JPH05282991A - Photoelectron emission plane - Google Patents

Abstract

PURPOSE:To realize a sensitive photoelectron emission plane having a simple structure by producing electron holes by incident light and emitting electrons into the external vacuum atmosphere. CONSTITUTION:When light is applied on the boundary between an internal anode 21 and a semiconductor 11 from the outside, electron holes are excited within the internal anode 21. The hot electron holes pass through a barrier to be implanted into the semiconductor 11. Electrons are implanted thereinto from an internal cathode 22. An electric field is applied to the semiconductor 11 by electrodes 21, 22 provided on both surfaces thereof and a power supply 43, and the implanted electrons are transferred to the internal anode 21, the part of which is emitted into a vacuum atmosphere to be caught by an external anode 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is sensitive to incident light,
The present invention relates to a photoemission surface that emits electrons into an external vacuum.

[0002]

2. Description of the Related Art Conventionally, a photoelectron emitting surface composed of an alkali metal or antimony has been known and used for a photomultiplier tube or the like. Further, a photoelectron emission surface composed of a compound semiconductor such as GaAs or InP is also known. In each of these conventional photoelectron emitting surfaces, photoelectrons are directly generated by incident light and are emitted into an external vacuum.

[0003]

All of the conventional photoelectron emitting surfaces have insufficient sensitivity, and therefore various measures have been taken to increase the sensitivity. As one example, it has been proposed to multiply photoelectrons by electron multiplication, but in this case, it is necessary to provide an avalanche multiplication region immediately before the photoelectron emission surface, which complicates the structure.

The present invention has been made in view of the above-mentioned conventional techniques, and completely changes the idea of the conventional photoelectron emitting surface. That is, photoelectrons are not directly generated by the incident light, but holes are once generated by the incident light, the electrons to be emitted are indirectly derived by using the holes as a trigger, and the electrons are emitted into an external vacuum. , Overcoming the drawbacks of the prior art.

[0005]

That is, the present invention provides a semiconductor in which a pair of internal electrodes consisting of an internal anode and an internal cathode is set on a photoelectron emission surface which is sensitive to light and emits electrons toward an external anode. , An electric field applying means for applying a predetermined electric field in the semiconductor between the pair of internal electrodes, a light irradiating means for irradiating the interface between the internal anode and the semiconductor with light, and holes generated in the internal positive and near polar electrodes by this light irradiation. Is injected into the semiconductor,
Equipped with an internal cathode means for promoting injection of electrons from the internal cathode to the semiconductor and an emission means for emitting electrons injected from the internal cathode to the outside from the surface of the internal anode, and the emitted electrons are captured by the external anode. It is characterized by doing so.

[0006]

According to the present invention, the incident light causes holes to be generated in the vicinity of the internal anode and injected into the semiconductor.
Then, this serves as a trigger to inject electrons from the internal cathode into the semiconductor, and the electrons are emitted to the outside from the surface of the internal anode. Here, since the amount of emitted electrons is controlled by the amount of generated holes and is multiplied by the avalanche, a highly sensitive photoelectron emitting surface can be realized with a simple structure.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail based on embodiments with reference to the accompanying drawings.

FIG. 1 is a structural diagram of the most basic embodiment of the photoelectron emitting surface of the present invention. As shown, the semiconductor 1 _1, a pair of electrodes formed for example above and below the GaAs wafer, for these internal anode 2 ₁ and the inner cathode 2 _2.
Although the electrode material will be described later, in this example, both the internal cathode 2 ₂ and the internal anode 2 ₁ are made of AuG having an ohmic junction.
e / Ni / Au. The internal anode 2 ₁ is made sufficiently thin so as not to interfere with electron emission and to efficiently irradiate the interface between the internal anode 2 ₁ and the semiconductor 1 ₁ with light.

At the interface between the internal anode 2 ₁ and the semiconductor 1 ₁ ,
Whether the junction is an ohmic junction or a Schottky junction, a potential barrier is always formed.
The height of the barrier, depending on the type and material semiconductor type of bonding is generally 1/2 or 2/3 of the band gap energy of the semiconductor 1 _1. This value determines the limiting wavelength of this photoemission surface. When the semiconductor 1 ₁ is GaAs, the band gap energy at room temperature is 1.43e
V and the limit wavelength is 1300 nm to 1700 nm
It will be about.

