JP2728672B2 - Semiconductor laser device, double hetero wafer, and method of manufacturing the same - Google Patents

Description

The present invention relates to a visible light semiconductor laser having a current confinement effect and an optical waveguide effect, and in particular, to a chemical vapor deposition method using an organic metal ( The present invention relates to a semiconductor laser device, a double hetero wafer, and a method for manufacturing the same, which are suitable for manufacturing by the MOCVD method.

(Prior Art) Single crystal InGaAlP is an important material for obtaining a short wavelength semiconductor laser among III-V compound semiconductors. In recent years, room temperature operation of a semiconductor laser using a double hetero wafer grown by a molecular beam epitaxy (MBE) method or an MOCVD method has been reported, and in particular, a device lifetime exceeding 1,000 hours has been reported in the MOCVD method.

Conventionally, in the MOCVD method, Se has been used as an n-type dopant, and hydrogen selenide (H ₂ Se) has been used as a raw material thereof. However, almost no investigation has been made on the controllability when the InGaAlP material is doped with Se. In FIG. 3, H ₂ Se was used as a doping material for Se, and GaAs was used.
The doping efficiency when s, In _1-xy Ga _x Al _y P is grown on a GaAs substrate by MOCVD is shown. FIGS. 4 and 5 show the growth temperature dependence of the doping efficiency of InGaP and InAlP.

From FIG. 3, FIG. 4 and FIG.
When AlP is grown by MOCVD, the following three problems are found.

(I) The doping efficiency varies greatly depending on the composition, making uniform doping difficult, and is particularly noticeable at the boundaries between layers having different compositions.

(Ii) Since InGaAlP has a doping efficiency about one order of magnitude higher than that of GaAs, when InGaAlP is grown on the GaAs layer, the memory effect, diffusion, etc., when the Se concentration in GaAs is set to about 1 × 10 ¹⁸ cm ^−3. In the InGaAlP material close to the GaAs layer,
The e concentration becomes a very large value close to 1 × 10 ¹⁹ cm ⁻³ , which is a major cause of shortening the life.

(Iii) Further, since the doping efficiency changes depending on the substrate temperature, and particularly in the case of InAlP, the carrier concentration largely changes due to a minute change in the substrate temperature, so that stable doping is difficult.

(Problems to be Solved by the Invention) As described above, when an n-type InGaAlP / GaAs heterojunction, which is indispensable for application, is grown by MOCVD using H ₂ Se as a doping material, controllability, quality, etc. are important. Problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a double hetero wafer having a high quality InGaAlP / GaAs hetero junction and a method for manufacturing the same.

[Configuration of the invention]

(Means for Solving the Problems) The present invention uses Si as a dopant for the n-type cladding layer when crystal growing a laser wafer by MOCVD, thereby reducing the difficulty of controlling the carrier concentration of the n-type cladding layer. Resolve. That is, the invention according to the semiconductor laser device includes a first conductivity type clad layer formed on a GaAs substrate,
An active layer, a second conductivity type cladding layer, and the GaAs
In _x Ga _1-xy Al _y P (1 ≦ y
≦ 1), the first conductive type clad layer or the second
The conductive cladding layer is characterized by being doped with Si.

In the above, the carrier concentration of the first conductivity type clad layer or the second conductivity type clad layer doped with Si is less than 5 × 10 ¹⁷ cm ⁻³ .

Next, the invention relating to the double hetero wafer is applied on a GaAs substrate.
In a double hetero wafer including a double hetero junction structure portion composed of In _x Ga _1-xy Al _y P (0 ≦ y ≦ 1), the first conductive type clad layer or the second conductive type clad layer of the conducting portion is
It is characterized by being doped with Si.

In the above, the carrier concentration of the first conductivity type clad layer or the second conductivity type clad layer doped with Si is less than 5 × 10 ¹⁷ cm ⁻³ .

