JPH07211982A - Semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To provide a highly reliable semiconductor light emitting device which can be manufactured at a high yield by forming an ohmic contact between a P-type InGaAsP layer and non-alloy type metallic electrode without performing any impurity diffusing process. CONSTITUTION:After forming an Si3N4 film 34 on the surface of a P-type InGaAsP contact layer 33 having a band-gap wavelength of 1.5-1.55mum and containing impurities at a concentration of 4X1018 to 6X10cm<-3>, a contact window 35 is formed by partially etching the film 34. Then an ohmic contact is formed as a non-alloy type metallic electrode by successively vapor-depositing a Ti layer 36, Pt layer 37, and Au layer 38 and performing heat treatment in a hydrogen atmosphere. Therefore, the reliability and manufacturing yield of a semiconductor light emitting device are improved, because the introduction of a lattice defect to the contact layer 33 caused by the diffusion of Zn which is a P-type impurity and the positional change of a P-N junction caused by the movement of Zn in a double hetero layer 32 including an active layer can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device such as a long wavelength band semiconductor laser mainly used for optical fiber communication.

[0002]

2. Description of the Related Art With the spread of optical fiber communication in recent years,
There is a demand for long-term reliability of the devices that make up the system. An InGaAsP / InP based semiconductor laser used as a light source is one of the key devices constituting the system. One of the causes of impairing the long-term reliability of this semiconductor laser is the diffusion of Au from the electrodes.
As the P-side electrode, an Au / Zn electrode has been widely used because an ohmic contact can be easily obtained, but since it is an alloy type electrode, Au diffuses into the crystal. Therefore, recently, a method using a non-alloy type electrode such as Ti / Pt / Au is becoming mainstream. In the alloy type electrode, Au easily diffuses into the crystal and long-term reliability cannot be obtained, whereas in the non-alloy type electrode, Au and the crystal do not come into contact with each other.
However, it does not diffuse and is excellent in terms of long-term reliability.

Hereinafter, as a conventional semiconductor light emitting device,
InGaAsP / InP based semiconductor laser using a Roy type electrode
User will be described as an example. FIG. 3 shows a first conventional example.
FIG. 3 is a sectional view of an InGaAsP / InP semiconductor laser of FIG.
1, 1 is an N-type InP substrate, 2 is a double-layer structure including an active layer
B layer, 3 is a P-type I having a band gap wavelength of 1.3 μm
nGaAsP contact layer, 4 is Si₃N _Four Membrane, 5 is S
i₃ N_Four The film formed by selectively removing the film 4
Contact window, 6 of the P-type InGaAsP contact layer 3
The impurity concentration selectively formed on the surface is 1 × 10¹⁹cm
^-3Zn diffusion region, 7 is a Ti layer, 8 is a Pt layer, and 9 is Au.
It is a layer.

The manufacturing method is as follows:
Includes an active layer by liquid phase epitaxial growth (LPE)
Double hetero layer 2 and P-type InGaAsP contact layer
3 are sequentially formed, and then a P-type InGaAsP contact layer is formed.
On the surface of No. 3 by CVD method₃ N_Four Deposit the membrane 4 and
By the usual photolithography process and etching process
Si₃ N_Four The contact window 5 is formed by selectively removing the film 4.
To achieve. Zn from the contact window 5 as a P-type impurity
Diffused into the P-type InGaAsP contact layer 3
1 × 10¹⁹cm^-3Zn diffusion region 6 of is selectively formed
To do. The reason for forming the Zn diffusion region 6 will be described later.
However, the contact layer 3 of this composition raises the surface by diffusion.
If the concentration is not increased, ohmic co-
This is because the contact cannot be formed. Then steam
H as pre-treatment₂ SO_Four : H₂ O ₂ : H₂ O = 1:
Surface treatment with 1: 5 mixed solution and electron beam evaporation method
Thus, the Ti layer 7, the Pt layer 8 and the Au layer 9 are sequentially deposited.
After vapor deposition, heat treatment is performed in a hydrogen atmosphere to form a P-side electrode.
ing. In this structure, P-type InGaAsP contact layer
A Ti layer 7 which is a non-alloy type electrode is formed on the surface of 3,
The structure is such that the Au layer 9 does not contact the semiconductor layer.

However, in the first conventional example, Au is used.
Although it is possible to prevent the diffusion of Al into the crystal, many lattice defects are introduced into the Zn diffusion region 6 by the Zn diffusion process, which causes a problem of deterioration of characteristics. Also, 500
Since diffusion is performed at a high temperature of ℃, Zn which is a P-type impurity in the crystal moves, the PN junction position changes, the device characteristics (eg, threshold current) become unstable, and the yield decreases. There was a flaw. Further, a method of increasing the Zn doping amount of the P-type InGaAsP contact layer 3 without performing Zn diffusion so that the surface Zn concentration is 1 × 10 ¹⁹ cm ⁻³ has been considered, but the doping amount is 6 × 10 ¹⁸ cm 3. ^-3
The above high concentration causes a new problem that the crystallinity deteriorates.

