JP2642403B2 - Manufacturing method of semiconductor laser - Google Patents

Description

The present invention relates to a semiconductor laser using an InGaAlP-based semiconductor material, and more particularly to a method for manufacturing an internal current confinement type semiconductor laser.

(Prior art) In recent years, chemical vapor deposition (hereinafter referred to as MOCV)
In method, abbreviated as D method), the In _1-XY Ga _X Al _Y P
(0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and visible light semiconductor lasers utilizing this technology have been attracting attention.

FIG. 2 is a sectional view showing a schematic structure of an internal current confinement type semiconductor laser using an InGaAlP-based material. 11 in the figure is n-
A GaAs substrate, and an n-GaAs buffer layer
12, n-InGaAlP cladding layer 13, InGaP active layer 14, p-InGaAlP
After the clad layer 15, the p-InGaP cap layer 16 and the n-GaAs block layer (current blocking layer) 17 are sequentially grown, a stripe portion (window portion by etching) is formed on the n-GaAs block layer 17 by photolithography. It is formed. Next, the p-GaAs contact layer 18 and the p ⁺ -GaAs contact layer 19 are regrown on the cap layer 16 and the block layer 17 exposed in the stripe portion, and the electrodes 21 and 22 are formed to complete the semiconductor laser. When a current is supplied to this semiconductor laser, the current is confined only to the stripe portion, and laser oscillation occurs.

However, this type of semiconductor laser has the following problems. That is, the interface at the stripe portion between the growth layer (12,..., 17) formed by the first crystal growth and the regrown layer (18, 19) formed by the second crystal growth, that is, p-InG
At the interface between the aP cap layer 16 and the p-GaAs contact layer 18, a voltage drop occurs due to the band discontinuity between InGaP and GaAs. For this reason, the operating voltage of the semiconductor laser is increased, so that power consumption is increased and heat generation is increased.
There has been a problem that the element characteristics are deteriorated and the life is shortened.

The voltage drop due to the band discontinuity is p
This is more remarkable when the carrier concentration of the -InGaP cap layer is low, and therefore, it is conceivable to increase the carrier concentration of the p-InGaP cap layer 16. However, when zinc or the like is used as the p-type impurity, the carrier concentration of the p-InGaP cap layer exposed to the stripe portion during the second crystal growth must be sufficiently increased due to the high vapor pressure of zinc. Was difficult.

(Problems to be Solved by the Invention) As described above, conventionally, in an internal current confinement type semiconductor laser using an InGaAlP-based semiconductor material, the uppermost layer (p-InGaP) of a double hetero junction in a stripe portion for current confinement. ) And the regrown contact layer (p-GaAs), a voltage drop occurs due to band discontinuity, which has been a factor of deteriorating device characteristics.

The present invention has been made in view of the above circumstances, and an object thereof is to reduce a voltage drop due to band discontinuity at an interface between a top layer of a double heterojunction made of an InGaAlP-based semiconductor material and a regrown contact layer. It is an object of the present invention to provide a method of manufacturing a semiconductor laser capable of suppressing the problem and improving the device characteristics.

[Constitution of the Invention] (Means for Solving the Problems) The gist of the present invention is that a p-type impurity is added from the gas phase to the uppermost layer (p-InGaP cap layer) of the double heterojunction in contact with the p-GaAs contact layer. By re-diffusion, the carrier concentration of the p-InGaP cap layer and the like in the stripe portion is sufficiently increased.

That is, according to the present invention, the In _1-XY Ga _X Al _Y P (0
≦ x ≦ 1, 0 ≦ y ≦ 1) After growing the double heterojunction portion and the n-type GaAs current blocking layer sequentially, the current blocking layer is etched in a stripe shape, and then the p-type GaAs contact layer is regrown. In the method of manufacturing a laser, the growth temperature of the contact layer is set lower than the growth temperature of the double hetero junction, and the p-type impurity is introduced into the crystal growth furnace for forming the contact layer from before the start of regrowth. This is a method in which the contact layer is grown and formed after flowing to a growth temperature.