Next, the invention according to the method for manufacturing a semiconductor laser device, a GaAs substrate is placed in a reaction furnace used for crystal growth, and a group III and V group source gas is introduced into the reaction furnace and the substrate is heated. In on the substrate by metalorganic chemical vapor deposition
_1-xy Ga _x Al _y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1)
In the step of forming the conductive type clad layer, the active layer, and the second conductive type clad layer, silane gas is used for doping the first conductive type clad layer.

Next, in the method for manufacturing a double hetero wafer, a GaAs substrate is placed in a reaction furnace used for crystal growth, group III and V group source gases are introduced into the reaction furnace, and the substrate is heated.
In _1-xy Ga _x Al _y P on the substrate by metal organic chemical vapor deposition
Using silane gas for doping the first conductivity type cladding layer during the step of forming the first conductivity type cladding layer, the active layer, and the second conductivity type cladding layer composed of (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) It is characterized by.

In the above description, silane is used as a doping material by MOCVD for doping GaAs and In _1-xy Ga _x Al _y P. The use of this silicon as a dopant was achieved by recognizing that the doping efficiency of silicon can be obtained almost constant as shown in FIG. 2 and that the substrate temperature dependency was extremely low.

(Function) The present invention can set the carrier concentration of each layer of the semiconductor laser element uniformly and with good reproducibility,
In addition, a semiconductor laser having a long life can be manufactured.

(Embodiment) An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a schematic sectional view showing the configuration of a semiconductor laser device according to one embodiment of the present invention. As shown in FIG.
On a -GaAs substrate 11, a Si-doped n-GaAs buffer layer 12 and a Si-doped n-InGaP buffer layer 13 are formed. On this n-InGaP buffer layer 13, a Si-doped n-I
A double heterojunction structure comprising an nAlP cladding layer 14, an In _0.5 Ga _0.5 P active layer 15, and Mg-doped p-InAlP cladding layers 16, 17, 18 is formed. Here, the p-InGaAl
The P cladding layer 17 has a low Al composition and acts as an etching stop layer described later. Further, a p-InGaAlP contact layer 19, a p-GaAs layer 20, and a Se-doped n-GaAlAs current blocking layer 21 surrounding the p-InGaAlP contact layer 19 and the p-GaAs layer 20 formed on the confined portion on the p-InGaAlP cladding layer 18 are provided. A p-GaAs contact layer 22 is formed. Further, the p-GaAs
The contact layer 22 and the n-GaAs substrate 11 are provided with electrodes 23 and 24, respectively, as metal layers.

The feature of this structure is that Si is used as a dopant for the n-type cladding layer of the double hetero junction. At the double hetero junction, the carrier concentration profile of the cladding layer and the active layer is narrow, so precise control of the carrier concentration profile is necessary. However, when Si is used as a dopant, (i)
Composition dependence of doping efficiency (especially GaAs buffer and InGa
(Ii) the memory effect is small, (iii) the carrier concentration change due to the growth temperature is small, and the controllability of the carrier concentration profile is higher than that of the conventional Se. Is good. On the other hand, when the current blocking layer is formed on the mesa-processed cladding layer 18 by regrowth using the MOCVD method, the introduction of defects at the regrowth interface and the growth surface approach the (111) plane, so that the Si Is used as a dopant (although the difference in the segregation coefficient between GaAs and InGaAlP is small, so diffusion is small and controllability of the formation region is good). As a result, there is a case where the current blocking layer becomes P-type and does not function sufficiently. Therefore, in this embodiment,
Se without such a phenomenon is used as a dopant for the current blocking layer. Se has a large segregation coefficient difference between GaAs and InGaAlP and a large diffusion, but the carrier concentration of the current blocking layer is required to be 3 × 10 ^-8 cm ^-3 or more for high output.
In addition, it is adopted to always be n-type.

The contact layer (intermediate contact layer) 19 is for the purpose of reducing the electric resistance between the cladding layer 18 and the contact layer 20, and has a larger band gap than the contact layer 20, Any crystal having a smaller band gap or a superlattice having an equivalent band gap may be used.

