is formed.

Further, a dielectric layer 310 made of SiO _{2 is formed} by sputtering so as to cover the upper cladding layer 308.
(Thickness: about 0.5 μm).

Finally, the substrate 300 side and the ridge structure 309
On the sides, an n-side electrode 320 and a p-side electrode 322 are formed, respectively. Thus, a ridge-type semiconductor laser device is obtained.

Hereinafter, the supply of raw materials in the process of manufacturing the quantum well structure 306 will be described in more detail with reference to FIG.

FIG. 5 shows an opening / closing sequence of a shutter for controlling a material supply of a material supply source of the MBE growth apparatus when the quantum well structure 306 is formed. “Ga1 source” and “Ga2 source” refer to supply sources that supply gallium raw materials at different supply amounts by using molecular beam sources having different intensities. "In1 source" and "In2 source"
Indicates a supply source that supplies indium raw materials at different supply amounts by using molecular beam sources having different intensities. “As source” and “N source” indicate a source that supplies an arsenic raw material and ammonia at a constant supply amount, respectively. The supply amounts of these supply sources may be appropriately set according to the growth conditions. Note that “ON” (open) and “OF”
"F" (closed) indicates that the raw material is supplied and not supplied, respectively. For example, regarding the supply of gallium, "Ga1
By controlling the opening and closing of the shutters of the "source" and the "Ga2 source", the total supply amount of gallium can be controlled. That is, when both the shutters of the “Ga1 source” and the “Ga2 source” are “open”, the supply amount of gallium is equal to the supply amount of the “Ga1 source” and the “Ga2 source”.
And only one of the “Ga1 source” and the “Ga2 source” is “open”.
The supply amount of gallium is the supply amount of one of the “Ga1 source” and the “Ga2 source”.

As shown in FIG. 5, Ga _0.80 In _0.20
From the growth of the N _0.022 As _0.978 quantum well active layer 306a,
Ga _0.98 In _0.02 N _0.022 As _0.978 Quantum barrier layer 306b
When the growth is switched to, the source supply ratios of the group III elements gallium and indium are changed, and the source supply ratios of the group V elements arsenic and nitrogen are kept constant.

As described above, in forming the interface portion of the semiconductor layer during the fabrication of the quantum well structure, by keeping the supply amount (concentration) of the nitrogen source constant without switching, it is an essential object of the present invention. , Band gap and lattice constant can be avoided. Therefore, the composition of the interface between the quantum well layer and the quantum barrier layer and the steepness of the energy gap are improved. further,
It is also possible to suppress the occurrence of phase separation or clustering caused by instability of the interface state due to a change in the supply amounts of arsenic and nitrogen. By this effect, a structure of the quantum well layer / quantum barrier layer in which the composition at the interface and the steepness of the energy gap are further improved can be obtained.

According to the present embodiment, the oscillation threshold can be reduced by about 20% (about 80 mA) and the slope efficiency can be improved to 0.4 W / A, as compared with the conventional device.

(Fourth Embodiment) A buried semiconductor laser device according to a fourth embodiment of the quantum well structure optical semiconductor device according to the present invention will be described below with reference to FIGS. 6A and 6B. Will be described. The main difference between this embodiment and the above-described embodiment is that, in this embodiment, an optical waveguide layer is provided on at least one of the upper and lower sides of the quantum well structure.

As shown in FIG. 6A, an n-type GaAs substrate 300 and an n-type GaAs
and s buffer layer 302, an n-type Al _0.4 Ga _0.6 As lower cladding layer 304, a _{Ga a In 1-a N b} As 1-b lower optical waveguide layer 405, a quantum well structure 406, Ga _c In _1-c
N _d As _1-d upper optical waveguide layer 407 and p-type Al _0.4 Ga
_{A 0.6} As upper clad layer 308, a p-type GaAs cap layer 318, and a semi-insulating InGaP layer 410 are provided. The semi-insulating InGaP layer 410 includes the lower cladding layer 304, the lower optical waveguide layer 405, and the quantum well structure 3
, An upper optical waveguide layer 407, an upper cladding layer 308, and a cap layer 318.
Are provided on both sides. Note that n
The side electrode 320 is formed, and the p-type GaAs cap layer 31 is formed.
8 and the p-side electrode 322 are formed on the InGaP layer 410.

Ga _a In _{1 -a Nb} As _{1 -b} Lower Optical Waveguide Layer 4
The gallium composition a of 05 gradually decreases from 1.0 to 0.94 from the substrate 300 side in the layer stacking direction. Note that a = (0.405−
The condition of 1.11b) / (0.405-0.035b) is satisfied. This allows Ga _a In _{1-a Nb} As
_As shown in FIG. _{6B, the 1-b} lower optical waveguide layer 405 has an energy gap (difference in energy level between the conduction band and the valence band) while lattice-matching with the substrate 300. (The lower side in FIG. 6B) gradually decreases in the layer stacking direction.