When light (hν) is applied to the interface between the internal anode 2 ₁ and the semiconductor 1 ₁ from the outside, holes are excited in the internal anode 2 ₁ by the applied light. Since the energy of this hot hole has the same energy as the irradiated light energy, if the photon energy of the irradiation light is higher than the previous barrier, the hot hole will cross the barrier and be injected into the semiconductor 1 ₁ . To be done. This hole injection can also be by other means. Then, electrons are injected from the inner cathode 2 ₂ to counter this. Since the electric field is applied to the semiconductor 1 ₁ by the electrodes 2 ₁ and 2 ₂ provided on both sides and the power source 4 ₃ , the injected electrons are carried to the internal anode 2 ₁ and a part of them is placed in a vacuum. It is radiated and captured by the external anode 2 ₃ .

To further increase this electron emission,
At a immediately before the internal anode 2 ₁ as shown below, it is better to cause the avalanche by a high electric field. Therefore conditions required, it semiconductor 1 ₁ is a high-resistance semiconductor as semi-insulating GaAs, also the bias electric field as the average electric field zero.
That is, the electric field is about 5 kV / cm or more. The upper limit of the electric field strength is not particularly limited, but it is 2.5 kV / V in consideration of the fact that it operates in a low average electric field, which is a feature of the present invention, and the distinction from other phenomena. cm or less.

[0012] high resistance semiconductor 1 _1, upon application of a high electric field of this degree is in the vicinity of the internal anode 2 ₁ that concentration of the electric field is generated, it has been found by the inventors of the study. Injecting excess electrons and holes into the high electric field region existing near the internal anode 2 ₁ lowers the resistivity of the semiconductor 1 ₁ .

When a constant bias voltage is applied between the electrodes 2 ₁ and 2 ₂ , the resistivity in the semiconductor 1 ₁ decreases and the electric field in that region decreases. Field intensity near the internal anode 2 _1, correspondingly to the reverse electric field is increased. Such a manner, so that avalanche multiplication by the injected electrons in the vicinity of the internal anode 2 ₁ occurs. As a result, the electrons injected from the internal cathode 2 ₂ are carried to the internal anode 2 ₁ by the electric field in the semiconductor 1 ₁ ,
Further avalanche multiplication within the anode 2 near _1, also are accelerated become hot electrons.

[0014] Internal anode 2 ₁ surface is an alkali metal such as Cs, or are covered with a layer 3 ₁ of the alkaline oxides, which reduces the vacuum barrier as viewed from the semiconductor 1 _1. Therefore, the electrons carried to the inner anode 2 ₁ are easily radiated into the vacuum and captured by the outer anode 2 ₃ . This is the basic operation of the photoemissive surface of the present invention.

FIG. 2 shows the above operation mechanism on the energy band diagram. FIG. 5A is a potential diagram immediately after holes 5 ₄ are injected from the internal anode 2 ₁ by light irradiation. That is, a pair of electron 5 ₁ and hole 5 ₂ is generated in the internal anode 2 ₁ by light (hν), and the hole 5 ₄ is injected into the semiconductor 1 ₁ .

FIG. 2B is a potential diagram of an operating state in which avalanche multiplication is induced by injection, a large amount of holes are generated, and electrons are injected from the internal cathode to neutralize charges. ing. That is, a large number of electron-hole pairs in the avalanche multiplication region 5 ₅ occurs, flow holes of this is to the inside cathode 2 _2. Corresponding to this, many electrons 5 ₃ flow into the semiconductor 1 ₁ from the internal cathode 2 ₂ .

At this time, holes are generated in the avalanche region, and this plays a role of hole injection from the anode to the cathode as described above, whereby the entire increased current is passed. The current is further increased by adding an additional current due to the light irradiation, and this becomes a photocurrent gain. As described above, the hole currents include those generated by the avalanche and those generated by the anode, both of which are generated in the vicinity of the anode, and are therefore difficult to distinguish. In the text, it is described as being typically injected from the anode.

As can be seen from the above description, applying an electric field to the semiconductor 1 ₁ and irradiating the internal anode 2 ₁ with light is the basis of the operation of the photoelectron emitting surface of the present invention. Further, in the above embodiment, with respect to the electron injection from the inner cathode 2 _2, it was treated as in particular that there is no interfere. However, the potential barrier existing at the interface between the internal anode 2 ₂ and the high resistance semiconductor 1 ₁ may interfere. In this case, irradiating the interface between the internal cathode 2 ₂ and the semiconductor 1 ₁ with light also helps increase the photoelectric sensitivity. That is, in the internal cathode 2 ₂ as well as in the internal cathode 2 ₁ , electrons are injected by internal photoelectron radiation, and the electron injection rate limiting can be removed.

By devising the means of light irradiation, various types of photoelectron emitting surfaces can be constructed. Hereinafter, this will be described with reference to FIGS.

