JPH06112517A - Crystal growing method - Google Patents

Abstract

PURPOSE:To provide a crystal growing method by which a crystal for avalanche photodiodes having good characteristics can be economically grown. CONSTITUTION:In a crystal growing process in which a crystal for avalanche photodiodes is grown by successively growing a buffer layer 2, light absorbing layer 3, composition-gradient layer 4, multiplying layer 5, and cap layer 6 on an InP-crystal substrate 1 by the epitaxial vapor growth method by using groups III and V organic metal compounds as gaseous starting materials, only the layer 3 is grown at >=600 deg.C, with the other layers 2, 4, 5, and 6 being grown at <=600 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a crystal for an avalanche photo diode (abbreviation APD).

[0002]

2. Description of the Related Art Crystals for APD are vapor phase growth method (CVD method)
, And has a layered structure as shown in FIG.

That is, n-type indium phosphide (InP) crystal substrate 1 formed by a pulling method or the like is n-
InP buffer layer 2, n-type indium gallium arsenide or n-InGaAs (P)
The light absorption layer 3 represented by the general formula (3), the composition gradient layer 4 whose composition changes gently, the multiplication layer 5 made of n-InP, and the cap layer 6 made of InGaAsP are sequentially formed.

Each of these semiconductor layers contains a Group III element and a V element.
Although it is composed of a compound of group V element, arsine (AsH ₃ ) or phosphine (PH
₃ ) and other hydrides were used.

Then, APD has been manufactured using this crystal. However, since these AsH ₃ and PH ₃ are extremely toxic gases, tert-butylarsine [(CH ₃ ) ₃ CAsH _{2 is used} as an alternative gas from the viewpoint of safety.
Abbreviation TBA] and tertiary butyl phosphine [(CH ₃ ) ₃
It was necessary to use a gas having a low toxicity such as CPH ₂ (abbreviation: TBP).

[0006]

When forming a compound semiconductor such as InP or InGaAs by the CVD method, a metal organic vapor phase epitaxial growth method (Metal Organic Vapor Epitaxial Growth Method) using TBA or TBP, which is less toxic, as a gas for supplying a group V element is used. Ph
ase Epitaxy (abbreviated as MOVPE method) is known and is used for forming semiconductor lasers and light emitting diodes.

Here, as a source gas of the group III element, In
Is trimethylindium [(CH ₃ ) ₃ In Abbreviation TMI
] And triethylindium [(C ₂ H ₅ ) ₃ In abbreviation TEI]
Regarding Ga, trimethylgallium [(CH ₃ ) ₃ Ga abbreviated as T
MG] and triethylgallium [(C ₂ H ₅ ) ₃ Ga abbreviation TEG] are used.

However, MOVP using TBA or TBP
Method E has not yet been used in the manufacture of APD. That is, the conventional APD crystal growth method is III
TMI and TEG are used as the source gas of the group element, and AsH ₃ and PH ₃ are used as the source gas of the group V element, and vapor phase growth has been performed while maintaining the substrate temperature at 600 ° C. or higher.

However, when the source gas of the group V element is replaced with an organic compound, there is a problem that the raw material cost increases. Further, when the substrate temperature is 600 ° C. or higher, there is a problem that a high-quality crystal cannot be formed unless the supply amount of the group V element is increased.

Therefore, MOVP using TBA or TBP
When the method E is used, it is necessary to put into practical use a crystal growth method which has good crystal quality and is economical.

[0011]

[Means for Solving the Problems] The above-mentioned problems are obtained by using a group III organometallic compound and a group V organic compound as source gases and by vapor phase growth on a buffer layer, a light absorption layer,
In the step of growing a crystal for APD by sequentially performing epitaxial growth on a compositionally graded layer, a multiplication layer, and a cap layer,
This can be solved by configuring the crystal growth method, which is characterized in that the growth of the light absorption layer is performed at a temperature of 600 ° C or higher, and the growth of each layer except the light absorption layer is performed at a temperature of 600 ° C or lower. .