On the other hand, the gallium composition c of the Ga _c In _1-c N _d As _1-d upper optical waveguide layer 407 is from 0.94 to 1.0 in the direction of layer stacking from the substrate 300 side. It is increasing gradually. Note that c = (0.4 between c and d.
05-1.11d) / (0.405-0.035d). This allows Ga _c In _1-c N
_The energy gap of the dAs _{1 -d} upper optical waveguide layer 407 gradually increases from the substrate 300 side toward the layer stacking direction.

The quantum well structure 406 is made of undoped Ga.
_0.85 In _0.15 N _0.026 As _0.974 Quantum well active layer 406a
And an undoped Ga _0.80 In _0.20 N _0.024 As _0.976 quantum barrier layer 406b.
The quantum well active layer 406a has a compressive strain of 0.5% with respect to the GaAs substrate 300, and has a thickness of about 50 nm. The quantum well active layer 406a has an energy gap of about 0.855 eV and a lattice constant of about 5.681 °. On the other hand, the quantum barrier layer 406b is formed on the GaAs substrate 30.
It is lattice-matched to zero and has a thickness of about 120 nm. The quantum barrier layer 406b has an energy gap of about 1.03.
eV and the lattice constant is 5.632 °.

Hereinafter, the manufacturing process of the above-described semiconductor laser device will be described.

In this production process, trimethyl gallium (TMG), trimethyl indium (TMI) and trimethyl aluminum (TMI) were used as raw materials for Group III elements such as gallium, indium and aluminum, respectively.
An organometallic gas such as A) is used, and hydrides such as arsine and ammonia are used as raw materials for group V elements such as arsenic and nitrogen, respectively. Note that hydrogen selenide (H ₂ Se) is used as a raw material of the n-type impurity, and diethyl zinc (DEZ) is used as a raw material of the p-type impurity.

First, n-type GaAs is deposited at a substrate temperature of 700 ° C. (optimum growth temperature of the GaAs layer) by MOCVD.
An n-type GaAs buffer layer 302 having a thickness of about 0.3 μm and an n-type Al _0.4 Ga _{0.6 having a} thickness of about 1.0 μm are formed on a substrate 300.
And an As lower cladding layer 304 are sequentially formed.

Subsequently, while adjusting the supply amounts of ammonia and arsine, the substrate temperature is lowered to about 500 ° C. in order to improve the rate of incorporation of nitrogen into the GaInNAs film. Thereafter, the above-mentioned Ga is formed on the lower cladding layer 304.
_a In _{1-a Nb} As _1-b Lower optical waveguide layer 405 is 0.3 μm
Formed to a thickness of

Next, undoped Ga _0.85 In _0.15 N
_0.026 As _0.974 quantum well active layer 406a and undoped Ga _0.90 In _0.20 N _0.024 As _0.976 quantum barrier layer 406b
And form The quantum well structure 406 is formed by stacking the quantum well active layer 406a and the quantum barrier layer 406b for two periods.

Subsequently, while adjusting the supply amounts of ammonia, arsine and the like, the above G
0.3μ and _{a a In 1-a N b} As 1-b upper optical waveguide layer 407
It is formed to a thickness of m.

Thereafter, the temperature of the substrate is raised to about 700 ° C., and while supplying materials such as ammonia and arsine,
A 1.0 μm thick p-type Al _0.4 Ga _0.6 As upper cladding layer 308 and a p-type GaAs cap layer 318 are formed.

Subsequently, by a usual photolithography process,
A stripe-shaped resist pattern having a width of 1.5 μm is formed on the cap layer 318. Next, using the resist patterning as a mask, the lower clad layer 304, the lower optical waveguide layer 405, and the quantum well are exposed by reactive ion beam etching (RIBE) using chlorine gas so that a part of the surface of the buffer layer 302 is exposed. Well structure 406,
The upper optical waveguide layer 407, the upper cladding layer 308, and the cap layer 318 are selectively etched to form a mesa structure 409 having a width of 1.5 μm.

Further, on the buffer layer 302 on both sides of the mesa structure 409, an InGaP layer 4 serving as a light / current confinement layer is formed.
10 is formed to a thickness of about 3.1 μm.

Finally, an n-side electrode 320 is formed on the back surface of the substrate 300 by vacuum evaporation, and the cap layer 318 and the I-side electrode 320 are formed.
A p-side electrode 322 is formed on the upper surface of the nGaP layer 410.
Thus, a buried type semiconductor laser device is obtained.

