JPH07120512B2 - Transmissive photocathode and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission type photocathode made of a III-V group compound semiconductor and a method for producing the same.

[0002]

2. Description of the Related Art A GaAs transmission type photocathode is known as a transmission type photocathode that can be used in an image tube used under a low illuminance condition.
-73379 is known. This is shown in FIG. First, a GaAs substrate 1 is prepared, and an Al _X Ga _1-X As stop layer 2, a GaAs active layer 3 and an Al _X Ga _1-X As window layer 4 are deposited on the GaAs substrate 1 by liquid phase epitaxy. An antireflection SiO ₂ film 5 is deposited by a sputtering method or the like (see FIG. 3).
(See (a)). After that, the laminated structure shown in the figure is thermocompression-bonded to the glass window member 6 on the antireflection SiO ₂ film 5 side (FIG.
), The GaAs substrate 1 and the Al _x Ga ₁ -x As stop layer 2 are selectively etched, and the antireflection SiO ₂ film 5 and the Al _x Ga ₁ -x As window layer 4 are formed on the glass window material 6. It is possible to obtain a GaAs transmissive photocathode in which the GaAs active layer 3 is laminated (see FIG. 7C).

However, when the above-mentioned transmission type photocathode is used for an image tube or the like, problems such as a reduction in resolution and local image distortion occur. This means that dust may be present at the interface between the Al _X Ga _1-X As window layer 4 and the antireflection SiO ₂ film 5, or the surface of the Al _X Ga _1-X As window layer 4 may be damaged. Probable cause. Further, in the above-mentioned conventional technique, since the liquid phase growth method is used, it is conceivable that a wavy pattern is generated on the surface, which causes local image distortion.

The present invention has been made in view of the above-mentioned problems of the prior art, and when applied to an image tube, a transmission type photocathode capable of obtaining a high resolution and distortion-free image, and It is intended to provide a suitable manufacturing method.

[0005]

The first method according to the present invention
The manufacturing method is such that the etching stop layer and Al are not included on the substrate.
III-V compound semiconductor active layer, containing Al
III-V Group Compound Semiconductor Window Layer and III
Forming a laminated structure by depositing a protective layer of a group V compound semiconductor
First step of formation and thin Al oxide film on the surface of the window layer
The protective layer is selectively removed under the etching conditions for forming
The second step is to set the anti-reflection film on the surface of the Al oxide film.
The third step of forming and the laminated structure with an antireflection film
Adheres to the glass window material and selectively the substrate and stop layer
A fourth step of removing.

The second method of manufacturing a transmissive photocathode is as follows:
Etching stop layer on the substrate, Al-free III-
Active layer made of Group V compound semiconductor, Al-containing III-
Window layer made of Group V compound semiconductor, Al-free III
-Comprising a group V compound semiconductor and sufficiently thinner than the window layer
Layer, and this thin layer and selective etching II
A protective layer of a group IV compound semiconductor is deposited to form a laminated structure.
First step of forming and selectively removing the protective layer
The second step is to form an antireflection film on the surface of the thin layer.
The third step of forming and the laminated structure is protected by an antireflection film.
It adheres to the lath window material and selectively removes the substrate and stop layer.
And a fourth step of leaving.

The transmission type photocathode according to the present invention contains Al.
No active layer made of III-V compound semiconductor, Al
Window layer made of III-V compound semiconductor containing and reflection
The anti-reflection film is used to cover the laminated structure in which the anti-reflection film is sequentially deposited.
In the transmissive photocathode fixed to the window material made of lath, with the window layer
Between the antireflection film, Al is sufficiently thin compared to the window layer
A layer made of a III-V group compound semiconductor not included is interposed.
It is characterized by being.

[0008]

In the present invention, III containing no Al between the window layer and the antireflection film of the III-V group compound semiconductor containing Al is used.
-V group compound semiconductor or extremely thin layer of Al oxide film
, The interface between the window layer and the antireflection film has very good optical characteristics. Further, by using the vapor phase growth method in the above manufacturing process, the wavy pattern peculiar to the liquid phase growth method can be eliminated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and manufacturing method of the transmission type photocathode according to the first embodiment of the present invention will be described below with reference to the sectional views for each step of FIG.

First, a GaAs substrate 1 is prepared, and an Al _X Ga _1-X As stop layer 2, G is formed on the GaAs substrate 1 by vapor phase epitaxy.
The aAs active layer 3, the Al _x Ga ₁ -x As window layer 4 and the GaAs protective layer 7 are epitaxially grown (FIG. 1).
(See (a)). Here, regarding the Al _X Ga _{1 -X} As stop layer 2, the Al composition ratio X = 0.5, considering the selective etching of the GaAs substrate 1 by NH ₄ OH + H ₂ O ₂ .
The film thickness is about 2 μm. The thickness of the GaAs active layer 3 is set to about the diffusion length of electrons, which is about 2 μm. A
The composition ratio X and the film thickness of the l _X Ga _{1 -X} As window layer 4 determine the threshold value on the short wavelength side of the transmission type photocathode, and in the example, X =
The thickness is 0.5 and the thickness is about 2 μm. GaAs protective layer 7
Is a feature of the present invention, and may be finally removed in a later step to realize surface protection and contamination prevention. Therefore, it may be thin, and is about 0.8 μm in the embodiment.

