JP2000323015A - Electron emission element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron emission element having a good electron emission characteristic. SOLUTION: This electron emission element has an electron supply layer 1 constituted of an n-GaN layer, an electron transfer layer 2 for transferring electrons to the surface side and constituted of non-doped (intrinsic) Alx Ga1-x N(0<=x<=1) having an gradient composition as to Al containing ratio x, a surface layer 3 constituted of non-doped AlN having a negative affinity(NEA). A band gap of the electron transfer layer 2 constituted of Alx Ga1-x N almost continuously increases from the electron supply layer 1 to the surface layer 3, and the electron affinity approaches negative or zero. When applying a voltage V so that the surface electrode 4 becomes positive, the band of Alx Ga1-xN is bent. Thereby current mainly caused by a diffuse current flows from the electron supply layer 1 to surface layer 3 via the electron transfer layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electron-emitting device having a surface layer made of a material having a negative or substantially negative electron affinity.

[0002]

2. Description of the Related Art Conventionally, an electron-emitting device is provided with a cathode made of a refractory metal material such as tungsten (W) and an anode opposed to the cathode with a space therebetween, and heats the cathode to a high temperature. The structure is based on a hot cathode method (electron gun method) that emits electrons from a solid into a vacuum. 2. Description of the Related Art In recent years, as an electron beam source replacing an electron gun, a cold-cathode type micro electron-emitting device has been receiving attention. As such an electron-emitting device, a field-emission device and a pn-junction device having a surface coated with a low work function material are generally reported.

A field emission type electron-emitting device is provided with a cone-shaped emitter portion formed of a high melting point metal material such as silicon (Si) or molybdenum (Mo), and this emitter portion is provided with a space therebetween. An extraction electrode, and applying a voltage to the extraction electrode to obtain a high electric field (> 1 × 10
^{By generating 9} V / m), electrons are emitted from the emitter section, and there is an advantage that downsizing can be achieved by using fine processing technology.

On the other hand, a pn junction type electron-emitting device using a semiconductor material has a negative electron affinity by providing a coating layer of a low work function material such as cesium (Cs) on a semiconductor surface composed of a p-type layer. This is a state where a bias voltage is applied to the element, and electrons are emitted from the p-type semiconductor surface layer into a vacuum.

[0005]

Here, the characteristics commonly required of the cold cathode type micro-electron emitting element are that it is easy to emit electrons at a relatively small operating voltage (for example, the electron affinity of the emitter material). That the emitted electron beam can be easily controlled, that the surface of the emitter section is chemically stable due to its stable electron emission characteristics, and that it has excellent wear resistance and heat resistance. It is.

However, the above-described various conventional electron-emitting devices have the following disadvantages.

The field emission type device has a disadvantage that the operating voltage is relatively high because electrons are emitted by a high electric field. In addition, since the amount of emission current largely depends on the shape and surface state of the emitter portion, and it is difficult to form a large number of cone-shaped emitters with good uniformity, there is a problem that the controllability of the emission current amount is poor. .

In a pn junction type electron-emitting device using a semiconductor material, a coating layer of a low work function material such as cesium (Cs) is indispensable on the surface of the p-type semiconductor in order to easily emit electrons. However, since the coating layer has poor stability, there is a problem with the stability and life of the device.

SUMMARY OF THE INVENTION An object of the present invention is to use a material whose electron affinity is negative or substantially negative close to zero in order to obtain a state in which electrons can be easily emitted with good stability. By providing a means for efficiently supplying electrons to the surface layer, which is an electron-emitting portion, by using a configuration, it is possible to provide a new type of electron-emitting device that can be driven at a low voltage and has extremely good electron-emitting characteristics. is there.

[0010]

According to a first aspect of the present invention, there is provided a first electron-emitting device which is provided with a semiconductor layer functioning as an electron supply layer and separated from the semiconductor layer, and has a negative or near zero electron affinity. And a composition gradient layer interposed between the semiconductor layer and the surface layer, wherein the composition is changed so that the electron affinity decreases in a direction from the semiconductor layer toward the surface layer; A surface electrode provided on the surface layer for applying a voltage so as to supply electrons from the semiconductor layer to the outermost surface of the surface layer.

Accordingly, the composition gradient layer, which is a region where electrons move, is configured so that the electron affinity changes from a large state to a small state toward the surface layer, and thus functions as an electron supply layer. By applying a voltage between the semiconductor layer and the surface electrode and supplying electrons to the surface layer via the composition gradient layer, electrons are easily emitted from the surface layer having a negative electron affinity into a vacuum. The voltage applied at that time depends on the element configuration, but may be as high as about 10 V. Therefore, an electron-emitting element that can be driven at a low voltage and emit electrons with high efficiency can be realized.

In the first electron-emitting device, by applying a semiconductor material which is not doped to the composition gradient layer, electrons can be efficiently supplied from the electron supply layer to the surface layer.

[0013] In the first electron-emitting device, the composition gradient layer is formed such that at least a part of the composition gradient layer has a band gap that extends almost continuously from the semiconductor layer to the surface layer. This is preferable because the movement of the electrons in becomes smooth.

In the first electron-emitting device, since the surface layer contains aluminum nitride (AlN), an element having high electron emission efficiency can be obtained by utilizing the negative electron affinity characteristic of the AlN surface. It is preferable because it is possible.

[0015] In the first electron-emitting device, by further comprising a coating layer provided on the surface layer and made of a material different from the surface layer, the state of electron emission can be adjusted or the surface layer can be adjusted. This is preferable since the protection of the film can be achieved.

In the first electron-emitting device, since the coating layer contains a material having a negative or near-zero electron affinity, the electron-emitting state can be adjusted and the surface layer can be efficiently protected while being protected. It is preferable because it is possible to maintain an excellent electron emission characteristic.

In the first electron-emitting device, it is preferable that the coating layer contains aluminum nitride (AlN).

In the first electron-emitting device, the region including the composition gradient layer and the surface layer is formed such that the closer to the outermost surface, the more Al
Al _x Ga _1-x N (0 ≦
x ≦ 1) is preferable because the composition gradient layer and the surface layer can be easily formed with high quality.

In the first electron-emitting device, the surface electrode is preferably in Schottky contact with the surface layer, so that electrons can be supplied from the electron supply layer with good controllability.

In the first electron-emitting device, the surface electrode includes a first region and a second region in which an energy barrier between the surface layer and the surface layer is larger than an energy barrier between the surface layer and the first region. It is preferable to have such a structure since the electron current can be concentrated on the first region of the surface electrode and the emission current density can be increased.

In the first electron-emitting device, the surface electrode has a pattern for controlling the distribution of the emitted electrons, so that the electron beam having a desired distribution can be controlled and created. Is preferred.

In the first electron-emitting device, an insulator layer provided on the surface electrode so as to open at least a part of the surface electrode, and an insulator layer provided on the insulator layer, By further providing a control electrode for accelerating and controlling electrons emitted to the outside from the surface layer, an acceleration / control mechanism of the emitted electron flow can be integrated.

In a second electron-emitting device according to the present invention, a semiconductor layer functioning as an electron supply layer and a surface layer formed of a material having a negative or near zero electron affinity are provided separately from the semiconductor layer. A superlattice layer interposed between the semiconductor layer and the surface layer, and a superlattice layer formed by stacking a plurality of layers for resonantly transmitting electrons supplied in a direction from the semiconductor layer to the surface layer; And a surface electrode for applying a voltage so as to supply electrons from the semiconductor layer to the outermost surface of the surface layer.

Also in this case, by applying a voltage to the surface electrode, electrons are efficiently transported from the semiconductor layer to the outermost surface of the surface layer via the sub-band formed in the superlattice layer. Thus, an element in which electrons are emitted with high efficiency only by applying a low voltage can be obtained.

In the second electron-emitting device, the superlattice layer alternately includes two mixed crystals represented by Al _x Ga ₁ -xN (0 ≦ x ≦ 1) having different component ratios. It is preferable to adopt a configuration in which a high-quality superlattice layer can be easily formed.

