JPS63204760A - Hot electron device - Google Patents

Abstract

PURPOSE:To obtain three terminal devices having characteristics of high mutual conductance and speed switching by possessing a semiconductor region where avalanche amplification is induced and a means through which electrons having high energy or holes are injected into an avalanche amplification region. CONSTITUTION:When a relatively low voltage V is impressed under a gate voltage VG of zero, a few of carriers are injected into potential transient part regions of junction parts respectively and are accelerated by electric fields of the transient part regions and then act as an element current. As it is what is called a reverse direction current, its current value IS is extremely small. With the enlargement of electric fields at the potential transient part regions, energy that is obtained by a small number of the carriers from the electric fields increases as well. If energy comes to the extent of of a semiconductor energy gap, it excites electrons of a valence band at a conduction band and then the electrons and holes are generated. As the newly generated electrons and holes are again accelerated by the electric fields and similar processes are repeated, the electric current rapidly increases. The rise time of this current is exceedingly acute because the above phenomenon exhibits breakdown characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a three-terminal device having high mutual conductance characteristics and high-speed switching characteristics.

[Conventional technology]

Many semiconductor three-terminal devices have been proposed to date. Although there are various device structures, the principle of operation is basically the same. The first conceptual diagram to explain the operating principle is
As shown in the figure. The amount of water (current flow) flowing into the pipe is controlled by changing the cross-sectional area S of a gate installed in the middle of the pipe.

The gate cross section yS is adjusted by external input (gate voltage V.). The greater the change in water volume with a small external input, and the greater the water flow rate, the better performance can be expected as a high-speed device. Stimulus, high transconductance (g=aI/aVo) characteristics, and high velocity characteristics are important.

Conventional semiconductor 3-terminal devices can be roughly divided into two types:
It is classified into bipolar type and FET type.

In the bipolar type, the current flow is controlled by the barrier height, so the current I changes exponentially with respect to the control voltage v0. This is the reason why Bibo Type 2 has high g characteristics. However, carriers injected into the base move within the base due to thermal diffusion, so the moving speed is slower than the drift speed due to the electric field. On the other hand, FE
In the T-type, the current flow is rate-limited by the charge induced in the capacitance, and the current I changes proportionally to the voltage V. Therefore, compared to the bipolar type, gI! 1 has an inherently small drawback.

[Problem that the invention seeks to solve]

In view of the above drawbacks, the object of the present invention is to provide a three-terminal device with high transconductance characteristics and high speed switching characteristics.

[Means for solving problems]

A major feature of the present invention is that high-energy electrons or holes are injected into a semiconductor region that causes avalanche amplification, and this is used as a trigger to induce avalanche amplification. The operating principle is completely different from conventional technology. According to the concept of operation explained in FIG. 1, the production of water within the syvibe due to the application of an external input corresponds to a rapid increase in the amount of water. As will be described later, since this phenomenon is a breakdown characteristic, the current change is extremely large. Therefore, high g-force characteristics can be achieved. Furthermore, since the carriers are accelerated by the electric field in the avalanche amplification region, their moving speed is also high.

〔Example〕

(First Embodiment) FIG. 2 shows a first embodiment of the present invention. 1 is a P-type semiconductor, 2 is an N-type semiconductor, 3 is a tunnel film made of an insulator or semiconductor, and 4 is a gate electrode. The thickness of the tunnel film must be made thin enough to allow electrons or holes to move from the gate electrode 4 to the boundary region of the 9 PN junction by tunneling.

The element voltage V is positive in the direction opposite to the PN junction, and the gate voltage vG is positive in the direction in which the gate ionization potential is negative with respect to the ground. Figure 3 (a), (b) + (c)
shows a schematic diagram of the energy band in the X direction.

FIG. 3(a) shows the case where neither ■ nor vG is applied. In order to maintain the carrier distribution of the PN junction in a thermal equilibrium state, a potential transient region (depletion layer) is generated at the PN junction. When a relatively low voltage V is applied to (b),
[C] shows the case where a relatively high voltage V is applied. FIG. 4 schematically shows the relationship between the element current and the element voltage V. The operating principle will be explained below with reference to FIGS. 3 and 4.

First, consider the case where a relatively low voltage V is applied when vo is zero (FIG. 3(b)). Minority carriers (electrons for P type, holes for N type) are injected into the potential transition region of the junction, are accelerated by the electric field in the transition region, and become a device current. However, since it is a so-called reverse current, its current value Is is extremely small. (2) Potential transition region When the electric field is increased, the energy that minority carriers obtain from the electric field also increases. When this energy reaches approximately the energy gap Δ of the semiconductor, electrons in the valence band are excited to the conduction band, producing electrons and holes (FIG. 3(C)). The newly generated electrons and holes are again accelerated by the electric field and the same process is repeated, resulting in a sudden increase in current (Figure 4). This is called the avalanche amplification phenomenon. Therefore, the critical voltage■. The current increases rapidly after . Since this phenomenon is a breakdown characteristic, the rise of this current is extremely sharp.