Next, the above laminated structure is taken out from the epitaxial growth apparatus and the GaAs protective layer 7 is selectively etched. In this case, as an etchant, for example, N
When H ₄ OH + H ₂ O ₂ is used, the etching rate for GaAs is about 16 μm / min, so that the GaAs protective layer 7 is removed in a few seconds, and the surface of the Al _X Ga _{1 -X} As window layer 4 has a uniform thickness of several angstroms. The Al ₂ O ₃ film 8 having a thickness is automatically formed, and the etching is stopped (see FIG. 1B). Therefore, the washed surface is exposed by washing with water and drying, and the antireflection SiO ₂ film 5 is immediately deposited (see FIG. 7C). Then, it is thermocompression bonded to the glass window material (see FIG. 3D). Here, since the antireflection SiO ₂ film 5 is used for mediating adhesion and for antireflection, for example, a CVD film of about 0.2 μm may be used. Further, it is desirable that the glass window material has a small difference in coefficient of thermal expansion from GaAs.

Next, the GaAs substrate 1 is selectively removed using NH ₄ OH + H ₂ O ₂ etchant, and then Al _X Ga _1-X As stop layer 2 is formed using HF (hydrofluoric acid) or the like.
Is etched to obtain a transmission type photocathode in which the clean GaAs active layer 3 is exposed. In addition, Al _X Ga _1-X As
In order to automatically form the Al ₂ O ₃ film 8 on the surface of the window layer 4 and selectively remove the protective layer thereon, A
Any III-V compound semiconductor that does not contain 1 may be used.
Therefore, the protective layer 7 is formed of InGaAs, GaAs
P, GaAsSb, etc. can be substituted.

According to the embodiment, the interface where the Al ₂ O ₃ film 8 intervenes is extremely clean and flat, and the defect density can be suppressed to 10 defects / cm ² (conventionally 100 defects / cm ² ) . Servant
Therefore, the dust that tends to adhere to defects is extremely clean.
Is difficult to adhere to the flat Al ₂ O ₃ surface, so Al _X
The dust at the interface between the Ga _{1 -X} As window layer 4 and the antireflection SiO ₂ film 5 is reduced, and an image tube with an extremely high resolution is realized. Further, in the Al ₂ O ₃ film 8, since Al atoms are strongly connected to oxygen atoms, Al _X Ga _{1 -X} A
Al atoms in the s-window layer 4 will not diffuse into the antireflection SiO ₂ film 5 and deteriorate.

Next, the structure of the transmission type photocathode according to the second embodiment of the present invention and the manufacturing method thereof will be described with reference to the sectional views of each step of FIG.

First, a GaAs substrate 1 is prepared, and Al _x Ga ₁ -x As stop layer 2 and GaA are formed in the same manner as in the first embodiment.
The s active layer 3 and the Al _X Ga _1-X As window layer 4 are epitaxially grown. Then, an Al-free III-V group compound semiconductor, for example, a GaAs window layer 41 is formed on the Al _X Ga _1-X As window layer 4 to a thickness of several tens of angstroms. Since the GaAs window layer 41 absorbs incident light, it is desirable that it be as thin as possible. However, if it is too thin, it cannot serve as a stopper for etching the AlGaAs film on it, so a thickness of, for example, several tens of angstroms is desirable. An AlGaAs protective layer 71 is deposited on this, and a GaAs protective layer 72 is deposited thereon (FIG. 2).
(See (a)).

The laminated structure formed by the above-mentioned metal organic chemical vapor deposition method is taken out from the growth apparatus, and NH ₄ OH + H ₂ O ₂ is used as an etching solution to form the GaAs protective layer 7.
2 is removed, and then HF is used as an etchant to remove the AlGaAs protective layer 71. Then, the ultra-thin GaAs window layer 41 is exposed, and etching is automatically stopped (see FIG. 2B).

After washing with water and drying, the surface of the GaAs window layer 41 becomes extremely clean, and the oxide film is not naturally formed as in the case of using AlGaAs as the window layer. The body is set in a CVD device or the like to form an antireflection SiO ₂ film 5 having a thickness of about 0.2 μm (see FIG. 3C). Here, the material of the antireflection film may be not only SiO _2, but also Si ₃ N _4, etc., or may be a mixed film or a laminated film of SiO ₂ and SiN _x . After that, the laminated structure is thermocompression bonded to the glass window material 6 in the antireflection SiO ₂ film 5 in the same manner as in the first embodiment (see FIG. 3D), and the GaAs substrate 1 and Al _X Ga are deposited.
_{The 1-X} As stop layer 2 is etched to expose the GaAs active layer 3 (see FIG. 8E). As a result, the desired transmissive photocathode is obtained.

