JPH0377391A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To reduce the solid-phase diffusion of impurities into an N-type InP clad layer and an InGaAsP active layer from a P-type InP substrate by arranging a P-type InGaAsP impurity diffusion preventing layer between the P-type InP substrate and a P-type InP buffer layer. CONSTITUTION:A P-type InGaAsP impurity diffusion preventing layer 1 is arranged between a P-type InP substrate 31 and an InGaAsP active layer 33. Since the diffusion length of impurities (Zn) in the InGaAsP which composes the P-type InGaAsP impurity diffusion preventing layer 1 is 1/2-1/4 of the diffusion length of impurities in InP which compose a P-type InP buffer layer 32, when a P-type InGaAsP impurity diffusion preventing layer 1 is provided between the P-type InP substrate 31 and the P-type InP buffer layer 32, it provides an effect for preventing impurity diffusion equivalent to that a P-type InP buffer layer 32 having double or three times the thickness of the P-type InGaAsP impurity diffusion preventing layer 1 is provided. Accordingly, the layer lamination can be formed more thinly compared with the case where only the P-type InP buffer layer 32 is arranged on a conventional P-type InP substrate 31.

Description

[Detailed Description of the Invention] [Summary] Regarding a semiconductor laser, I
The purpose of the present invention is to provide a semiconductor laser that can reduce solid-phase diffusion of impurities into an nGaAs p active layer and an n-type InP cladding layer and improve device characteristics. A semiconductor laser having a mesa portion in which a p-type InP buffer layer, a p-type, n-type, or non-doped active layer, and an n-type InP cladding layer are successively formed on a p-type InP substrate. A p-type 1nGaAsP impurity diffusion prevention layer is provided between the p-type InP bumper layer and the p-type InP bumper layer.

[Industrial application field]

The present invention relates to a semiconductor laser, and can be applied, for example, to a buried type semiconductor laser having a mesa portion having a non-doped InGaAsP active layer on a p-type InP substrate. The present invention relates to a semiconductor laser that can improve device characteristics by reducing solid phase diffusion of impurities from an nP substrate to an InGaAsP active layer.

I rh, Ga A SP A buried semiconductor laser equipped with a mesa portion having an active layer is used, for example, in long wavelength band optical communications, and as optical communication systems progress and become popular, the range of usage environments is changing. Especially since 70
It is desired to improve the properties at high temperatures of about ~80°C. Conventionally, this semiconductor laser has generally used an n-type InP5 plate with few defects (relatively good characteristics), but when an n-type InP substrate is used, an n-type X n, a P substrate is used. It is possible to obtain a larger gain (compared to A buried semiconductor laser including a mesa portion having a GaAsP active layer is attracting attention.

[Conventional technology]

FIG. 3 is a cross-sectional view showing the structure of a conventional semiconductor laser.
This is a case where the present invention is applied to a buried semiconductor laser having a mesa portion having an nGaAsP active layer.

In this figure, 31 is a p-type 1n, P substrate, 32 is a p-type InP bathoqua layer, 33 is a p-type or n-type, or non-doped 1nGaAsP active layer, and 34 is an n-type 1r
The hP first cladding layer 35 is a mesa portion that becomes an active region, and includes a p-type InP buffer layer 32 and an InGaAsP active layer 3.
3 and an n-type InP first cladding N34. 36 is a p-type InP first buried layer, 37 is an n-type InP second buried layer, 38 is a p-type InP third buried layer, 39 is an n-type InP second ground layer, and 40 is an n-type InP buried layer.
Type 1nGaAsP: 2 contact layers, 41 is p electrode, 42
is an n-electrode.

Next, the manufacturing method will be explained.

First, p-type! p-type InP buffer layer 3 on nP substrate 31
2. After sequentially shaping the InGaAsP active layer 33 and the n-type InP first cladding layer 34 and forming a Sun film over the entire surface of the n-type InP first cladding layer 34, a mask for mesa etching is formed. Next, this SiO□ film is patterned.Then, the remaining Si serves as a mask for mesa etching.

