JP3205589B2 - Semiconductor thin film growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a growth method in which a semiconductor thin film is subjected to etching and other processing, and then a semiconductor thin film is regrown thereon.

[0002]

2. Description of the Related Art Systems using optical components used for optical disks, compact disks, and the like require a semiconductor laser that oscillates in a single longitudinal mode. In order to obtain a single longitudinal mode oscillation with a semiconductor laser, a distributed feedback type using a diffraction grating (Distributed Feedback:
DFB) laser or distributed reflection type (Distrib)
utd Bragg Reflector (DBR)
There is a laser and development is underway. In order to realize a semiconductor laser having a single longitudinal mode oscillation structure and a transverse mode control structure, it is necessary to form a diffraction grating and a current confinement structure in the laser structure. Is repeatedly performed.

For example, in a method of manufacturing a DFB semiconductor laser, a step of imprinting a diffraction grating on a p-Al ₀ .25 Ga _{0 .75} As guide layer and then regrowing an n-GaAs current block layer and a current path N-GaAs
After the current block layer was partially removed by etching to form a stripe, the p-Al ₀ .7 Ga ₀ .3 As clad layer,
There is a step of regrowing the GaAs contact layer. In the case of this regrowth step, the regrowth temperature is 750 ° C. or higher. However, if the regrowth is performed at such a high temperature, the p-type dopant (Zn) is re-evaporated from the p-type guide layer 15 in the stripe, The carrier concentration decreases to about 2 × 10 ¹⁷ cm ⁻³ . As a result of the decrease in carrier concentration, the barrier height against electrons in the p-type layer decreases, and when the semiconductor laser device operates at a high temperature, 10 out of the carriers injected into the active layer.
Since about% overflows into the p-type layer, there is a problem that the threshold current sharply increases.

[0004]

It is known that the doping efficiency of an AlGaAs film grown using Zn as a p-type dopant decreases as the growth temperature increases, but the present inventor actually used the reduced pressure MOCVD method. When the doping efficiency of the AlGaAs film grown using Zn as a p-type dopant was determined, the result of FIG. 10 was obtained. As can be seen from FIG. 10, the doping efficiency sharply decreases on the high temperature side because Zn re-evaporation becomes more severe as the temperature becomes higher. Next, FIG. 11 shows the carrier concentration measured after annealing an AlGaAs film doped with Zn at 1 × 10 ¹⁸ cm ⁻³ at 600 ° C. to 800 ° C.
As shown in FIG. 11, when the temperature of the Zn-doped film is raised again, Zn is re-evaporated vigorously as described above.
There is a problem that the carrier concentration is significantly reduced.

In the conventional manufacturing method, when growing a p-type layer, 1
Although a carrier concentration of × 10 ¹⁸ cm ^-3 can be ensured, the p-type dopant (Zn) is re-evaporated from the p-type guide layer in the stripe because regrowth is performed at 750 ° C. or higher after the etching step. , Carrier concentration is 2 × 10 ¹⁷ cm ^-3
To a degree. For this reason, the barrier height for electrons in the p-type layer decreases, and at the time of high-temperature operation, about 10% of the carriers injected into the active layer overflow into the p-type layer, so that the threshold current rapidly increases. there were.

[0006] In a device manufacturing process in which the etching process and the semiconductor thin film regrowth process are required to be repeated on the Zn-doped p-type layer, the dopant of the underlying p-layer is evaporated by heat during the regrowth. However, the carrier concentration decreased, and it was difficult to accurately control the value as designed. A similar problem occurs with a p-type dopant such as Mg.

The present invention has been made in consideration of the above problems, and has as its object to perform processing such as etching on a p-type layer semiconductor thin film doped with a p-type dopant such as Zn or Mg, and It is an object of the present invention to regrow a semiconductor thin film while controlling a change in carrier concentration of a semiconductor thin film of a p-layer serving as a base in a step of regrowing a semiconductor thin film thereon.

[0008]

According to the present invention, there is provided a process for performing a process such as etching on a p-type semiconductor thin film doped with a p-type dopant such as Zn or Mg, and then re-growing the semiconductor thin film thereon. When the substrate temperature is raised to the regrowth starting temperature, the gas of the organometallic compound of the dopant metal is supplied onto the substrate to suppress evaporation of the dopant in the underlying p-type layer, and to carry the carrier of the underlying semiconductor thin film layer. An object of the present invention is to provide a method for regrowing a semiconductor thin film while suppressing a change in concentration and controlling a carrier concentration to a value close to a designed value.

