JP2764985B2 - Bipolar junction transistor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a bipolar junction transistor with low power consumption and ultra-high speed operation.

(Prior art) Currently, gallium arsenide (hereinafter GaAs) is used as a high-speed operation element.
A heterojunction bipolar transistor (HBT) using aluminum gallium arsenide (AlGaAs) is about to be put to practical use. Hot electron transistors (HET) and HBTs using a heterojunction of germanium (Ge) and GaAs have been proposed as devices with higher speed and lower power consumption. For example, the book "Applied Physics Letters" by N. Chand (Applied
Physics Letters, Vol. 48, No. 7, page 484
Type Ge as emitter, base and collector as GaAs
Although HETs used for the base barrier layer and the base-collector barrier layer have been proposed, the drawback of a small current amplification factor, which is a problem unique to HET, has not been solved. In addition, since the conduction band discontinuity of Ge and GaAs is as small as about 80 meV, it does not operate unless the temperature is substantially lower than the liquid nitrogen temperature. H. Kroemer (Proceedi, "Proceedings of zi IEE")
ngs of the IEEE), vol. 70, no. 1, page 13, n
HBTs using n-type GaAs as collector and n-type GaAs as collector based on p-type Ge as emitter,
Has a drawback that the collector current cannot be increased due to a lower conduction band density than Ge and silicon (Si), and the junction resistance with metal is large. These are factors that hinder high-speed operation of the device. ing.

(Problems to be Solved by the Invention) The problems of the collector current value of GaAs / GeHBT being small and the contact resistance being large are solved.
An object of the present invention is to provide a bipolar junction transistor (BJT) that has a larger current amplification factor than an HET using an s heterojunction and can operate at room temperature.

(Means for Solving the Problems) The present invention relates to a bipolar junction transistor using n-type germanium for an emitter and a collector, p-type germanium for a base, a depletion layer between an emitter and a base, and gallium arsenide for a depletion layer between a base and a collector. It is. Further, the bipolar transistor is characterized in that the emitter layer and the collector layer are doped to a high concentration n-type so that electrons are degenerated, and the base layer is doped to a high concentration p-type so that holes are degenerated. It is a junction transistor.

(Function) The BJT using Ge is advantageous in high-speed operation including integration even when it has high mobility in both potential and hole, low contact resistance, and low operating voltage. However, it is a narrow hand gap semiconductor. Therefore, there are disadvantages such as a small breakdown voltage and a large leak current. The characteristics of GaAs hardly change with temperature, but the contact resistance increases, and the base resistance (R _B ) and the base / collector junction capacitance (C
_BC ), the time constant R _B * C _BC cannot be reduced, which is a major obstacle to high-speed operation. In addition, since the forbidden bandwidth is large, the operating voltage is large and the power consumption cannot be reduced. In the BJT according to the present invention, the emitter (E), the base (B), and the collector (C), which are in contact with an external circuit, use Ge having a low Schottky barrier height with various metals. As a result, the resistance of each electrode can be reduced. The built-in voltage between the emitter and the base is about 0.6 V, which is determined by the junction of Ge pn, and low power consumption can be realized. Also, by using GaAs for a portion serving as a depletion layer separating each electrode portion, 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. GaAs has a relative dielectric constant of 13.1
Since it is smaller than Ge of 16.0, the emitter / base junction capacitance (C _EB ) and C _BC are small, and are suitable for high-speed operation together with low electrode resistance. Further, by doping the layers E, B, and C to such an extent that the layers are degenerate, the properties of the respective electrodes become metallic, and higher-speed operation can be expected.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

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 stacked on a semi-insulating GaAs substrate 1 by molecular beam epitaxy. The doping concentration and layer thickness of each layer are as follows.

Emitter layer Sb-doped Ge 1 * 10 ¹⁹ cm ^-3 3000Å Emitter layer / base depletion layer Non-doped GaAs 300Å Base layer Ga-doped Ge 1 * 10 ¹⁹ cm ^-3 500Å Base layer / collector depletion layer Non-doped GaAs 3000Å Collector layer Sb-doped Ge 1 * 10 ¹⁹ cm ^-3 4000Å Ge layer dopants are n-type antimony (Sb) and p-type
Gallium (Ga) was used for the mold. Sb enables high-concentration doping of 1 * 10 ¹⁹ (cm ⁻³ ) using an ionized Knudsen cell. Kawanaka et al., Fifth International Conference on Molecular Beam
Epitaxy "(Fifth International Conference on
As shown from page 575 of Molecular Beam Epitaxy, Ge on GaAs becomes n-type when grown on GaAs (2 * 2) structure by observation of surface superstructure by reflection high energy electron diffraction (RHEED), and GaAs ( It is known that when grown on (2 * 4), (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 growing each layer, CF ₄ gas and CCl ₂ F ₂
The GaAs layer and the Ge layer were etched out using gas. AuGeSb for emitter and collector electrodes as ohmic electrodes
And Al as a base electrode. In the above structure, the collector depletion layer is designed to be as thick as 3000 °, but sufficient withstand voltage can be obtained even at about 1500 °.

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

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a bipolar junction transistor according to the present invention. FIG. 2 is an energy band diagram of the type described in claim 1 of a bipolar junction transistor according to the invention. FIG. 3 is a schematic sectional view of a conventional GaAs / GeHET. In the figure, 1 ... a semi-insulating GaAs substrate, 2 ... n-type Ge layer, 3 ... intrinsic
GaAs layer, 4 ... p-type Ge layer, 5 ... intrinsic GaAs layer, 6 ... n
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 GaAs
Barrier layer, 14 ... n-type Ge collector layer.

Claims (2)

(57) [Claims] 1. A bipolar junction transistor using n-type germanium for an emitter and a collector, p-type germanium for a base, gallium arsenide for a depletion layer between an emitter and a base, and a depletion layer between a base and a collector. 2. The bipolar transistor according to claim 1, wherein the emitter layer and the collector layer are of an n-type having a high concentration such that electrons are degenerated, and the base layer is of a p-type having a high concentration such that holes are degenerated. Bipolar junction transistor characterized by doping.