Therefore, a second conventional example was considered as a method for obtaining ohmic contact without increasing the impurity concentration.
FIG. 4 shows InGaAsP / InP as a second conventional example.
2 is a cross-sectional view of a semiconductor laser, 11 is an N-type InP substrate, 12 is a double hetero layer including an active layer, 13 is a P-type InGaAs contact layer having a Zn concentration of 5 × 10 ¹⁸ cm ⁻³ , and 14 is Si ₃ N ₄ films, 15 are contact windows formed by selectively removing the Si ₃ N ₄ film 14, 16
Is a Ti layer, 17 is a Pt layer, and 18 is an Au layer. The difference from the first conventional example is that the contact layer is made of InGaAs. Since InGaAs has a smaller bandgap than InGaAsP, ohmic contact can be obtained even at a relatively low concentration. In this example, P-type InGa
Although the Zn concentration of the As contact layer 13 was 5 × 10 ¹⁸ cm ⁻³ , sufficient ohmic property was obtained and the crystallinity was also good.

However, the surface of the InGaAs layer is easily oxidized, and sufficient contact cannot be obtained unless the deposition pretreatment before electrode formation is surely performed. Therefore, as a general method, the surface is thinly etched to remove the oxide layer. However, H ₂ SO used as an etchant
_With a mixed solution of ₄ : H ₂ O ₂ : H ₂ O = 1: 1: 20, it is difficult to etch the surface thinly (about 0.1 μm) because the etching rate is very large, about 5.0 μm / min. Is. Further, if the mixing ratio of hydrogen peroxide (H ₂ O ₂ ) is decreased to lower the etching rate, there is a problem that the etching rate becomes unstable due to the decomposability of hydrogen peroxide (H ₂ O ₂ ).

[0008]

In the first conventional example, A
Although it is possible to prevent the diffusion of u into the crystal, Zn must be diffused to increase the surface concentration, which causes the deterioration of the characteristics and the yield reduction. Further, in the second conventional example, since the etching rate of the P-type InGaAs contact layer 13 is very large, the pretreatment for vapor deposition is difficult, which causes a decrease in manufacturing yield.

The present invention solves the above-mentioned problems.
An object of the present invention is to provide a semiconductor light emitting device having high reliability and high yield by forming an ohmic contact between a P-type InGaAsP layer and a non-alloy type metal electrode without performing an impurity diffusion step.

[0010]

In order to achieve this object, a semiconductor light emitting device of the present invention is a P-type InGaAsP.
A non-alloy type metal electrode is provided on the surface of the layer, and P type InGaA
Band gap wavelength of sP layer is 1.5 μm to 1.55
The composition is characterized in that it has a composition of μm and the impurity concentration of the P-type InGaAsP layer is set from 4 × 10 ¹⁸ cm ⁻³ to 6 × 10 ¹⁸ cm ⁻³ .

[0011]

According to this structure, since the band gap wavelength of the P-type InGaAsP layer is 1.5 to 1.55 μm, by setting the impurity concentration to 4 × 10 ¹⁸ cm ⁻³ or more, the non-alloy type electrode can be obtained. And ohmic contact can be formed. Further, by setting the impurity concentration of the P-type InGaAsP layer to 6 × 10 ¹⁸ cm ⁻³ or less, the crystallinity is good and the surface morphology is not deteriorated even if impurities are doped into the crystal.

The bandgap wavelength is 1.5-1.
H ₂ SO ₄ : H of P-type InGaAsP layer of 55 μm composition
_The etching rate for a mixed solution of ₂ O ₂ : H ₂ O = 1: 1: 20 is as small as about 0.2 μm / min, and the pretreatment for electrode deposition can be stably performed. Therefore, it is not necessary to diffuse the P-type impurity to the surface of the P-type InGaAsP layer by the diffusion process, it is possible to prevent the introduction of lattice defects and the movement of the impurity in the active region, and improve the reliability and yield of the device. You can

[0013]

EXAMPLES First, the inventors of the present invention have used P-type InGaAs.
The relationship between the Zn concentration of the P contact layer and the heat treatment temperature after the Ti / Pt / Au electrode, which is a non-alloy type metal electrode, is
The compositions having band gap wavelengths of 1.3 μm and 1.5 μm were examined. The result is shown in FIG. In FIG. 2, the Zn concentration in the P-type InGaAsP contact layer is plotted on the vertical axis and Ti is plotted on the vertical axis.
FIG. 7 is a diagram showing a region where ohmic contact is obtained, with the horizontal axis representing the heat treatment temperature after forming the / Pt / Au electrode.
Reference numeral 21 is a boundary line indicating a region having a bandgap wavelength of 1.3 μm and 22 is an ohmic contact region having a bandgap wavelength of 1.5 μm. It is shown that the regions having a higher Zn concentration than the boundary lines 21 and 22 have ohmic contacts, and the regions having a lower Zn concentration than the boundary lines 21 and 22 have Schottky contacts.

