JPS63202975A - Manufacture of phototransistor - Google Patents

Abstract

PURPOSE:To form a base layer having an inclination type energy band gap, with superior controllability and reproducibility, by performing a vapor phase epitaxy changing the radiation amount of light. CONSTITUTION:On an n-type GaAs substrate 1, a collector layer 2 of an n-type GaAs layer is grown, and thereon, a p-type AlxGa1-xAs (x<=0.2) base layer 3 is grown while the radiation amount of KrF eximer laser light 4 is gradually increased. In this process, the Al composition (x) of the growth layer increases up to 0.2 in proportion to the increase of radiation amount of the laser light 4. The energy band gap gradually varies with the change of the composition. By forming the base layer 3 in the manner in which a vapor growth or especially an organic metal vapor growth is applied, while the radiation amount of light projected on the epitaxial growth surface is changed, the base layer whose composition gradually changes can be formed with excellent controllabily and reproduciablity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a phototransistor capable of converting an optical signal into an electrical signal.

2. Description of the Related Art There is a phototransistor that converts an optical signal into an electrical signal by utilizing the fact that when a base layer receives light, the potential between the base and emitter is lowered and a current amplification effect occurs. By making the energy bandgap of the base layer of this phototransistor sloped so that it gradually widens from the collector layer to the emitter layer as shown in Figure 2, we can reduce the carrier transit time through the base region. Therefore, a high-speed response becomes possible. Conventionally, such a graded bandgap phototransistor has been manufactured by epitaxially growing each layer using a molecular beam epitaxy method. In particular, in the formation of the base layer, epitaxial growth is performed by gradually changing the temperature of the cell containing the raw material and changing the supply amount, that is, the molecular dose, so that the composition gradually changes while lattice matching is achieved. The semiconductor layer has a graded bandgap in which the energy bandgap gradually widens from the collector layer to the emitter layer.

Problems to be Solved by the Invention However, it is difficult to change the temperature of the cell with good control and good reproducibility, and it is also difficult to change the composition with good control and good reproducibility. This also causes variations in device characteristics with each growth.

Furthermore, epitaxial growth itself is a molecular beam epitaxy method that requires a high degree of vacuum, making it difficult and expensive to maintain the growth equipment, and generally not being mass-producible compared to other growth methods, resulting in lower device manufacturing costs. There was a problem that the price would become high.

The present invention has been made in view of these points, and allows the composition of the base layer to be changed with good control and reproducibility.
It is an object of the present invention to provide a method for manufacturing a graded bandgap phototransistor that is inexpensive to manufacture.

Means for Solving the Problems The technical means of the present invention for solving the above problems are as follows:
- sandwiched between a collector layer made of a semiconductor having a conductivity type and an emitter layer made of a semiconductor having the same conductivity type as the collector layer; The method includes the step of forming a base layer made of a semiconductor whose composition gradually changes from the layer toward the emitter layer by a vapor phase growth method while changing the amount of light irradiation. It is.

For production The effect of this technical means is as follows.

The base layer is formed by vapor phase epitaxy, particularly organometallic vapor phase epitaxy, while varying the amount of light irradiated onto the epitaxial growth surface.

It is possible to vary the composition of the grown layer depending on the weight. Therefore, epitaxial growth can be performed using a vapor phase growth method that is easy to maintain, inexpensive, and suitable for mass production using a molecular beam epitaxy apparatus, and can be easily controlled by simply changing the amount of light irradiation. Again, it is possible to form base firewood whose composition gradually changes.

EXAMPLE Hereinafter, as an example of the present invention, a method of manufacturing an AIGaAs phototransistor having a sloped bandgap will be described with reference to FIG. The epitaxial growth method is optically excited metal organic vapor phase epitaxy (photoexcited MOV).
PE method) was used. Al, Ga.