For example, in the structure of the photoelectron emitting surface according to the above description, the semiconductor 1 ₁ has a diode structure of the internal anode 2 ₁ and the internal cathode 2 ₂ , but the internal anode 2 ₁ is divided into two parts and separated. of the under three-pole structure of the bias, the anode 2 ₄ photoholes injection can also be operated separately in the internal anode 2 ₁ for photoelectric emission (Figure 3). As shown, the power supply 4 ₃ is connected to the internal anode 2 _1, power 4 ₄ is connected to the hole injecting anode 2 _4.

[0021] In order to increase the aperture ratio for electron emission, an internal anode 2 ₁ which has been thinned, it may be changed to the partial electrode such as a mesh pattern. In this case, if the inner anode 2 ₁ is thick, light is irradiated only to the electrode interface portion in the peripheral portion of the electrode opening portion, so that it is necessary to thin the inner anode 2 ₁ as well. However, as the light to be irradiated, when than the wavelength corresponding to the band gap energy of the semiconductor 1 ₁ long wavelength light, the situation is quite different.

The structural diagram in this case is shown in FIG. In this case, the light hν emitted from intervals of the internal cathode 2 ₁ to the semiconductor 1 ₁ is reflected by the inner cathode electrode 2 ₂ backside for transmitting a high-resistance semiconductor 1 _1, an internal anode 2 ₁ and the semiconductor 1
The interface ₁ will be irradiated with light. Therefore, in this case, the internal anode 2 ₁ may not be particularly thinned.

[0023] Further, it may be irradiated from the semiconductor 1 ₁ wafer side. An example of this is shown in FIG. The light incident from one side surface is reflected by the other side surface and irradiates the interface between the internal anode 2 ₁ and the semiconductor 1 ₁ . With this configuration,
This structure is suitable for a device that emits electrons by the light from a semiconductor laser formed on the same semiconductor wafer.

Furthermore, it is also possible to irradiate the light from inside the cathode 2 ₂ side. In this case, either inside the cathode 2 ₂ is thinned for light transmission, there must be in the mesh electrode shape (Fig. 6).

The electrodes used in the present invention will be described.
First, regarding the internal cathode 2 ₂ , when holes are injected into the semiconductor 1 ₁ , electrons that neutralize the holes must be easily injected from the internal cathode 2 ₂ into the semiconductor 1 ₁ . Therefore, as the internal cathode 2 ₂ materials, ohmic bonding material is suitable as not to electronic block. As such a material, Au
Examples include alloy metals mainly containing Ge, AgInGe, AuSn and the like. Further, a metal electrode via an N ⁺ thin layer may be used.

Further, in the case where both the internal cathode 2 ₂ and the internal anode 2 ₁ are irradiated with light as described above, the internal cathode 2 ₂ may be an electron blocking electrode, that is, a Schottky electrode. This is because the dark current can be suppressed low. Examples of the metal having a Schottky junction include Au, Al, WSi, and TiPtAu.

For the internal anode 2 ₁ , the optimum electrode material is determined from another point of view. Internal anode 2 ₁ to semiconductor 1
A Schottky type electrode material is suitable as an electrode material suitable for injecting holes into ₁ . This is because the potential barrier for holes is lowered in this case. However, when using the Schottky junction, vacuum level as viewed from the semiconductor 1 _1, i.e. to the electron affinity increases, it would prevent electron emission. When an ohmic junction is used, hole injection is somewhat hindered, but not electron emission. Therefore, as the internal anode 2 ₁ material, either can be used.

When the semiconductor 1 ₁ is an n-type semiconductor substrate,
Since the internal cathode 2 ₂ is an ohmic electrode, the internal anode 2 ₁
Is preferably an n ⁺ type electrode. The internal anode 2 ₁ may be of various types such as a pn junction or a Schottky junction whose injection state can be controlled by a bias to reduce dark current. Further, in order to lower the potential barrier at the time of injecting holes by light irradiation and extend the limit wavelength on the long wavelength side, this pn junction may be a heterojunction.

FIG. 7 shows a structural diagram of this embodiment, and FIG. 8 shows an energy band diagram. Another semiconductor 1 ₂ having a bandgap energy different from that of the semiconductor 1 _{1 is formed} on the semiconductor 1 1.
Is formed, the internal anode 2 ₁ is formed thereon, and further the adsorption layer 3 ₁ made of an alkali metal or its oxide is formed. In this structure, when a hole 5 ₂ paired with an electron 5 ₁ is generated at the internal anode 2 ₁ by the incidence of light (hν), it is injected into the semiconductor 1 ₁ . Then, avalanche multiplication area 5
_A large number of electron-hole pairs are generated at ₅ , and holes are generated by the internal cathode 2
₂ , and electrons are emitted from the inner anode 2 ₁ . It is also possible to form a junction of the semiconductor 1 ₂ having a small energy gap also on the side of the internal cathode 2 ₂ so as to have a function of injecting electrons by light to a longer wavelength side.

