JPH0475347A - Hetrojunction bipolar transistor - Google Patents

Abstract

PURPOSE:To make it possible to obtain HBT whose current gain is enhanced by installing an interposition layer comprising InGaAsP between a collector layer and a base layer. CONSTITUTION:A conduction band between a base layer 6 and a collector layer 4 can be smoothly connected by means of an extremely low level of spiking by interposing a graded layer 5 between the base layer 6 and the collect layer 4. In terms of HBT 1 having the graded layer 5 thus obtained, the current amplification factor is 490, which provides current gain two times and more times compared with 210 of the prior art HBT 2. HBT 1 rarely depends on the collector current voltage when it is turned on.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in heterojunction bipolar transistors using compound semiconductors.

[Conventional technology]

Heterojunction bipolar transistor (Hetero-j
unction Bipolar Transistor
rs (hereinafter abbreviated as HBT) is expected to have a high current amplification factor and high speed as a next-generation electronic device, and is currently being actively researched and developed mainly in the GaAs/AlGaAs system.

Recently, development of InP-based HBTs that are lattice-matched to InP is also progressing. Since InP-based HBTs use InGaAs for their base layer, the turn-off voltage determined by the bandgap is almost the same as that of silicon bipolar transistors, and is expected to be compatible with existing circuits. It has potential. Furthermore, this HBT has the advantage that it can be integrated with an InP-based light-emitting optical device.

As an InP-based HBT, n is used in the emitter layer and collector layer.
-1nP + InP using p-1nGaAs as base layer
double heterojunction bipolar transistor (D-HB
There is a T). However, this device had the problem that the heterojunction introduced between the base and collector formed a spike-like barrier in the conduction band of the energy band, making it impossible to obtain current gain, as shown in Figure 4. . Therefore, recently, an InP layer with a higher impurity concentration than the collector layer is inserted between the base and collector to lower the conduction band barrier and obtain a large current gain (IEEE Electron Device Let
t,, Vol, 9. No, 5p, 253.19
88).

[Problem to be solved by the invention]

However, as described above, even if an InP layer having a higher impurity concentration than the collector layer is inserted between the base and the collector, there is a problem that a spike-like conduction band barrier still remains.

[Means and actions to solve the problem]

The present invention provides a heterojunction bipolar transistor that solves the above problems, and includes a collector layer made of InP, a base layer made of InGaAs, and an emitter layer made of InP. In between the base layers
It is characterized in that an intervening layer made of GaAsP is provided.

As described above, the present invention provides an intervening layer made of InGaAsP between the collector layer and the base layer.
This is based on the idea that the hetero bandgap between the InP base layer and the InP collector layer becomes smaller, and the spike-like barrier also becomes smaller. In particular, if this intervening layer is a graded layer of InGaAsP whose bandgap wavelength is gradually changed, the heterobandgap will be smoothly connected, and the spike-like barrier will be extremely small. The thickness of this intervening layer needs to be thinner than the electron diffusion length of InGaAsP.

〔Example〕

Hereinafter, the present invention will be described in detail based on Examples.

Table 1 shows the constituent materials of the heterojunction bipolar transistor of this example.

That is, as shown in FIG. 1, InP (
λ, =0.92u) Buffer layer 2, n-1nGaAs
(λ.

= 1.67xm) The sub-collector layer 3, n-1nP collector layer 4, each has a gap wavelength (λ,) of 1 from the substrate side.
．． 00m, 1.20x, 1.30JllI n-1
Graded layer 5 of nGaAsP, p-1 nGaAs
(λ, -1.677II+) base layer 6, n4nP emitter layer 7, n-InGaAs (λ.

= 1.67xm) are sequentially laminated. 9 is a collector electrode, 10 is a base electrode, 11 is an emitter electrode, and 12 is an insulating film. In the embodiment of the above structure, by interposing the graded layer 5 between the base layer 6 and the collector layer 4, the conduction band between the base layer 6 and the collector layer 4 is extremely small, as shown in FIG. It is tied relatively smoothly with spikes. HBT (HBTI) with graded layer 5 obtained in this way
) and conventional HBT without graded layer 5 (HBT
The transistor characteristics of 2) are shown in FIGS. 3(a) and 3(b). In the HBTI of this embodiment, the current amplification factor is 490,
A current gain more than twice that of 210 of HBT2 was obtained. Furthermore, in the HBT1, the dependence of the current on the collector voltage was also very small after the HBT1 was turned on.

It goes without saying that in the above embodiment, p and n may be reversed.

〔Effect of the invention〕

As explained above, according to the present invention, since the intervening layer made of InGaAsP is provided between the collector layer and the base layer, there is an excellent effect that an HBT with improved current gain can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view of an embodiment of a heterojunction bipolar transistor according to the present invention, FIG. 2 is an explanatory diagram of the conduction band between the base and collector of the same embodiment, and FIG. 3(a) is an explanatory diagram of the same embodiment. FIG. 3(b) is a transistor characteristic diagram of a conventional example, and FIG. 4 is an explanatory diagram of a conduction band between the base and collector of a conventional heterojunction bipolar transistor. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Puff layer, 3... Sub-collector layer, 4... Collector layer, 5... Graded layer, 6... Base layer, 7... Emitter layer, 8 °゛°Cap layer, 9...Collector electrode, 10...Base electrode, 11...Emitter electrode, 12...Insulating film.

Claims (1)

[Claims] A heterojunction bipolar transistor in which a collector layer made of InP, a base layer made of InGaAs, and an emitter layer made of InP are sequentially laminated, characterized in that an intervening layer made of InGaAsP is provided between the collector layer and the base layer. Heterojunction bipolar transistor.