Mesa etching is performed using the film as a mask, and the n-type InP first craft layer 34, the InGaAsP active layer 33, and the p-
After etching unnecessary portions of the InP buffer layer 32 to form a mesa portion 35, a first p-type InP buried layer 36 and a second n-type InP layer 36 are formed so as to bury the sides of the mesa portion 35.
buried layer 37, and p-type Inp third buried layer 3
Form 8 in sequence. Next, after removing the Sin film used as the mesa part/notching mask, the n-type InP first film was removed.
cladding N34 and p-type InP third buried layer 3
n-type InP second cladding layer 39 and n-type 1
The n Q a A 3 P contact layer 40 is formed one after another. Then, p-type InP substrate 31 and n-type 1nGaAs
P: p so as to make contact with the r7 tact layer 40, respectively.
After forming the electrode 41 and the n-electrode 42, they are separated at the cavity length to complete a semiconductor laser having the structure shown in FIG. 3.

The semiconductor laser using the p-type InP substrate 31 shown in FIG. This has the advantage that it is possible to improve the characteristics at lower temperatures.

[Problem to be solved by the invention]

However, in the semiconductor laser shown in FIG. 3 using the n-type InP substrate 31, in order to make it easier to make ohmic contact, as in the case of the p-type contact layer constituting the semiconductor laser using the n-type InP substrate, a certain amount of concentration is required. Although it is desirable to use a p-type InP substrate 31 with a high
The nP substrate 31 is subjected to high-temperature heat treatment (60
Since the substrate is exposed to high-temperature heat treatment for a long time (around 0°C), the solid phase diffusion of p-type impurities from the p-type IrnP substrate 31 progresses, and the InGaAsP active Jii 33 and the n-type InP first and second cladding layers 34 There was a problem that p-type impurities invaded into the .39 layer, resulting in deterioration of device characteristics such as a decrease in luminous efficiency. N-type InP first and second cladding layers 3
If a p-type impurity invades 4.39 and inverts it to p-type, laser operation will no longer be possible.

As a means to solve the above problem, InGaAsP active layer A
The concentration of the p-type InP buffer layer 32 at the bottom of
P type with a long distance to 33! Semiconductor lasers are known that reduce the influence of solid phase diffusion from the nP substrate 31 to some extent, but in general, when the concentration is low, the resistivity increases, and when stacked thickly, the series resistance of the element increases, making it difficult to operate the laser. However, it has the disadvantage that its characteristics at high temperatures actually worsen due to heat generation.

Note that the above problem does not occur in a semiconductor laser using an n-type InP substrate. Specifically, Z n of the p electrode
/Au, etc. (to make it easy to make open contact with
A P contact layer is formed, but since this is the final layer of crystal growth, the time spent at high temperature after crystal growth is
It is much shorter than a semiconductor laser using a P substrate, and solid-phase diffusion of impurities from the contact layer hardly affects other semiconductor crystals.

Therefore, the present invention aims at p-type I by high-temperature heat treatment during the growth process.
It is possible to reduce solid phase diffusion of impurities from the nP substrate to the InGaAsP active layer and the n-type InP craft layer,
An object of the present invention is to provide a semiconductor laser that can improve device characteristics.

[Means to solve the problem]

In order to achieve the above object, the semiconductor laser according to the present invention includes a p-type InP substrate and the p-type! p-type rnP buffer layer on nP substrate, p-type or n-type, or undoped 1nGa
In a semiconductor laser having a mesa portion in which an AsP active layer and an n-type InP craft layer are sequentially formed, the p
p-type 1nG between the p-type InP substrate and the p-type InP buffer layer
An aAsP impurity diffusion prevention layer is provided.

[Effect]

In the present invention, as shown in FIG. 1, an n-type 1 n, GaA
It is configured to provide an sP impurity diffusion prevention layer t.