In the second electron-emitting device, it is preferable that the surface layer contains aluminum nitride (AlN).

The second electron-emitting device also preferably further comprises a coating layer provided on the surface layer and made of a material different from the surface layer.

Also in the second electron-emitting device, the coating layer preferably contains a material having an electron affinity of negative or close to zero.

Also in the second electron-emitting device, it is preferable that the coating layer contains aluminum nitride (AlN).

A third electron-emitting device according to the present invention includes a semiconductor layer functioning as an electron supply layer and a surface layer provided with a distance from the semiconductor layer and made of a material having a negative or near zero electron affinity. An electron transfer layer provided between the semiconductor layer and the surface layer for supplying electrons in a direction from the semiconductor layer toward the surface layer, and at least partly on the surface layer in Schottky contact. And a surface electrode for applying a voltage so as to supply electrons from the semiconductor layer to the outermost surface of the surface layer.

By applying a voltage between the semiconductor layer and the Schottky surface electrode, electrons can be supplied from the semiconductor layer to the surface layer with good controllability via the electron transfer layer. Electron emission element having a high density can be obtained.

In the third electron-emitting device, it is preferable that the composition of the electron transfer layer is changed so that the electron affinity decreases in the direction from the semiconductor layer toward the surface layer.

In the third electron-emitting device, it is preferable that the composition of the electron transfer layer is changed so that the band gap increases in the direction from the semiconductor layer toward the surface layer.

Also in the third electron-emitting device, the electron transfer layer is formed of a superlattice layer formed by stacking a plurality of layers for resonantly transmitting electrons supplied from the semiconductor layer toward the surface layer. Preferably, it is configured.

In the third electron-emitting device, it is preferable that the surface layer contains aluminum nitride (AlN).

Also in the third electron-emitting device, the region including the electron transfer layer and the surface layer has a smaller A
Al _x Ga _1-x N (0
≦ x ≦ 1).

In the third electron-emitting device, the surface electrode includes a first region having a smaller area than the semiconductor layer provided in contact with only a part of the surface layer;
And a second region having an energy barrier between the surface layer and the first region that is larger than the energy barrier between the surface layer and the first region.

In this case, the second region has a larger area than the first region, and is made of a material having a higher resistance to ion bombardment than the material forming the first region. This is preferable because the durability of the electron-emitting device is improved.

The semiconductor device further includes an insulator layer formed on a region of the surface layer other than a region in contact with the first region of the surface electrode, and a second region of the surface electrode includes the insulator layer. Since the layer is provided from the side surface to the upper surface of the layer, the electron flow can be concentrated on the first region where electrons are easily emitted, so that a more efficient electron-emitting device can be configured.

In the third electron-emitting device, it is preferable that the second region of the surface electrode has a thickness larger than that of the first region.

The fourth electron-emitting device of the present invention comprises a solid layer functioning as an electron control layer, a surface layer provided on the solid layer and made of a material having a negative or near zero electron affinity, A surface electrode provided in contact with the layer, for applying a voltage between the solid layer and the outermost surface of the surface layer,
An external electrode provided with the space between the surface electrode and the space, and a sealing member for keeping a space between the surface electrode and the external electrode in a reduced pressure state.

Electrons emitted from the surface layer into the space under reduced pressure through the solid layer, which controls the amount of emitted electrons by the applied voltage value, are accelerated by the positive voltage applied to the external electrodes, and Reach That is, the kinetic energy of the emitted electrons can be controlled by the voltage value applied to the external electrodes. In addition, the amount of emitted electrons can be controlled by the voltage applied between the solid layer and the surface electrode, so that the current flowing to the external electrode provided with the space between the surface electrode and the space can be controlled. Therefore, the amount of emitted electrons itself is controlled by a voltage value applied between the solid layer and the surface electrode, and further, electrons are accelerated in a space under reduced pressure and collected by an external electrode, thereby enabling signal amplification and switching operation. It becomes possible to function as an element (vacuum transistor).

This device is composed of a solid layer / surface layer from which electrons can be easily emitted as described above, and is configured to accelerate the emitted electrons in a reduced pressure space. In addition, there is an advantage that low-voltage driving is possible.

[0044] In the fourth electron-emitting device, the solid layer is provided between the semiconductor layer functioning as an electron supply layer and the semiconductor layer and the surface layer, and is formed in a direction from the semiconductor layer to the surface layer. A configuration having at least a composition gradient layer in which the composition is changed so that the affinity is reduced can be adopted.

In the fourth electron-emitting device, it is preferable that the composition of the composition gradient layer is changed so that the band gap increases in a direction from the semiconductor layer toward the surface layer.

In the fourth electron-emitting device, it is preferable that the composition gradient layer has a band gap that at least partially extends almost continuously from the semiconductor layer to the surface layer.

In the fourth electron-emitting device, the region including the composition gradient layer and the surface layer has the A
Al _x Ga _1-x N (0
≦ x ≦ 1).

In the fourth electron-emitting device, the solid layer is interposed between the semiconductor layer functioning as an electron supply layer and the semiconductor layer and the surface layer to resonate electrons supplied from the semiconductor layer. A configuration having at least a superlattice layer in which a plurality of layers for transmitting light are stacked can be employed.

In the fourth electron-emitting device, the surface layer is preferably made of aluminum nitride (AlN).

In the fourth electron-emitting device, the surface electrode includes a first region having a smaller area than the semiconductor layer provided in contact with only a part of the surface layer;
And a second region in which the energy barrier between the surface layer and the surface layer is larger than the energy barrier between the surface layer and the first region.

In the fourth electron-emitting device, the second
Is preferably made of a material having an area larger than that of the first region and having a higher resistance to ion bombardment than the material forming the first region.

The fourth electron-emitting device also includes an insulator layer formed on a region of the surface layer other than the first region in contact with the surface electrode, and a second region of the surface electrode. Is preferably provided from the side surface to the upper surface of the insulator layer.

[0053]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a negative electron affinity (Nega
The present invention relates to an electron-emitting device using a semiconductor material or an insulator material having tive electron affinity (NEA). Hereinafter, before describing each embodiment of the present invention, the principle of an electron-emitting device using a NEA material (hereinafter, referred to as a “NEA electron-emitting device”) will be described.

FIG. 1 shows an example of the NEA material, aluminum nitride (Al).
FIG. 3 is a perspective view showing a configuration of a NEA electron-emitting device using N). As shown in FIG. 1, the NEA electron-emitting device of the present invention comprises an electron supply layer 1 for supplying electrons, an electron transfer layer 2 for transferring electrons supplied from the electron supply layer 1 to the solid surface side, A surface layer 3 made of a NEA material and a surface electrode 4 for applying a voltage to move electrons from the electron supply layer 1 to the surface layer 3 are provided.

Here, the electron supply layer 1 is made of n-type GaN.
The electron transfer layer 2 which is made of (n-GaN) and smoothly transfers electrons from the electron supply layer 1 to the surface layer 3 is non-doped and has an Al _x Ga _1- gradient composition in which the Al content x changes continuously. _{An example in which xN} (x is a variable that increases almost continuously from 0 to 1), the surface layer 3 is made of AlN which is a true NEA material, and the surface electrode is made of a metal such as platinum (Pt) However, the configuration of each part of the NEA electron-emitting device of the present invention is not limited to this.

Hereinafter, the electron affinity, which is an important property for the basic characteristics of the present invention, and the structure of an electron transfer layer necessary for smoothly moving electrons will be described.

Electron Affinity “Electron Affinity” in a semiconductor material indicates an energy value required to extract electrons existing at the conduction band edge into a vacuum, and has a value specific to the material. Hereinafter, the concept of “negative electron affinity” (NEA) will be described.

