JPH0666318B2 - Heterojunction bipolar semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a heterojunction bipolar semiconductor device,
By forming a base layer that is thin enough to generate a two-dimensional carrier gas layer between high-resistance barrier layers,
Even if the base layer is thinned in order to increase the speed, the resistance value can be kept low and the breakdown voltage can be kept high.

[Industrial application field]

The present invention relates to an improvement of a bipolar semiconductor device utilizing a heterojunction of GaAs / AlGaAs system or Ge / GaAs system, for example.

[Conventional technology]

In recent years, high-speed bipolar semiconductor devices have been known in which thin semiconductor layers are stacked to allow a current to flow in the vertical direction. For example, heterojunction bipolar transistors (heteroju
nction bipolar transistor (HBT) is one of them,
Such a type of bipolar semiconductor device has a large current driving capability, that is, a large transfer conductance gm, and therefore the time for charging / discharging the load capacitance is short. Therefore, the device itself as a whole is speeded up.

[Problems to be solved by the invention]

The speed in the bipolar semiconductor device as described above depends on the time during which the carrier travels in the base layer.

Therefore, if the base layer is made thin, the transit time of the carrier is shortened and the speed is increased.

However, if the base layer is simply thinned, the base resistance will increase and the speed will rather decrease.

Therefore, it is necessary to perform high-concentration impurity doping on the base layer to increase its conductivity. For such a high-concentration impurity-doped base layer,
When the emitter layer or the collector layer, which is doped with an impurity of the opposite conductivity type at a high concentration, is joined, the breakdown voltage naturally lowers.

The present invention, in a bipolar semiconductor device having a heterojunction, even if the base layer is thinned in order to further increase the speed,
The base resistance does not increase and the breakdown voltage does not decrease.

[Means for solving problems]

In the heterojunction bipolar semiconductor device according to the present invention, a one-conductivity-type semiconductor base layer (for example, p ⁺ -type GaAs base) having a thickness such that a two-dimensional carrier gas layer (for example, the two-dimensional hole gas layer 10) can be generated. Layer 3) and a non-doped or low-concentration opposite conductivity type semiconductor barrier layer (for example, i-type or n ^- type Al) which is laminated with one conductivity type semiconductor base layer sandwiched therebetween and has a wider energy band gap than that.
GaAs barrier layers 2 and 4) and semiconductor layers of opposite conductivity type and collector layers (for example, n ⁺ -type GaAs emitter layer 5 and n ⁺ -type GaAs collector layer 1) which are laminated via the barrier layer and face each other. It is prepared to be prepared.

[Action]

With such a structure, even if the base layer is thin, the two-dimensional carrier gas layer substantially acts as a base, so that the resistance value is sufficiently low and the base layer has a high concentration. Even if it is doped to the emitter layer, a high resistance spacer layer is interposed between the emitter layer and the collector layer, so that the breakdown voltage is kept high.

〔Example〕

FIG. 1 shows a cutaway side view of an essential part of an embodiment of the present invention. The present embodiment relates to the npn type.

In the figure, 1 is an n ⁺ type GaAs collector layer, 2 is an i type (or n ⁻ type) AlGaAs barrier layer, 3 is a p ⁺ type GaAs base layer, 4 is an i type (or n ⁻ type) AlGaAs barrier layer 5 is an n ⁺ type GaAs emitter layer, 6 is a p ⁺ type base contact region, 7 is an emitter electrode, 8 is a base electrode, and 9 is a collector electrode. In this embodiment, the collector layer 1 also serves as the substrate.

The following is an example of various data of each part in this embodiment.

(1) About n ⁺ type GaAs collector layer 1 Impurity concentration: 1 × 10 ¹⁸ to 10 ¹⁹ [cm ⁻³ ] (2) About i type (or n ⁻ type) AlGaAs barrier layer 2 Thickness: 500 [Å] ( 3) About p ⁺ type GaAs base layer 3 Thickness: 100 [Å] or less Impurity concentration: 1 × 10 ¹⁸ to 10 ¹⁹ [cm ^-3 ] (4) About i type (or n ⁻ type) AlGaAs barrier layer 4 Thickness Length: 300 to 500 [Å] (5) About n ⁺ type GaAs emitter layer 5 Thickness: 1000 [Å] or more Impurity concentration: 1 × 10 ¹⁸ [cm ^-3 ] or more (6) p ⁺ type base contact region No. 6 Impurity concentration: 5 × 10 ¹⁸ to 10 ¹⁹ [cm ⁻³ ] FIG. 2 shows an energy band diagram immediately below the emitter electrode 7 in the embodiment described with reference to FIG. The same symbols as those used in the figures represent the same parts or have the same meanings.