Therefore, n-type InP due to high temperature heat treatment during the growth process
From the substrate 31 to the InGaAsP active layer 33 and the n-type! n
Solid-phase diffusion of impurities into the P first and second cladding layers 34 and 39 can be reduced, and device characteristics can be improved. Details will be explained in Examples.

〔Example〕

1 and 2 are diagrams for explaining one embodiment of the semiconductor laser according to the present invention, FIG. 1 is a sectional view showing the structure of one embodiment, and FIGS. 2(a) to 2(d) are It is a figure explaining the manufacturing method of one Example.

In these figures, the same reference numerals as in FIG. 3 indicate the same or corresponding parts, and 1 indicates p-type In, Ga As P
Impurity diffusion prevention layer, 2 is a mesa part, n-type 1 nGaAs
P impurity diffusion impurity diffusion prevention type 11P buffer N32,
It is composed of an InGaAsP active layer 33 and an n-type InP first ground layer 34. 3 is Sin.

It is a membrane.

Next, the manufacturing method will be explained.

First, as shown in FIG. 2(a), an n-type InP group vi,3 with a surface index of (100) was grown by liquid phase epitaxial growth.
P type on top of 1! nGaAs P impurity diffusion prevention layer 1
(Zn doped, carrier concentration IXIO”7., thickness 0
．． 2 μrn, band gap energy 1.24 eV)
, p-type 1 n P buffer layer 32 (Cd doped, carrier concentration 1xlQ"/cj, thickness 0.5μrrh),
InGaAsP active layer 33 (thickness 0.15 μm, band gap energy 0.95 eV) and n-type InP craft layer 34 (Sn doped, carrier concentration lXl0”/c
d, thickness 0.4 μm) are sequentially grown.

In this way, p type! P type between nP substrate 31 and n type 1rhP buffer N32! By providing the nGaAs P impurity diffusion prevention layer 31, the p-type! nP substrate 31 and InGaA
Even if the distance between the sP active layers 33 is the same, 1nGaAsP
Since the solid phase diffusion length of impurities in the n-type InP substrate 31 is smaller than that in InP, the effect of preventing solid phase diffusion of impurities from the n-type InP substrate 31 can be increased.

Next, as shown in FIG. 2(b), the entire surface of the n-type InP first cladding layer 34 is coated with Sin,
A film 3 is formed and this film 3 is patterned using a conventional photolithography technique to form a mask for mesa etching. At this time, a Sin film 3 having a width of 3 μm and functioning as a mask for mesa etching is formed in the <011> direction. Next, using the Sjow film 3 that functions as a mesa etching mask as a mask, n-type inP is etched by wet etching using a bromine-based etching solution.
First cladding layer 34, InGaAsP active layer 33, p
The mesa portion 2 is formed by selectively etching the InP type buffer layer 32 and the p-type InGaAsP inert diffusion stop layer l.

Next, as shown in FIG. 2(C), p-type InP is first buried Ii! by liquid phase epitaxial growth again. 13
6 (cd doped, carrier concentration 2XIO"/-1 thickness 0.2urn), n-type InP second implant 7137
(Te-doped, Ki + 'J 71 degrees I XIO'/cf
fl, thickness 0.3 μm) and p-type InP third buried layer 38 (Cd-doped, carrier concentration 2 XIO”/c
d, thickness 0.2 μm) are sequentially grown.

Next, as shown in FIG. 2(d), after removing the Sin film 3 used as a mesa etching mask with a hydrofluoric acid solution, p-type 1, n
G a A s P impurity diffusion prevention layer 1 and p-type 1
An n-type InP second cladding 1139 (Te doped, carrier concentration 1xlQ") is formed on the n, P third buried layer 38.
/i, thickness 0.5 μm) and n-type InGaAsP contact layer 40 (Te doped, carrier concentration 2xIQ''/d
, thickness 0.25. crm) are grown sequentially.

Then, p-type InP substrate 31 and n-type 1 nGaAsP
After forming a p-electrode 41 and an n-electrode 42 so as to make contact with the contact layer 40, they are separated at the cavity length, thereby completing a semiconductor laser having the structure shown in FIG.