According to this embodiment, the optical waveguide layer having an energy gap between these layers is provided between the cladding layer and the quantum well structure.
The light confinement coefficient of the quantum well layer increases, and the degree of freedom in device design increases.

Further, according to the present invention, the interface structure between the N-based semiconductor layer and the nitrogen-free layer having good crystallinity is provided between the optical waveguide layer and the cladding layer located outside the quantum well structure. Can be formed, so that non-radiative recombination can be prevented.

As the above N-based semiconductor, InGaAsN
Alternatively, GaAsN is used, but InG is used for the following reasons.
aAsN is more preferred. In the case of GaAsN having a band gap in a wavelength band of 1.1 μm, a high value of 2% is required as the nitrogen concentration, and the GaAs substrate has a tensile strain of about 0.5% with respect to the GaAs substrate. For this reason, when forming a guide layer having a relatively large thickness, lattice relaxation occurs and a good crystal cannot be obtained. In contrast,
InGaAsN-based materials have a band gap in the same wavelength band as GaAsN, and when lattice-matched to GaAs, have a composition of In _0.05 Ga _0.95 As _0.984 N _{0.016 and} a low nitrogen concentration that causes mixing instability. Can be used.

According to this embodiment, a semiconductor laser device having an oscillation threshold reduced by about 25% (about 75 mA) as compared with the conventional device can be obtained.

In this embodiment, the Ga composition ratio of the optical waveguide layer is gradually changed from 1.0 to 0.94 (and from 0.94 to 1.0). A similar effect can be obtained even if the structure changes in steps of, for example, 0.02. Further, the cladding layer of the present embodiment is A
An InGaAsAl layer containing a small amount of nitrogen and indium, an InGaAsN layer containing no aluminum, or InG
The cladding layer can be composed of an aAsPN layer or the like. Even in this case, the laser device is manufactured by forming a band gap structure that smoothly connects the optical waveguide layer and the clad layer without changing the group III or V group composition element without deteriorating the crystallinity of the clad layer. Can be.

It goes without saying that the mixed crystal ratio and the layer thickness of the quantum well layer and the quantum barrier layer described in the above embodiments can take various values without departing from the gist of the present invention.

In the above embodiment, the quantum well structure and the optical waveguide layer are formed of InGaAsN. However, these layers may be formed of a material containing Al or Tl as a group III element and Sb or the like as a group V element. The same effect can be obtained by forming with an N-based semiconductor.

Further, the growth method, the growth temperature, and the specific structure of the semiconductor layer are not limited to those described in the above embodiments. It is needless to say that the method or the structure described above may be used.

[0101]

According to the present invention, the following effects can be obtained.

Since the quantum well layer and the quantum barrier layer are both formed of a III-V compound semiconductor containing nitrogen and another group V element, the conventional mixing at the interface between the quantum well layer and the quantum barrier layer is performed. Eliminate instability. As a result, a structure of a quantum well layer / quantum barrier layer having an interface having a steep composition and a steep energy gap can be formed. Therefore, the slope efficiency of the semiconductor laser device can be improved and the threshold value can be reduced.

Further, III-containing nitrogen and other group V elements
By using a quantum barrier layer made of a group V compound semiconductor, a barrier layer having a smaller energy gap can be formed as compared with the conventional example using a Ga (Al) As layer as the quantum barrier layer. Thereby, even when the quantum well layer is made thick, the band discontinuity difference between the quantum well layer and the quantum barrier layer can be reduced so that the level of the quantum well level becomes one. As a result, it is possible to suppress a jump in the oscillation wavelength due to a change in the oscillation level, which occurs when a large number of levels exist in the quantum well.

Further, since the lattice constant A _well of the quantum well layer is set to be larger than the lattice constant A _barrier of the quantum barrier layer, a structure in which electrons and holes are confined in the quantum well can be obtained. Further, by making the strain stresses of the quantum well layer and the quantum barrier layer opposite to each other and equal in magnitude, phase separation at the interface due to the strain can be suppressed.

Furthermore, by keeping the supply amount of the group V source material containing nitrogen constant and forming the quantum well layer and the quantum barrier layer continuously, phase separation or clustering or the like which is likely to occur when the supply amount of the group V source material is switched. Can be suppressed. Therefore, the state of the interface between the quantum well layer and the quantum barrier layer is stable, and the structure of the quantum well layer / quantum barrier layer having the interface having the sharpness of the composition and the sharpness of the energy gap can be reliably formed. .