Also in the transmission type photocathode of the second embodiment, the Al _X Ga _{1 -X} As window layer 4 and the antireflection SiO ₂ film 5 are formed.
Ultra-thin GaAs window layer 41 where defects are less likely to occur at the interface of
Are intervened, the optical characteristics of the surface of the Al _x Ga ₁ -x As window layer 4 can be improved. Therefore, the resolution of the image tube can be improved. The III-V group compound semiconductor materials used in the above-described examples can also be combined in various ways, and are summarized as follows.

(First combination) Substrate: GaAs stop layer: Al (Ga) InAs active layer: Ga _1-x In _x As window layer: AlGaInAs ultrathin film: GaAs protective layer: AlGa (In) As (second combination) Combination) Substrate ... GaAs Stop Layer ... Al (Ga) AsSb Active Layer ... GaAs _y Sb _1-y Window Layer ... AlGaAsSb Ultrathin Film ... GaAs Protective Layer ... AlGaAs (Sb) (Third Combination) Substrate ... InP Stop Layer ... Al (Ga) InAsP active layer _{... in x Ga 1-x As} y P 1-y window layer ... AlInAsP very thin ... InP protective layer ... AlInP (fourth combination of) substrate ... GaAs stop layer ... Al (Ga) AsP active layer GaAs _y P _1-y window layer AlGaAsP ultrathin film GaAs protective layer Al (Ga) AsP

[0020]

As described above in detail, according to the present invention, a group III-V compound semiconductor containing no Al is present between the window layer and the antireflection film of the group III-V compound semiconductor containing Al.
Interposing an extremely thin layer of body or Al oxide film
Thus, the interface between the window layer and the antireflection film has extremely good optical characteristics. Further, by using the vapor phase growth method in the above manufacturing process, the wavy pattern peculiar to the liquid phase growth method can be eliminated. Therefore, when applied to an image tube, it is possible to provide a transmissive photocathode capable of obtaining a high-resolution and distortion-free image, and a manufacturing method suitable for this.

[Brief description of drawings]

1A to 1C are cross-sectional views of a transmission type photocathode according to a first embodiment for each manufacturing process.

2A to 2D are cross-sectional views of manufacturing steps of a transmission type photocathode according to a second embodiment.

3A to 3D are cross-sectional views of manufacturing steps of a transmission type photocathode according to a conventional example.

[Explanation of symbols]

1 ... GaAs substrate 2 ... Al _X Ga _1-X As stop layer 3 ... GaAs active layer 4 ... Al _X Ga _1-X As window layer 5 ... Antireflection SiO ₂ film 6 ... Glass window material 7, 71, 72, ... Protective layer 8 ... Al ₂ O ₃ film 41 ... GaAs window layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Kifun 1 1126, Nomachi, Hamamatsu City, Shizuoka Prefecture 1126 Hamamatsu Photonics Co., Ltd. (72) Masashi Ota 1126, 1126 Nomachi, Hamamatsu City, Shizuoka Prefecture Tonics Co., Ltd.

Claims (5)

[Claims] 1. An etching stopper layer, an active layer made of a III-V group compound semiconductor not containing Al, and an Al layer on a substrate.
And a window layer made of a III-V compound semiconductor containing
A first step of depositing a protective layer of a II-V compound semiconductor to form a laminated structure, and selectively removing the protective layer under etching conditions in which a thin Al oxide film is formed on the surface of the window layer. And a third step of forming an antireflection film on the surface of the Al oxide film, and fixing the laminated structure to the window material made of glass by the antireflection film, the substrate and the stop layer. And a fourth step of selectively removing the photocathode. 2. The method for manufacturing a transmissive photocathode according to claim 1, wherein the first step is performed by a vapor phase growth method. 3. A layered structure in which an active layer made of a III-V group compound semiconductor containing no Al, a window layer made of a III-V group compound semiconductor containing Al, and an antireflection film are sequentially deposited, and the antireflection layer is formed. In a transmissive photoelectric surface fixed to a glass window material with a film, a III-V group compound semiconductor that is sufficiently thin and does not contain Al is provided between the window layer and the antireflection film as compared with the window layer. A transmissive photocathode, characterized in that an intervening layer is interposed. 4. An etching stopper layer, an active layer made of a III-V group compound semiconductor not containing Al, and an Al layer on a substrate.
Window layer made of a III-V group compound semiconductor containing Al, a layer made of a III-V group compound semiconductor not containing Al, which is sufficiently thinner than the window layer, and a III-V group capable of selective etching with the thin layer A first step of depositing a protective layer of a compound semiconductor to form a laminated structure, a second step of selectively removing the protective layer, and a third step of forming an antireflection film on the surface of the thin layer. And a fourth step of fixing the laminated structure to a window member made of glass with the antireflection film and selectively removing the substrate and the stop layer. Manufacturing method. 5. The method of manufacturing a transmissive photocathode according to claim 4, wherein the first step is performed by a vapor phase growth method.