Further, in the present invention, the p-type impurity is flowed into a growth furnace together with phosphine to raise the temperature to the growth temperature of the contact layer, phosphine is switched to arsine before the start of growth of the contact layer, and metalorganic vapor phase epitaxy is performed. This is a method in which a p-type GaAs contact layer is grown and formed.

(Operation) According to the present invention, a p-type impurity is flowed into a crystal growth furnace for forming a regrowth contact layer from before crystal growth (before temperature rise), and the growth temperature of the regrowth layer is further reduced. By setting the temperature lower than the growth temperature of the double hetero junction, the carrier concentration of the uppermost layer (for example, the p-InGaP cap layer) of the double hetero junction in the stripe portion can be increased. For this reason, a voltage drop due to band discontinuity between InGaP and GaAs can be reduced, and the voltage-current characteristics of the semiconductor laser can be greatly improved, and the device characteristics can be improved. Further, by flowing phosphine (PH ₃ ) or the like together with a p-type impurity such as zinc (Zn) into a crystal growth furnace for regrowth and raising the temperature, it is possible to suppress P loss in the stripe portion and to achieve good regrowth. An interface can be obtained.

FIG. 5 shows the band structure at the hetero interface between p-GaAs and p-InGaP. The carrier concentration of p-GaAs is 5 × 10 ¹⁸ cm ⁻³ , and the carrier concentration of p-InGaP is (a) 1 × 10 ¹⁷ cm ^−3.
-3 , (b) is 2 × 10 ¹⁸ cm ⁻³ . Fig. 5 (a)
As shown in (2), when the carrier concentration of p-InGaP is low, when a current flows from p-GaAs to p-InGaP, the notch at the hetero interface is large, and this causes a hole barrier to cause a voltage drop. On the other hand, as shown in FIG. 5B, when the carrier concentration of p-InGaP is high,
Since the notch at the hetero interface becomes smaller, the voltage drop becomes smaller. In other words, it can be seen that the voltage drop at the interface between p-GaAs and p-InGaP can be suppressed by increasing the carrier concentration of p-InGaP.

Here, in the first crystal growth step, it is necessary to set a growth temperature as high as about 700 ° C. in order to obtain an InGaAlP-based double hetero junction having good morphology and good crystal quality (for example, Journal of Crystal). Growth 77 (198
6) 374-379). However, when Zn is used as a p-type impurity, the carrier pressure of p-InGaP cannot be sufficiently increased when the growth temperature is high because Zn has a high vapor pressure. Therefore, a step of setting the growth temperature when forming the p-GaAs regrowth contact layer lower than the growth temperature of the double hetero junction, flowing Zn before growth, and raising the temperature to the growth temperature of the regrown layer. As a result, p
-Zn can be diffused into InGaP to increase the carrier concentration. This is because, by setting the regrowth temperature lower than the growth temperature of the double hetero junction, the amount of Zn supply in the crystal growth furnace before the regrowth is reduced to the p-InGa of the double hetero junction.
This is because the Zn partial pressure in the crystal growth furnace becomes higher than the vapor pressure of Zn in p-InGaP, even if the amount of Zn supplied when growing P is the same. Thereafter, when the p-GaAs contact layer is regrown, the voltage drop at the regrowth interface becomes very small.

In addition, when elevating the temperature to the growth temperature of the regrown contact layer, by flowing PH ₃ together with the p-type impurity into the crystal growth furnace, it is possible to prevent evaporation of P from p-InGaP in the stripe portion. it can. Then, the PH ₃ to the growth immediately before the p-GaAs by performing regrowth is switched to A _S H _3, it is possible to form a good regrowth interface.

(Examples) Hereinafter, details of the present invention will be described with reference to the illustrated examples.