From FIG. 2, the band gap wavelength is 1.3 μm.
In the P-type InGaAsP contact layer having the composition, the boundary line 2
As shown by 1, the ohmic contact cannot be obtained unless the Zn concentration is 1 × 10 ¹⁹ cm ⁻³ or more. In this case, the Zn concentration is 6 × 1 as described in the conventional example.
At a high concentration of 0 ¹⁸ cm ^-3 or more, the crystallinity deteriorates, so that ohmic contact could not be obtained while maintaining the stability of characteristics and high yield.

On the other hand, the bandgap wavelength is 1.5 μm.
In the P-type InGaAsP contact layer of m composition, the boundary line 22 has a Zn concentration near 4 × 10 ¹⁸ cm ⁻³ . As a result, good crystallinity can be maintained and good ohmic contact can be obtained. Zn concentration is 4 ×.
The range is from 10 ¹⁸ cm ⁻³ to 6 × 10 ¹⁸ cm ⁻³ . As a result, it was found that ohmic contact can be formed with the Ti / Pt / Au electrode which is a non-alloy type metal electrode.

An embodiment of the present invention utilizing this fact will be described with reference to the drawings by taking an InGaAsP / InP semiconductor laser as an example. FIG. 1 is a sectional view of an InGaAsP / InP-based semiconductor laser as an example. 31 is an N-type InP substrate, 32 is a double hetero layer including an active layer, 33 is a band gap wavelength of 1.5 μm
P-type InGaAs with a Zn concentration of 5 × 10 ¹⁸ cm ^{-3 in} composition
P contact layer, 34 is Si ₃ N ₄ film, and 35 is Si ₃ N
₄ A contact window formed by selectively removing the film 34, 36 is a Ti layer, 37 is a Pt layer, 38 is an Au layer,
39: Au / Ge / Ni layer, 40: Ti layer, 41: Au
It is a layer. The manufacturing process will be described below.

A double hetero layer 32 including an active layer and a P-type InGaAsP contact layer 33 are sequentially formed on the N-type InP substrate 31 by ordinary liquid phase epitaxial growth. The P-type InGaAsP contact layer 33 has a thickness of 0.4.
Zn as a P-type impurity with a concentration of 5 × 10 ¹⁸ cm ⁻³ . Next, a Si ₃ N ₄ film 34 having a film thickness of 3000 Å is formed on the surface of the P-type InGaAsP contact layer 33 by the plasma CVD method. Then, a part of the Si ₃ N ₄ film 34 is selectively removed by a normal photolithography process and an etching process to form a contact window 35 to expose a part of the surface of the P-type InGaAsP contact layer 33.

Next, as a pretreatment for vapor deposition, H ₂ SO ₄ : H ₂ O is used.
_The surface of the P-type InGaAsP contact layer 33 is treated with a mixed solution of ₂ : H ₂ O = 1: 1: 20 for 30 seconds to form about 0.1.
μm etching. Thus, since the P-type InGaAsP contact layer 33 has a bandgap wavelength of 1.5 μm, the etching rate is about 0.2 μm / min and InG.
It is smaller than aAs and the etching amount can be controlled sufficiently.

Next, a Ti layer 36, a Pt layer 37 and an Au layer 38 are formed as a non-alloy type metal electrode by an electron beam evaporation method.
Are sequentially deposited. The thickness of each layer is 500 Å for the Ti layer 36, 1000 Å for the Pt layer 37, and 2 μm for the Au layer 38. Next, this is heat-treated at 400 ° C. in a hydrogen atmosphere to form an ohmic contact. The contact resistance at this time is 3 × 10 ^-4 Ω
The value was cm ² , which was a sufficiently small value that was comparable to that of an Au-based alloy type electrode. Finally, the substrate 31 is made to have a thickness of 120 μm by a normal polishing process, and the N-side electrode A
The u / Ge / Ni layer 39, the Ti layer 40, and the Au layer 41 are sequentially formed and alloyed at 340 ° C. in a hydrogen atmosphere.