In the figure, 10 is a two-dimensional hole gas layer, E _C is the bottom of the conduction band, E _F is the Fermi level, E _V is the top of the valence band, e ⁻ is the electron, and the + sign inside ○ is positive. The electric charge and the-mark in the circle indicate negative electric charge.

As can be seen from the figures, in the above-described embodiment, as the base layer 3 for controlling the electron flow flowing from the emitter layer 5 to the collector layer 1, a hole supplied from a p-type dopant forms a heterojunction. Since the two-dimensional hole gas layer 10 is generated due to the existence of the barrier in the barrier, it is used. That is, in the two-dimensional hole / gas layer 10,
Due to the increase of the Fermi energy based on the dimensionality and the screening effect, there is a hole gas of high mobility, so that it is used as a base of low resistance. The base layer 3 is highly doped in order to realize a sufficiently low base resistance value, but since the barrier layer 2 or 4 is interposed between the base layer 3 and the collector layer or the emitter layer 5, the breakdown voltage is high. Is maintained high enough.

When forming the p ⁺ -type GaAs base layer 3 in the above-mentioned embodiment, it is preferable to apply the planar doping method as a means for introducing the p-type dopant in a high concentration. This is the case, for example, for molecular beam epitaxy (M).
For example, in order to grow a p-type GaAs layer by applying a technique capable of forming an ultra-thin layer such as the BE) method, the growth of a GaAs film and, if possible, a thin p-type similar to a monoatomic layer. The growth of the impurity film is repeated, and as a result, a GaAs layer containing a high concentration of p-type impurities is obtained. Further, although the npn type is targeted in the above-mentioned embodiment, it is needless to say that the present invention can be applied to the pnp type if the conductivity types of the respective semiconductor layers are reversed.

〔The invention's effect〕

In a heterojunction bipolar semiconductor device according to the present invention, a one-conductivity-type semiconductor base layer having a thickness capable of generating a two-dimensional carrier gas layer, and a one-conductivity-type semiconductor base layer sandwiched between the one-conductivity-type semiconductor base layer and A non-doped or low-concentration opposite conductivity type semiconductor barrier layer having a wider energy band gap, and an opposite conductivity type semiconductor emitter layer and a collector layer (or a substrate) which are laminated via the barrier layer and face each other. It is configured with. According to this structure, the base layer is so thin that the two-dimensional carrier gas layer is generated, so that
The carrier travels in the base layer for a very short time, which is fast, and when compared with a homojunction bipolar semiconductor device having no heterostructure, it can be compared with a normal heterojunction bipolar semiconductor device. It is possible to lower the base resistance, and even if the base resistance is low, the breakdown voltage is maintained sufficiently high due to the existence of the barrier layer, and the heterojunction on the emitter layer side allows the base resistance to be high. The ability to inject hot electrons into the layer further improves its speed.

[Brief description of drawings]

FIG. 1 is a side view of a main part of an embodiment of the present invention, and FIG. 2 is an energy band diagram of the embodiment shown in FIG. In the figure, 1 is an n ⁺ type GaAs collector layer, 2 is an i type (or n ⁻ type) AlGaAs barrier layer, 3 is a p ⁺ type GaAs base layer, 4 is an i type (or n ⁻ type) AlGaAs barrier layer 5 is an n ⁺ type GaAs emitter layer, 6 is ap ⁺ type base contact region, 7 is an emitter electrode, 8 is a base electrode, 9 is a collector electrode, and 10 is a two-dimensional hole gas layer.

Claims (1)

[Claims] 1. A one-conductivity-type semiconductor base layer having a thickness with which a two-dimensional carrier gas layer can be generated, and a one-conductivity-type semiconductor base layer sandwiched between the one-conductivity-type semiconductor base layer and an energy band gap in comparison therewith. It is characterized by comprising a wide non-doped or low-concentration opposite conductivity type semiconductor barrier layer, and opposite conductivity type semiconductor emitter layer and collector layer (or substrate) which are laminated via the barrier layer and oppose each other. Heterojunction bipolar semiconductor device.