JPH0680871B2 - Semiconductor laser device - Google Patents

Description

The present invention relates to a structure of a semiconductor laser having an oscillation wavelength in a short wavelength visible region of 700 nm or less.

[Prior Art] The progress of the information society has been remarkable in recent years, and among them, the development of optical information processing technology such as optical communication centering on a semiconductor laser and an optical disk is remarkable. Under such circumstances, the needs for semiconductor lasers having an emission wavelength in the visible region are rapidly increasing. Currently 780nm
An AlGaAs semiconductor laser with an oscillation wavelength has been put to practical use as a light source for compact discs and video discs. However, especially in the optical disc for information memory,
In order to handle a larger amount of information, it is necessary to reduce the spot diameter after focusing, which requires a semiconductor laser that oscillates at a shorter wavelength.

A semiconductor material having an energy gap corresponding to such a short wavelength region is lattice-matched to a GaAs substrate (Al _x G
a _1-x ) _y In _1-y P is drawing attention. Since this material is difficult to grow by the conventional liquid phase epitaxy method (LPE method),
Recently, research and development have become active with the molecular beam epitaxy method (MBE method) and the vapor phase growth method (MO-CVD method) using an organic metal as growth methods. The growth is carried out by substantially the transport law rule by using the MBE method and MO-CVD method, (Al _x Ga
It became possible to grow _1-x ) _y In _1-y P.

Here, MO-CVD having a semiconductor layer of (Al _x Ga _1-x ) _y In _1-y P
The structure of a semiconductor laser manufactured by the method is shown in FIG. This semiconductor laser has an n-type Ga _0.5 I on an n-type GaAs substrate 1.
n _0.5 P buffer layer 2 (layer thickness 0.5 μm), n-type (Al _0.6 Ga
_0.4 ) _0.5 In _0.5 P clad layer 3 (layer thickness 1 μm), undoped Ga _0.5 In _0.5 P active layer 4 (layer thickness 0.08 μm), p-type (Al
_0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 5 (layer thickness 1 μm), Ga
_{A 0.5} In _0.5 P cap layer 6 (layer thickness 0.2 μm) is continuously grown by MO-CVD method. After that, proton ions are implanted into a portion other than the oscillation stripe region to a depth of 0.8 μm to form a high resistance region 7. Then, the n-type and p-type electrodes 8 and 9 are formed of AuGe / Ni and AuZn / Au. With such a manufacturing method, it becomes possible to manufacture a laser having a shorter wavelength than before.

However, these growth methods have the following drawbacks as compared with the LPE method. In other words, in these growth methods, the surface of the growing layer during growth is not covered with the metal melt like the LPE method and is not protected, so that contaminants such as oxygen, water vapor and hydrocarbons in the atmosphere are taken in during the growth. It's easy. Therefore, it was not easy to obtain good quality crystals. In particular, it contains a large amount of Al used in the cladding layer of a laser having a double heterojunction structure such as this semiconductor laser (Al _x Ga
Regarding the _1-x ) _y In _1-y P (X0.6) layer, it was not easy to obtain a crystal layer having a low electric resistance and a high thermal conductivity due to the incorporation of contaminants. However, in such a laser, the characteristics of this clad layer, that is, the characteristics of the AlGaInP clad layer 5 having a stripe-shaped current path and close to the surface of the growth layer which is Mouton on the heat sink poses a serious problem. That is, the high electrical resistivity of the clad layer 5 not only raises the element resistance, but also causes a heating effect by Joule heat. Further, the high thermal resistance causes an increase in threshold current due to an increase in junction temperature. Therefore, high temperature continuous oscillation of the semiconductor laser has become impossible.

Therefore, to improve such drawbacks, AlGaInP
AlGaAs with lower electric resistance and better thermal conductivity
Attempts were made to replace part of the AlGaInP cladding layer. An example of this is shown in FIG. The semiconductor laser of this example is similar to the laser shown in FIG.
_0.5 In _0.5 P buffer layer 2, n-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5
P clad layer 3, Ga _0.5 In _0.5 P active layer 4 (layer thickness 0.08μ
m) is grown by the MO-CVD method, and then continuously grown into p-type (Al
_0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 5 (layer thickness 0.3 μm) is laminated. After that, the supply of the group III and the raw material to be the p-type dopant is stopped, and the flow rate of PH ₃ is gradually reduced to reduce AsH ₃
By increasing the flow rate, AsH ₃ a group V raw material from PH ₃
After complete switching to TMG (trimethylgallium) and TMA (trimethylaluminum) and p
P-type Al _0.85 Ga _0.15 As clad layer 10 (layer thickness 0.7 μm) by supplying DMZn (dimethyl zinc) as a type dopant, p
A type GaAs cap layer 11 (layer thickness 0.2 μm) is grown. After that, the high resistance region 7 is formed by implanting proton ions into a portion other than the oscillation stripe region. Further, the n-side electrode 8 and the p-side electrode 9 are formed to complete the manufacturing. By replacing a part of the clad layer with AlGaAs in this way, the electric resistance and thermal resistance of the clad layer can be reduced, and therefore high-temperature continuous-wave oscillation of the semiconductor laser is facilitated.

