JPH02288233A - bipolar transistor - Google Patents

Abstract

PURPOSE:To obtain a bipolar transistor wherein electrons pass a base in a short time and which can operate at a high speed, by setting the composition of materials on the emitter side on the boundary between an emitter and the base so that the value of (x) be in a specified range in an NPN-type bipolar transistor prepared by using GaSb as the material of the base and by using AlxGa1-xSb as the material of the emitter. CONSTITUTION:In a bipolar transistor prepared by using GaSb as a material of a base, AlxGa1-xSb is used as a material of an emitter on the boundary with the base. In a case A of x =0.2, electrons are injected from a point L of the emitter to a point L of the base. However, the energy of the electrons is small since they are injected to the bottom of the point L, while the electrons pass the base in a long time and the motion of the transistor slows down, since the speed of the electrons is low. In a case B of X=0.5, on the other side, the electrons are injected from the point L of the emitter into a high-energy area of the point L of the base. Since the energy of the electron is large and the speed is high, in this case, the electrons pass the base in a short time and the transistor operates at a high speed. Accordingly, the value of (x) has an optimum value, and the transistor operates at the highest speed when the electrons are injected into as large a spot of the point L of the base as possible. As to the range of (x) satisfying this condition, a range from 0.3 to 0.6 is advisable.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a bipolar transistor having a heterostructure, and in particular to a bipolar transistor that enables high-speed operation by controlling the composition of the emitter material. .

[Prior art and its problems] As conventional bipolar transistor materials, in a Si bipolar transistor, 3i is used for the emitter, base, and collector, and in m-V compound semiconductors, AlxGaAs is used for the emitter, and the base and collector are made of 3i. For the collector, a high-speed transistor was used, such as using GaAS (for example,
ceeding IEEE, Vol.

70, 1982. p. 13).

However, in 3i, the electron speed is low, so there is a problem in terms of high speed.On the other hand, in transistors using GaAs as the base, although the electron speed is considerably improved, the operating voltage is large due to the large band gap. The problem is that it requires a lot of power.

In order to lower the operating voltage, if GaSb is used for the base as a material with a small band gap, the operating voltage can be reduced to about half.

However, in Qa3b, the energy difference between the point and the L point is 0.1 eVL, so the electrons are distributed to the L point where the electron velocity is low, and the base time of the electron is long.
This inevitably led to the problem that the transistor operation became slow.

An object of the present invention is to solve such conventional problems and to provide a bipolar transistor that allows electrons to pass through the base at a higher speed and is capable of high-speed operation.

[Means for Solving the Problems] The present invention uses (3a3b) as a base material and A j! x Ga 1-x S as an emitter material.
In the npn type bipolar F transistor using b,
The bipolar transistor is characterized in that the material composition on the emitter side at the boundary between the emitter and the base is such that the value of X is in the range of 0.3 to 0.6.

[Function] In a bipolar transistor using GaSb as the base material, Al is used as the emitter material at the boundary with the base.
Ga1-x5b (x: O,:3~0.6>
Explain why it operates at high speed when using .

In the conventional method, the value of X in the composition of Ga1-xSb of the emitter is not particularly limited, and the optimum value has not been determined. Therefore, depending on the value of X, the transistor may not operate at high speed.

Figure 1 shows the hand structure from emitter 1 to base 2 of the transistor when X = 0.2ct'j and 0.5, and this is the structure when A is x = 0.2.
B has the structure when x=0.5. In Beth [,L,
This shows the energy at the bottom of point X.

As can be seen from the figure, when x = 0.2, electrons are injected from point L of the emitter to the bottom point of the base, but since they are injected at the bottom of point L, the electrons Energy is small and velocity is small. Therefore, the time taken for electrons to pass through the base is long, and the operation of the transistor becomes slow.

On the other hand, when x=0.5, electrons are injected from point L of the emitter to the high energy region of point L of the base. In this case, the energy of the electrons is high and the speed of the electrons is high, so the time taken for the electrons to pass through the base is shortened, and the transistor operates at high speed. When the value of X becomes larger and electrons are injected into the base's X point, the energy of the electrons as seen from the bottom of the X point is small, so the electron velocity becomes smaller.

Therefore, there is an optimum value for the value of X, and the transistor operates at the highest speed when the injection is made as large as possible at the L point of the base. The range of the value of X corresponding to such a band structure is preferably from 0.3 to 0.6.

To examine this experimentally, it is sufficient to examine the dependence of the current gain of the transistor on the value of X.

FIG. 2 shows the measured layer structure of the transistor, and FIG. 3 shows the measurement results.

In FIG. 2, 21 is a substrate, 22 is an insulating layer, 23 is a four-knob collector, 24 is a collector, 25 is a base, 26 is an emitter, and 27 is a contact. The base 25 is made of GaSb doped with Be at 1X 1019 cm-3, and the layer thickness is 100 cm.
It was set to 0 A. The composition on the emitter side of the boundary region between the emitter 26 and the base 25 was varied from x=0 to 0.7.

Looking at the results in FIG. 3, it can be seen that the current gain begins to increase when the value of X is about 0.3, reaches a maximum value at 0.5, and decreases at 0.7. In a bipolar transistor, if the doping concentration of the base is constant, the current gain and the base transit time of electrons are approximately inversely proportional to each other, so that the larger the current gain, the shorter the base transit time. The shorter the base transit time, the faster the transistor operates, so the larger the current gain, the better the performance of the transistor. The range where a large current gain is obtained, that is, the range where X is 0
．． A range of 3 to 0.6 is a range in which a transistor using 3a3b as a base can be operated at high speed.

[Example] Next, examples of the present invention will be described.

In this embodiment, the base 25 of the emitter 26 in FIG.
A material was prepared in which the material composition at the boundary with x was set to x=0.5. P-type GaSb is used as the substrate 21, and AR is used as the insulating layer 22 thereon. , 7 Gao,
3. Grow 5000 S b, grow 5000 n-Garb as sub-collector 23, then grow 5000 n-Qa3b as collector 24, 1000 p-Garb as base 25, emitter 26.
As, n −A! Q, 5G a 0.5 S b has grown to 1500 people, and on top of that, as contact 27, n
-AflxGal-xSb through the gradient composition structure, (
Grow 1000 3a3b members.

In this structure, a transistor was fabricated by a method such as etching, and when the current gain was measured, a large value of 160 was obtained, which was about 10 times larger than when x=0.2. Therefore, as a transistor operation, 10
Double speed was jqed.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a bipolar transistor in which electrons have a short base passage time and can operate at high speed.

[Brief explanation of drawings]

Figure 1 is a diagram showing the band structure from emitter 1 to base 2 of the transistor when x = 0.2 and 0.5, Figure 2 is a block diagram showing the transistor structure where the current gain was measured, FIG. 3 is a diagram showing measurement results in which the value of current gain is plotted against the value of X. 1.26...Emitter 2,25...Base 3
...Conduction band 4...Valence band 21...
Substrate 22... Insulating layer 23... Sub collector 24... Collector 21... Contact

Claims (1)

[Claims] (1) np using GaSb as the base material and Al_xGa_1_-_xSb as the emitter material
1. An n-type bipolar transistor, wherein the material composition on the emitter side at the boundary between the emitter and the base is such that the value of x is in the range of 0.3 to 0.6.