As described above, the long wavelength limit of the photoelectron emitting surface of the present invention is determined by the size of the potential barrier formed between the internal anode 2 ₁ and the semiconductor 1 ₁ .
Potential barrier to the more band gap energy is small becomes small, it is possible to use a semiconductor with a smaller band gap energy that can as the semiconductor 1 _1. In such an attempt, all of the semiconductor 1 ₁ may be replaced with a semiconductor having a small band gap energy, but another semiconductor 1 ₂ may be replaced just before the anode as shown in FIG. This is because, as a whole, the semiconductor 1 ₁ having a large bandgap energy is used, so that the dark current can be suppressed to be low, and the high-resistance semiconductor 1 ₁ can be easily used. Alternatively, the Schottky barrier height can be selected by combining a metal and a high resistance semiconductor, and these selection materials are also included in the scope of the patent of the present application.

[0031] keep then touch on the semiconductor 1 ₁ of resistivity. In the mechanism of the photoelectron emission surface of the present invention, holes are injected by light irradiation, and electrons are injected for neutralization, so that electron emission to a vacuum occurs. It takes a certain amount of time to neutralize the charge, which is called a dielectric relaxation time. The dielectric relaxation time is determined by τ = εε ₀ / σ. Here, ε and ε ₀ are the relative permittivity of the semiconductor and the vacuum permittivity. Further, σ is the conductivity of the semiconductor. Thus, the semiconductor 1 ₁ If too high resistance, the response speed of the photoelectric emission surface is very slow. To solve this, it is necessary to make the transit time of the carrier between the internal electrodes shorter than the dielectric relaxation time τ. Therefore, the distance between the internal electrodes is preferably 80 μm.

Further, increasing the electric conductivity to obtain the responsiveness does not make sense because the electric field concentration means for the anode applied in the present invention cannot be used. Therefore, the carrier concentration of the semiconductor 1 ₁ for use in the photo-electron emission surface of the present invention is desirably 10 ¹⁴ cm ^-3 or less. Aside from the problem of response speed, the high-resistance semiconductor used in the present invention may be semi-insulated, and it has been found that impurities contained for carrier compensation are not affected. Examples of semiconductors semi-insulated by carrier compensation are Cr: GaAs, CrO: GaAs, Fe: I.
nP etc. are mentioned.

Further, as a feature of the present invention, when light having a two-dimensional spatial distribution is irradiated, it is possible to perform electron emission while preserving the spatial distribution. This is because, since the semiconductor used in the present invention has a high resistivity and an electric field is applied in parallel, there is almost no exchange of charges in the lateral direction of the semiconductor wafer.

As described above, the present invention is a photoelectron emitting surface which is completely different from the conventional ones, has a simple structure, is sensitive to long wavelengths, and is highly sensitive to avalanche multiplication. It is a radiation surface.

[0035]

According to the present invention, the incident light causes holes to be generated in the internal anode and injected into the semiconductor. Then, this serves as a trigger to inject electrons from the internal cathode into the semiconductor, and the electrons are emitted to the outside from the surface of the internal anode. Here, the amount of emitted electrons is controlled by the amount of holes generated and is multiplied by the avalanche, so that high sensitivity can be realized with a simple structure.

Therefore, on the photoelectron emitting surface of the present invention, photoelectrons generated by light irradiation, particularly infrared light, can be efficiently emitted and electron can be multiplied.
It is also characterized by a simple structure and the ability to store a two-dimensional distribution. At present, a good photoelectron emission surface in the long wavelength region has not been realized, and the application range of the photoelectron emission surface of the present invention is wide.

[Brief description of drawings]

FIG. 1 is a structural diagram of a photoelectron emitting surface according to an embodiment of the present invention.

FIG. 2 is an energy band diagram for FIG.

FIG. 3 is a structural diagram of a photoelectron emission surface according to an embodiment of the present invention when the internal anode is divided into a hole injection anode and an electron emission electrode.

FIG. 4 is a structural diagram of a photoelectron emitting surface of an example in which the internal anode is in a mesh shape.