[Problems to be Solved by the Invention] However, in the above manufacturing method, when switching from the AlGaInP layer to the growth of the AlGaAs layer, it is necessary to switch the growth by exposing the AlGaInP layer containing a large amount of easily oxidizable Al to the atmosphere. There is. Therefore, during this growth switching period, high density non-radiative recombination centers are formed at the interface between the AlGaInP clad layer and the AlGaAs clad layer, which causes device deterioration and reliability of the device during long-term operation. It was causing a decline.

Therefore, the present invention provides a semiconductor laser having excellent high temperature characteristics and high reliability by stacking the AlGaAs cladding layer on the AlGaInP cladding layer and improving the quality of the interface between the AlGaInP and AlGaAs. The purpose is to provide.

[Means for Solving Problems] The present invention provides a first clad layer, an active layer, and
A semiconductor laser device in which a second clad layer is sequentially laminated, wherein the second clad layer sequentially comprises a clad layer made of either AlGaInP or AlInP, GaInP,
It is characterized in that it is formed by laminating a thin film buffer layer made of any one of GaP and InP and a clad layer made of AlGaAs.

[Operation] In the semiconductor laser according to the present invention, the second cladding layer is made of Al.
It has a two-layer structure of a clad layer made of GaInP or the like and a clad layer made of AlGaAs, and a thin buffer layer is formed between the two clad layers. The crystallinity at the interface between both cladding layers is improved with almost no consideration of absorption loss.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of a proton-injected stripe structure semiconductor laser according to the first embodiment of the present invention. n-type Ga
N-type Ga _0.5 In _0.5 P buffer layer 2 (layer thickness 0.5
μm), n-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 3
(Layer thickness 1 μm), undoped Ga _0.5 In _0.5 P active layer 4 (layer thickness 0.08 μm), p-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 5 (layer thickness 0.3 μm), p-type Ga _0.5 In _0.5 P buffer layer 12
(Layer thickness 0.005 μm) is continuously laminated by MO-CVD method. After that, the supply of the group III raw material and the raw material to be the p-type dopant is stopped to stop the growth, and the group V raw material is changed from PH ₃ to AsH.
After switching to ₃ , the p-type Al _0.85 Ga _0.15 As clad layer 10 (layer thickness 0.7 μm) and the p-type GaAs cap layer 11 (layer) were supplied by supplying TMG and TMA as group III raw materials and DMZn as p-type dopant. Thickness 0.2 μm). Then, the high resistance region 7 is formed by implanting proton ions into a portion other than the oscillation stripe region.
To form. Finally, the n-side electrode 8 and the p-side electrode 9 are formed to complete the manufacturing.

In the above embodiment, the GaInP buffer layer 12 containing no Al is deposited on the p-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P cladding layer 5. Then, the group V source material is switched from PH ₃ to AsH ₃ after the deposition of the buffer layer 12. For this,
When the crystal growth was stopped due to the switching of the group V gas, the buffer layer
The surface of 12 does not undergo surface deterioration due to oxidation of Al. Therefore, p-type Al _0.85 Ga deposited on the surface of the buffer layer 12
The quality of the interface with the _0.15 As cladding layer 10 can be significantly improved.

Since the Ga _0.5 In _0.5 P buffer layer 12 has the same energy gap as the active layer 4, it absorbs laser light.
Therefore, in the present invention, when the energy gap of the crystal to be the buffer layer is smaller than the energy of the laser oscillation light, the thickness of the buffer layer is made extremely thin, and the buffer layer becomes the quantum well, and its equivalent energy gap is the laser oscillation. By making the energy larger than the light energy, the absorption loss of the laser light by the buffer layer can be ignored. Further, when the buffer layer is extremely thin, about 100 Å or less, even if GaP or InP that does not have lattice matching with the substrate is used for the buffer layer, the strained quantum well can be grown without deterioration of crystallinity. Moreover, for example, Ga _0.7 In having a larger energy gap than that of GaP or the active layer.
_If a crystal such as _0.3 P is used for the buffer layer, the thickness of the buffer layer can be determined without the constraint that the equivalent energy gap as a quantum well is made larger than the energy of laser oscillation light. However, if the thickness is too large, the strain will be relaxed by misfit dislocations. Therefore, in this case as well, it is desirable that the thickness of the buffer layer be about 100 Å or less.

