JPH0582454A - Manufacture of semiconductor epitaxial layer - Google Patents

Abstract

PURPOSE:To decrease the trap concentration of an impurity level, by growing an InxGa1-xAsyP1-y layer on an InP substrate by an organic metal vapor epitaxial growth method, while the InP substrate temperature is kept higher than or equal to a specified value. CONSTITUTION:By using an MOVPE method and keeping the temperature of a substrate at 610 deg.C, the following are epitaxially grown in order on an n<+>InP substrate 1; a buffer layer 2 composed of n<+>InP, an N-type In0.84Ga0.16 As0.36P0.64 layer 3, and an N-type InP layer 4. The thickness of the N-type In0.84Ga0.16As0.36P0.64 layer 3 and that of the N-type InP layer 4 are 2mum. A p<+>n junction diode is formed by diffusing Zn in the N-type InP layer 4, and the trap concentration of the impurity level Et2 in the N-type In0.84Ga0.16As0.36 P0.64 layer 3 is measured by an ICTS method. Said trap concentration is lower than or equal to 2X10<11>cm<-3> which is the detection limit of an ICTS equipment. That is, the trap concentration can be decreased.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a method for manufacturing an In _x Ga _1-x As _y P _1-y layer which constitutes a semiconductor laser used for optical communication in the 1 μm band and is formed by epitaxial growth on an InP substrate. Regarding

[0002]

2. Description of the Related Art Semiconductor lasers use various compound semiconductors depending on the oscillation wavelength. In the case of an oscillation wavelength of 1 μm band, InP is used as a substrate and an In _x Ga _1-x As _y P _1-y layer is used. Is epitaxially grown, and a laser is constituted by using this layer as an oscillation source. That is, as shown in FIG. 2 n ⁺
On the InP substrate 1, a n ⁺ -InP buffer layer 2, an In _x Ga _1-x As _y P _1-y layer 3, and an n-InP layer 4 are sequentially formed on the InP substrate 1 by metal organic vapor phase epitaxy (MOVPE). Then, zinc (Zn) is diffused into the n-InP layer 4 to form p.
^{The +} layer 5 is formed so that a p ⁺ n junction diode is formed.

In _x Ga epitaxially grown here
The properties of the _1-x As _y P _1-y semiconductor layer are uniquely determined by the composition ratio of As forming the layer, and the energy diagram of this compound semiconductor can be expressed as shown in FIG. That is, when the composition of As is represented by y, when the value of y is 0, the energy gap of the forbidden band 10 between the filling band 8 and the conduction band 9 is large at about 1.3 eV, but the value of y increases. The energy gap gradually decreases to less than 1.0 eV. Further, impurity levels represented by E _t1 and E _t2 in the figure exist in the forbidden band.

Here, the emission wavelength of the InP laser uses a wavelength band of 1.3 μm or 1.55 μm because it is necessary to reduce the transmission loss of the optical fiber that propagates this laser beam. In order to oscillate, those having a composition in which the y value is in the region of 0.03 to 0.36 and the region of 0.66 to 0.98 in the energy diagram of FIG. 3 are used.

However, In _x Ga _1-x As _y P having this composition
_{In the 1-y} semiconductor layer, _{one of the} impurity levels represented by E _t1 and E _t2 is a mid-gap represented by 1/2 E _g in the figure.
There is a problem that it is crossing or approaching. Here, the impurity level existing in the vicinity of the midgap acts as a recombination center between the electron in the conductor 9 and the hole in the filling band 8 in the oscillation operation of the laser beam, and lowers the light emission efficiency. In order to increase the leakage current, it is necessary to reduce the trap concentration of the impurity level.

However, the relationship between the trap concentration of the impurity level near the midgap and the growth condition of the In _x Ga _1-x As _y P _{1- y} layer has not been sufficiently studied so far.

[0007]

It is known that the impurity level existing in the vicinity of the midgap acts as a recombination center to reduce the light emission efficiency and increase the leakage current. Therefore, it is necessary to reduce the trap concentration of this impurity level, and it is a challenge to realize this.

[0008]

[Means for Solving the Problems] The above-mentioned problems are caused by In _x Ga _{1- x} on the InP substrate by metalorganic vapor phase epitaxial growth.
When growing the As _y P _1-y layer, the InP substrate temperature was set to 610 ° C.
This can be solved by configuring the method for manufacturing a semiconductor epitaxial layer, which is characterized by holding the above.

[0009]

In the In _x Ga _1-x As _y P _1-y layer grown by the MOVPE method as shown in FIG. 3, the impurity levels of E _t1 and E _t2 are present. produces an oscillation wavelength of μm
In the area of the composition of As is 0.03 to 0.36 impurity level E _t2 near the y = 0.1 is cross to the mid-gap. Further, in the region where the composition of As is 0.66 to 0.98, the impurity level E _t1 crosses the midgap near y = 0.7.

Here, of course, in the In _x Ga _1-x As _y P _1-y layer having a composition in which the value of y is around 0.1 and around 0.7,
Impurity levels E _t2 and E _t1 act as recombination centers, but are slightly deviated from 0.03 to 0.36 and 0.66 to 0.98.
It seems that it also acts as a recombination center in the region of.