FIGS. 2A and 2B are energy band diagrams showing the energy states of semiconductor materials having negative and positive electron affinity values, respectively. As shown in FIG. 2B, the Fermi level of the semiconductor is E _f , the energy level at the conduction band edge is E _c , the energy level at the valence band edge is E _v , and the band gap is E _{g. Assuming} that the level is E _vac , the electron affinity に お_{け る} in a general semiconductor is χ = E _vac −E _c >
0. That is, it has a positive electron affinity. On the other hand, depending on the type of semiconductor, there is a state where χ = E _vac −E _c <0, as shown in FIG. That is, such a semiconductor material, for example, AlN has a negative electron affinity.

Here, as shown in FIG. 2B, in the case of a semiconductor having a positive electron affinity, in order to extract electrons existing at the conduction band edge into vacuum, an energy barrier having a size of χ is required. Because it exists, it is necessary to give energy by that much. Therefore, it is usually necessary to apply energy to the electrons by heating or to apply a high electric field to allow the energy barrier to tunnel through the energy barrier in order to emit the electrons.

On the other hand, as shown in FIG. 2A, in the case of a semiconductor having a negative electron affinity, there is no energy barrier for electrons existing at the conduction band edge on the surface.
Electrons are easily released into a vacuum. That is, there is no need for extra energy for extracting electrons existing on the semiconductor surface into a vacuum.

However, as shown in FIGS. 2A and 2B, electrons generally present in the conduction band of a semiconductor material have an energy distribution, so that even if the electron affinity value χ is positive, However, if χ is sufficiently small, the efficiency is reduced, but it is possible to emit some electrons with low energy. Therefore, in this specification, "NE
"A material" means not only a material having a negative electron affinity (a true NEA material as shown in FIG. 2A),
It also includes a material (pseudo-NEA material) having a positive electron affinity such that the value of χ is substantially zero.

The NEA materials known so far include gallium arsenide (GaAs) and gallium arsenide (Gas).
Cesium (Cs) or cesium oxide (Cs-) which is a low work function material on a semiconductor surface such as P) and silicon (Si).
O), cesium antimony (Cs-Sb), rubidium oxide (Rb-O) and the like are known to be thinly coated. However, in these structures, since the above-mentioned surface adsorption layer has poor stability, high vacuum The NEA state cannot be maintained unless it is below.

As a NEA material not using a surface adsorption layer, in addition to diamond, AlN, etc., Al _x Ga ₁ -xN having a high Al content ratio x also has a negative electron affinity as described below.

FIG. 3 is a view showing measured data of electron affinity of an Al _x Ga ₁ -xN based semiconductor material. In this figure, the horizontal axis represents the Al content ratio x in Al _x Ga ₁ -xN. Here, the Al content ratio x refers to Ga in Al _x Ga ₁ -xN.
And the Al content in the Al content, and Al _x Ga _1-x N
It does not mean the Al content ratio in the whole. The same applies hereinafter. According to this figure, when x = 0, that is, the electron affinity of GaN is ~ 3.3 eV, indicating a positive electron affinity characteristic, but the electron affinity value decreases as the Al content ratio x increases, and x> 0 It can be seen that the electron affinity value is almost 0 or negative in the region of .65. Therefore, x =
The electron affinity of AlN, which is Al _x Ga ₁ -xN of _1, is in a negative state.

Electron Transfer Layer It is effective for efficient electron emission to use a material having a negative or substantially zero electron affinity for the surface layer from which electrons are emitted in the electron-emitting device. It is believed that there are generally no electrons in the conduction band of the NEA material at equilibrium. Therefore, it is necessary to efficiently supply electrons to the surface layer made of a material that easily emits electrons by some method.

As an example of the configuration, in order to effectively supply electrons from the electron supply layer 1 (positive electron affinity) in which a large number of electrons are present to the surface layer 3 (negative electron affinity) in the NEA state, an electron affinity value is set. Is conceivable through an intermediate layer (electron transfer layer 2) in which is gradually reduced.

FIGS. 4A and 4B show the configuration of FIG. 1 comprising the electron supply layer 1, the electron transfer layer 2, the surface layer 3 and the surface electrode 4. FIG. 4 is an energy band diagram when no voltage is applied to the slab (equilibrium state) and when a forward bias of voltage V is applied. As described above, the electron transfer layer 2 is selected from a material whose electron affinity 徐 々 に gradually decreases toward the surface. By carefully selecting the material, the composition ratio of the material is changed. This can be achieved by:

In the present configuration example, n-type doped GaN (carrier density: up to 4 × 10
¹⁸ / cm ³ ), an undoped Al _x Ga ₁ -xN layer (0 ≦ x ≦ 1) having a graded composition as the electron transfer layer 2, an AlN layer as the surface layer 3, and Pt as the surface electrode 4. ing. Electron transfer layer 2 made of Al _x Ga ₁ -xN with gradient composition
Is that at the portion in contact with GaN, which is the electron supply layer 1, x =
0, that is, AlN that does not contain Al and is the surface layer 3
X = 1, that is, a configuration not containing Ga. In the meantime, the x value is gradually increased, that is, the composition is inclined so that the Al content increases toward the surface. With such a structure, the electron affinity of the electron transfer layer 2 made of Al _x Ga ₁ -xN is positive at the portion in contact with the electron supply layer 1, but as shown in FIG. As the Al content increases, the electron affinity value decreases, and the portion in contact with the surface layer 3 is in the same negative state as AlN. Therefore,
The electron affinity of the electron transfer layer decreases almost continuously from the electron supply layer 1 to the surface layer.

As the electron transfer layer 2, a composition gradient Al _x Ga _{1 -x}
When N is used, the above configuration can be regarded as a continuous increase of the band gap. FIG.
is a diagram showing an Al content ratio dependence of the band gap of the _{x Ga 1-x N (0} ≦ x ≦ 1). In the figure, the horizontal axis represents the Al content ratio x, and the vertical axis represents the band gap E _g (eV) in the composition. As shown in the figure,
The E _g value of Al _x Ga ₁ -xN is not strictly a straight line with an increase in x, but increases in a relationship close to a straight line.
Therefore, as in the present configuration example, the electron transfer layer Al _x Ga ₁ -xN
Is that at the portion in contact with GaN, which is the electron supply layer 1, x =
0, that is, the same band gap as GaN (Eg = 3.4
eV), and x = 1 in a portion in contact with AlN which is the surface layer 3, that is, the same band gap (Eg = Eg = AlN) as AlN.
6.2 eV). In the middle of the process, the x value was gradually increased, that is, by tilting the composition so that the Al content increased toward the surface, Al _x Ga _{1 -x}
The band gap of the electron transfer layer 2 made of N is almost continuously widened from the electron supply layer 1 to the surface layer as the Al content increases. Since such an arrangement is a mixed crystal of the Al _x Ga ₁ -xN based semiconductor, it can be realized as a single crystal thin film by epitaxial growth with a change in the composition of the raw material.

In the equilibrium state as shown in FIG. 4A, a large number of electrons are present in the conduction band of the electron supply layer 1, but the energy level at the conduction band edge of the surface layer 3 is high. Therefore, the electrons do not reach the outermost surface. On the other hand, when a forward bias (positive voltage is applied to the surface electrode) is applied to such a structure, the energy band is bent as shown in FIG. As a result, electrons existing in the electron supply layer 1 move toward the surface layer 3 due to the concentration gradient and the potential gradient. That is, an electron current flows. Since Al _x Ga ₁ -xN as the electron transfer layer 2 and AlN as the surface layer 3 are non-doped, electrons injected from the electron supply layer 1 into the electron transfer layer 2 and the surface layer 3 are positive. It can move without being captured by recombination with a hole or the like. In addition, since the composition gradient in the electron transfer layer 2 is continuously performed, an energy barrier that hinders electron transfer is not formed at the conduction band edge, so that it is advantageous in that electrons can be efficiently sent to the surface.