As raw materials for As, trimethylaluminum (TMAlj: Al(CH3) 3 ) and )limethylgalium A (TiVG; Ga (CHs)) are used, respectively.
s )-Altay (A s Hs ), and as n-type and p-type impurity raw materials, hydrogen selenide (H2S e )-dimethylzinc (DMZn; z21(
CH3) 2) and hydrogen (CH3) 2) as the carrier gas.
H2) ffi was used. As a light source for irradiation, a KrFex6.\simmer laser (wavelength: 249 nm) was used. The total flow rate of each growth layer was 5 l/min, and the pressure inside the crystal growth furnace during growth was reduced to 100 Torr. The temperature of the substrate during growth is n
A collector layer 2 of an n-type GaAs layer is grown to a thickness of 1.4 μm on a GaAs-type substrate 1 (FIG. 1a). Next KP
Type AA'xGa1-. As(x=≦0.2) base layer 3
′! The 1-KrFz ximer laser beam 4 grows by 0.4 μm while gradually increasing the irradiation amount of the ximer laser beam 4 (FIG. 1b). Thermal decomposition of TMAI, which is the raw material for A/, is accelerated by irradiation with laser light 4, so the amount of TMAI that is the raw material for A/ is
The composition X of A4 in the growth layer increases to 0.2. Along with this change in composition, the energy band gap also gradually changes. The irradiation amount of the laser beam 4 is changed by changing the pulse period from 0 to 70, since the laser beam 4 is a pulse irradiation.
1-2. By gradually increasing the irradiation amount of laser beam 4 within the range of 1.4W/6F! changed to.

Next, laser light f1.4W/cr! While irradiating n-type A1
1o, 45Gao, 5sAS: The r-mitter layer 6 is 1.4μm1 and the laser beam is stopped and the n+ type GaA
The s-contact layer 6 is sequentially grown to a thickness of O and OS μm (FIG. 1C).

After that, the emitter layer 5 and the base layer 3 are selectively etched in order to form electrodes.
(Figure 1d). and nfi
Collector layer 2, which is a GaAs layer, and contact layer 6
An n-type electrode 7 was formed on the surface of the base layer 3, and a p-type electrode was formed on the surface of the base layer 3 (FIG. 1e).

According to the manufacturing method described above, the base layer 3 has an energy gap ranging from 1.42ev of GaAs to AIo
, 2G ao, aA 8 to 1.8 eV gradually changing from the collector layer 2 to the emitter layer 5, and forming a base layer having a graded energy band gap with good control and high reproducibility. became possible.

Furthermore, since the growth method is the MOVPE method, compared to the molecular beam epitaxy method, the equipment is simple and easy to maintain, is inexpensive, and is excellent in mass production, so the manufacturing cost has been reduced.

The photodetection response speed of the graded bandgap phototransistor manufactured as described above was about 20 ps when the applied voltage was Ov, and there was almost no difference in device characteristics compared to the conventional one.

In the embodiments described above, a case was described in which a photoexcited MOVPE method was used for epitaxial growth.
This can also be achieved using the Epitaxy method.

Furthermore, only the base layer may be grown in a vapor phase while changing the amount of light irradiation, and the other growth layers may be grown by another growth method, such as a liquid phase growth method. In addition, KrF excimer laser light was used as the irradiation light source, but Ar laser was used.

Excimer laser sources other than KrF, such as CO2 laser, He-Cd laser, and ArF+XeF, may also be used. Ma9
A, - the irradiation dose can be changed by changing the pulse period)
However, in the above embodiments, Aj? Although the case of a GaAs-based phototransistor has been explained, InGaAsP-based and AlGaIn
Graded bandgap transistors using other m-v group compound semiconductors such as P-based semiconductors and U-W of ZnSSe-based
The present invention is also applicable to graded bandgap phototransistors using group compound semiconductors.

Effects of the Invention As described above, according to the present invention, a base layer having a graded energy band gap can be formed with good control and reproducibility by performing vapor phase growth while changing the amount of light irradiation. ), and variations in device characteristics can be reduced. In addition, although the epitaxial growth method also uses light irradiation, it is a vapor phase growth method, so compared to the conventional molecular beam epitaxy method, the equipment is simpler and easier to maintain and manage, the equipment cost is lower, and it is superior in mass production. Therefore, manufacturing costs can be reduced, which has a great industrial effect.

10,,-7

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the manufacturing process of a graded bandgap phototransistor according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of the energy band of the graded bandgap phototransistor. 2... Collector layer, 3... Base layer,
4... Laser light, 5... Emitter layer. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (3)

[Claims] (1) a collector layer made of a semiconductor having one conductivity type;
The emitter layer is sandwiched between an emitter layer made of a semiconductor having the same conductivity type as the collector layer, and is made of a semiconductor having a conductivity type opposite to the collector layer, and the energy gap is inclined from the collector layer to the emitter layer. 1. A method for manufacturing a phototransistor, comprising the step of forming a base layer made of a semiconductor whose composition gradually changes so that the composition changes, by a vapor phase growth method while changing the amount of light irradiation. (2) The method for manufacturing a phototransistor according to claim 1, wherein the vapor phase growth method is a metal organic vapor phase growth method using an organic metal as a raw material. (3) The method for manufacturing a phototransistor according to claim 1, wherein the light source used for light irradiation is a laser light source.