FIGS. 5(a) and 5(b) show schematic diagrams of energy bands in two directions at the center of the potential transient region.

The gate electrode was made of metal. FIG. 5(a) shows the thermal equilibrium state, and FIG. 5(b) shows the case when vG is applied. When vG is applied, high-energy electrons (hot electrons) are injected into the junction by a tunneling phenomenon through the tunnel film 3 (FIG. 5(b)). Since the energy of this electron is higher than that of the electron injected into the PN semiconductor, it becomes a trigger for excitation of the electron to the conduction band. Therefore, ■o'
t - critical voltage V lower than the critical voltage VC when no application is applied
At c1, the current begins to flow rapidly (see Figure 4).

Here, as the power supply voltage, the voltage V between vcl and vc
Consider the case where A is applied. When vG is not applied, the element current is an extremely small value I8, but when V is applied, it becomes a large value, and the change in element current Δ■ (output current)
can be made extremely large. Therefore, a large mutual conductance g1 can be achieved. Furthermore, since the carriers are accelerated by the electric field in the potential transition region, their speed can be greater than the thermal diffusion speed. The above operation can be similarly achieved when hot holes are injected from the gate electrode.

As a semiconductor forming a PN junction, Si T GaA
It can be anything, such as s. In order to reduce power consumption, narrow energy gap semiconductors such as InAs, InSb, and GaSb are suitable. This is a critical voltage ■ because the energy gap Δ is small. This is because it is possible to make it smaller. As a tunnel film, Sigh
, an insulator such as Al2O5, or a semiconductor such as AlGaAs. The gate electrode is formed of a metal such as Au or AA, or a semiconductor such as Sin GaAs.

Next, specific materials, characteristics, etc. will be explained.

(1) Specific materials The P-type semiconductor 1 and the N-type semiconductor 2 are as follows.

Basically, any semiconductor may be used as long as it can form a PN junction. Ink is used for avalanche photodiodes.

GaAs + Ge, etc., and other semiconductors that have not been realized as photodiodes due to the wavelength of light, Si
, SiC, etc., as well as InAs, InSb, Garb, and GaInAs, which are expected to reduce the operating voltage and power consumption of this device because they cause electron avalanche amplification in low electric fields.
, pbTe, CdTe, and other narrow energy gap semiconductors.

The tunnel membrane 3 has the following structure.

It is used to create an energy barrier for the depletion layer formed in the junction region between the P-type semiconductor (1) and the N-type semiconductor (2), and is divided into two types: insulators and semiconductors. As an insulator, SiO! , SiO+SiN+Alto
n, etc., and also compounds of semiconductors 1 and 2 (formation methods include natural oxidation, anodic oxidation, plasma oxidation, etc.). As a semiconductor, a semiconductor having a lower electron affinity than the semiconductors 1 and 2, for example, if the semiconductor 1.2 is Si, it is Sin, InP, etc., and the semiconductors 1 and 2 are GaIn.
For As, GaAs.

Examples include AlGaAs and AA'As.

The gate electrode 4 is a metal such as Au AJI MOL In or a degenerate semiconductor.

(2) Regarding the thickness of the tunnel film 3.

Since it is necessary to tunnel hot electrons (holes) from the gate electrode 4 into the depletion layer formed in the junction region between the P-type semiconductor 1 and the N-type semiconductor 2, the thickness of the tunnel film 3 is large enough to accommodate electrons or holes. It is necessary to make it extremely thin so that the tunneling phenomenon becomes noticeable. Numerically, it would be sufficient if it was less than the teacher.〇 (3) Performance g, ratio M of the number of electrons or holes generated by avalanche amplification to the number of hot electrons (holes) injected with respect to 11 is ideally Mccl/(1(V/V
c)") Here, V is the reverse voltage applied to the PN junction, vc is the critical voltage that causes avalanche amplification, and n (<1) is a constant. From this, the element current factor for the injection current factor 0 is Find the ratio of I/Io ”M” 1/(1(V/Vc)”
). Therefore, ■=■. Ideally, I/Io would be infinite. Also, if the gate voltage is vo, the mutual conductance g1 is g, :aI/ava, so gm ideally has an infinite size.In reality, the voltage drop due to parasitic resistance or the voltage drop at the edge of the junction M is a finite value because the electric field is no longer uniform in the depletion layer due to concentration of the electric field around the depletion layer and is restricted.
, the rise of the current near Vc is slightly slower. The degree of this slowing largely depends on the structure, material, etc. of the device, so it is difficult to quantitatively evaluate it. However, compared to conventional three-terminal devices, g! , l can be expected.

About speed.

Electrons or holes basically move at a saturation velocity V in a high electric field. (Due to the time required for avalanche amplification, the average velocity will be less than the saturation velocity.