Al _x G having a composition gradient as described above
By applying the a _1-x N layer as the electron transfer layer 2,
It is possible to move efficiently from the n-GaN layer having a positive electron affinity to the surface layer 3 (AlN) having a negative electron affinity. The electrons injected into the electron transfer layer 2 and the surface layer 3 in this manner can be easily taken out in a vacuum since the surface layer is in the NEA state.

Next, the basic structure of the present invention shown in FIG.
A comparison is made with a conventionally reported pn junction type NEA element.

FIGS. 23A and 23B are a sectional view of a pn junction type NEA element using a surface adsorption layer and an energy band diagram when a forward bias is applied. In the case of this configuration, FIG.
The portion corresponding to the electron supply layer is formed of n-type GaAs (n-type semiconductor layer), the portion corresponding to the electron transfer layer is formed of p-type GaAs (p-type semiconductor layer), and the portion corresponding to the surface layer is formed. It can also be considered to be constituted by a Cs-O adsorption layer. In this case, a GaAs layer and Cs-O
While none of the layers alone are NEA materials,
Due to the bending of the energy band near the surface in the junction state, the energy level at the conduction band edge of the p-type semiconductor becomes higher than the vacuum level, so that the NEA state is effectively realized on the surface. Therefore, electrons are injected from the n-type layer and Cs
By supplying -O to the adsorbed p-type semiconductor surface, electrons can be taken out in a vacuum.

However, in order to take out electrons from the surface in the NEA state in such a configuration, the relationship between the semiconductor layer used as the base material and the surface adsorption layer is important.
When a non-doped intrinsic semiconductor layer is used in place of the type semiconductor layer, even if a surface adsorption layer exists, NE
A state cannot be obtained.

From the above viewpoints, a comparison between the structure of the present invention and the conventional structure shows that, in the conventional structure, p is not a true NEA material.
Although the NEA state is obtained by the correlation between the type semiconductor layer and the surface adsorption layer, in the present invention, since the electron affinity of the surface layer itself is negative or close to zero,
This is advantageous in that the semiconductor layer does not need to be limited to p-type and an unstable surface adsorption layer is not required. In addition, in the case of the conventional configuration, a hole current irrelevant to electron emission flows through the device due to the use of the p-type layer. Not flowing. That is, this does not cause the injected electrons to be lost due to recombination with holes and increases the ratio of the emitted electron current to the device current, so that an extremely efficient device can be realized.

As described above, with respect to the semiconductor layer functioning as an electron supply layer as shown in FIG. 4, a composition gradient layer whose composition changes so that the electron affinity decreases in the direction toward the surface layer. By stacking and further forming an electron-emitting device comprising a surface layer made of a material having a negative or near zero electron affinity, electrons are easily supplied to the surface in the true NEA state by the action of the composition gradient layer, and the vacuum is applied. It can be taken out inside.

However, in the present configuration example, the case where the composition of the electron transfer layer changes continuously has been described. However, the present invention is not limited to this case, and even when the composition changes stepwise or slightly discontinuously. There is no problem as long as the movement of electrons does not become a major obstacle. If the composition changes so that the electron affinity of the electron transfer layer decreases toward the surface as a whole, the effects of the present invention can be obtained.

In the above description, the electron affinity value of the electron transfer layer 2 is controlled by continuously inclining the composition up to the surface layer 3, and electrons are efficiently supplied from the semiconductor layer 1 to the surface layer 3. Although the configuration has been described, the configuration of the electron transfer layer 2 that obtains such an effect is not limited to this.

For example, a semiconductor represented by Al _x Ga ₁ -xN is used as the electron transfer layer 2 in the same manner as in the above configuration example, but the configuration is stopped when the maximum value of x is smaller than 1. Will be described.

FIGS. 6A and 6B show the case where the electron transfer layer is used.
Al_xGa_1-xN (0 ≦ x ≦ y and y <1) applied
The equilibrium state of the NEA electron-emitting device and
FIG. 3 is an energy band diagram showing an energy state of the laser beam.
As shown in FIG. 6A, in this configuration example, the electron supply layer 1
(N-GaN), which functions as an electron transfer layer 2
Doped Al_xGa_1-xN layer (0 ≦ x ≦ y and y <1)
Is formed, an AlN layer is further laminated as the surface layer 3.
ing. In such a structure, as shown in FIG.
As described above, the energy transfer is applied to the interface between the electron transfer layer 2 and the surface layer 3.
Bell discontinuity occurs. Energy in this conduction band
The value of the barrier is determined by Al applied to the electron transfer layer. _xGa_1-xN layers
It is determined by the Al content ratio y (maximum value of x).
Is too large, electrons injected from the electron supply layer are effective.
It cannot be moved to the surface layer 3 efficiently. Hence the main structure
In the case of an example, it is preferable that 0.5 ≦ y ≦ 0.8.

Then, as shown in FIG. 6B, a forward bias is applied between the electron supply layer and the surface electrode (a positive voltage is applied to the surface electrode).
Is applied, the energy bands of the electron transfer layer and the surface layer bend according to the applied voltage value. As a result, electrons move from the electron supply layer to the surface layer 3 due to the concentration gradient and the potential gradient as described above. At that time, the surface layer 3
When the thickness of the AlN layer applied to the semiconductor layer is somewhat thin and the height of the energy barrier formed in the conduction band is low to some extent,
The electrons reaching the interface between the electron transfer layer and the surface layer can pass through the energy barrier by tunneling and move to the outermost surface. In other words, it can be taken out from the surface layer made of a material having a negative or near zero electron affinity. The thickness of the surface layer capable of performing such tunneling transmission is not limited, and may be about 10 nm or less, depending on the thickness of the electron transfer layer and the Al composition ratio.

[0082] As described above, even when applied as an electron transfer layer composition gradient Al _x Ga _{1 -x} N layer having a discrete energy barrier in the conduction band, a positive n-GaN layer which is an electron affinity It is possible to move efficiently and even to the surface layer having negative electron affinity. The electrons injected into the electron transfer layer and the surface layer in this manner can be easily taken out in a vacuum since the surface layer is in the NEA state.

The above description has been made of the configuration in which the electron affinity value of the electron transfer layer 2 is controlled by the composition gradient and electrons are efficiently supplied from the semiconductor layer 1 to the surface layer 3. This is not the case.

For example, FIG. 7 shows that the electron transfer layer 2 is made of Al
A semiconductor represented by _x Ga _1-x N, configuration of the electron-emitting device in the case of applying a superlattice layer formed by laminating two layers having different Al content ratio (e.g., GaN and AlN layers) are alternately It is a figure which shows typically. In this type of electron-emitting device, the electrons supplied from the electron supply layer 1 are transported by the superlattice layer by alternately stacking layers having an appropriate composition and an appropriate number of times as an electron transfer layer 2. Resonant transmission is performed through the sub-bands formed in the band portion, so that the band is efficiently moved to the surface layer 3.

The electron supply layer 1 can be made of, for example, n-GaN, similarly to the above configuration. The parameters of each layer used for the electron transfer layer are as follows. As one layer, the Al content ratio x is 0 ≦ x ≦ 0.2, and the other is preferably 0.6 ≦ x ≦ 1. Are each 5-10
nm, but not limited to this. The number of laminations is preferably about 2 to 5 sets. In general, the surface layer 3 is laminated on the electron transfer layer 2, and the structure of the outermost layer used for the electron transfer layer having a superlattice structure is such that the electron affinity such as AlN is negative or negative. When the layer is made of a material close to 0, this layer has the same function as the surface layer, so that the formation of a new surface layer can be omitted.

