JPH02181932A - Bipolar junction transistor - Google Patents

Abstract

PURPOSE:To be provided with a high current-amplification factor, a low contact resistance and a high breakdown-strength property and to realize a low power consumption and an ultrahigh-speed operation by a method wherein n-type germanium is sued for an emitter and a collector, p-type germanium is used for a base and gallium arsenide is used for a depletion layer between the emitter and the base and for a depletion layer between the base and the collector. CONSTITUTION:Ge whose Schottky barrier height with reference to various metals is low is used for an emitter electrode part 7, a base electrode part 8 and a collector electrode part 9 which come into contact with an external circuit. Thereby, it is possible to lower a resistance of the individual electrode resistances. A built-in voltage between the emitter and the base is about 0.6V which is decided by a p-n junction of the Ge; a low power consumption can be realized. In addition, when GaAs is used for parts to be used as depletion layers which isolate the individual electrodes 7, 8, 9, a breakdown strength between the base and the collector is decided by a breakdown strength of the GaAs. Accordingly, a leakage current is small even at room temperature, and a breakdown voltage is large. In addition, a specific permittivity of the GaAs is small at 13.1 as compared with that of the Ge at 16.0; accordingly, a junction capacitance CEB between the emitter and the base and the junction capacitance CBC between the base and the collector are small; the electrode resistances are small; accordingly, this transistor is suitable for a high-speed operation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a bipolar junction transistor with low power consumption and ultra-high speed operation.

(Prior art) Currently, gallium arsenide (hereinafter referred to as GaAs) is used as a high-speed operating element.
) A heterojunction bipolar transistor (HBT) using aluminum gallium oxide (AIGaAs) is about to be put into practical use. As an element with even higher speed and lower power consumption, the hot electron transistor (HE) uses a heterojunction of germanium (Ge) and GaAs.
T) and HBT have been proposed. For example, N.

The literature by Chand (N, Chand) et al. “Applied.

Physics Letters J (Applied Phy
sics Letters, Vol. 48, No. 7, page 484, a HET using n-type Ge as the emitter, base, and collector and GaAs as the emitter/base barrier layer and base/collector barrier layer has been proposed, but there are The problem of low current amplification factor has not been solved. Furthermore, the conduction band discontinuity of Ge and GaAs is 80
Since it is small, on the order of meV, it does not operate unless the temperature is substantially lower than the temperature of liquid nitrogen. Also, H. Kramer (H,
Kroemer) in the literature [Proceedings of Zui I.
dings of the IEEE) Volume 70, No. 1
As shown from page 3, the HB uses n-type GaAs as the emitter, p-type Ge as the base, and n-type GaAs as the collector.
Although T has been studied for a long time, GaAs has disadvantages compared to Ge and silicon (Si), such as a low conduction band density of states, an inability to obtain a large collector current, and a high junction resistance with metals. These are factors that hinder high-speed operation of the device.

(Problem to be solved by the invention) Problems such as the small collector current value and large contact resistance of GaAs/GeHBTs are solved, and the current amplification rate is lower than that of HETs using Ge/GaAs heterojunctions. An object of the present invention is to provide a bipolar junction transistor (BJT) which has a large resistance and can operate at room temperature.

(Means for Solving the Problems) The present invention includes n-type germanium in the emitter and collector.
This is a bipolar junction transistor using p-type germanium for the base, gallium arsenide for the emitter/base depletion layer, and the base/coke 2 depletion layer.

Furthermore, the bipolar junction transistor is characterized in that the emitter layer and the collector layer are doped with a high concentration of n-type to the extent that electrons are degenerated, and the base layer is doped with a high concentration of p-type to the extent that holes are degenerated. It is a bipolar junction transistor.