Further, by providing an optical waveguide layer having an energy gap between these layers between the cladding layer and the quantum well structure, the degree of freedom in device design such as a light confinement coefficient is increased.

When InGaAsN and GaAs, which can be used as an N-based semiconductor for forming a quantum well structure, are compared with each other, if they have the same band gap, the concentration of nitrogen which causes mixing instability is small and the GaAs layer has The effect of the present invention can be more sufficiently achieved by using InGaAsN that lattice-matches.

[Brief description of the drawings]

FIG. 1 is a structural view of a semiconductor laser device according to a first embodiment of the present invention, FIG. 1 (a) is a cross-sectional view, and FIG.

FIG. 2 is a diagram showing evaluation results obtained by calculating from data of an X-ray diffraction method for a semiconductor laser device obtained according to the first embodiment of the present invention.

FIGS. 3A and 3B are structural diagrams of a semiconductor laser device according to a second embodiment of the present invention, FIG. 3A is a sectional view, and FIG. 3B is a diagram showing a band structure of a quantum well structure.

FIG. 4 is a structural sectional view of a semiconductor laser device according to a third embodiment of the present invention.

FIG. 5 is a diagram showing an opening / closing sequence of a shutter for controlling a material supply of a material supply source of an MBE growth apparatus when a quantum well structure of a semiconductor laser device according to a third embodiment of the present invention is manufactured.

FIG. 6 is a structural view of a semiconductor laser device according to a fourth embodiment of the present invention, (a) is a sectional view, and (b) is a view showing a hand structure of a quantum well structure.

FIG. 7 is a diagram showing the relationship between the composition of In and N and the lattice constant or band gap of a GaInNAs-based material.

FIG. 8 is a sectional structural view of a conventional GaInNAs-based strained quantum well structure semiconductor laser device.

FIG. 9 is a diagram showing current-light output characteristics of a conventional GaInNAs-based strained quantum well structure semiconductor laser device.

[Explanation of symbols]

100 p-type GaAs substrate 102 p-type GaAs buffer layer 104 p-type Al _0.3 Ga _0.7 As lower cladding layer 106, 206, 306, 406 Quantum well structure 106a, 206a, 306a, 406a GaInN
As quantum well layer 106b, 206b, 306b, 406b GaInN
As quantum barrier layer 108 n-type Al _0.3 Ga _0.7 As first upper cladding layer 109 mesa structure 110 current confinement structure 112 n-type InGaP layer 113 p-type InGaP layer 114 n-type InGaP layer 116 n-type Al _0.3 Ga _0.7 As second Upper cladding layer 118 n-type GaAs cap layer 120, 322 p-side electrode 122, 320 n-side electrode 300 n-type GaAs substrate 302 n-type GaAs buffer layer 304 n-type AlGaAs lower cladding layer 308 p-type AlGaAs upper cladding layer 309 ridge structure 310 Dielectric layer 318 p-type GaAs cap layer 405 GaInNAs lower optical waveguide layer 407 GaInNAs upper optical waveguide layer 409 Mesa structure 410 InGaP layer

Claims (7)

[Claims] 1. A quantum well structure made of a group III-V compound semiconductor having an active region having a quantum barrier layer and a quantum well layer formed of two or more group V elements containing a group III element and nitrogen. An optical semiconductor device, wherein the quantum barrier layer is formed of a group III element and two or more group V elements containing nitrogen. 2. The group III element is selected from a group including Al, Ga, In and Tl, and the group V element is selected from a group including As, P and Sb in addition to the nitrogen.
3. The optical semiconductor device having a quantum well structure according to item 1. 3. The quantum well structure optical semiconductor device according to claim 1, wherein the value of the lattice constant of the quantum well layer is larger than the value of the lattice constant of the quantum barrier layer. 4. The crystal structure of the quantum well layer and the quantum barrier layer has a strain, and the strain stress of the quantum well layer and the strain stress of the quantum barrier layer are equal in magnitude and in the same direction. 4. The quantum well structure optical semiconductor device according to claim 1, wherein the direction is opposite. 5. The quantum well structure according to claim 1, wherein a composition of said group V element contained in said quantum well layer is equal to a composition of said group V element contained in said quantum barrier layer. Optical semiconductor device. 6. An optical waveguide layer for transmitting light from the active region is provided on at least one of the upper and lower sides of the active region, wherein the optical waveguide layer includes a group III element and nitrogen. The quantum well structure optical semiconductor device according to any one of claims 1 to 5, wherein the quantum well structure optical semiconductor device is formed of at least one kind of group V element. 7. The quantum well structure optical semiconductor device according to claim 6, wherein the energy gap of the optical waveguide layer changes stepwise or continuously.