The wafer thus formed was cleaved to form a resonator and at the same time formed into a chip, which was then bonded on a silicon submount with Au / Sn solder and mounted on a package. After measuring the initial characteristics of this device, a reliability test was conducted at 70 ° C. and a constant optical output of 5 mW. As a result of estimating the life of this element from the deterioration rate after 5000 hours, it was about 500,000 hours, which was about 5 times as long as that of the element using the conventional Au-based alloy type electrode. Also, the manufacturing yield is a laser oscillation threshold of 15 mA.
Below, about 80 under the condition that the external differential efficiency is 0.30 W / A or more.
%Met. This is about 30% compared to the case of the first conventional example
Is an improvement.

As described above, according to this embodiment, the P type I
The band gap wavelength of the nGaAsP contact layer 33 is set to 1.5 μm and the Zn concentration is set to 5 × 10 ¹⁸ cm ⁻³ , so that the crystallinity is not deteriorated and the impurity diffusion step is not performed. Since an ohmic contact can be formed with the electrode, a semiconductor light emitting device having extremely high reliability and high yield can be realized.

Further, the band gap wavelength is 1.5 μm
The InGaAsP produced by this method has a higher etching rate than InGaAs.
It is small enough and easy to control. This allows surface treatment
It can be performed stably and the manufacturing yield is significantly improved.
You can In this example, P-type InGa
The Zn concentration of the AsP contact layer 33 is set to 5 × 10.¹⁸cm^-3
However, as can be seen from Fig. 2, the heat treatment temperature was set to a slightly high value.
4x10 by combing¹⁸cm^-3But it is possible. Well
Also, the crystallinity does not deteriorate 6 × 10 ¹⁸cm^-3Heat treatment
Ohmic contact by lowering the processing temperature to about 340 ° C
Obtainable. That is, P-type InGaAsP converter
The Zn concentration of the tact layer 33 is 4 × 10.¹⁸cm^-3From 6x
10¹⁸cm^-3By adjusting the heat treatment temperature in the range of
The non-alloy type electrode and the alloy without deteriorating the crystallinity.
It is possible to form a dynamic contact. In addition, P-type InGa
Doping to form AsP contact layer 33
As an impurity, instead of Zn, Cd (cadmium
P) type impurities such as
The concentration is the same as that of Zn.

Further, in this embodiment, P-type InGaAs is used.
Band gap wavelength of 1.5 μ as the P contact layer 33
Although the InGaAsP layer of m composition was used, if the bandgap wavelength is 1.5 μm to 1.55 μm, the etching rate of the pretreatment for vapor deposition is as small as about 0.2 μm / min and it can be used because it hardly changes.

[0024]

According to the present invention, the P-type InGaAsP layer has a bandgap wavelength of 1.5 to 1.55 μm and an impurity concentration of 4 × 10 ¹⁸ cm ⁻³ to 6 × 10 ¹⁸ cm ^−3. It is possible to form a ohmic contact with a non-alloy type electrode without deteriorating the crystallinity and without performing an impurity diffusion step, thereby realizing a semiconductor light emitting device having extremely high reliability and high yield. You can

The bandgap wavelength is 1.5-1.
InGaAsP having a composition of 55 μm has a sufficiently smaller etching rate than InGaAs and is easy to control. For this reason,
The surface treatment can be performed stably, and the manufacturing yield can be significantly improved.

[Brief description of drawings]

FIG. 1 shows InGaAsP / in one embodiment of the present invention.
It is a sectional view of an InP-based semiconductor laser.

FIG. 2 is a P-type InGaAs according to an embodiment of the present invention.
It is a figure showing the relation between Zn concentration of a P contact layer and heat treatment temperature.

FIG. 3 shows InGaAsP / InP in the first conventional example.
FIG. 3 is a cross-sectional view of a system semiconductor laser.

FIG. 4 InGaAsP / InP in the second conventional example
FIG. 3 is a cross-sectional view of a system semiconductor laser.

[Explanation of symbols]

 31 N-type InP substrate 32 Double heterolayer including active layer 33 P-type InGaAsP contact layer 36 Ti layer (non-alloy type metal electrode) 37 Pt layer (non-alloy type metal electrode) 38 Au layer (non-alloy type metal electrode)

Claims (1)

[Claims] 1. A semiconductor light emitting device comprising a non-alloy type metal electrode on the surface of a P-type InGaAsP layer, wherein the band gap wavelength of the P-type InGaAsP layer is 1.
In addition to the composition of 5 μm to 1.55 μm,
A semiconductor light emitting device, wherein the impurity concentration of the InGaAsP layer is 4 × 10 ¹⁸ cm ⁻³ to 6 × 10 ¹⁸ cm ⁻³ .