JP2000021296A - Semiconductor photo-electric cathode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor photo-electric cathode capable of increasing quantum efficiency by forming a semiconductor optical absorption layer with high crystallinity. SOLUTION: This semiconductor photo-electric cathode has a semiconductor optical absorption layer 3 formed on a buffer layer 2 on a substrate 1 and for converting incident light into an electron; and an alkali metal-containing layer 5 formed on the semiconductor optical absorption layer 3 and for emitting the electron into vacuum. The buffer layer 2 has first and second amorphous semiconductor layers 2a, 2c and a single crystal semiconductor layer 2b locating between the first and the second amorphous semiconductor layers 2a, 2c. Since the buffer layer 2 has such constitution, the crystallinity of the semiconductor optical absorption layer 3 formed on the buffer layer 2 is improved, the life of an electron existing in the semiconductor optical absorption layer 3 is lengthened, and quantum efficiency is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor photocathode which converts incident light into electrons and outputs the electrons.

[0002]

2. Description of the Related Art A conventional semiconductor photocathode is described, for example, in Japanese Patent Application Laid-Open No. 62-133633. The semiconductor photocathode is made of a compound semiconductor, converts incident light into electrons, and outputs the electrons.

[0003]

However, the quantum efficiency is not yet sufficient, and further improvement is required. The quantum efficiency is proportional to the degree to which electrons generated in the semiconductor light absorbing layer in response to the incidence of light are released into vacuum.
If a factor such as a defect such as an electron capture or recombination exists in the light absorbing layer, the lifetime of the electrons generated in the light absorbing layer is shortened, and the diffusion length is shortened. Therefore, the ratio of electrons that can reach the surface of the photocathode from the light absorbing layer decreases, and the quantum efficiency decreases. The present invention has been made in view of such a problem, and an object of the present invention is to provide a light absorbing layer having higher crystallinity and a semiconductor photocathode capable of increasing quantum efficiency.

[0004]

In order to solve the above problems, a semiconductor photocathode according to the present invention comprises a semiconductor light absorbing layer provided on a buffer layer interposed between the semiconductor photocathode and converting incident light into electrons. And a semiconductor photocathode provided on the semiconductor light absorption layer and provided with an alkali metal-containing layer for emitting electrons into a vacuum, wherein the buffer layer is composed of first and second amorphous semiconductor layers, and first and second amorphous semiconductor layers. A single crystal semiconductor layer interposed between the amorphous semiconductor layers.

In the present semiconductor photocathode, since the buffer layer has the above structure, the crystallinity of the semiconductor light absorbing layer formed thereon can be improved. The alkali metal-containing layer is provided on the semiconductor light absorption layer and emits electrons into a vacuum, and preferably contains at least one of K, Rb, and Cs, which are alkali metals.

It is preferable that the first and second amorphous semiconductor layers and the single crystal semiconductor layer are made of a GaN or AlN compound semiconductor, the substrate is made of sapphire, and the semiconductor light absorbing layer is made of GaN. In
The crystallinity of the semiconductor light absorbing layer can be further improved. Note that GaAs is provided between the buffer layer and the semiconductor light absorbing layer.
An 1N layer may be further provided.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a semiconductor photocathode according to an embodiment will be described. The same reference numerals are used for the same elements or elements having the same functions, and overlapping descriptions are omitted.

FIG. 1 is a sectional view of a semiconductor photocathode according to an embodiment. The present semiconductor photocathode includes a substrate 1, a buffer layer 2 (2a to 2c) on the substrate 1, a semiconductor light absorbing layer 3 on the buffer layer 2, and an alkali metal-containing layer 5 formed on the semiconductor light absorbing layer 3. ing. The semiconductor light absorbing layer 3
A conventionally known high-concentration electron transport layer or the like which forms a heterojunction with the high-concentration layer or the alkali metal-containing layer 5 may be provided. Hereinafter, the present photocathode will be described as a type in which light is incident from the surface side, that is, a reflective semiconductor photocathode.

When light enters the light absorption layer 3, a hole / electron pair is generated in the layer 3 in response to the light. The electrons diffuse in the layer 3 and travel toward the alkali metal-containing layer 5. The alkali metal-containing layer 5 lowers the surface work function of the light absorbing layer 3 and easily emits generated electrons into vacuum. The emitted electrons are applied to an anode 101 (FIG. 7) provided outside the photocathode.
See).

Since the crystallinity of the light absorbing layer 3 depends on the crystallinity of the buffer layer 2 as the base, the quantum efficiency can be increased by improving the crystallinity.

The buffer layer 2 includes a first amorphous semiconductor layer 2a on the substrate 1, a single crystal semiconductor layer 2b on the first amorphous semiconductor layer 2a, and a second amorphous semiconductor layer 2c on the single crystal semiconductor layer 2b. .