FIGS. 8A and 8B are energy band diagrams showing the equilibrium state of the NEA electron-emitting device using the superlattice layer as the electron transfer layer and the energy state when a forward bias is applied. As shown in FIG. 8A, in this configuration example, two sets of a non-doped AlN layer and a non-doped GaN are alternately stacked on the electron supply layer 1 (n-GaN). An AlN layer is stacked. In such a structure, as shown in FIG. 8A, a subband having a discontinuous energy level is formed in the superlattice layer of the electron transfer layer 2. Then, as shown in FIG. 8B, when a forward bias (positive voltage is applied to the surface electrode) is applied between the electron supply layer and the surface electrode, the energy band of the superlattice layer bends according to the applied voltage value. . At this time, by applying an optimum voltage, when the allowable energy levels of the adjacent quantum well portions become coincident, the electrons are resonantly transmitted through the subband and can easily move in the superlattice layer. become. As a result, the electrons that have resonated and transmitted through the electron transfer layer having several superlattice structures from the electron supply layer have a higher energy level than the vacuum level or an equivalent energy level near the surface layer. Layers can be more easily released into vacuum. In this case, the applied voltage at which electrons are emitted from the surface layer is a discrete value determined by the structure of the superlattice layer, and shows an applied voltage dependency different from that of the above configuration example.

As described above, as shown in FIG. 7, a superlattice layer in which layers having different compositions are laminated on a semiconductor layer functioning as an electron supply layer, and a material having a negative or near zero electron affinity is formed. With the structure of the electron-emitting device having the surface layer, it is possible to easily supply electrons to the surface in the true NEA state by the action of the superlattice layer and to extract the electrons into a vacuum.

Next, various embodiments of the electron-emitting device obtained by applying the above basic structure of the present invention will be described below.

First Embodiment FIG. 9 is a sectional view showing the structure of a NEA electron-emitting device according to a first embodiment of the present invention. As shown in the figure,
The NEA electron-emitting device of the present embodiment includes a sapphire (alumina single crystal) substrate 11 and an n-GaN layer 12 provided on the sapphire substrate 11 and functioning as an electron supply layer.
An Al _x Ga ₁ -xN layer 13 provided on the n-GaN layer 12 and functioning as an electron transfer layer as a composition gradient layer in which the Al composition ratio x changes almost continuously from 0 to 1. Al
and a AlN layer 14 that functions as a surface layer provided on the _x Ga _1-x N layer 13. Further, a lower electrode 15 provided on the n-GaN layer 12 and a surface electrode 16 provided on the AlN layer 14 and in Schottky contact with the AlN layer 14 are provided. Here, the Al _x Ga _{1 -x} N layer 1
No. 3 has a gradient composition in which the Al content ratio x is approximately 0 at the bonding surface with the n-GaN layer 12 and the Al content ratio is approximately 1 at the bonding surface with the AlN layer 14. Further, the surface electrode 16 in the present embodiment is formed of a metal film having a single composition (for example, nickel (Ni), titanium (Ti), platinum (Pt)), and has a thin first region 16a (film). (A thickness: 5 to 10 nm) and a second region 16b (thickness: 100 nm or more) having a large thickness around the second region 16b.

Since the electron-emitting device of this embodiment has substantially the same structure as the example of the basic structure of the NEA electron-emitting device shown in FIG. 1, by applying a forward bias as described above, n -The electrons supplied from the GaN layer 12 (electron supply layer) are moved in the Al _x Ga _{1 -x} N layer 13 (electron transfer layer) with good controllability, and the efficiency is reduced from the AlN layer 14 (surface layer) to vacuum. Can be released well.
At this time, naturally, electrons that flow into the surface electrode 16 exist.
By appropriately setting the film thickness and area of the second region, electrons can be mainly extracted from the thinner first region 16a of the surface electrode 16.

Here, a method for manufacturing the NEA electron-emitting device of this embodiment will be described.

First, the MOC was placed on the sapphire substrate 11.
After a GaN buffer layer (not shown) is formed by reacting trimethylgallium (TMG) and ammonia (NH ₃ ) by VD method, silane (Si
H ₄ ) is added to form an n-GaN layer 12 which is an electron supply layer. Next, after stopping supply of SiH _{4 as} a doping gas, trimethylaluminum (TMA) is introduced, and Al _x Ga is added while gradually increasing the amount of Al added.
_The formation of the _1-x N layer 13 is started, and the supply of TMG is gradually reduced from the middle to thereby increase the Al content ratio of Al.
_The xGa1 _-xN layer 13 is formed continuously. By finally setting the Al content ratio x to 1, that is, the Ga content ratio to 0, the AlN layer 14 as the surface layer is changed to the Al _x Ga _{1 -x} N layer 13.
Can be formed continuously. At this time, the reaction temperature may be gradually changed in order to grow the high quality Al _x Ga ₁ -xN layer 13. By such a method, the n-GaN layer 12 as the electron supply layer, the Al _x Ga ₁ -xN layer 13 as the electron transfer layer, and the AlN layer 1 as the surface layer
4 can be formed continuously and with high quality. In this embodiment, the thickness of each layer is set to n-Ga
N layer: 4 μm, Al _x Ga _1-x N layer: 0.07 μm, Al
N layer: 0.01 μm.

The method of forming each layer of GaN, Al _x Ga ₁ -xN, and AlN is not limited to the above method. For example, it is also possible to use an MBE method or the like instead of the MOCVD method. As another method of forming an Al _x Ga ₁ -xN layer having a graded composition, for example, a thin Al layer is epitaxially grown on a GaN layer, and this is subjected to a heat treatment so that the lower the A, the lower the A
It is also possible to form an Al _x Ga ₁ -xN layer in which the 1 content ratio is small and the Al content ratio is large as it is closer to the surface.

Next, the n-GaN layer 12 serving as an electron supply layer
Then, a lower electrode 15 is formed. At this time, since the sapphire used as the substrate is an insulator, no electrode can be provided on the back surface of the sapphire substrate 11. Then, n
-Etching is performed to a certain depth from the surface to expose a part of the GaN layer 12, and the lower electrode 15 (material: Ti / A) is formed on the n-GaN layer surface exposed by this etching process.
1) was formed by a vacuum evaporation method.

Further, a surface electrode 16 is formed on the AlN layer 14 which is a surface layer. The material is appropriately selected, but Pt, Ni, Ti and the like are preferably used. Also, the forming method is not limited, but an electron beam evaporation method is generally used. Note that the first region 16a of the surface electrode 16 that functions as an electron emission portion is preferably as thin as possible in order to increase electron emission efficiency. Therefore, when the entire surface electrode 16 is formed, the first region 16a and the second region 16b may be formed separately. In the present embodiment, the film thickness of each region is set to the first
Area: 5 nm, second area: 200 nm.

The size of each region was set to φ20 μm for the first region and φ50 μm for the second region.

As a result of applying a forward bias of about ² to 10 V between the lower electrode and the surface electrode to the NEA electron-emitting device having the structure of the first embodiment, 10 ² to An emission electron current of about 10 ³ (A / cm ² ) was confirmed.

Note that even when there is no first region 16a, that is, when the center of the surface electrode 16 is a space, it is possible to emit electrons although the efficiency is reduced.

Second Embodiment The NEA electron-emitting device having the structure of the first embodiment has a function of collecting electrons emitted only by having a function of emitting electrons in a vacuum. Not necessarily. Therefore, as shown in FIG. 10, by providing an electrode serving as an anode near the NEA electron-emitting device, the emitted electrons can be accelerated / collected.

FIG. 10 is a sectional view showing the structure of a NEA electron-emitting device according to the second embodiment of the present invention. As shown in the figure, in the present embodiment, in addition to the structure of the first embodiment, an anode electrode 17 facing the surface layer with a space therebetween is provided. By applying an appropriate bias voltage to the anode electrode 17, the emitted electron flow can be easily controlled. Also,
If a phosphor or the like is applied to the anode surface, light emission due to the electron irradiation can be obtained, so that a display device such as a display using the light emission can be configured.

In this embodiment, the anode electrode 17 is arranged at a position spatially separated from the NEA electron-emitting device. However, the present invention is not limited to this. A configuration integrated with the emission element is also possible.