(Function) BJTs using Ge have high mobility for both electrons and holes, low contact resistance, and low operating voltage, and are advantageous for high-speed operation even when integrated, but they are narrow bandgap semiconductors. Therefore, it has drawbacks such as low breakdown voltage and large leakage current. The characteristics of GaAs do not change much with temperature, but the contact resistance increases, and the time constant R8*C8o, which is expressed by the base resistance (RB) and the base l-collector junction capacitance (C8o), cannot be made small, making it difficult for high-speed operation. It becomes an obstacle. Furthermore, since the forbidden band width is large, the operating voltage is large and power consumption cannot be reduced. In the BJT according to the present invention, each electrode part of the emitter (E), base (B), and collector (C) that contacts the external circuit has a low Schottky barrier height with various metals.
Use e. This allows the resistance of each electrode to be lowered. Also, the built-in voltage between emitter and base is G
The voltage generated by the pn junction of e is about 0.6V, and low power consumption can be achieved. In addition, by using GaAs for the depletion layer separating each electrode part, the breakdown voltage between the base and the collector is determined by the breakdown voltage of GaAs. Therefore, the BJT of the present invention has a small leakage current and a large breakdown voltage even at room temperature. Furthermore, GaAs has a dielectric constant of 13.1 and Ge's 16
．． Since it is smaller than 0, the emitter l base junction capacitance (C
F, B) and CBo are small and, together with the low electrode resistance, are suitable for high-speed operation. Furthermore, E, B.

By heavily doping each layer of C to the extent of degeneracy, the properties of each electrode become metallic, and even higher speed operation can be expected.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

On a semi-insulating GaAs substrate 1, an n-type Ge layer 2, an intrinsic GaAs layer 3, a p-type Ge layer 4,
An intrinsic GaAs layer 5 and an n-type Ge layer 6 were sequentially laminated. The doping concentration and layer thickness of each layer are as follows.

Emitter layer sb doped Ge 1*10
am 3000 emitter layer/base depletion layer non-doped GaAs 3000 base layer l collector depletion layer non-doped GaAs 3000 Gei dopants were antimony (hereinafter referred to as sb) for n-type and gallium (Ga) for p-type. sb enabled doping at a high concentration of 1*10 (cm) using an ionization Knudsen cell. References by Yochu et al. “Fifth International Conference on Molecular Beams,
Epitaxy J (Fifth International
nalConference on Molecula
r Beam Epitaxy) As shown on page 575, Ge on GaAs was determined by observation of the surface superstructure by reflection high energy electron diffraction (RHEED).
When grown on a (2*2) structure, it becomes n-type, and GaAs (
2*4).

It is known that when grown on (4*2), it becomes p-type. Therefore, n-type Ge may be grown on GaAs (2*2), and p-type Ge may be grown on GaAs (2*4). After each layer was grown, the GaAs layer and Ge layer were etched out using CF4 gas and CCI□F2 gas. AuGeS for emitter and collector electrodes as ohmic electrodes
b, A1 was used as the base electrode. In the above structure, the collector depletion layer is designed to be thick with 3000 layers, but sufficient breakdown voltage can be obtained even with about 1500 layers.

(Effects of the invention) The BJT manufactured with the above structure has a high current amplification factor, low contact resistance, high voltage resistance, and a turn-on voltage of 0.
．． Since it operates with a sufficiently large current at a low value of 5V, low power consumption and ultra-high speed operation are expected.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a bipolar junction transistor according to the present invention. FIG. 2 is an energy band diagram of a bipolar junction transistor according to the invention of the type claimed in claim 1; FIG. 3 is a schematic cross-sectional view of a conventional GaAs/GeHET. In the figure, 1... semi-insulating GaAs substrate, 2... n-type Ge layer,
3... Intrinsic GaAs layer, 4. P-type Ge layer, 5... Intrinsic GaAs layer, 6. N-type Ge layer, 7... Emitter electrode, 8... Base electrode, 9... Collector electrode. , 10・
... n-type Ge emitter layer, 11... n-type GaAs barrier layer, 12... n-type Ge base layer, 13... n-type G
aAs barrier layer, 14... n-type Ge collector layer.

Claims (1)

[Claims] 1) n-type germanium in the emitter and collector, p-type germanium in the base, a depletion layer between the emitter and the base,
A bipolar junction transistor that uses gallium arsenide for the base/collector depletion layer. 2) In the bipolar transistor according to claim 1, the emitter layer and collector layer are doped with an n-type concentration so high that electrons are degenerated, and the base layer is doped with a p-type concentration so high that holes are degenerated. A bipolar junction transistor featuring