That is, in the above embodiment, as shown in FIG. 1, a p-type!
An nGaAsP impurity diffusion prevention N1 is provided. The diffusion length of the impurity (Zn) in InGaAsP constituting the p-type 1nGaAsP impurity diffusion prevention layer 1 provided here is p-type!
1/2 of that in InP constituting the nP buffer layer 32
~1/4, therefore, by providing a p-type 1nGaAsP inert diffusion prevention layer l between the p-type InP substrate 31 and the p-type InP buffer layer 32, the p-type X n, Ga
The impurity diffusion prevention effect is equivalent to that of adding a p-type In, P buffing layer 32 two to three times as thick as the AsP impurity diffusion prevention layer 1. For this reason, the conventional p-type I
Compared to the case where only the p-type InP buffer layer 32 is provided on the nP substrate 31, by providing the p-type InGaAs P impurity diffusion prevention layer 1, it is possible to form a thinner layer. InGa from the InP substrate 31
The solid-phase diffusion of impurities into the AsP active layer 33 and the n-type InP first and second cladding layers 34 and 39 is performed using the conventional p-type 1
rxP buffer Jl! 32, which improves the device characteristics.

I can do that. In addition, p-type InP substrate 31 and r nGaA
Since the distance between the sP active N33 can be reduced, there is no fear that the series resistance will increase and heat will be generated.

Moreover, the case of only the conventional p-type InP buffer layer 32 and the case of the p-type InP buffer layer 32 are
Comparing the threshold current in the case of this example in which the InGaAsP type impurity diffusion prevention layer 1 was provided, the threshold current was 25rnA in the conventional case at 28°C.
In this example, the threshold value was lowered to 11 mA, and it was confirmed that the device characteristics were improved. In addition, conventionally, both of this example and p-type! nP substrate 31 and InGa
The distance between the AsP active layers 33 is the same distance of 0.7 μm,
Further, the carrier concentration in each layer was made the same.

In the present invention, a preferable type B for preventing light emission of the p-type 1nGaAsP inert diffusion prevention layer l due to carrier leakage from the InGaAsP active layer 33 is p-type InP.
The thickness of the buffer layer 32 may be about 0.5 μm.

Furthermore, in the present invention, the InGaAsP active layer 33
A preferable embodiment for preventing light emitted from the P-type 1n, GaAsP impurity diffusion prevention layer from being absorbed by the p-type InGaAsP impurity diffusion prevention layer, which has a larger band gap than the InGaAsP active layer 33, is layer 1
It can be configured using

〔Effect of the invention〕

According to the present invention, p-type I
It is possible to reduce solid phase diffusion of impurities from the nP substrate to the InGaAsP active layer and the n-type KnP cladding layer,
This has the effect of improving device characteristics.

l...p-type 1nGaAsP impurity diffusion prevention layer,
2...Mesa part, 31...P2 type InP substrate, 32...P type 1nP buffer layer, 33-
---1 n Ga As P active layer, 34...
...n-type InP first cladding layer, 39...
n-type InP second cladding layer.

[Brief explanation of drawings]

1 and 2 are diagrams for explaining one embodiment of a semiconductor laser according to the present invention. FIG. 1 is a cross-sectional view showing the structure of one embodiment, and FIG. The explanatory diagram, FIG. 3, is a sectional view showing the structure of a conventional example. A cross-sectional view showing the structure of one embodiment.

Claims (1)

[Claims] A p-type InP substrate, a p-type InP buffer layer, a p-type or n-type, or a non-doped InP substrate on the p-type InP substrate.
In a semiconductor laser having a mesa portion in which a GaAsP active layer and an n-type InP cladding layer are sequentially formed, a p-type I layer is formed between the p-type InP substrate and the p-type InP buffer layer.
A semiconductor laser characterized by being provided with an nGaAsP impurity diffusion prevention layer.