That is, regarding the former, the value of y is
As it becomes less than 0.1, the trapped amount of electrons in the conduction band increases and the trapped amount of holes in the filling band decreases. Further, as the value of y becomes larger than 0.1, the trapped amount of electrons in the conduction band decreases and the trapped amount of holes in the filling band increases, but the impurity level E _t2 is reset within the range of 0.03 to 0.36. It works as a bond center. Therefore, in order to increase the luminous efficiency, it is necessary to reduce the trap concentration of E _{t2 which} acts as a recrystallization center.

As a method of reducing the trap concentration of the impurity level existing in the In _x Ga _1-x As _y P _1-y semiconductor, the inventor can supplement the lack of the group 5 element constituting this compound semiconductor. I thought it was necessary. That is, the boiling points of the elements constituting this quaternary compound are about 2000 ° C. for In and 2403 for Ga.
℃, As sublimate at 613 ℃ (28 atm), P is 280.5 ℃,
The group 5 elements As and P are much lower than the group 3 elements In and Ga.

Therefore, the inventor has constructed a compound semiconductor.
It was considered that supplementation of the lack of As and P would reduce the trap concentration. That is, In _x Ga _1-x As _y by the MOVPE method
In the growth process of the P _1-y layer, it was considered that As and P components were evaporated from the growth layer to generate defects, which increased the trap concentration of the impurity level.

Usually, in the epitaxial growth of the In _x Ga _1-x As _y P _1-y layer and the InP layer, from the viewpoint of preventing the evaporation of As and P components, the substrate temperature is 600 ° C. or less, for example 57
Growth is carried out at 0 ° C. However, the inventor is MO
On the contrary, when the In _x Ga _1-x As _y P _1-y layer is formed by the VPE method, it is better to increase the substrate temperature because the decomposition of the source gas is accelerated and the epitaxial growth region becomes oversaturated.
We thought it might prevent the evaporation of As and P components,
The composition of _0.84 Ga _0.16 As _0.36 P _0.64 is selected, the compound semiconductor layer is formed by the MOVPE method while changing the substrate temperature, and the ICTS
The trap concentration of the impurity level E _t2 was measured by the (Isothermal Capacitance Transient Spectroscopy) method.

FIG. 1 shows the result, and the substrate temperature is 570
° C. trap concentration impurity level E _t2 compound semiconductor layer epitaxially grown while maintaining the contrast is 6.2 × 10 ¹³ cm ^-3, the trap concentration when epitaxially grown at a substrate temperature of 615 ° C. at a detection limit Yes 2 × 10 ¹¹ cm
^{It was -3} or less, and did not change even when the substrate temperature was 650 ° C. This means that the inventor's prediction is correct. Therefore, the present invention reduces the trap concentration of the impurity level by carrying out MOVPE while keeping the substrate temperature at 610 ° C. or higher, thereby improving the emission efficiency of the semiconductor laser and reducing the power consumption. ..

[0016]

EXAMPLE As shown in FIG. 2, MO was formed on the n ⁺ InP substrate 1.
Using the VPE method, the substrate temperature was set to 610 ° C., and a buffer layer made of n ⁺ InP 2, an n-In _0.84 Ga _0.16 As _0.36 P _0.64 layer 3, and an n-InP layer 4 were sequentially epitaxially grown.
Here, n-In _0.84 Ga _0.16 As _0.36 P _0.64 Layer 3 and n-InP
The thickness of each layer 4 is 2 μm. Next, Zn is changed to n-In
As a result of measuring the trap concentration of the impurity level E _{t2 in} the n-In _0.84 Ga _0.16 As _0.36 P _0.64 layer 3 by diffusing in the P layer 4 to form a p ⁺ n junction diode, the ICTS method was used. The detection limit of the device was 2 × 10 ¹¹ cm ⁻³ or less.

On the other hand, as in the conventional case, the substrate temperature is 570 ° C. and the p ⁺ n junction diode is formed in the ICT.
N-In _0.84 Ga _0.16 As _0.36 P _0.64 layer 3 measured by S method
The trap concentration of the impurity level E _{t2 in} the above was 6 × 10 ¹³ cm ⁻³ , and it was possible to reduce the trap concentration by two digits or more as compared with this.

[0018]

INDUSTRIAL APPLICABILITY By implementing the present invention, In _x Ga _1-x As _y P
It is possible to reduce the trap concentration of the impurity level during the growth of the _1-y epitaxial layer, which improves the emission efficiency of the semiconductor laser and reduces the power consumption, thus extending the life of the semiconductor laser. It has become possible.

[Brief description of drawings]

FIG. 1 is a relationship diagram between a growth temperature and a trap concentration of an n-In _0.84 Ga _0.16 As _0.36 P _0.64 layer.

FIG. 2 is a schematic diagram showing a configuration of a semiconductor laser.

FIG. 3 is an energy diagram of an In _x Ga _1-x As _y P _1-y compound semiconductor layer.

[Explanation of symbols]

1 n ⁺ InP substrate 3 n-In _x Ga _1-x As _y P _1-y layer 4 n- InP layer

Claims (1)

[Claims] 1. When the In _x Ga _1-x As _y P _1-y layer is grown on the InP substrate by the metalorganic vapor phase epitaxial growth method, the InP substrate temperature is kept at 610 ° C. or higher. A method for manufacturing a semiconductor epitaxial layer, comprising: