JPH03266333A - Solid-state electron emitting device - Google Patents

Abstract

PURPOSE:To improve electron emitting efficiency by forming a heterojunction with different band gaps in a base region and injecting electrons to the base region from an emitter region and at the same time applying reverse bias to the base region and a collector region. CONSTITUTION:When a reverse bias is applied between a base and an emitter with an electric power source 10, electrons in the emitter layer 2 are injected into a first base region 3. The electrons cross a heterojunction between a second base region 4 and the region 3 while running on the base. At that time, the discontinuity ALPHAEC of the bands of the heterojunction is about 0.3eV and owing to the energy level difference, the electrons injected into the base become thermal electrons. The thermal electrons are accelerated further by the electric field between the base 4 and the collector 5 and spring out to vacuum. The collector layer 5 is thinned and Cs, etc., is deposited on the surface so as to make the work function of the surface small and increase the electron emitting amount.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state electron emitting device having an NPN transistor configuration.

[Conventional technology] As a conventional solid-state electron emitting device, J. Vac.

Scv, TechnoR, B4(1), 1986.
There is a device like the one introduced in P2O3. The energy band diagram of the NPN type transistor structure among these is as shown in FIG. In this configuration, electrons are injected from the emitter into the base region, and some of the electrons that pass through the extremely thin base become hot electrons in the electric field between the base and collector, increasing their kinetic energy and being emitted into the vacuum. This is how it was done.

[Problems to be Solved by the Invention] However, in the conventional example described above, the electric field between the base and the collector alone does not provide sufficient kinetic energy to the electrons, so it is difficult to extract the electrons into a vacuum. Furthermore, as a solution to the above problem, there is an energy band diagram as shown in FIG.

This method attempts to give kinetic energy to electrons by using the band discontinuity width ΔEc created at the junction by joining semiconductors with different band gaps between the emitter and base to form a heterojunction. Met. However, according to this configuration, since the heterojunction is formed within the depletion layer between the emitter and the base, ΔEc is smaller than ΔEc formed outside the depletion layer, which has the disadvantage of low electron emission efficiency. there were.

That is, an object of the present invention is to provide a solid-state electron emitting device that solves the above-mentioned problems.

[Means and effects for solving the problem] The present invention is characterized by an emitter region having a first band gap, a base region having the first band gap, and a base region having a first band gap. A base region having a narrow second bandgap forms a heterojunction within the same base region, and a collector region having an electron emitting surface is provided thereon, and electrons are injected from the emitter region into the base region. In addition, the solid state electron emitting device is configured to emit electrons from the electron emitting surface by applying a reverse bias to the base region and the collector region.

Further, the first band gap (first base region)
and the second band gap (second base region), AfxGa (+-xl As (where 0≦x≦1)
and GaAs+1xGa N -xi P (where 0
≦x≦1) and Si, GaAs and Ge, Si and Ge
, InAs and GaSb, ZnSe and GaAs,
A solid state electron emitting device using either ZnSe and Ge or CdS and InP is distinctive.

Further, a solid-state electron-emitting device in which a material having an alkali metal component is attached to the electron-emitting surface of the collector region, and a solid-state electron-emitting device in which a region with a higher concentration than the surrounding area is provided in the base region. It is also characterized by

That is, in the present invention, in an NPN transistor configuration, a heterojunction of P-type semiconductors with different band gaps is provided in a P-type semiconductor region corresponding to the base layer, and a heterojunction of P-type semiconductors with different band gaps is provided between the emitter and the emitter side in the base region. It is made up of a semiconductor.

This effect will be explained using the energy band diagram in FIG. According to this configuration, as shown in Fig. 2, the band discontinuity ΔEc in the conduction band is reliably formed at the position where the energy potential of electrons is the highest, so thermoelectrons are generated at the position where the potential energy is highest. can do. Furthermore, it has become possible to form the maximum band discontinuity ΔEc, and for this reason, it has become possible to impart greater kinetic energy to electrons than in the past, resulting in greater electron emission efficiency.

[Example] Hereinafter, the present invention will be specifically explained in detail with reference to Examples.

FIG. 1 is a cross-sectional configuration diagram showing an embodiment of the present invention using an N-type GaAs substrate. In this figure, 2 is an N-type AρxGa + -XAS layer that acts as an emitter.

Here, X is a constant representing the composition of the mixed crystal, and 0≦x≦1
has the value of 3 is a first base layer made of the same semiconductor as the emitter, 4 is a second base layer made of GaAs semiconductor, and 5 is a collector layer made of the same semiconductor as the second base. The collector layer contains Cs (cesium) and Cs-0 (
Cesium-oxygen) or Ba may also be attached.

6 is an ohmic contact electrode for the N-type semiconductor, 7
is an ohmic contact electrode for a P-type semiconductor.