Next, these materials will be described. In the first embodiment, sapphire (Al ₂ O ₃ )
P-type GaN (more than the electron diffusion length and several tens nm to several μm in thickness, impurity concentration is uniform in the depth direction and 1 × 10 ¹⁶ to 10 ¹⁹ / cm ³ ) as the semiconductor light absorbing layer 3, Cs—O is used as the alkali metal-containing layer 5. Further, the alkali metal-containing layer 5 contains at least one of K, Rb and Cs, which are alkali metals. As the alkali metal-containing layer 5, Cs-O is used instead of Cs-O.
I, Cs-Te, Cs-Sb, Sb-Rb-Cs or S
b-K-Cs can also be used. Note that Mg or Zn can be used as the p-type dopant.

In the first embodiment, GaN (10 to 50 nm in thickness) is used as the first amorphous semiconductor layer 2a, GaN (several μm in thickness) is used as the single crystal semiconductor layer 2b, and GaN is used as the second amorphous semiconductor layer 2c. Thickness 10-50
nm).

The second mode is the same as the first mode, except that the impurity concentration of the p-type GaN semiconductor light-absorbing layer 3 increases in the depth direction from the surface side and is distributed in an inclined manner. From several tens to 100 nm.

In a third embodiment, a p-type GaAlN layer having a constant composition in the thickness direction or a p-type GaAlN layer having a constant composition in the thickness direction is provided between the second amorphous semiconductor layer 2c and the light absorbing layer 3 in the first or second embodiment. P-type GaAlN graded layer 2d (thickness 10 nm or more, p-type impurity
(Distributed in a region exceeding 0 nm).
This structure is shown in FIG.

In a fourth embodiment, a GaN layer other than the light absorbing layer 3 in any one of the first to third embodiments is formed by A
This is replaced with an 1N layer. Note that in any one of the first to third embodiments, a part of the GaN layer,
For example, only the material of the amorphous semiconductor layer 2a may be replaced with an AlN layer. When all of the GaN layers other than the light absorption layer 3 are replaced with AlN layers, they operate as a transmission type photocathode.

As described above, the semiconductor photocathode includes a semiconductor light absorbing layer 3 provided on the buffer layer 2 interposed between the substrate 1 and the semiconductor light absorbing layer 3 for converting incident light into electrons. In a semiconductor photocathode provided with an alkali metal-containing layer 5 for emitting electrons into a vacuum, the buffer layer 2 includes first and second amorphous semiconductor layers 2a and 2c, and first and second amorphous semiconductor layers 2a and 2c. A single-crystal semiconductor layer 2b interposed between the amorphous semiconductor layers 2a and 2c. In the present semiconductor photocathode, since the buffer layer 2 has the above configuration, the crystallinity of the semiconductor light absorbing layer 3 formed thereon can be improved. Thereby, the lifetime of the electrons therein can be improved, and the quantum efficiency can be increased.

In the semiconductor photocathode, the first and second amorphous semiconductor layers 2a and 2c and the single crystal semiconductor layer 2b are made of a GaN or AlN compound semiconductor, the substrate 1 is made of sapphire, The absorption layer 3 is made of GaN. In this case, the semiconductor light absorbing layer 3
Can be further improved in crystallinity.

Next, a method of manufacturing the semiconductor photocathode according to the above embodiment will be described.

In the following description, a semiconductor layer is formed by MOCVD (metal organic chemical vapor deposition),
Alternatively, an HVPE (halogen vapor phase epitaxy) method is used. When a semiconductor layer is formed, these forming methods are used. When a GaN layer is formed, TMG (trimethylgallium) and ammonia gas are used as raw materials.
When a layer is formed, TMAl (trimethylaluminum) and ammonia gas are used, and when GaAlN is formed, TMG, TMAl and ammonia gas are used. In the case where a p-type impurity is added so as to have a concentration distribution in the thickness direction of the semiconductor layer, the p-type impurity is added to the layer while varying the amount of the p-type impurity during the growth of the semiconductor layer. When forming a uniform p-type impurity concentration distribution in the thickness direction of the semiconductor layer, a certain ratio of p-type impurities is added to the inside of the layer during the growth of the semiconductor layer.

FIG. 2 is a sectional view showing the first intermediate member of the semiconductor photocathode. First, the substrate 1 is prepared, and the first amorphous semiconductor layer 2a is formed on the substrate 1. Growth temperature is 500 ~
600 ° C.

FIG. 3 is a sectional view showing a second intermediate member of the semiconductor photocathode. Thereafter, a single-crystal semiconductor layer 2b is formed on the first amorphous semiconductor layer 2a. The growth temperature is 700 ~
1100 ° C.

FIG. 4 is a sectional view showing a third intermediate member of the semiconductor photocathode. Next, a second amorphous semiconductor layer 2c is formed over the single crystal semiconductor layer 2b. The growth temperature is 500-60
0 ° C.