FIG. 1 is a sectional view showing a manufacturing process of a semiconductor laser according to one embodiment of the present invention. First, as shown in FIG. 1 (a), an n-GaAs buffer layer 12, an n-InGaAlP cladding layer 13 having a thickness of 1 μm, and an InGaP active layer 14 having a thickness of 0.1 μm are formed on an n-GaAs substrate 11 by MOCVD. Then, a p-InGaAlP cladding layer 15 having a thickness of 1 μm, a p-InGaP cap layer 16 having a thickness of 0.05 μm, and an n-GaAs blocking layer (current blocking layer) 17 having a thickness of 1 μm are continuously grown. The growth temperature in the first crystal growth step was set at 700 ° C. in order to obtain good crystallinity of the double hetero junction (12, 16).

Next, using photolithography technology, FIG.
As shown in the figure, a stripe-shaped groove is formed in the current block layer 17. At this time, n-GaAs is completely etched in the stripe portion, and p-InGaP is exposed on the surface.

Next, the processed substrate having the structure shown in FIG.
It is placed in a crystal growth furnace as shown in the figure, and the p-GaAs contact layer 18 and the p ⁺ -
The GaAs contact layer 19 is continuously grown. In FIG. 3, reference numeral 20 denotes the processing substrate, 31 denotes a quartz reaction tube, 32 denotes a susceptor, and 33 denotes a high-frequency heating coil.

The time of second crystal growth step, prior to growth of a regrown contact layer into the reaction tube 31 with dimethyl zinc as an impurity raw material from (heating earlier) (DMZ) keep flowing PH _3, regrown layer The temperature is raised to the growth temperature. Here, the growth temperature of the regrown layer was set to 600 ° C., which is 100 ° C. lower than the growth temperature of the double hetero junction in the first crystal growth step. The supply amount of DMZ was set to be the same as the supply amount of DMZ when p-InGaP was grown in the first crystal growth step. 60
After raising the temperature to 0 ° C., by switching the PH ₃ to A _S H _3, are sequentially grown and formed a p-GaAs contact layer 18 and the p ⁺ -GaAs contact layer 19.

At the stage after the first crystal growth, the carrier concentration of the p-InGaP cap layer 16 was 3 × 10 ¹⁷ cm ⁻³ ,
After performing the second crystal growth, p
It was confirmed that the carrier concentration of the -InGaP cap layer 16 was increased to 2 × 10 ¹⁸ cm ⁻³ . Further, by supplying PH ₃ with DMZ before regrowth started, p at the stripe portion
-Evaporation of P from InGaP was suppressed, and a good regrowth interface was obtained. Thereafter, by attaching electrodes 21 and 22 on the substrate side and the contact layer side, respectively, an internal current confinement type semiconductor laser as shown in FIG. 2 is completed.

FIG. 6 is a characteristic diagram showing the growth temperature dependence of the carrier concentration of InGaP. The horizontal axis represents the ratio between the molar flow rate of the group III raw material and the molar flow rate of DMZ, and indicates the DMZ supply rate. As the growth temperature Tg increases, the evaporation of Zn from the growth surface increases, so that the carrier concentration decreases. Increasing the growth temperature from 600 ° C. to 700 ° C. reduces the carrier concentration by a factor of about 5. n, p−G
To sufficiently suppress the voltage effect at the hetero interface of aAs / p-InGaP, the carrier concentration of p-InGaP must be at least 1 × 1
It must be at least ¹⁸ cm ^-3 . However, the first growth needs to be performed at 700 ° C. or higher in order to obtain a double heterostructure having good crystal quality, so that p-InGaP
It is difficult to make the carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more. For this reason, it is important to increase the carrier concentration of p-InGaP in the stripe portion by performing Zn diffusion during regrowth.