The semiconductor laser device of this example had an oscillation wavelength at room temperature of 660 nm and a threshold current of 45 mA, and was capable of continuous oscillation up to 70 ° C. or higher.

Next, FIG. 2 shows a sectional structural view of a ridge waveguide structure semiconductor laser which is a second embodiment of the present invention. This embodiment is based on the MBE device disclosed in Japanese Patent Laid-Open No. 61-225817 and the Japanese Patent Laid-Open No. 6-225817.
It is grown by the MBE method using the method for manufacturing a semiconductor device disclosed in Japanese Patent Laid-Open No. 1-2232608. The basic structure of the MBE device is shown in FIG. Hereinafter, description will be given by using FIG. 2 and FIG. 3 together. After etching with sulfuric acid etchant, GaAs substrate 13 with a natural oxide film formed on the surface in In
Stick it on the Mo block, open the valve 51 and open the material introduction room 52
To insert. Next, after closing the valve 51 and evacuating to 10 ⁻⁷ to 10 ⁻⁸ Torr or less, the valve 53 is opened to transfer the substrate 13 to the substrate heating chamber 54 and close the valve 53. The substrate is gradually heated to 400 ° C. in the substrate heating chamber 54, and gas is discharged to about 10 ⁻¹⁰ Torr. In this way, the substrate 13 that has completed the initial gas discharge is transferred to the pretreatment chamber 55, the valve 56 is closed, and about 10 ⁻⁶ to 10 ⁻⁵ To
Gradually heat to 600 ℃ while irradiating As ₄ molecular beam of rr to obtain a clean substrate surface condition. The pretreatment chamber 55 in this embodiment is basically an MBE growth chamber capable of growing AlGaAs. Then, the n-type GaAs buffer layer 14 is continued.
After growing (layer thickness 0.5 μm) at 560 ℃, lower the substrate temperature to 400 ℃ while irradiating As ₄ molecular beam and quickly
3 is transferred to the p-type growth chamber 57. Then, close the valve 58 and gradually irradiate with P ₂ molecular beam of about 10 ⁻⁶ to 10 ⁻⁵ Torr.
After heating to 520 ° C., the growth of the n-type Ga _0.5 In _0.5 P buffer layer 15 (layer thickness 0.5 μm) is started. Then, by opening and closing the shutter, the n-type Al _0.5 In _0.5 P clad layer 16 (layer thickness 1 μm
m), undoped (Al _0.05 Ga _0.95 ) _0.5 In _0.5 P active layer 17
(Layer thickness 0.7 μm), p-type Al _0.5 In _0.5 P clad layer 18 (layer thickness 0.3 μm), p-type GaP buffer layer 19 (layer thickness 0.004 μm)
Grow MBE continuously. After the growth, the substrate temperature is lowered to 400 ° C. while irradiating the P ₂ molecular beam, and then the substrate is transferred to the pretreatment chamber 55. After irradiating As ₄ molecular beam to raise the substrate temperature gradually to 520 ° C., the growth of p-type Al _0.85 Ga _0.15 As clad layer 20 (layer thickness 0.7 μm) was started, and the substrate temperature was increased to 620 Raise to ℃. Subsequently, p-type GaAs cap layer 21 (layer thickness 0.2 μm), n-type Al _0.5 Ga _0.5 As current blocking layer 22 (layer thickness 0.7 μm), n-type GaAs contact layer 23 (layer thickness)
0.2 μm) is continuously grown. After growth, I on the back side of the substrate
n is removed by etching with HCl, and further polished to reduce the thickness of the entire wafer to about 100 μm. Next, the contact layer 23 and the current blocking layer in the portion including the oscillation stripe region
22 with sulfuric acid system over a stripe region 23 having a width of about 25 μm.
It is selectively removed by etching using an HF (hydrogen fluoride) etchant. After that, the mesa part for the oscillation stripe
Two striped trenches 25 are formed on both sides of the trench 24 by leaving the buffer layer 19 on both sides by selective etching using sulfuric acid-based and HF-based etchants. Next, a SiNx film 26 having a thickness of 0.2 μm is formed in the groove by plasma CVD, and the n-type electrode AuGe / Ni / Au layer 27 and the p-type electrode AuZn / Au layer 2 are formed.
Forming eight. In this embodiment, it is possible to oscillate with a low threshold current of 30 mA or less by mounting the growth layer side on a heat sink by the refractive index waveguide type stripe structure. Further, as in the present embodiment, the buffer layer 19 can be used as an etching stop layer for selective etching by utilizing the difference in chemical property from the cladding layer 20.

