JPH0831590B2 - Semiconductor device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a semiconductor device capable of high-speed operation, and more particularly to a hot electron transistor.

(Prior Art) One of active semiconductor devices considered to be capable of high-speed operation
One hot electron transistor (THETA, HET)
There is. For example, M. Heiblum by Solid State Elct
ronics, Vol.24, p343, 1981). This device injects high-energy electrons from the emitter into the base, so that the electrons pass through the base at high speed and the base transit time is short. Therefore, it is suitable for high-speed operation.

FIG. 3 shows a schematic sectional view of a conventional HET. Third
In the figure, 1 is a substrate, 2 is a collector layer made of an n-type semiconductor, 3 is a collector barrier layer made of an undoped semiconductor having a conduction band energy higher than that of the collector layer, 4
Is a base layer made of the same kind of semiconductor as the collector layer, 5
Is a thin emitter barrier layer made of an undoped semiconductor having a conduction band energy higher than that of the base layer and capable of tunneling electrons, 6 is an emitter layer made of the same kind of semiconductor as the collector layer, 7 is a collector electrode, 8 is a base electrode, 9 is an emitter electrode.

The operation of this conventional structure is performed by using the semi-insulating GaAs as the semiconductor substrate 1, the collector layer 2, the base layer 4, and the emitter layer 6.
As a fourth structure showing the band structure, n-GaAs having a donor concentration of about 1 × 10 ¹⁸ cm ^{−3 is used} as the collector barrier layer, Al _0.2 Ga _0.8 As is used as the collector barrier layer 3, and Al _0.3 Ga _0.7 As is used as the emitter barrier layer 5.
This will be described with reference to the drawings.

FIG. 4 shows a schematic band structure extending from the emitter layer 6 to the collector layer 2 in FIG. In Fig. 4, 10 is the bottom of the conduction band and Ef is the Fermi level.

As shown in Fig. 4, the potential difference between the emitter and the base is 0.
When the Fermi level of the base layer is set lower than that of the emitter layer at about 3 V, the electrons in the emitter layer 6 tunnel through the emitter barrier layer 5 and move to the base layer 4. The electrons obtain energy (about 0.3 eV) due to the potential difference between the emitter and the base, and become hot electrons, most of which pass through the base and reach the collector barrier layer 3.
Since the energy difference at the bottom of the conduction band between the GaAs base layer and the Al _0.2 Ga _0.8 As collector barrier layer is about 0.15 eV, if the Fermi energy of the collector layer 10 is made lower than that of the base layer 4, it becomes hot. The electrons enter the collector barrier layer, are accelerated by the electric field of the collector barrier layer, and move to the collector layer.

Thus, in this device, the electrons injected from the emitter to the base become hot electrons and pass through the base layer 4 and the collector barrier layer 3 at high speed,
High speed operation is possible.

(Problems to be solved by the invention) However, although the conventional HET has the above-mentioned advantages, the current gain ([collector current] / [base current]) is small, so that sufficient speedup cannot be achieved. Not achieved.

A part of the electrons injected from the emitter to the base loses energy due to scattering in the base layer having a high impurity concentration, so that it cannot enter the collector barrier layer and becomes a base current. In the conventional HET, the frequency of plasmon scattering coupled to lattice vibrations in the base layer is high, and the number of electrons that reach the collector layer due to the loss of energy due to scattering is about the same as the number of electrons that reach the collector layer. Therefore, the current gain cannot be increased.

An object of the present invention is to eliminate the drawbacks of the conventional HET and provide a semiconductor device capable of operating at an ultra-high speed.

(Means for Solving Problems) A semiconductor device of the present invention has an emitter layer made of an n-type first semiconductor and a bottom of a conduction band having a higher energy than a bottom of a conduction band of the emitter layer. An emitter barrier layer made of a second semiconductor having a thickness capable of tunneling electrons and having a low impurity concentration, and a third impurity diffusion layer having a lower conduction band energy lower than that of the conduction band of the emitter barrier layer. An undoped base layer made of a semiconductor, and a thin base layer made of a high-concentration n-type fourth semiconductor having a bottom of a conduction band having an energy lower than that of the conduction band of the undoped base layer,
A collector barrier consisting of a fifth semiconductor of low impurity concentration having a conduction band bottom that is lower than or equal to the conduction band bottom of the undoped emitter layer and higher than the conduction band bottom of the thin base layer. It is characterized in that it has a structure in which a layer and a collector layer made of an n-type sixth semiconductor are stacked.

(Operation) In the semiconductor device of the present invention, electrons injected from the emitter to the base region hardly lose energy due to plasmon scattering because the base region in which a high concentration of impurities exists is very narrow. Therefore, a high current gain can be obtained and an ultrahigh speed operation can be performed.

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

FIG. 1 is a schematic sectional view showing an embodiment of the present invention.
In FIG. 1, those having the same numbers as those in FIG. 3 are the same as those in FIG. 3 and perform the same functions. Reference numeral 16 denotes an emitter layer made of an n-type first semiconductor, and 15 has a bottom of a conduction band having a higher energy than that of the conduction band of the emitter layer 16 and has a thickness such that electrons can tunnel, and a second impurity layer having a low impurity concentration. , An undoped barrier layer 14 made of a third semiconductor having a low impurity concentration and having a bottom of a conduction band having a lower energy than that of the conduction band of the emitter barrier layer 15.
Is a thin base layer made of a high-concentration n-type fourth semiconductor having a conduction band bottom having a lower energy than that of the undoped base layer 14, and 12 is the undoped base layer 14
Lower energy and thinner base layer than the bottom of the conduction band
A collector barrier layer made of a fifth semiconductor having a low impurity concentration has a bottom of a conduction band whose energy is higher than that of the conduction band of 13, and a collector layer 11 made of an n-type sixth semiconductor.

