JPH06209007A - Hetero junction bipolar transistor - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an InP / InGaAs heterojunction bipolar transistor (HBT) formed on a Si substrate with a structure in which defects existing in the crystal have little adverse effect on the characteristics of the HBT. . [Structure] The above purpose is InP / InGaAs formed on a Si substrate.
This can be solved by using an HBT that is characterized in that a quaternary mixed crystal layer or a quaternary mixed crystal layer having a composition that is gradually changed is provided between the base layer and the emitter layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heterojunction bipolar transistor (HBT), and more particularly to an HBT having a structure suitable for high speed operation.

[0002]

2. Description of the Related Art A typical element of a bipolar transistor using a III-V group compound semiconductor is an HBT using a wide bandgap semiconductor for the emitter, which is basically a combination of GaAs and AlGaAs in terms of practicality. The composition of the semiconductor material used is the most important. This AlGaAs / GaAs HBT
In the two, in order to lower the and turn-on voltage to increase the emitter injection efficiency, Al was varied Al composition _X G
a _1-X As (gradually changing the value of x)
Attempts have been made to form at the base (E / B) interface.

In recent years, HBTs combining InP and InGaAs have been actively developed. This is because the electron mobility in the InGaAs layer is high, and therefore it is more suitable for high-speed operation than the AlGaAs / GaAs HBT. However, the InGaAs layer was used as the collector layer.
HBT has a problem that the breakdown voltage is low. To solve this problem, a double hetero structure using an InP layer as the collector is adopted. In this case, the base /
The band discontinuity of the conduction band existing between the collectors (B / C) occurs as a new problem. In order to solve this new problem, InGaAsP whose composition was changed between B / C or
Inserting a mixed crystal layer such as InGaAlAs is performed.

Since the InP substrate is easily damaged and expensive, it has been started to produce the above InP / InGaAs HBT on another substrate. At present, Si is used as the substrate. It is used. Due to the large difference in lattice constant between the Si substrate and InP or InGaAs,
InP / InGaAs HBTs fabricated on the substrate have many defects such as dislocations. However, the defects existing in the neutral base region do not affect the characteristics of the HBT, and thus show relatively good device characteristics. This property is unique to InP / InGaAs-based HBTs fabricated on Si substrates and is not observed in AlGaAs / GaAs-based HBTs fabricated on Si substrates. However, in InP / InGaAs HBTs, defects mainly at the E / B interface adversely affect the device characteristics. Specifically, it is a phenomenon that the current gain is small when the collector current density is small. If this adverse effect can be eliminated, despite many crystal defects,
It becomes possible to fabricate a device exhibiting further excellent characteristics.
By the way, InP / InGaA fabricated on InP substrate with lattice matching.
Since the s-series HBT has few defects, a large current gain is obtained even when the collector current density is small.

[0005]

The prior art has the above-mentioned problems.

An object of the present invention is to solve the above problems of the prior art and to form InP / InGaAs formed on a Si substrate.
It is to provide a HBT having a structure in which defects existing in the crystal of the system HBT do not have a bad influence on the characteristics of the HBT.

[0007]

[Means for Solving the Problems] The above-mentioned object is to provide a base layer for InP / InGaAs HBTs formed on a Si substrate.
This can be solved by using an HBT characterized in that a quaternary mixed crystal layer or a quaternary mixed crystal layer whose composition is gradually changed is provided between the emitter layers (E / B).

[0008]

[Function] By inserting the mixed crystal layer, defects existing between E / B become electrically inactive, and thereby,
The current gain can be increased even when the collector current density is low.

[0009]

EXAMPLES The structure of the HBT of the present invention will be described in detail below with reference to examples.

FIG. 1 shows one embodiment of HBT of the present invention, Si.
A cross-sectional view showing the schematic structure of InP / InGaAs on the substrate.
InP n-type emitter layer, 2 for InGaAsP quaternary mixed crystal, 3 for
InGaAs p-type base layer, 4 is an undoped InGaAs collector layer, 5 is an InGaAs electrode layer, and 6 is a Si substrate. InGa
In the AsP quaternary crystal, the lattice constant is equal to that of the InP substrate, and the composition is changed so that the band gap changes continuously. FIG. 2 is a diagram showing an energy band diagram in this case. The lattice constant of the quaternary mixed crystal layer of No. 2 matches the lattice constant of InP, and the band gap is gradually changed by gradually changing the composition of In, Ga, As, and P. Further, the impurity concentration is equal to or lower than the doping concentration of the emitter.

InP / InGaAs HBT fabricated on Si substrate
Although many defects such as dislocations are present in the Al2O3, the defects existing in the neutral base region do not affect the characteristics of the HBT, and thus show relatively good device characteristics. But this H
In BT, only defects existing at the E / B interface adversely affect the device characteristics. That is, since the defects existing at the InP / InGaAs interface affect the device characteristics, the InGaAsP quaternary mixed crystal layer is provided at this interface in the present invention. In FIG. 1, since the base region is heavily doped, the depletion layer mainly extends to the emitter side. Therefore, the film thickness of the InGaAsP quaternary mixed crystal layer is
The depletion layer may have a thickness (about 200 nm) or less and an electron de Broglie wavelength (about 5 nm) or more. That is, in the present invention, In
By inserting an InGaAsP quaternary mixed crystal layer with a thickness of about 5 to 200 nm at the P / InGaAs interface, it is possible to reduce adverse effects on device characteristics and to increase the current gain even when the collector current density is small. can do.

In the above example, the case where InGaAsP is used as the quaternary mixed crystal has been described, but the present invention can be applied to the InGaAlAs mixed crystal and to the quaternary mixed crystal such as InGaAlAsP. You can

[0013]

As described above, by using the InP / InGaAs HBT formed on the Si substrate as the HBT having the constitution of the present invention, the problems of the prior art can be solved and the existence of HBT in the crystal can be solved. It was possible to provide an HBT with a configuration in which the resulting defects have less adverse effects on the properties of the HBT.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an embodiment of an HBT of the present invention.

FIG. 2 is an energy band diagram of the HBT shown in FIG.

[Explanation of symbols]

1 ... n-type InP emitter layer, 2 ... InGaAsP quaternary mixed crystal layer,
3 ... p-type InGaAs base layer, 4 ... undoped InGaAs collector layer, 5 ... n-type InGaAs electrode layer, 6 ... Si substrate.

Claims (1)

[Claims] 1. An InP / InGaAs heterojunction bipolar transistor formed on a Si substrate, characterized in that a quaternary mixed crystal layer or a quaternary mixed crystal layer whose composition is gradually changed is provided between a base layer and an emitter layer. And a heterojunction bipolar transistor.