Third Embodiment In the first embodiment, the AlN layer 14 is used as the surface layer, but the Al content ratio x of Al _x Ga ₁ -xN is 0.1.
If it is in the range of 65 or more, since it is a NEA material, 0.6
Al _x Ga ₁ -xN in the region of 5 ≦ x ≦ 1 may be used for the surface layer.

FIG. 11 is a sectional view showing the structure of a NEA electron-emitting device according to the third embodiment of the present invention. As shown in the figure, in the present embodiment, an n-GaN layer 12 as an electron supply layer and a lower electrode 15 in contact with the n-GaN layer 12 are provided on a sapphire substrate 11. On the n-GaN layer 12, Al _x Ga _1-x N
A layer 13 is provided. Here, in the present embodiment, no AlN layer is provided. The reason is that, in the first embodiment, the AlN layer, which is a NEA material, is used as the surface layer. However, if the Al content ratio x of Al _x Ga ₁ -xN is 0.65 or more, NEA is used similarly to AlN. This is because Al _x Ga ₁ -xN in the region of 0.65 ≦ x ≦ 1 can be applied to the surface layer because it can be a material. That is, Al _x Ga
_By configuring the vicinity of the surface of the _1-x N layer 13 so that the Al content ratio x is equal to or greater than 0.65, the upper portion 18 of the Al _x Ga _1-x N layer 13 that functions as a surface layer, The function can be divided into a lower part 19 functioning as a moving layer and a lower part.

For example, in this embodiment, Al _x Ga
_A structure obtained by continuously changing the Al content ratio x of the _1-x N layer 13 from the electron supply layer side to stop the epitaxial growth when reaching Al _0.9 Ga _0.1 N can be applied.
_After reaching the composition of _0.9 Ga _0.1 N, several n
A structure obtained by epitaxially growing a layer having a thickness of about m may be used.

Further, as described above, even if the electron affinity of the surface layer does not necessarily reach a negative value, a substantial portion of electrons distributed in the conduction band has an energy level higher than the vacuum level. What is necessary is that the composition has an appropriate electron affinity value. That is, even if it is not made of a true NEA material, it may be made of a material that substantially realizes the NEA state.

On the upper portion 19, which is the surface layer of the Al _x Ga ₁ -xN layer, a surface electrode 16 made of a metal in Schottky contact is provided. The metal used for the surface electrode 16 and its configuration are the same as those used in the first embodiment.

Further, in the structure shown in FIG. 11, the anode electrode is not provided, but as in the second embodiment, the anode electrode is further provided opposite to the surface electrode 16 so that the converged electrons are provided. Accelerates flow with anode electrode /
It becomes possible to collect.

As in the first embodiment, the NEA having this configuration
By applying a forward bias (positive voltage to the surface electrode 16) to the electron-emitting device, electrons supplied from the n-GaN layer 12 (electron supply layer) can be transferred to the Al _x Ga ₁ -xN layer with good controllability. By moving inside the layer portion 19, the Al _x Ga ₁ -xN layer surface 18 functioning as a surface layer can be efficiently released into a vacuum.

Fourth Embodiment In the third embodiment, the Al in the NEA state is used.
_Although the upper part of the xGa ₁ -xN layer (0.65 ≦ x <1) is used as the surface layer, NEA such as an AlN layer is directly formed thereon.
Materials may be deposited. In the case of this configuration, a structure in which an energy barrier exists in the conduction band described with reference to FIG. 6 can be used, or a structure in which a coating layer made of AlN is provided can be considered. In any case, electrons can be efficiently extracted into a vacuum as described above.

[0110] On such an Al _x Ga _1-x N layer, N
In a configuration in which the EA material is further added, Al _x Ga
_{Even when} the Al content ratio of the _1-xN layer is 0 ≦ x ≦ 0.65, if the film thickness of the NEA material such as the AlN layer formed on the surface is an appropriate value (5 to 10 nm). Since the electrons injected from the electron supply layer can be tunnel-transmitted to the surface, a similar effect can be obtained by the mechanism described above.

Fifth Embodiment FIG. 12 is a sectional view showing the structure of a NEA electron-emitting device according to a fifth embodiment of the present invention. In the present embodiment, in addition to the structure of the first embodiment, Al _x Ga ₁ -xN
A buried insulating layer (or a buried p-type layer) 20 formed in the layer 13.

In the present embodiment, N in the first embodiment is used.
In addition to the function of the EA electron-emitting device, the Al _x Ga _1-x N layer 1
The electron flow moving through the Al _x Ga ₁ -xN layer, which is an electron transfer layer, is narrowed by the buried insulating layer 20 provided inside 3 to increase the density of electrons reaching the surface electrode 16a, which is the main electron emitting portion. Things. For example, if the opening diameter is φ5μ
When the embedded insulating layer 20 of m was inserted, a current density of about 2 × 10 ³ (A / cm ² ) was obtained due to the concentration effect of the electron flow.

Note that also in this embodiment, the surface electrode 16
Of the first region 16a functioning as an electron emitting portion,
In order to increase the electron emission efficiency, it is preferable that the thickness be as thin as possible.

Even when there is no first region 16a, that is, when the center of the surface electrode 16 is a space, it is possible to emit electrons although the efficiency is reduced.

In this embodiment, the AlN layer 1
4 is used as the surface layer, but if the Al content ratio x of Al _x Ga ₁ -xN is 0.65 or more, it is a NEA material.
Al _x Ga ₁ -xN in the region of 0.65 ≦ x ≦ 1 may be used for the surface layer. Further, even when an AlN layer is further formed thereon, it can be considered as a structure in which an AlN coating layer is provided. In any case, electrons can be efficiently extracted into a vacuum as described above.

In this embodiment, Al _x Ga ₁ -xN
Even when the Al content ratio of the layer is 0 ≦ x ≦ 0.65,
By setting the thickness and the like of the AlN layer used as the surface layer to an appropriate value as described above, the injected electrons can be tunnel-transmitted to the surface, and the same effect can be obtained.

Sixth Embodiment FIG. 13 is a sectional view showing the structure of a NEA electron-emitting device according to a sixth embodiment of the present invention. In the present embodiment, the surface electrodes 16a, 16b in the first embodiment
Instead, a surface electrode 21 having a first region 21a and a second region 21b made of metals having different work functions is provided. Here, the relationship between the work function φ _{M1 of the} metal forming the first region 21a and the work function φ _M2 of the metal forming the second region 21b is φ _M1 <φ _M2. It is a target. Further, the thickness d _{M1 of} the metal constituting the first region 21 a and the second region 21
The relationship of the film thickness d _M2 of the metal forming b is d _M1 <d _M2 . The metal material constituting each region is not particularly limited as long as it satisfies the above relationship, but is appropriately selected from the viewpoint of ease of formation and the like. For example, the first
(I.e., titanium (Ti), magnesium (Mg), europium (Eu), barium (Ba), strontium (Sr))
However, examples of the metal having a large work function that forms the second region 21b include platinum (Pt), chromium (Cr), tungsten (W), nickel (Ni), and gold (Au).

In the structure shown in FIG. 13, no buried insulating layer (buried p-type layer) is provided, but Al _x
A buried insulating layer may be provided in the Ga _1-x N layer 13.
Further, in the structure shown in FIG. 13, an anode electrode is not provided, but an anode electrode may be provided facing the surface layer.

In this embodiment, the first region 21a of the surface electrode 21 has a work function φ larger than that of the second region 21b.
Therefore, in addition to the effects of the above embodiment, the following effects can be obtained.

When a forward bias is applied to the surface electrode 21, the region of the AlN layer 14 where the first region 21a is disposed is closer to the energy barrier formed between the surface layer 14 and the second region 21b. Therefore, the current supplied from the electron supply layer starts flowing before the region where the second region 21b is arranged. Therefore, the first area 21
a functions as an electron emission portion, and the second region 21b functions as a signal connection portion with the outside.