[0012]

When the APD is used, as shown in FIG. 1, a buffer layer / light absorption layer / composition gradient layer / multiplication layer / cap layer are sequentially epitaxially grown on the n-InP crystal substrate to form the grown layer. A region in which the conductivity type has been changed by implanting impurities into the double layer and an electrode are formed around this region, the upper electrode is made negative, the electrode formed on the n-InP crystal substrate is made positive, and a reverse bias is applied. I am using it.

Therefore, it is necessary that the current (dark current of APD) that flows when a reverse bias is applied between the electrodes is as small as possible. This is because the growth temperature of the light absorption layer made of n-InGaAs (P) is It is known that the higher the number, the less.

That is, as the growth temperature is higher, the number of deep impurity levels is smaller, which results in a smaller dark current. Therefore, the substrate temperature is kept higher than 600 ° C., for example, 620 ° C. to perform the vapor phase growth. Then, it is possible to reduce the current value to the same level as that grown by the liquid phase growth method.

On the other hand, in the case of forming a compound semiconductor composed of a V · III group element by the CVD method, the flow rate of the gas of any element, for example, the gas of the group III element is kept constant and the vapor pressure is taken into consideration to determine the flow rate ratio. However, there is a problem that the actual flow rate ratio of group V element gas and group III element gas (hereinafter abbreviated as V / III ratio) increases as the substrate temperature rises. When the substrate temperature is kept at 620 ° C as in the conventional case. Has a problem that in order to form an n-InP forming a buffer layer or a multiplication layer, a high quality crystal cannot be produced unless the V / III ratio is 150 or more.

Therefore, according to the present invention, when the crystal for APD is grown, the substrate temperature is properly used, and when the light absorption layer made of n-InGaAs (P) is formed, the temperature is 600 ° C. or higher.
When forming an InP layer or the like, the substrate temperature is lowered to 600 ° C. or lower, which makes it possible to set the V / III ratio to 100 or lower.

[0017]

EXAMPLE An n-InP substrate having a thickness of 0.3 mm formed by the pulling method was set in a MOVPE apparatus, TMI and TEG were used as group III source gases, and TBP and TBA were used as group V source gases.
And hydrogen sulfide (H ₂ S) as an n-type dopant.

Further, hydrogen (H ₂ ) was used as the carrier gas, and the total flow rate including the raw material gas was kept at 8 liters / minute. First of all, after decompressing the inside of the equipment, TBP is 40ccm.
Evacuate while supplying H ₂ containing the
The substrate was raised to 600 ° C over 15 minutes while maintaining at 20 torr.

Next, TMI was supplied at 0.5 ccm and the V / III ratio was maintained at 80 to grow a buffer layer of n-InP. Next, raise the substrate temperature to 620 ° C and increase the V / III ratio to 20.
Then, a light absorption layer made of n-InGaAs (P) was grown.

Next, after lowering the substrate temperature to 600 ° C. and forming a composition gradient layer in which the composition gradually changes from InGaAs (P) to InP at this temperature, the V / III ratio is kept at 80 and n-InP is maintained. A double layer was formed, and then a cap layer was formed while maintaining the V / III ratio at 80 to produce an APD crystal.

The APD produced using such a crystal had a dark current as small as 10 nA, and the surface was not roughened, and the characteristics were excellent.

[0022]

According to the present invention, in MOVPE using organic group V such as TBP and TBA, crystals for APD with a small dark current can be produced with a small amount of the organic group V raw material.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the composition of a crystal for APD.

[Explanation of symbols]

 2 buffer layer 3 light absorption layer 5 multiplication layer

Claims (1)

[Claims] 1. A buffer layer, a light absorption layer, a composition gradient layer, a multiplication layer and a cap layer are formed on an InP crystal substrate by vapor phase growth using a Group III organometallic compound and a Group V organic compound as source gases. In the step of growing the crystal for avalanche photodiode by sequentially performing epitaxial growth, only the growth of the light absorption layer is performed at a temperature of 600 ℃ or more, and the growth of each layer except the light absorption layer is 600 ℃ or less. A method for growing a crystal, which is performed at the temperature of.