However, the order remains unchanged. ) Therefore, if the length of the depletion layer is L, the transit time t of electrons (holes) in the depletion layer is t~L/v.

becomes. ■ does not depend much on the type of semiconductor, 107
If o L = 10 nm, which is on the order of cm/s, t
=o, ip3. This speed is about one to two orders of magnitude faster than conventional three-terminal devices.

(Second Embodiment) FIG. 6 shows a second embodiment of the present invention. The gate electrode 4 is made of a metal such as Au or AJ and has a structure in which it is brought into direct contact with the junction. Schematic diagrams of energy bands in two directions at the center of the potential transition region are shown in FIGS. 7(a) and 7(b). A Schottky barrier is formed at the interface between the junction boundary region and the gate electrode. When vo is applied, hot electrons or hot holes are injected into the junction by tunneling through the Schottky barrier. The operating principle, functions, etc. are the same as in the first embodiment, except for the means for injecting hot electrons and hot holes.

Next, specific materials will be explained.

The material of the P-type semiconductor 1 and the N-type semiconductor 2 is the first metal. For example, if 1.2 is GaAs, it is Au.

AJ, Ti/AJ, WS i Ta, etc.
If 1 and 2 are InSb, Ag*Au, etc. can be mentioned.

There is a slight difference in performance between tunnel injection and Schottky injection, but there is essentially no difference.

(Third Embodiment) FIG. 8 shows a third embodiment of the present invention. The avalanche amplification region consists of a superlattice 6 consisting of a semiconductor 5 and a semiconductor 6 having a small electron affinity, and an N-type semiconductor 7,
It is formed by the structure sandwiched by 8. FIG. 9 shows a schematic diagram of the energy band in the X direction when a voltage close to the critical voltage is applied.

The potential difference generated at the interface between semiconductors 5 and 6 in the superlattice portion accelerates carriers, causing avalanche amplification. As a means for injecting hot electrons or hot holes, tunnel injection through the tunnel film or Schottky barrier described in the first and second embodiments is used.

As the semiconductor 5, GaAa, InAs, GaIn,
AS, semiconductor 6 is AJxGa 1-, As
etc. By locally varying the value of X so as to form a tilted band structure, the electric field in the semiconductor 6 can be made zero when a voltage close to the critical voltage is applied.

If a gate electrode is formed in this portion, hot electrons or hot holes can be uniformly injected over this region. 7 and 8 are semiconductors (P type.

It may be of N type (through type shown in FIG. 8) and may be the same as the semiconductor 5 described above. Therefore, the injection efficiency can be increased compared to the first embodiment, and furthermore, high gfl can be achieved. The operating principle, functions, etc. are the same as in the first embodiment.

〔Effect of the invention〕

As explained above, the hot electron device according to the present invention has high-speed characteristics and high mutual conductance characteristics, and is widely applied as a basic three-terminal device such as an ultra-high-speed LSI or an ultra-high frequency amplifier circuit.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram explaining the basic operating principle of a conventional semiconductor three-terminal device. FIG. 2 is a diagram showing a first embodiment of a hot electron device according to the present invention and explaining its basic structure. The figure is a schematic diagram of the energy band in the X direction of the hot electron device of the first example, FIG. 4 is a schematic diagram of the device current/device voltage characteristics of the hot electron device of the first example, and FIG. is a schematic diagram of energy bands in two directions at the center of the potential transition region of the hot electron device of the first embodiment, and FIG. 6 shows the second embodiment of the hot electron device according to the present invention and explains its basic structure. FIG. 7 is a schematic diagram of energy bands in two directions at the center of the potential transition region of the hot electron device according to the second embodiment, and FIG. 8 is a diagram showing the third embodiment of the hot electron device according to the present invention. FIG. 9 is a schematic diagram of the energy band in the X direction of the hot electron device of the third embodiment. 1... P-type semiconductor 2... N-type semiconductor 3... Tunnel film 4... Gate electrode 5... Semiconductor 6... Semiconductor with electron affinity υ smaller than the electron affinity of semiconductor 5 7. 8...Semiconductor (P type, N type) Figure 1 Figure 2 Figure 3

Claims (5)

[Claims] (1) A hot electron device comprising a semiconductor region that causes avalanche amplification and means for injecting high-energy electrons or holes into the avalanche amplification region. (2) The hot electron device according to claim 1, wherein the injection means is performed by tunneling using an insulator or a semiconductor as a barrier. (3) The hot electron device according to claim 1, wherein the injection means is performed by a tunneling phenomenon using a Schottky barrier between a metal and a semiconductor. (4) The hot electron device according to claim 1, wherein the avalanche amplification region is constituted by a depletion layer of a PN semiconductor junction. (5) The hot electron device according to claim 1, wherein the avalanche amplification region is constructed of a superlattice of semiconductors having different electron affinities.