According to the present embodiment, the first region 21a is formed of a metal having a work function smaller than that of the metal forming the second region 21b, and has a film thickness smaller than that of the metal forming the second region 21b. By forming the first region 21a with a thin metal, electrons can be emitted from the first region 21a in a concentrated manner, so that the electron emission efficiency can be further improved as compared with the above embodiment.

For example, by the same conditions as in the above embodiment,
When ass voltage is applied, 1 × 10 ^Four(A / cm^Two)degree
Was obtained. In this case,
As the metal of the first region 21a, the thickness is 5 nm and the diameter is φ.
20 μm of titanium (Ti) is added to the metal of the second region 21b.
Platinum with a thickness of 200 nm and a diameter of 200 μm
(Pt) was used.

In this embodiment, a Ti film having a thickness of 5 nm is used.
However, it is preferable that the first region 21a of the surface electrode 21 functioning as an electron emission portion be as thin as possible in order to increase the electron emission efficiency.

Seventh Embodiment FIG. 14 is a sectional view showing the structure of a NEA electron-emitting device according to a seventh embodiment of the present invention. As shown in FIG. 1, in the present embodiment, an n-GaN layer 12 serving as an electron supply layer is provided on a sapphire substrate 11 and the n-GaN
And a lower electrode 15 in contact with the layer 12. Here, in the present embodiment, no AlN layer is provided. In the Al _x Ga ₁ -xN layer 13, the vicinity of the upper portion 18 which is a surface layer has a negative electron affinity because the Al content ratio x is equal to or greater than 0.65. Function as A lower portion 19 of the Al _x Ga ₁ -xN layer 13 other than an upper portion functioning as a surface layer functions as an electron transfer layer.

For example, in this embodiment, Al _x Ga
The _1-x N layer of Al content ratio x to be applied structure obtained stop epitaxial growth when the continuously changed reached Al _0.9 Ga _0.1 N from the electron supply layer side, Al _0.9
After reaching the composition of Ga _0.1 N, the composition is further increased to several nm.
A structure obtained by epitaxially growing a layer having a thickness of about the same may be used. Further, as described above, even when the electron affinity of the surface layer does not necessarily reach a negative value, that is, even when the surface layer is not formed of a true NEA material, the surface layer is formed of a material capable of substantially realizing the NEA state. It should just be done.

In the present embodiment, as in the sixth embodiment, the first structure made of metals having different work functions is used.
Electrode 2 having region 21a and second region 21b
1 is provided. About the metal used and its conditions, from what was demonstrated by said 6th Embodiment,
It is appropriately selected.

In this embodiment also, the second region 21b
The first metal due to a metal whose work function is smaller than that of the metal constituting
Region 21a, and the first region 21a is made of a metal having a thickness smaller than that of the metal constituting the second region 21b.
With this configuration, electrons can be emitted from the first region 21a in a concentrated manner, so that the electron emission efficiency can be further improved as compared with the above embodiment.

In the structure shown in FIG. 14, no anode electrode is provided, but an anode electrode may be provided facing the surface layer.

In this embodiment, 0.65 ≦ x
Although Al _x Ga ₁ -xN in the region of ≦ 1 is used as the surface layer, when an AlN layer is further formed thereon, it can be considered as a structure provided with an AlN coating layer. Electrons can be efficiently extracted in a vacuum.

In this embodiment, Al _x Ga ₁ -xN
Even when the Al content ratio of the layer is 0 ≦ x ≦ 0.65,
By setting the thickness and the like of the AlN layer used as the surface layer to an appropriate value as described above, the injected electrons can be tunnel-transmitted to the surface, and the same effect can be obtained.

Eighth Embodiment FIG. 15 is a sectional view showing the structure of a NEA electron-emitting device according to an eighth embodiment of the present invention. As shown in FIG. 13, the structure of the NEA electron-emitting device of this embodiment is the same as that of FIG.
The structure is apparently the same as that of the sixth embodiment shown in FIG. Then, the sapphire substrate 11, the n-GaN layer 12, the Al _x
The structures of the Ga _1-x N layer 13, the AlN layer 14, and the lower electrode 15 are the same as those in the sixth embodiment.

In this embodiment, instead of the surface electrodes 21a and 21b in the sixth embodiment, a first region 22a and a second region 22b made of metals having different resistances to ion bombardment are used. Surface electrode 22 having
Is provided. The metal material constituting each region is appropriately selected. For example, as the metal constituting the first region 22a, titanium (T
i), magnesium (Mg), europium (Eu),
While the second region 22b is made of barium (Ba), strontium (Sr), or the like, the second region 22b has high resistance to ion bombardment such as tungsten (W) and molybdenum (M).
o), tantalum (Ta) or the like.

In the structure shown in FIG. 15, no anode electrode is provided, but an anode electrode may be provided facing the surface layer.

In this embodiment, since the second region 22b of the surface electrode 22 is made of a metal having high ion impact resistance, the following effects are obtained in addition to the effects of the above-described embodiment.

When a forward bias is applied to the surface electrode 22, electrons are mainly emitted from the region of the AlN layer 14 where the first region 22a is arranged. When electrons are emitted from the surface layer of the electron-emitting device into a vacuum, the electrons collide with gas molecules in the residual gas and generate ions before reaching an anode electrode (not shown). Since these ions are accelerated toward the surface electrode 22, the ions collide with the surface electrode at a high speed, that is, so-called ion bombardment occurs. At this time, the ion bombardment consumes the electron-emitting portion in the surface electrode, so that N
There is a concern that the life of the EA electron-emitting device will be shortened. Therefore, as shown in the present embodiment, by forming the second region 22b of the surface electrode with a metal having high ion resistance, the region where ions collide can be dispersed and the consumption of the surface electrode can be reduced. .

According to the present embodiment, the durability of the NEA electron-emitting device can be higher than that of the above-described embodiment by applying a metal having high ion impact resistance to the second region 22b.

Ninth Embodiment FIG. 16 is a sectional view showing the structure of a NEA electron-emitting device according to a ninth embodiment of the present invention. In the present embodiment, in addition to the structure of the above-described embodiment, an insulator film 23 made of an oxide film, a nitride film, or the like, which is partially opened, is provided. Is provided with a first region 24a of the surface electrode 24, and a second region 2a of the surface electrode 24 is provided on a portion extending from the side surface to the upper surface of the insulator film 23.
4b is provided. The first region 24a functions as an electron emission portion, and the second region 24b mainly functions as a signal connection portion with the outside.

In the present embodiment, both the first region 24a and the second region 24b of the surface electrode are made of metal that makes Schottky contact with the surface layer, for example, titanium (Ti), magnesium (Mg), europium having a small work function. (E
u), barium (Ba), strontium (Sr) and the like. And, in particular, the first region 24a
Is provided as a thin film having a thickness of 10 nm or less.
4b has a relatively large thickness of 100 nm or more. However, the second region 24b is formed of a metal different from the first region 24a, for example, platinum (P) having a large work function.
t), chromium (Cr), tungsten (W), nickel (Ni), gold (Au), or the like.

In the present embodiment, since the surface electrode 24 is constituted by the region where the insulator film 23 is inserted and the region where the insulating film 23 is not inserted, the following effects are obtained in addition to the effects of the above-described embodiment. Can be

When a forward bias is applied to the surface electrode 24, the AlN layer 14 is in contact with the first region 24a of the surface electrode functioning as an electron emission portion at the bottom of the opening of the insulator film, and is insulated from the other regions. Because it is in contact with the body membrane,
The electron flow supplied from the electron supply layer and traveling through the electron transfer layer converges only in the first region 24a. Therefore, according to the present embodiment, a thin surface electrode layer (first region 24)
With the configuration of a), electrons can be emitted from the first region 24a in a concentrated manner, so that the electron emission efficiency can be further improved as compared with the above embodiment.

In the structure shown in FIG. 16, no anode electrode is provided, but an anode electrode may be provided facing the surface layer.