Further, the band gap of the intermediate contact layer 19 may be gradually changed from the clad layer 18 to the contact layer 20 in the same manner as the portion in contact with the clad layer 18 and the contact layer 20.

Here, FIG. 6 shows a relationship between an energizing time and an operating current in an energizing test at 40 ° C. and 3 mW when the carrier concentration of the n-cladding layer is changed in the semiconductor laser according to the present embodiment.
The carrier concentration of the p-cladding layer was 2 × 10 ¹⁷ cm ⁻³ , the carrier concentration of the active layer was 1 × 10 ¹⁶ or less, the stripe width of the laser was 7 μm, and the resonator length was 300 μm. As a result, when the carrier concentration of the n-cladding layer exceeded 5 × 10 ¹⁷ cm ⁻³ , the operating current rapidly increased due to the initial energization, and stable continuous oscillation became impossible. However, when the carrier concentration of the n-cladding layer was less than 5 × 10 ¹⁷ cm ⁻³ , the operating current was stable at about 70 mA, and these semiconductor lasers operated stably for 1000 hours or more. Therefore, n
If Si is used as the impurity on the cladding layer side and the carrier concentration is less than 5 × 10 ¹⁷ cm ⁻³ , a highly reliable semiconductor laser with a low threshold value can be obtained.

Next, a method of manufacturing the semiconductor laser device having the above configuration will be described.

The growth method is trimethylindium (TMIn), trimethylgallium (TMGa)
An MOCVD (metal organic chemical vapor deposition) method is used under reduced pressure by selecting and using each of trimethylaluminum (TMAl), group V hydride arsine (AsH ₃ ), and phosphine (PH ₃ ). Then, the pressure is 15-35 Torr, the GaAs substrate temperature
The growth was performed at 745 to 755 ° C. at a growth rate of 2 μm / h or more. Also,
Monosilane (SiH ₄ ), hydrogen selenide (H ₂ Se), dimethyl zinc (DMZn), and cyclopentagenenyl magnesium (Cp ₂ Mg) were used as doping raw materials.

As the silane gas, monosilane, disilane, trisilane, or an organic silane or a halogenated silane in which these hydrogens are substituted with an alkyl group or a halogen element, specifically, monochlorosilane, dichlorosilane, trichlorosilane, tetrachlorosilane, Monomethylsilane, dimethylsilane, trimethylsilane and the like can be used without particular limitation.

First, a (100) n-GaAs substrate 11 (Si-doped, 3 × 10 ¹⁸ c
m ⁻³ ) 0.5 μm thick n-GaAs first buffer layer 12
(Si-doped, 5 × 10 ¹⁷ cm ⁻³ ), 0.5 μm thick, n-InGaP
Second buffer layer 13 (Si-doped, 5 × 10 ¹⁷ cm ⁻³ ), thickness 1.
0 μm n-In _0.5 Al _0.5 P first cladding layer 14 (Si-doped,
5 × 10 ¹⁷ cm ^-3 ) 0.06 μm thick In _0.5 Al _0.5 P active layer 1
5, a 0.2 μm thick p-InAlP second cladding layer 16 (Mg doped, 1 × 10 ¹⁸ cm ⁻³ ), a 0.01 μm thick p-InGaP third cladding layer 17 (Mg doped, 17 μm thick) acting as an etching stop layer 1 × 10 ¹⁸ cm ⁻³ ), 1 μm thick p-In _0.5 Al _0.5 P fourth cladding layer 18 (Mg doped, 1 × 10 ¹⁸ cm ⁻³ ), 0.01 μm thick p as an intermediate contact layer -In _0.5 Al _0.5 P 1st
A contact layer 19 and a 0.5 μm-thick p-GaAs second contact layer 20 (Mg doped, 1 × 10 ¹⁸ cm ⁻³ ) were sequentially grown to form a double hetero wafer.