[0009]

According to the present invention, in a step of performing processing such as etching on a p-type semiconductor thin film doped with a p-type dopant such as Zn or Mg and then re-growing the semiconductor thin film thereon, the substrate temperature is reset. When raising the temperature to the growth start temperature, by flowing the gas of the organometallic compound of the dopant metal over the substrate, the change in the carrier concentration of the underlying semiconductor thin film is controlled, and while controlling the carrier concentration to a value close to the design, The semiconductor thin film can be regrown. For this reason, it becomes possible to control the carrier concentration to a value close to the design in a device manufacturing process that requires repetition of the etching process and the semiconductor thin film regrowth process.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. (Embodiment 1) FIG. 1 shows a DF according to a first embodiment of the present invention.
It is sectional drawing which shows the schematic structure of a B-type semiconductor laser. In the figure, 10 is an n-GaAs substrate, 11 is an n-GaAs buffer layer, 12 is an n-Al ₀ .5 Ga ₀ .5 As clad layer,
13 non-doped _{Al 0 · 13 Ga 0 · 87} As active layer, 14 _{p-Al 0 · 5 Ga 0} · 5 As carrier charge-barrier layer, 15 p
_{-Al 0 · 25 Ga 0 · 75} As guide layer, 16 p-Al _{0 · 6}
Ga _{0 ·} 4 As etch stop layer, 17 n-Ga
As current blocking layer 18 is _{p-Al 0 · 7 Ga 0} · 3 As cladding layer, 19 denotes the p-GaAs contact layer 20 is a diffraction grating, 21 is a p-side electrode, 22 is an n-side electrode, respectively.

In this semiconductor laser, n
Since the -GaAs current blocking layer 17 is located close to the active layer 13 and the n-GaAs layer 17 functions as a light absorbing layer, a difference in the complex refractive index occurs between the inside of the stripe and the outside of the stripe. Horizontal light confinement is achieved.

Next, the effect of the built-in diffraction grating will be described. That is, light in only the resonator direction is amplified by the diffraction grating, and laser oscillation occurs when the light reaches a certain threshold. The oscillation wavelength λ at that time is expressed by the following equation.

Λ = 2 · n _eff · Λ / m (m = 1, 2, 3,.
...) Where n _eff is the equivalent refractive index and Λ is the period of the diffraction grating. Therefore, the oscillation wavelength λ can be changed by changing the period Λ of the diffraction grating.

Next, a method of manufacturing a semiconductor laser having the above-described structure according to the present invention will be described. 2 to 7 are views showing a manufacturing process of the semiconductor laser shown in FIG.

First, a group III organic metal (trimethylgallium / trimethylaluminum) and a group V hydride (arsine) are used as raw materials, hydrogen selenide is used as an n-type dopant material, and diethyl zinc is used as a p-type dopant material. As shown in FIG. 2, an n-GaAs buffer layer 11 having a thickness of 0.5 μm and an n-Al ₀ layer having a thickness of 0.8 μm are formed on a GaAs substrate 10 having a plane orientation (100) by a reduced pressure (100 torr) MOCVD method. _{· 5} Ga _{0 · 5} As cladding layer 12, a thickness of 0.08μm undoped Al _{0 · 13} Ga
_{0 · 87} As active layer 13, p-Al _{0 · 5} having a thickness of 0.05μm
Ga _{0 ·} 5 As Kiyarya-barrier layer 14, a thickness of 0.15μ
The _{p-Al 0 · 25 Ga 0} · 75 As guide layer 15 of m is continuously growing. The growth so far is performed at a growth temperature of 750 ° C.

Subsequently, as shown in FIG.
Then, a third-order diffraction grating 25 having a period of 3468 ° is formed on the photoresist using a two-beam interference exposure apparatus. Then, as shown in FIG. 4, a thickness of 0.15μm by chemical etching _{p-Al 0 · 25 Ga 0} · 75
The diffraction grating 20 having a depth of 0.1 μm is transferred to the As guide layer 15.