In the regrowth method according to the present invention, the regrowth temperature and the flow rate of the p-type impurity at the time of temperature rise are very important parameters. By diffusing Zn to the carrier concentration of 1 × 10 ¹⁸ cm ^-3 or more stripe portion during regrowth, at the growth temperature dependency of the relation between the carrier concentration of the InGaP shown in FIG, 1 × 10 ¹⁸ cm The growth temperature during re-growth and the D during temperature rise within the range of the growth temperature and the DMZ supply amount where carrier concentration of ^-3 or more can be obtained.
Experiments have shown that the MZ supply amount should be set. In other words, when the growth temperature during regrowth is set to 650 ° C, [DMZ
/ III]> 1. When Tg is 600 ° C,
A carrier concentration of 1 × 10 ¹⁸ cm ⁻³ is obtained with [DMZ / III]> 0.4. In other words, a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more can be obtained even at 650 ° C.
^{Since the} Zn supply amount range in which a carrier concentration of ¹⁸ cm ^-3 can be obtained is widened, reproducibility at the time of forming a Zn diffusion layer is improved. Conversely, if the temperature during regrowth is lower than 600 ° C, III
As a result, the decomposition efficiency of the group material decreases, and a regrown layer having good crystal quality cannot be formed.

Thus, according to the method of the present embodiment, when the p-GaAs contact layer 18 is regrown, the growth temperature is set lower than the growth temperature of the double hetero junction, and the temperature is raised in the crystal growth furnace for regrowth. By flowing DMZ before, the carrier concentration of the p-InGaP cap layer 16, which is the uppermost layer of the double hetero junction, can be sufficiently increased. Therefore, p-
Voltage drop due to band discontinuity between the InGaP cap layer 16 and the P-GaAs contact layer 18 can be suppressed, and the voltage-current characteristics of the semiconductor laser can be greatly improved to improve device characteristics. Become.

In addition, the present inventors set the growth temperature in the laser device (example device) manufactured in the above-described process and the first and second crystal growth processes to 700 ° C. before the growth of the regrown contact layer. The characteristics were compared with a laser device (conventional device) made without flowing DMZ. First, the operating voltage at 3 mW and 25 ° C. of the conventional device was 2.8 to 3.5 V, and the variation between devices and between wafers was large. On the other hand, the working voltage of the example device is about 2.3 V, which is 0.5
About 1.2V lower. In addition, variations in operating voltage between elements and wafers were small, and good reproducibility was exhibited. Furthermore, the temperature characteristics of the laser element have been greatly improved, and the life characteristics have been dramatically improved.

FIG. 4 is a sectional view showing a manufacturing process of a semiconductor laser according to another embodiment of the present invention. In this method, first the fourth
As shown in FIG. 1A, an n-InGaAlP cladding layer 42, an InGaP active layer 43, and a p-InGaAlP
First cladding layer 44, p-InGaP etch stop layer 45, p-InG
aAlP second cladding layer 46, p-InGaP cap layer 47 and p-G
a As contact layer 48 is grown and formed,
An iO ₂ film 49 is formed.

Next, as shown in FIG. 4B, the contact layer 48 and the cap layer 47 are etched using the etchant (Br ₂ + HBr + H ₂ O) using the SiO ₂ film 49 as a mask until the contact layer 48 reaches the clad layer 46. Further, selective etching with hot phosphoric acid is performed to remove the contact layer 46 by etching as shown in FIG. 4 (c).

Next, as shown in FIG.
-Regrow the GaAs block layer 51. In growing the block layer 51, trimethyl gallium and arsine were used as source gases. As a result, no GaAs was grown on the SiO ₂ film 49. Thereafter, as shown in FIG. 4E, the SiO ₂ film 49 is removed, and the contact layer 48 is further removed.

Next, as shown in FIG.
Regrow the GaAs contact layer 52; At this time, p-Ga
At the time of growing the As contact layer 52, a p-type impurity is flowed into the growth furnace before the start of the growth as in the previous embodiment, and the regrowth temperature is the growth temperature of the double hetero junction (42, to, 48). Set lower than.

