JPH0325026B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is applicable to hot electron transistors (HET) or
THETA (Tunneling Hot Electron Transfer
This paper concerns improvements to a newly developed semiconductor device called an amplifier. Microelectronics is currently making remarkable progress, and in order to make further progress, research is being conducted to realize new semiconductor devices based on operating principles different from conventional transistors. Although the HET is a semiconductor device based on such a new operating principle, there is a strong desire to realize expected characteristics such as amplification factor. [Prior art] As shown in the potential diagram in Figure 2a, HET
It has three regions: an emitter, a base, and a collector, and potential barrier regions between the emitter and the base and between the base and the collector. For example, when a bias voltage V _BE that makes the emitter a negative potential with respect to the base is applied to this device at a temperature of 77 K, electrons will move through the emitter-base barrier φ _E
penetrates through the tunnel effect and enters the base area. These electrons have approximately the same energy, and due to the potential difference V _BE between the emitter and base, the electrons in the base region have approximately eV _BE with respect to the conduction band edge.
is at a higher energy level. The electrons move towards the collector in the hot electron state due to this energy, and the mean free path in this direction (X direction in the figure), which is the sum of collisions between electrons, between electrons and between lattices, and between electrons and impurity atoms, is le. When,
The probability that a hot electron will pass through the base region of length d _B is exp(-d _B /le). In this process, the energy of hot electrons decreases, but if the center value of the distribution is eV _BE −ΔE and the width is 2δ, then eV _BE −ΔE−δ is larger than the barrier height φ _C on the collector side with respect to the base region. At some point, most of the emitter current I _E crosses the barrier φ _C on the collector side and reaches the collector. Therefore, the characteristics of this semiconductor device, such as operating time and common base current amplification factor α=I _C /I _E (I _C is collector layer current), are largely controlled by the energy of hot electrons. A schematic side sectional view of a conventional example in which this HET is embodied as a semiconductor device is shown in FIG. 2b. In the figure, 21 is an n-type gallium arsenide (GaAs) substrate;
2 is an n-type GaAs collector layer, 23 is an aluminum gallium arsenide (AlGaAs) barrier layer, and 24 is an n-type
GaAs base layer, 26 is AlGaAs barrier layer, 27
is an n-type GaAs emitter layer, 28 is a collector electrode,
29 is a base electrode, and 30 is an emitter electrode. The collector layer 22 to emitter layer 27 of the semiconductor device of this conventional example are constructed as shown in the example below, for example.

[Problem that the invention seeks to solve]

In _{the Al} . Therefore, the energy distribution of electrons tunneling through the barrier layer 26 of the conventional example and reaching the base layer 24 tends to be lower than the Fermi level _EFE of the emitter layer 27, or the number of electrons tends to decrease. This effect increases as the thickness increases. In the conventional example, the barrier layer 26 between the emitter layer and the base is made of Al _0.3 Ga _0.7 As.
The barrier height φ _E for the GaAs emitter layer 27 is
It is about 0.22eV, and if the bias voltage V _BE is about 0.3V as mentioned earlier, as in Fig. 2a,
The energy level at the lower end of the conduction band of the barrier layer 26 is below the Fermi level _EFE of the emitter layer 27 near the interface with the base layer 24, forming a region that does not function as a potential barrier. Even in this region, the scattering or trapping due to deep levels cannot be avoided, which poses a problem when improving the characteristics of HET. For example, when the bias voltage V _BE =0.30V, if the Al composition ratio of the barrier layer ₂₆ is increased to Although it is possible to form a region with a level lower than that of _FE , the barrier layer 26
If the Al composition ratio X is increased, the number of deep levels will increase, and the objective will not be achieved. [Means for Solving the Problem] The problem is that an n-type GaAs collector layer 2 doped with silicon, a non-doped Al _0.3 Ga _0.7 As first barrier layer 3, and a silicon-doped n-type GaAs collector layer 2 are formed on an n-type GaAs substrate 1. The n-type GaAs base layer 4 doped with Al _0.3 Ga _0.7 As and the undoped GaAs layer 5
a second barrier layer 6 and a silicon-doped n-type
A collector electrode 8 made of gold germanium/gold is in contact with the back surface of the substrate 1, a base electrode 9 is in contact with the base layer 4, and an emitter electrode 1 is in contact with the emitter layer 7.
The solution is provided by a hot electron transistor according to the invention comprising 0. [Operation] According to the present invention, as shown in the potential diagram of FIG. 1a, the Al _0.3 Ga _0.7 As barrier layer 6 on the emitter side and
A non-doped GaAs layer 5 is provided between the GaAs base layers 4 to change the potential gradient due to the emitter bias V _BE between the Al _0.3 Ga _0.7 As barrier layer 6 and the GaAs
It will be shared with layer 5. Note that the thickness of these two layers is Al _0.3 when a predetermined emitter bias V _BE is applied to obtain high-energy hot electrons.
The lower end of the conduction band of the Ga _0.7 As barrier layer 6 is normally distributed so as to be equal to the Fermi level _EFE of the emitter layer 7 near the interface with the non-doped GaAs layer 5. With this structure, electrons that tunnel from the emitter layer 7 through the barrier layer 6 and enter the base layer 4 do not pass through the AlGaAs layer, which does not have a barrier effect, as in the conventional example, and the electrons due to the levels in the AlGaAs layer impact is minimized. [Example] The present invention will be specifically explained below with reference to an example whose schematic side sectional view is shown in FIG. 1b. In this example, the impurity concentration is, for example, 2×10 ¹⁸ cm
^-3 n-type GaAs substrate 1 by molecular beam epitaxial growth (MBE), etc.
Collector layer 2, AlGaAs barrier layer 3, n-type GaAs
Base layer 4, GaAs layer 5 according to the invention, AlGaAs
A barrier layer 6 and an n-type GaAs emitter layer 7 are epitaxially grown in sequence as shown in the example below.

〔Effect of the invention〕

As explained above, according to the present invention, the energy level and tunneling confirmation of hot electrons injected into the base region are increased, and characteristics improvements such as an improvement in the current amplification factor of HET are realized, and the development thereof is greatly advanced. effect can be obtained

[Brief explanation of drawings]

FIG. 1a is a potential diagram of a hot electron transistor according to the present invention, FIG. 1b is a schematic side sectional view showing an embodiment of the present invention, FIG. 2a is a potential diagram of a conventional hot electron transistor, and FIG. 2b is a schematic side sectional view showing a conventional example. In the figure, 1 is an n-type GaAs substrate, 2 is an n-type
GaAs collector layer, 3 AlGaAs barrier layer, 4 n-type GaAs base layer, 5 non-doped GaAs layer according to the present invention, 6 AlGaAs barrier layer, 7 n-type
In the GaAs emitter layer, 8 is a collector electrode, 9 is a base electrode, and 10 is an emitter electrode.

Claims (1)

[Claims] 1 On an n-type GaAs substrate 1, a silicon-doped n-type GaAs collector layer 2 and a non-doped Al _0.3
Ga _0.7 As first barrier layer 3, silicon-doped n-type GaAs base layer 4, and non-doped GaAs
A layer 5, a non-doped Al _0.3 Ga _0.7 As second barrier layer 6, and a silicon-doped n-type GaAs emitter layer 7 are successively grown to form a collector electrode made of gold germanium/gold and in contact with the back surface of the substrate 1. 8. A hot electron transistor comprising a base electrode 9 in contact with the base layer 4 and an emitter electrode 10 in contact with the emitter layer 7.