Subsequently, the second contact layer 20 is removed by etching and selective growth using SiO ₂ as a mask (not shown).
Se-doped GaAs current blocking layer 21 (Se-doped, 5 × 10 ¹⁸ cm ⁻³ )
Was grown to a thickness of 0.5 μm. Then, except for the mask, p-GaAs
After the third contact layer 22 (Zn-doped, 1 × 10 ¹⁸ cm ⁻³ ) is grown and formed, a laser element having a cavity length of 250 μm and a stripe width of 5 μm is formed by a usual process to form a threshold current.
A low threshold of 40 mA was obtained. The light output increased linearly up to 30mW or more according to the drive current, and showed good current-light output characteristics without kink. Further, the distribution of the threshold current within the wafer and between the wafers was within ± 10%, and it was confirmed that extremely good reproducibility was achieved.

〔The invention's effect〕

According to the present invention, a high-quality double hetero-wafer for a visible light semiconductor laser can be grown and formed with good reproducibility, and there is a remarkable advantage that element characteristics can be improved, and reliability and reproducibility can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to one embodiment of the present invention, FIG. 2 is a diagram showing the doping efficiency of silicon according to the present invention, and FIG. 3 is a diagram showing the doping efficiency of MOCVD by H ₂ Se. , FIG. 4 and FIG. 5 are all InGaP and InA.
FIG. 6 is a diagram showing the growth temperature dependency in the doping of lP, and FIG. 6 is a diagram showing the energization time when the carrier concentration of the n-cladding layer is changed. 11 n-GaAs substrate 12 n-GaAs buffer layer 13 n-InGaP buffer layer 14 n-InAlP cladding layer (first conductivity type cladding layer) 15 InGaP active layer 16, 18 p-InAlP cladding layer (second conductivity type cladding layer) 17 p-InGaP etching stop layer 19 p-InGaP contact layer 20, 22 p-GaAs contact layer 21 n-GaAs current blocking layer 23 , 24 …… electrode

Claims (4)

(57) [Claims] The method according to claim 1 first conductivity type G _a As of the first and second conductivity type on a substrate _{In x Ga y All- xy P (} 0 ≦ x ≦ 1,0 ≦ y ≦ 1) active layer in the cladding layer In a semiconductor laser device having a double hetero junction structure sandwiched between the first conductivity type cladding layer and the first conductivity type cladding layer.
Si is doped, this has been doped Si to G _a As layer formed between the first conductivity type cladding layer and the substrate, further, a first conductivity type cladding layer wherein Si is doped or The carrier concentration of the second conductivity type cladding layer is 5
A semiconductor laser device characterized by being less than × 10 ₁₇ cm ₋₃ . 2. A method active layer in the first conductivity type G _a As of the first and second conductivity type on a substrate _{In x Ga y All- xy P (} 0 ≦ x ≦ 1,0 ≦ y ≦ 1) cladding layer in a double hetero wafer for a double hetero junction structure formed by interposing the Si is doped to the first conductivity type cladding layer, G _a as layer also Si is formed between the first conductivity type cladding layer and the substrate Wherein the carrier concentration of the first conductivity type cladding layer or the second conductivity type cladding layer doped with Si is less than 5 × 10 ₁₇ cm _-3. . 3. A Ga As substrate is placed in _a reaction furnace used for crystal growth, group III and V source gases are introduced into the reaction furnace, and the substrate is heated. Buffer layer In _1-xy Ga _x Al _y P made of G _a As by vapor phase epitaxy
In the step of forming a first conductivity type clad layer, an active layer, and a second conductivity type clad layer (0 ≦ x ≦ 1, 0 ≦ y ≦ 1), doping of the buffer layer and the first conductivity type clad layer is performed. A method of manufacturing a semiconductor laser device, wherein a silane gas is used for the method. 4. A Ga As substrate is placed in _a reactor used for crystal growth, group III and V source gases are introduced into the reactor, and the substrate is heated. Buffer layer In composed of G _a As by metal organic chemical vapor deposition
_1-xy Ga _x Al _y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1)
A method for manufacturing a double hetero wafer, wherein a silane gas is used for doping the buffer layer and the first conductivity type cladding layer in the step of forming the conductivity type cladding layer, the active layer, and the second conductivity type cladding layer.