[0017] Next, as shown in FIG. 5, by the MOCVD _{method, p-Al 0 · 6 Ga} 0 · 4 As etch stop layer 16 having a thickness of 0.02 [mu] m, a thickness of 0.5 [mu] m n-GaA
The s current block layer 17 is continuously grown. The second growth is performed at a growth temperature of 750 ° C., and at this time, the substrate temperature is increased to 750 ° C. while diethyl zinc flows on the substrate. This serves as a base p-Al _{0 · 25} Ga
A decrease in Kiyarya concentration of _{0 · 75} As guide layer 15 can be suppressed. Subsequently, as shown in FIG.
Current mask layer 17 by chemical etching using an ammonia-based etchant with
Is etched until the p-AlGaAs etching stop layer 16 is exposed. Further subsequently, until _{p-Al 0 · 25 Ga 0} · 75 As guide layer 15 is exposed by HF, the p-AlGaAs etch Sutotsupu layer 16 is removed by etching, the width of the bottom to form a stripe-shaped groove.

Next, a 2 μm-thick p
_{-Al 0 · 7 Ga 0 · 3} As cladding layer 18, a thickness of 1 [mu] m p
-The GaAs contact layer 19 is continuously grown. The third growth is also performed at 750 ° C., but the substrate temperature is increased to 750 ° C. while flowing diethyl zinc on the substrate, as in the second regrowth. As a result, a decrease in the carrier concentration of the p-Al ₀ .25 Ga ₀ .75 As guide layer 15 in the stripe can be suppressed. Thereafter, the p-type electrode 21 is formed on the p-GaAs contact layer 21 by a normal electrode forming process.
The semiconductor laser wafer having the structure shown in FIG. 1 was fabricated by applying an n-type electrode 22 to the lower surface of an n-GaAs substrate.

When the wafer thus obtained was cleaved to produce a DFB laser having a cavity length of 250 μm, the regrowth temperature on the p-type layer was lowered. Despite repeating the regrowth step, the decrease in the carrier concentration of the p-type layer can be suppressed, and the carrier that overflows from the active layer to the p-layer during high-temperature operation is reduced. No increase in threshold current was observed, and a semiconductor laser having excellent high-temperature operation characteristics was obtained.

In this embodiment, the regrowth is performed by the MOCVD method. However, the present invention can be applied to the case where the regrowth is performed by any growth method using an organometallic compound.
Further, in this embodiment, Zn is used as the p-type dopant, but the present invention can be applied to the case where another dopant is used.

(Embodiment 2) Next, a case where the present invention is applied to a semiconductor laser using an InGaAlP-based material will be described. In FIG. 8A, 31 is a Si-doped GaAs substrate, 32 is a Se-doped InGaAlP cladding layer, 33 is
Is a GaInP active layer, 34 is a Zn-doped InGaAlP
It is a cladding layer. These three layers are continuously grown in the first growth. Next, as shown in FIG. 8B, after forming the SiO ₂ mask 35, a ridge is formed by etching. At this time, the Zn-doped InGaAlP cladding layer 34 slightly remains in portions other than the ridge portion. Next, at the time of raising the substrate temperature to form the current block layer 36 by the second regrowth, diethyl zinc (DEZ) or dimethyl zinc (DMZ) is changed to PH ₃ until the substrate temperature reaches the growth temperature. Pour at the same time. Next, Si
The O ₂ mask 35 is removed, and the Zn-doped GaAs contact layer 37 is grown by the third regrowth as shown in FIG.

In the above manufacturing steps, by supplying a source of Zn to the substrate surface at the time of the second temperature rise of the growth, re-evaporation of Zn from the p-InGaAlP cladding layer 34 is suppressed, and the Zn carrier concentration is increased. The leakage current flowing to portions other than the ridge portion can be reduced without lowering, and a semiconductor laser having good characteristics can be obtained.

(Embodiment 3) Next, an embodiment of a semiconductor laser manufactured by an MOCVD growth method using an InP-based material will be described.

First, as shown in FIG. 9A, a Zn-doped InP substrate 41 is formed on a Zn-doped InP substrate 41 in the first growth.
A P cladding layer 42, an InGaAsP active layer 43, and a Se-doped InP cladding layer 44 are grown. Next, FIG.
As shown in (b), the substrate 41 is etched in a mesa shape using the SiO ₂ mask 45. Next, as shown in FIG. 9C, a Se-doped InP current blocking layer 46 and a Zn-doped InP current blocking layer 47 are grown in the second growth. Next, after removing the SiO ₂ mask 45, FIG.
As shown in (d), the Se-doped In
A P cladding layer 48 and a Se-doped InGaAsP contact layer 49 are grown.