8 is a P-type Be (beryllium) ion implantation region forming a contact to the base. 9. IO is a bias power supply. Each of layers 2 to 5 was formed by epitaxial growth using MBE, and had the following carrier concentration and thickness. That is, the emitter layer 2 is 5×1
0110l7'', the first base layer 3 is I x 1011
0l9", the second base layer 4 is 2 x 10"cm-3
The collector layer 5 is 3 x 1018 cm-3, the thickness of each layer is 7 x 10-' cm for the emitter layer 2, 5 x 10-' cm for the first base layer 3, and 8 x 10-' cm for the second base layer 4. -'cm, collector layer 5 is 5 x 10-
'cm' Note that the growth method, the carrier concentration of each layer, and the layer thickness are not limited to the above methods and values.

Next, the effect will be explained based on the energy band diagram when bias is applied in FIG. 2. When a forward bias is applied between the base and the emitter by the power supply 10, electrons in the emitter layer are injected into the first base region. The injected electrons cross the heterojunction between the second base region and the first base region while traveling through the base. At this time, the magnitude of band discontinuity ΔEc due to the heterojunction cannot be determined strictly, but ΔEC is about 0.3 eV for Aj'o3Gao, 7AS and GaAs, and this energy difference causes the electrons in the injected base to It becomes a thermoelectron. These thermoelectrons are further accelerated by the electric field between the base and the collector, and given enough kinetic energy, they can fly out into the vacuum. Here, when forming the collector layer 5, the thickness of the collector layer 5 is made as thin as possible so that electrons with large energy do not lose their energy due to scattering, etc., and the surface is coated with carbon dioxide.
By adding s (cesium), etc., the work function of the surface was lowered, and more electrons were emitted.

15 ■ Yu FIG. 3 shows a second embodiment of the invention.

The carrier concentration of the first base 3 and the second base 4 is I
The layer structure, layer thickness, and carrier concentration are the same as in Example 1 shown in FIG. 1, except that X 10''(cm-''). In this configuration, Be ions are implanted into P
+ region 12 was formed. By forming the depletion layer 11 as shown in the figure, the electric field formed between the base and collector of the region 12 is made higher than the electric field formed in other base regions. As a result, electron emission is now limited to only the region 12, making it possible to create a configuration in which electrons are emitted from a specific region. Furthermore, it has become possible to manufacture all of the present devices on the same plane, making it easy to integrate a large number of the present devices and to combine them with other devices.

[Effects of the Invention] As described above, according to the solid-state electron emitting device of the present invention, the following effects can be obtained.

■The base region of the NPN transistor has a structure with different band gaps (the band gap of the first base is smaller than the band gap of the second base), so the band gap is uniform between the base and emitter. The amount of carriers injected increases compared to the case where the base and the emitter have different band gaps, and the electrons injected into the base can be given a large amount of kinetic energy to become hot electrons. As a result, electron emission efficiency is significantly improved.

■Since electron-emitting devices can be manufactured using semiconductor materials, it is possible to integrate multiple electron-emitting devices on the same substrate or easily combine them with devices with other functions. .

As a result, integrated devices with new functions can be realized.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional configuration diagram of an apparatus showing a first embodiment of the present invention. FIG. 2 is an energy band diagram when a bias is applied to the first embodiment. FIG. 3 is a cross-sectional configuration diagram of an apparatus showing a second embodiment of the present invention. 4 and 5 are energy band diagrams in the conventional example. ■...N-type GaAs substrate 2 ・N-type ApXGa + + -xl As emitter layer 3 ・P-type Aj! xGa N -XI As first base layer 4...P-type GaAs second base layer 5...N-type GaAs collector layer 6.7...Ohmic contact electrode 8.12...
Be ion implantation layer 9.10... Power supply (bias) 11... Depletion layer

Claims (4)

[Claims] (1) an emitter region having a first bandgap;
a base region having the first bandgap; and a base region having the first bandgap.
A base region having a second bandgap narrower than the bandgap of A solid-state electron emitting device characterized by a structure in which electrons are injected and a reverse bias is applied to the base region and the collector region to emit electrons from the electron emitting surface. (2) As a combination of the first band gap and the second band gap, AlxGa_(_1_-_x_)As (where 0≦x≦
1) and GaAs, AlxGa_(_1_−_x_)P(
Here, 0≦x≦1) and Si, GaAs and Ge, Si and G
e, InAs and GaSb, ZnSe and GaAs, ZnS
The solid-state electron emitting device according to claim 1, characterized in that one of e and Ge, and CdS and InP is used. (3) The solid-state electron emitting device according to claim (1), wherein a material having an alkali metal component is attached to the electron emitting surface of the collector region. (4) The solid-state electron emitting device according to claim (1), wherein a region having a higher concentration than the surrounding area is provided in the base region.