Further, FIG. 4 shows a sectional structure of a self-aligned semiconductor laser according to a third embodiment of the present invention. This embodiment is the second
It was grown using the MBE apparatus shown in FIG. As in the embodiment of FIG.
_0.5 In _0.5 P Clad layer 16 is grown. After that, undoped Ga _0.5 In _0.5 P active layer 29 (layer thickness 0.07 μ
m), p-type Al _0.5 In _0.5 P clad layer 30 (layer thickness 0.3μ
m), the p-type GaInP buffer layer 31 (layer thickness 0.004 μm) is grown, and then the growth chamber is moved to move the n-type Al _0.5 Ga _0.5 As etching control layer.
32 (layer thickness 0.01 μm), n-type GaAs current blocking layer 33 (layer thickness 0.8
Grow up to μm). Next, In on the back surface of the substrate is removed with HCl, the current blocking layer 33 is selectively etched into a stripe-shaped groove with an ammonia-based etchant, and the etching control layer 32 is selectively etched with HF to form an oscillation stripe groove. To do. Next, p-type A by LPE growth
l _0.85 Ga _0.15 As After growing the clad layer 34 (outer groove layer thickness 0.2 μm) and the p-type GaAs cap layer 35 (layer thickness 0.3 μm), reduce the thickness to about 100 μm by wafer back surface polishing,
The n-side and p-side electrodes 36 and 37 are formed. The buffer layer 31 can be used not only as the MBE method and MO-CVD method as in this embodiment, but also as a buffer layer for LPE growth.

The example of applying the embodiment of the present invention to the proton injection stripe type, the ridge waveguide type, and the self-aligned type semiconductor laser has been described above. However, the present invention is not limited to the stripe structure, and almost all others. It can be widely applied to the stripe structure. Further, the active region is not limited to a single layer of GaInP or AlGaInP, but can be widely applied to a quantum well having a multi-layer structure or a semiconductor laser having a superlattice structure.

[Effects of the Invention] As described above, in the semiconductor laser of the present invention, the second cladding layer is formed in a two-layer structure of a cladding layer made of AlGaInP or the like and a cladding layer made of AlGaAs, and a thin film is formed between the two layers. By providing the buffer layer, it is possible to improve the crystallinity of the interface between the two clad layers without considering the absorption loss of the laser light due to the provision of the buffer layer. As a result, it is possible to realize a highly reliable semiconductor laser having a low electric resistance and a low thermal resistance, which is excellent in high temperature specification.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing the structure of a proton injection stripe type semiconductor laser according to the first embodiment of the present invention. FIG. 2 is a schematic sectional view showing the structure of the ridge waveguide type semiconductor laser according to the second embodiment of the present invention. FIG. 3 is a schematic diagram showing the structure of the MBE device used for growing the semiconductor lasers of FIGS. 2 and 4. FIG. 4 is a schematic sectional view showing the structure of the self-aligned semiconductor laser according to the third embodiment of the present invention. FIG. 5 is a schematic sectional view showing the structure of a conventional proton injection stripe type semiconductor laser. FIG. 6 is a schematic sectional view showing a device of a conventional semiconductor laser which is an improved type of FIG. In the figure, 4,17,29 are active layers, and 5,18,30 are p-type AlGaInP
Cladding layer, 12, 19, 31 are buffer layers, 10, 20, 32 are p-type Al
A GaAs clad layer is shown. In each drawing, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masafumi Kondo Masafumi Kondo 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (56) References JP 62-16592 (JP, A)

Claims (1)

[Claims] 1. A semiconductor laser device in which a first clad layer, an active layer, and a second clad layer are sequentially laminated on a semiconductor substrate, wherein the second clad layer is one of AlGaInP and AlInP. A semiconductor laser device comprising a clad layer made of one side, a thin film buffer layer made of any one of GaInP, GaP, and InP, and a clad layer made of AlGaAs.