In the above manufacturing process, when the substrate temperature is raised at the time of the _third regrowth, until the substrate temperature reaches the growth temperature, diethyl zinc (DEZ) or dimethyl zinc is simultaneously formed on the substrate surface with PH _3. (DMZ). By this DEZ or DMZ flow, FIG.
It is possible to prevent Zn from re-evaporating from the surface of the current block layer 47 during the temperature rise and to prevent the carrier concentration from decreasing and the function of the current block from deteriorating.

[0026]

As described above in detail, according to the present invention, a p-type semiconductor thin film doped with a dopant such as Zn or Mg is processed by etching or the like, and then an organometallic compound is applied thereon. When the substrate temperature is raised to the regrowth starting temperature in the step of regrowing the semiconductor thin film by the conventional growth method, the carrier concentration of the underlying semiconductor thin film changes by flowing the organometallic compound of the dopant metal onto the substrate. , And the semiconductor thin film can be regrown while controlling the carrier concentration to a value close to the designed value. By applying this method to the above-described method for manufacturing a semiconductor laser, a decrease in the carrier concentration of the p-type layer can be suppressed, and the number of carriers that overflow from the active layer to the p-type layer during high-temperature operation is reduced. DFB laser with excellent yield can be obtained with good yield, and a low-cost transverse mode control laser that oscillates in a single longitudinal mode can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a manufacturing process diagram of the semiconductor laser device shown in FIG. 1;

FIG. 3 is a manufacturing process diagram of the semiconductor laser device shown in FIG. 1;

FIG. 4 is a manufacturing process diagram of the semiconductor laser device shown in FIG. 1;

FIG. 5 is a manufacturing process diagram of the semiconductor laser device shown in FIG. 1;

FIG. 6 is a manufacturing process diagram of the semiconductor laser device shown in FIG. 1;

FIG. 7 is a manufacturing process diagram of the semiconductor laser device shown in FIG. 1;

FIG. 8 is a manufacturing process diagram of a semiconductor laser device according to a second embodiment of the present invention.

FIG. 9 is a manufacturing process diagram of a semiconductor laser device according to a third embodiment of the present invention.

FIG. 10 is a diagram showing the doping efficiency of an AlGaAs film grown using Zn as a dopant by a reduced pressure MOCVD method.

FIG. 11 is a diagram showing a change in carrier concentration with respect to an annealing temperature.

[Explanation of symbols]

Reference Signs List 10 n-GaAs substrate 11 n-GaAs buffer layer 12 n-Al ₀ .5 Ga ₀ .5 As cladding layer 13 non-doped Al ₀ .13 Ga _{0 .87} As active layer 14 p-Al ₀ .5 Ga ₀ .5 As carrier charge-barrier layer _{15 p-Al 0 · 25 Ga} 0 · 75 As guide layer _{16 p-Al 0 · 6 Ga} 0 · 4 As etch stop layer 17 n-GaAs current blocking layer _{18 p-Al 0 · 7 Ga} 0 _{・ 3} As 19 p-GaAs contact layer 20 diffraction grating

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-166285 (JP, A) JP-A-1-286486 (JP, A) JP-A-2-22879 (JP, A) JP-A-2- 206191 (JP, A) JP-A-60-66484 (JP, A) JP-A-62-176183 (JP, A) JP-A-1-222433 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 21/205 H01L 33/00

Claims (4)

(57) [Claims] 1. A semiconductor thin film including a layer doped with a p-type dopant is formed on a substrate, and after exposing at least a part of the layer doped with the p-type dopant, the semiconductor thin film is re-applied thereon. In the method for growing a semiconductor thin film, at least during the step of raising the temperature of the substrate to a temperature at which regrowth is started, the gas of the organometallic compound of the p-type dopant metal in the exposed layer is removed by the method described above. While being supplied on the substrate, the semiconductor thin film doped with the p-type dopant,
Al composition containing at least Al and its group III element
A method for growing a semiconductor thin film, wherein the ratio is 0.25 or less . 2. The method according to claim 1, wherein said p-type dopant is doped.
Ridge shape by exposing at least part of the layer
Is formed, and SiO2 is formed on the upper surface of the ridge shape.
Wherein the process is guided to a regrowth step.
2. The method for growing a semiconductor thin film according to item 1 . 3. The semiconductor thin film to be regrown is an n-type semiconductor film.
3. The method according to claim 1, further comprising a conductor layer.
A method for growing a semiconductor thin film as described above . 4. The p-type dopant is Zn or Mg.
The method for growing a semiconductor thin film according to any one of claims 1 to 3, wherein: