JPH0831592B2 - High speed transistor - 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 Elec
tronics, 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 n-GaAs having a donor concentration of about 1 × 10 ¹⁸ cm ⁻³ , Al _0.2 Ga _0.8 As as the collector barrier layer 3 and Al _0.3 Ga _0.7 As as the emitter barrier layer 5, the band structure is shown in FIG. It demonstrates using.

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 first 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.
First of GaAs base layer and Al _0.2 Ga _0.8 As collector barrier layer
Since the energy difference at the bottom of the conduction band of is about 0.15 eV,
If the Fermi energy of the collector layer 10 is set lower than that of the base layer 4, the hot 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 the Problems) A semiconductor device of the present invention has a first conduction band and a second conduction band having a symmetry different from the first conduction band and a bottom of the second conduction band. Of an n-type first semiconductor having a lower energy than that of the bottom of the first conduction band, and a second layer of the emitter layer.
An emitter barrier layer made of a second semiconductor having a first and second conduction band bottoms having a higher energy than the conduction band bottoms thereof and having a thickness allowing electron tunneling and having a low impurity concentration; An n-type third semiconductor having a bottom of a second conduction band having a lower energy than the bottom of the second conduction band and a bottom of a first conduction band having a lower energy than the bottom of the second conduction band A base layer, a second conduction band bottom having a lower energy than the emitter layer second conduction band bottom and a higher energy than the base layer first conduction band bottom, and a base layer first It has a structure in which a collector barrier layer made of a fourth semiconductor having a low impurity concentration having a first conduction band having an energy higher than that of the bottom of the conduction band and a collector layer made of an n-type fifth semiconductor are stacked. It is characterized by becoming.

(Operation) In the transistor of the present invention, electrons injected into the base layer travel in the second conduction band and almost never fall into the first conduction band to become a base current, so that a high current gain is obtained. Therefore, ultra high speed operation becomes possible.

(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 15 denotes an n-type first band having a first conduction band and a second conduction band having a symmetry different from that of the first conduction band and having a bottom energy of the second conduction band lower than that of the first conduction band. The emitter layer 14 made of a semiconductor has a bottom of the first and second conduction bands having a higher energy than that of the second conduction band of the emitter layer 15, and has a thickness capable of tunneling electrons and a low impurity concentration. An emitter barrier layer 13 composed of a second semiconductor of the second semiconductor layer, and 13 having an energy lower than the bottom of the second conduction band of the emitter layer 15 and an energy lower than the bottom of the second conduction band. A base layer made of an n-type second semiconductor having a bottom of a first conduction band, 12 is the emitter layer
Second energy having a lower energy than the bottom of the second conduction band of 15 and higher energy than the bottom of the first conduction band of the base layer 13
Collector layer of a low impurity concentration fourth semiconductor having a second conduction band having a higher energy than the bottom of the conduction band of the base layer 13 and the bottom of the first conduction band of the base layer 13, 11 is an n-type fifth
Is a collector layer made of a 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. Reference numeral 16 is the bottom of the second conduction band having a symmetry different from that of the first conduction band.

As shown in FIG. 2, when a voltage is applied between the emitter and the base so that the bottom of the second conduction band of the emitter layer is higher than the bottoms of the second conduction band of the base layer and the collector barrier layer,
The electrons existing in the second conduction band of the emitter layer tunnel through the emitter barrier layer and are injected into the second conduction band of the base layer. At this time, electrons are not injected into the first conduction band of the base layer due to the difference in symmetry of the conduction band. The electrons injected into the second conduction band gain energy due to the energy difference at the bottom of the second conduction band between the emitter and base,
Most of this becomes hot electrons and passes through the base to reach the collector barrier layer. In the base layer, some of the injected electrons lose energy due to the plasmon scattering coupled to the lattice vibration as in the conventional HET.
It is almost never lower than the bottom of the conduction band. This is because the probability of scattering from the second conduction band having a large density of states to the first conduction band having a small state density is generally small. Therefore, it is very small that the electrons injected into the base fall to the bottom of the first conduction band and contribute to the base current. Electrons that have passed through the base layer in the second conduction band are
Like T, it enters the collector barrier layer, is accelerated by the electric field of the collector barrier layer, and moves to the collector layer.

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 layer 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 the crystal growth method, and the thickness is 0.5 μm and the donor concentration is 1 on the semi-insulating GaAs substrate 1.
× 10 ¹⁸ cm ^-3 n-GaAs collector layer 11, 3000 Å thickness, undoped Al _0.2 Ga _0.8 As collector barrier layer 12, 500 Å thickness
The n-GaAs base layer 13 has a donor concentration of 1 × 10 ¹⁸ cm ^-3 , the thickness is 50Å and the undoped AlAs emitter barrier layer 14 has a thickness of 0.
N-Al _0.4 Ga _0.6 As with a donor concentration of 1 × 10 ¹⁸ cm ^-3 at 5 μm
The emitter layer 15 was sequentially grown. 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 are Au.
It was formed by Ge / Au vapor deposition and alloying. In this structure, the first conduction band is the Γ point and the second conduction band is the L point. A current gain of 10 was obtained for this HET.

In the above examples, only AlGaAs-based semiconductor materials are shown, but it is clear that the present invention can be applied to semiconductors such as InGaAlAs / InP-based and AlGaSb / InAs-based semiconductors and other various semiconductors. Further, the materials shown above are combinations in which the lattice constants are substantially the same, but materials having different lattice constants and strain may also be used. Further, although only the Γ point and the L point are shown as the combination of the first conduction band and the second conduction band, the combination of the Γ point and the X point, the L point and the X point, or the like may be used.

(Effects of the Invention) According to the transistor of the present invention, since the scattering of electrons in the base layer is suppressed, the current gain is significantly 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 first conduction band, 11 ...
Collector layer, 12 ... Collector barrier layer, 13 ... Base layer, 14 ... Emitter barrier layer, 15 ... Emitter layer, 16 ...
… The bottom of the second conduction band, Ef …… Fermi level.

Claims (1)

[Claims] 1. The energy of the bottom of the second conduction band is lower than that of the bottom of the first conduction band, which has a first conduction band and a second conduction band having a symmetry different from that of the first conduction band. It has an emitter layer made of an n-type first semiconductor and bottoms of first and second conduction bands having higher energies than those of the second conduction band of the emitter layer, and has a thickness low enough to allow electrons to tunnel. An emitter barrier layer made of a second semiconductor having an impurity concentration, a bottom of a second conduction band having an energy lower than that of the second conduction band of the emitter layer, and an energy lower than that of the second conduction band. First of
A base layer made of an n-type third semiconductor having a bottom of a conduction band of n, and an energy lower than that of the second conduction band of the emitter layer and lower than that of the first conduction band of the base layer. And a collector barrier layer made of a low impurity concentration fourth semiconductor having a first conduction band having a higher energy than the bottom of the second conduction band having a high temperature and a bottom of the first conduction band of the base layer; A high-speed transistor having a structure in which a collector layer made of a fifth semiconductor is laminated.