FIG. 5 is a structural diagram of a photoelectron emitting surface of an embodiment in which light is irradiated from the side wall of the substrate.

FIG. 6 is a structural diagram of a photoelectron emission surface of an example in which light is emitted from an internal cathode.

FIG. 7 is a structural diagram of a photoelectron emission surface of an example in which a limit wavelength is extended by a heterojunction.

FIG. 8 is an energy band diagram for FIG. 7.

[Explanation of symbols]

hν ... irradiation light, E _c ... conduction band, E _v ... valence band, E _vac
... vacuum level, 1 ₁ ... semiconductor substrate, 1 ₂ ... semiconductor having different band gap energies, 2 ₁ ... internal anode, 2 ₂
... Internal cathode, 2 ₃ ... External anode, 2 ₄ ... Internal anode for exclusive use of hole injection, 3 ₁ ... Adsorption layer on the anode surface of alkali metal or alkali oxide, 41 ₁ ... Ammeter, 42 ₂ ... Power supply for external extraction,
4 ₃ ... Semiconductor internal bias power supply, 4 ₄ ... Hole injection control power supply, 5 ₁ ... Excitation electron, 5 ₂ ... Excitation hole, 5 ₃ ... Injection electron, 5 ₄ ... Injection hole, 5 ₅ ... Avalanche multiplication region.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneo Yubara 1126-1 Ichinocho, Hamamatsu, Shizuoka Prefecture 1126 Hamamatsu Photonics Co., Ltd. Within the corporation

Claims (15)

[Claims] 1. A semiconductor in which a pair of internal electrodes consisting of an internal anode and an internal cathode is set on a photoelectron emission surface which is sensitive to light and emits electrons toward an external anode, and the semiconductor between the pair of internal electrodes. An electric field applying means for applying a predetermined electric field in the semiconductor, a light irradiating means for irradiating the interface between the internal anode and the semiconductor with light, and holes generated near the internal anode by the light irradiation are injected into the semiconductor. An internal cathode means for promoting injection of electrons from the internal cathode into the semiconductor, and an emission means for emitting electrons injected into the semiconductor from the internal cathode to the outside from the surface of the internal anode, The photoelectron emitting surface, wherein the emitted electrons are captured by the external anode. 2. The photoelectron according to claim 1, wherein the light irradiation means is configured to irradiate light to both the interface between the internal anode and the semiconductor and the interface between the internal cathode and the semiconductor. Radiating surface. 3. The semiconductor has a carrier concentration of 10 ¹⁴ c.
The photoelectron emitting surface according to claim 1 or 2, which is a high-resistance semiconductor having a m ^-3 or less. 4. The photoelectron emitting surface according to claim 3, wherein the high-resistance semiconductor is semi-insulating. 5. The high resistance semiconductor is GaAs or I.
The photoelectron emitting surface according to claim 3, which is a compound semiconductor mainly composed of nP. 6. The electric field generated by the electric field applying means is 0.5.
The photoelectron emitting surface according to claim 1 or 2, wherein the photoelectron emitting surface is configured to be not less than kV / cm and not more than 2.5 kV / cm. 7. The photoelectron emitting surface according to claim 1, wherein at least one of the internal anode and the internal cathode is an ohmic electrode. 8. The photoelectron emitting surface according to claim 1, wherein a barrier material is provided on the semiconductor immediately before the internal anode, and a bonding material is selected so that the height thereof can be adjusted. 9. The photoelectron emitting surface according to claim 8, wherein the junction is formed of a semiconductor heterojunction. 10. The photoelectron emission surface according to claim 1, wherein the light emitted by the light irradiation means has a wavelength longer than a wavelength corresponding to the bandgap energy of the semiconductor. 11. The photoelectron emitting surface according to claim 1, wherein the irradiation of light by the light irradiation unit and the emission of electrons by the emission unit are both performed at the internal anode. 12. The photoelectron emission surface according to claim 1, wherein the emission of electrons by the emission means is performed on a surface different from the light irradiation surface of the light irradiation means. 13. The photoelectron emitting surface according to claim 1, wherein an alkali metal or an oxide of an alkali metal is deposited on the surface of the internal anode. 14. The first internal anode, wherein the internal anode generates holes by light from the light irradiating means, and an avalanche multiplication region immediately before the first internal anode, which causes electrons to be emitted by the emitting means. The photoelectron emitting surface according to claim 1 or 2, wherein the photoelectron emitting surface comprises two internal anodes. 15. The space between the internal anode and the internal cathode is 80.
The photoelectron emission surface according to claim 1 or 2, wherein the photoelectron emission surface is not more than μm.