FIG. 2 is a band diagram for explaining the operation of the embodiment of the present invention. In FIG. 2, those having the same numbers as those in FIGS. 1 and 4 are the same as those in FIGS. 1 and 4 and have the same functions.

When a voltage is applied between the emitter and the base as shown in FIG. 2 and the bottom of the conduction band of the emitter layer is higher than the bottom of the conduction band of the undoped base layer, the electrons existing in the conduction band of the emitter layer are It tunnels through the emitter barrier layer and is injected into the conduction band of the undoped base layer. The electrons injected into the conduction band of the undoped base gain energy due to the inclination of the bottom of the conduction band due to the bias voltage between the emitter and the base, and become hot electrons to reach the thin base layer. At this time, since the undoped base layer has almost no impurities, there is no impurity scattering or plasmon scattering and the energy is hardly lost. In addition, even if energy is rarely lost due to lattice scattering and falls to the bottom of the conduction band, it can be accelerated again by the internal electric field to obtain sufficient momentum in the collector direction and sufficient energy to cross the collector barrier. Now, it is considered that the thin base layer contains a high concentration of impurities and has a large amount of impurity scattering and plasmon scattering, but since the thickness is extremely thin, there is not enough time to receive the scattering. Therefore, the electrons that have entered the thin base layer pass through the thin base and reach the collector barrier layer with little scattering. Therefore, it is very small that the electrons injected into the thin base drop to the bottom of the conduction band and contribute to the base current. The electrons that have entered the collector barrier layer are accelerated by the electric field of the collector barrier layer and move to the collector layer, as in the conventional HET.

As described above, according to the structure of the present invention, electrons injected from the emitter to the base hardly lose energy in the base region and contribute to the base current, so that a high current gain can be obtained. As a result, ultra-high speed operation becomes possible.

Next, the manufacturing method, structure, and characteristics of the device prepared according to this embodiment of the present invention will be described. MBE (Molecular Beam Epitaxy) is used as a crystal growth method, and the thickness is 0.5 μm and the donor concentration is 1 × on the semi-insulating InP substrate 1.
10 ¹⁸ cm ^-3 n-InGaAs collector layer 11, 3000 Å undoped In _0.59 (Ga _0.6 Al _0.4 ) _0.47 As collector barrier layer
12, n-InGaA with 100Å thickness and donor concentration of 2 × 10 ¹⁸ cm ^-3
s thin base layer 13, 900 Å thick, undoped In _0.53 (Ga
_0.5 Al _0.5 ) _0.47 As undoped base layer 14, undoped InAlAs emitter barrier layer 15 having a thickness of 50 Å, and n-InGaAs emitter layer 16 having a donor concentration of 1 × 10 ¹⁸ cm ^-3 and a thickness of 0.5 μm were sequentially grown. All these layers are lattice matched to the InP substrate. The base layer and collector layer were exposed by etching for forming electrodes. The collector electrode 7, the base electrode 8 and the emitter electrode 9 were formed by depositing and alloying AuGe / Au. 1 as the current gain of this HET
0 was obtained.

In the above examples, only InGaAlAs-based semiconductors were shown as semiconductor materials, but it is obvious that the present invention can be applied to semiconductors such as AlGaAs / GaAs-based and AlGaSb / InAs-based semiconductors and other various semiconductors. The materials shown above are combinations in which the lattice constants are the same, but materials having different lattice constants and strain may also be used. Further, although only a structure in which the thin base layer is uniformly doped at about 100Å is shown, a planar doping or a non-uniform doping structure in which only a part is doped may be used. A thin base layer may have a thickness of 200 Å or less and a donor concentration of 10 ¹⁸ to 10 ²⁰ cm ^-3 , but it is preferable that the base layer has a thickness of 200 Å.
¹⁸ cm ^-3 , 10 ¹⁹ cm ^{-3 for} 50Å, for planar doping
10 ²⁰ cm ^-3 is suitable.

(Advantages of the Invention) In the semiconductor device of the present invention, since the thickness of the doped base is small, the scattering of electrons can be reduced, so that the current gain is greatly improved and the ultra-high speed operation becomes possible.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the present invention, FIG. 2 is a band structure diagram thereof, FIG. 3 is a schematic sectional view of a conventional HET, and FIG. 4 is a band diagram thereof. 1 ... Substrate, 2 ... Collector layer 3 ... Collector barrier layer, 4 ... Base layer 5 ... Emitter barrier layer, 6 ... Emitter layer 7 ... Collector electrode, 8 ... Base electrode 9 ... Emitter electrode , 10 …… bottom of conduction band 11 …… collector layer, 12 …… collector barrier layer 13 …… thin base layer, 14 …… undoped base layer 15 …… emitter barrier layer, 18 …… emitter layer Ef …… Fermi quasi Rank

Claims (1)

[Claims] 1. An emitter layer made of an n-type first semiconductor and a bottom of a conduction band having a higher energy than a bottom of a conduction band of the emitter layer and having a thickness at which electrons can tunnel and a low impurity concentration. An emitter barrier layer made of a second semiconductor, an undoped base layer made of a third semiconductor having a low impurity concentration and a bottom of a conduction band having an energy lower than that of a conduction band of the emitter barrier layer, and an undoped base layer A thin base layer of a high concentration n-type fourth semiconductor having a conduction band bottom with an energy lower than that of the conduction band, and an energy lower than or equal to the conduction band bottom of the undoped emitter layer; A collector barrier layer made of a fifth semiconductor having a low impurity concentration and having a bottom of a conduction band whose energy is higher than that of the conduction band of the thin base layer; and a collector layer made of an n-type sixth semiconductor. A semiconductor device comprising a layer structure.