FIG. 5 is a sectional view showing a fourth intermediate of the semiconductor photocathode. Next, the semiconductor light absorption layer 3 is formed on the second amorphous semiconductor layer 2c. Finally, an alkali metal-containing layer 5 is formed thereon by a vapor deposition method or the like, and is activated to complete the semiconductor photocathode shown in FIG.

As described above, according to the photocathode according to the above embodiment, the light absorption layer 3 having high crystallinity can be provided by using the buffer layer 2, so that the quantum efficiency can be reduced. Can be increased.

Next, the phototube 10 using the semiconductor photocathode 100a will be described.

FIG. 7 is a perspective view of the photoelectric tube 10. The photoelectric tube 10 includes a vacuum container 102. Vacuum container 10
Reference numeral 2 denotes a hollow cylindrical glass container having a pressure of about 10 ^-8.
The inside is kept in a high vacuum of Torr.

The photoelectric tube 10 includes a cathode 100 and an anode 101 which are disposed inside a vacuum vessel 102 so as to face each other.
The cathode 100 includes a semiconductor photocathode 100a and a support plate 100b fixed thereto. The surface of the support plate 100b is arranged parallel to the tube axis direction of the vacuum vessel 102, and the exposed surface side of the support plate 100b directly faces the side wall of the vacuum vessel 102.

The cathode 100 is supported in the tube axis direction by a flat metal support 105 extending perpendicular to the tube axis direction and a lead pin 103 fixed thereto. Note that the support plate 100b and the support base 105 are formed from a metal such as Mo. The lead pin 103 extends from the bottom of the cathode 100, penetrates the bottom of the vacuum vessel 102, is connected to a cathode output terminal of an external power supply, and applies a potential lower than the potential of the anode 101 to the semiconductor photocathode 100a and the support plate 100b. Have given.

The anode 101 is disposed to face the alkali metal-containing layer side of the semiconductor photocathode 100a. The anode 101 is a metal electrode formed in a rectangular frame shape, and is supported by a metal lead pin 104. The lead pin 104 extends from the bottom of the anode 101, penetrates the bottom of the vacuum vessel 102, is connected to an anode output terminal of an external power supply via an external ammeter, and the anode 101 has a potential higher than the potential of the cathode 100. Is given. Note that the lead pins 103 and 104 are made of Kovar metal.

When the above-described voltage is applied between the cathode 100 and the anode 101 from the external power supply via the lead pins 103 and 104, an electric field from the anode 101 to the cathode 100 is generated. The light transmitted through the vacuum vessel 102 is the semiconductor photocathode 10
When the light enters the inside of Oa, the correspondingly generated electrons are emitted into a vacuum as described above. The emitted electrons are accelerated by the electric field between the anode 101 and the cathode 100, fly, are collected by the anode 101, and detected by an external ammeter.

[0032]

As described above, according to the photocathode of the present invention, a semiconductor light absorbing layer having high crystallinity can be provided by using a buffer layer having two amorphous semiconductor layers. Therefore, the quantum efficiency can be increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semiconductor photocathode according to an embodiment.

FIG. 2 is a sectional view showing a semiconductor photocathode intermediate.

FIG. 3 is a sectional view showing a semiconductor photocathode intermediate.

FIG. 4 is a sectional view showing a semiconductor photocathode intermediate.

FIG. 5 is a sectional view showing a semiconductor photocathode intermediate.

FIG. 6 is a cross-sectional view of another semiconductor photocathode according to the embodiment.

FIG. 7 is a perspective view of a photoelectric tube.

[Explanation of symbols]

2 ... buffer layer, 2a ... first amorphous semiconductor layer,
2nd amorphous semiconductor layer 2c, 2b ... single crystal semiconductor layer, 3 ... semiconductor light absorption layer, 5 ... alkali metal containing layer.

Claims (3)

[Claims] A semiconductor light absorbing layer provided on a buffer layer interposed between the semiconductor light absorbing layer and a substrate to convert incident light into electrons;
A semiconductor photocathode provided on the semiconductor light-absorbing layer and comprising an alkali metal-containing layer for emitting the electrons into a vacuum, wherein the buffer layer comprises first and second amorphous semiconductor layers; 2. A semiconductor photocathode comprising: a single crystal semiconductor layer interposed between two amorphous semiconductor layers. 2. The semiconductor device according to claim 1, wherein the first and second amorphous semiconductor layers and the single crystal semiconductor layer are made of a GaN-based or AlN-based compound semiconductor, the substrate is made of sapphire, and the semiconductor light absorbing layer is made of GaN. The semiconductor photocathode according to claim 1, wherein 3. The semiconductor photocathode according to claim 2, wherein said buffer layer further comprises a GaAlN layer between said buffer layer and said semiconductor light absorbing layer.