In the semiconductor laser thus produced,
As in the previous embodiment, the carrier concentration of the p-InGaP cap layer 47 can be sufficiently increased, and the voltage drop caused by the band discontinuity between InGaP and GaAs can be reduced. Therefore, the same effect as in the previous embodiment can be obtained.

The present invention is not limited to the above-described embodiments. In the embodiment, Zn was used as the p-type impurity, but other than this, a group III element such as magnesium or cadmium can also be used. Further, the element structure is not limited to those shown in FIGS. 2 and 4, but can be applied to an element requiring formation of a regrown layer after forming a double hetero junction. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described in detail above, according to the present invention, when forming a regrowth contact layer, the growth temperature of the regrowth layer is set lower than the growth temperature of the double hetero junction, and By flowing a p-type impurity into the crystal growth furnace before the temperature rise, the carrier concentration in the uppermost layer of the double hetero junction can be increased, and the device characteristics of the semiconductor laser can be improved.

[Brief description of the drawings]

1 to 3 are views for explaining a method of one embodiment of the present invention. FIG. 1 is a cross-sectional view showing a manufacturing process of a semiconductor laser, and FIG. 2 is a sectional view of a semiconductor laser formed by the process. FIG. 3 is a cross-sectional view showing a schematic structure of a crystal growth furnace, FIG. 4 is a process cross-sectional view for explaining a method of another embodiment of the present invention, and FIG. FIG. 6 is a schematic diagram for explaining the operation, and FIG. 6 is a characteristic diagram showing the growth temperature dependence of the carrier concentration of InGaP. 11 n-GaAs substrate, 12 n-GaAs buffer layer, 13 n-InGaAlP cladding layer, 14 InGaP active layer, 15 InGaAlP cladding layer, 16 p-InGaP cap layer, 17 ... n-GaAs block layer, 18 ... p-GaAs contact layer, 19 ... p ⁺ -GaAs contact layer, 20 ... processed substrate, 21, 22
…… electrode, 31 …… quartz reaction tube, 32 …… susceptor, 33 ……
High frequency heating coil.

Claims (4)

(57) [Claims] [Claim 1] an In _1-XY Ga on the n-type GaAs substrate _X Al _Y P (0 ≦ x
≦ 1,0 ≦ y ≦ 1) double heterojunction and n-type G
A method of manufacturing a semiconductor laser by sequentially growing an aAs current blocking layer, etching the current blocking layer in a stripe shape, and then regrowing a p-type GaAs contact layer, wherein the growth temperature of the contact layer is set to the double hetero junction. The p-type impurity is set to be lower than the growth temperature of the portion, and a p-type impurity is flowed into the crystal growth furnace for forming the contact layer before the start of regrowth, and after the temperature is raised to the growth temperature, the contact layer is grown. Forming a semiconductor laser. Wherein an In _1-XY Ga on the n-type GaAs substrate _X Al _Y P (0 ≦ x
≦ 1, 0 ≦ y ≦ 1), a double heterojunction is grown, the double heterojunction is etched to form a mesa stripe, and then n-type GaAs is formed on the side of the mesa stripe.
A method for manufacturing a semiconductor laser by growing a current blocking layer and then regrowing a p-type GaAs contact layer, wherein the growth temperature of the contact layer is set lower than the growth temperature of the double hetero junction, and A method of manufacturing a semiconductor laser, comprising: flowing a p-type impurity into a crystal growth furnace for forming a contact layer before starting regrowth, and growing the contact layer after heating to a growth temperature. . 3. A p-type impurity is flowed together with phosphine into a crystal growth furnace to raise the temperature to the growth temperature of the contact layer, phosphine is switched to arsine immediately before the contact layer growth circuit, and metalorganic vapor phase epitaxy is performed. 3. The method according to claim 1, wherein a p-type GaAs contact layer is grown. 4. An uppermost layer of the double hetero junction is a p-type.
3. The method according to claim 1, wherein the semiconductor laser is an InGaP cap layer.