In this embodiment, the AlN layer 1
4 is used as the surface layer, but if the Al content ratio x of Al _x Ga ₁ -xN is 0.65 or more, it is a NEA material.
Al _x Ga ₁ -xN in the region of 0.65 ≦ x ≦ 1 may be used for the surface layer. Further, even when an AlN layer is further formed thereon, it can be considered as a structure in which an AlN coating layer is provided. In any case, electrons can be efficiently extracted into a vacuum as described above.

In the present embodiment, Al _x Ga _{1 -x}
Even when the Al content ratio of the N layer is 0 ≦ x ≦ 0.65, the injected electrons can be applied to the surface by adjusting the thickness of the AlN layer used as the surface layer to an appropriate value as described above. The same effect can be obtained because tunnel transmission is possible.

Tenth Embodiment FIG. 17 is a sectional view showing the structure of a NEA electron-emitting device according to a tenth embodiment of the present invention. In the present embodiment, in addition to the structure of the first embodiment, an insulator film 25 such as an oxide film or a nitride film formed on the second region 16b of the surface electrode 16 is formed. And a control electrode 26 provided thereon.

The NEA electron-emitting device of the present embodiment has the functions of the above-described NEA electron-emitting device of the first embodiment.
It also has the function of controlling the flow of electrons emitted into a vacuum.

For example, when a forward bias is applied between the lower electrode 15 and the surface electrode 16 and an appropriate positive voltage is applied to the control electrode 26, the divergence of the electron flow emitted into the vacuum is applied to the control electrode 18. The effect can be suppressed by the effect of the applied bias. The manufacturing conditions of the element applied in this case include the electron supply layer 12, the electron transfer layer 13, the surface layer 1
4. The surface electrode 16 is the same as that used in the first embodiment. The size of the electron emission region (the opening of the control electrode 26) is 10 μm,
Has a thickness of 10 μm.

In this embodiment, the surface electrode 16
Of the first region 16a functioning as an electron emitting portion,
In order to increase the electron emission efficiency, it is preferable that the thickness be as thin as possible.

Even when there is no first region 16a, that is, when the center of the surface electrode 16 is a space, it is possible to emit electrons although the efficiency is reduced.

In this embodiment, the AlN layer 1
4 is used as the surface layer, but if the Al content ratio x of Al _x Ga ₁ -xN is 0.65 or more, it is a NEA material.
Al _x Ga ₁ -xN in the region of 0.65 ≦ x ≦ 1 may be used for the surface layer. Further, even when an AlN layer is further formed thereon, it can be considered as a structure in which an AlN coating layer is provided. In any case, electrons can be efficiently extracted into a vacuum as described above.

In this embodiment, Al _x Ga _{1 -x}
Even when the Al content ratio of the N layer is 0 ≦ x ≦ 0.65, the injected electrons can be applied to the surface by adjusting the thickness of the AlN layer used as the surface layer to an appropriate value as described above. The same effect can be obtained because tunnel transmission is possible.

In the structure shown in FIG. 17, the anode electrode is not provided. However, by providing the anode electrode opposite to the control electrode, the converged electron flow can be accelerated / collected by the anode electrode. Becomes possible.

Eleventh Embodiment FIG. 18 is a sectional view showing the structure of a NEA electron-emitting device according to an eleventh embodiment of the present invention. As shown in the drawing, the structure of the NEA electron-emitting device of this embodiment is apparently the same as the structure of the sixth embodiment shown in FIG. 9, but in this embodiment, an AlN layer ( thickness:
5 nm) and a GaN layer (thickness: 5 nm) were alternately laminated in two layers. In other words, the present configuration provides an AlN layer / GaN layer / AlN layer on the n-GaN layer 12.
Layer / GaN superlattice layer 27 is laminated, and an AlN layer 14 (surface layer) is further formed thereon. The surface electrode 16 is the same as in the first embodiment.

In the structure shown in FIG. 18, no anode electrode is provided, but an anode electrode may be provided facing the surface layer.

As a result of applying a forward bias of about 2 to 10 V between the lower electrode and the surface electrode to the NEA electron-emitting device having the structure of the eleventh embodiment, the applied voltage becomes Accordingly, 10 ² to 10 ³ (A / c
An emission electron current of about m ² ) was confirmed.

Twelfth Embodiment FIG. 19 is a view for explaining the configuration of the surface electrode portion of the NEA electron-emitting device applicable to each of the above embodiments. In each of the first to eleventh embodiments as described above, the distribution of the first region and the second region in the surface electrode is generally arbitrary, but is emitted by setting the distribution well. The shape and intensity distribution of the electron beam.

FIG. 19A is a perspective view of a surface electrode portion of a NEA electron-emitting device having a controlled surface electrode arrangement. The entire surface electrode 30 includes a first region 28 and a second region 29. In the present embodiment, the first region 28 mainly functioning as an electron emission region is the second region 2
It is distributed in a form scattered in a small size in the range surrounded by 9. The arrangement density generally employs a Gaussian distribution as shown in FIG. Note that FIG.
The first region 28 shown in (a) is the shape of the first region 16a in the first to fifth, tenth, and eleventh embodiments (see FIGS. 9 to 12, FIGS. 17, 18). The shape of the first region 21a in the sixth and seventh embodiments (see FIGS. 13 and 14) is the same as the shape of the first region 22a in the eighth embodiment (see FIG. 15).
Can be adopted as the shape of the first region 24a in the embodiment (see FIG. 16).

As shown in FIG. 19A, the surface electrode 30
There are many fine first region portions 28 therein, but as described above, the thickness of the metal electrode disposed in the first region 28 is about 5 to 10 nm, and the metal electrode is disposed in the second region 29. The thickness of the metal electrode is 100 nm or more. As a specific configuration example, the size of the entire surface region 30 is about 300 μm, and the first region 28 having a diameter of 5 μm
Approximately 00 pieces were arranged in a distribution (Gaussian distribution) such that the center of the surface electrodes was dense. With such a surface electrode configuration, it was confirmed that the spread of the emitted electron current was suppressed as compared with the case where electrons were uniformly emitted from the entire surface electrode.

As described above, according to the present embodiment, a large number of fine divided electron emission regions (first regions 28) are arranged in the surface electrode 30 and the distribution thereof is appropriately set, so that the electron emission regions are formed. The intensity distribution of the generated electron current can be controlled. At this time, by appropriately adjusting the size, shape, and number of the electron emission regions, the shape of the electron beam and the intensity distribution in the electron beam can be controlled to a desired distribution state, for example, a Gaussian distribution. As a result, an electron beam having a smaller spread can be obtained as compared with an electron beam obtained from a conventional single electron emission source that can obtain the same peak intensity. Note that the electron-emitting portion may be a through-hole and may be in a state where no metal film exists. Thirteenth Embodiment In this embodiment, an example in which the above NEA electron-emitting device is applied to a vacuum transistor will be described.

FIG. 20 is a sectional view showing the structure of a micro vacuum transistor according to the thirteenth embodiment. The micro vacuum transistor according to the present embodiment is similar to the ninth embodiment (FIG. 16).
(NEA electron-emitting device shown in FIG. 1). As shown in FIG. 20, the micro vacuum transistor of the present embodiment is
An n-GaN layer 52 functioning as an electron supply layer provided on a sapphire substrate 51; and a composition gradient layer provided on the n-GaN layer 52 and having a composition that changes almost continuously. Al _x Ga _1-x N layer 5 functioning as moving layer
3, an AlN layer 54 provided on the Al _x Ga _{1 -x} N layer 53 and functioning as a surface layer, a lower electrode 55 provided on the n-GaN layer 52, and A surface electrode 56 provided and in Schottky contact with the AlN layer 54
And a first layer formed on the AlN layer 54 and having an opening.
Of the insulating film 57 is provided. The first insulating film 57
Generally, it is made of silicon oxide or the like. Then, the AlN layer 54 exposed on the bottom surface of the opening of the first insulating film 57
From the surface of the AlN layer 54 exposed from the surface of the first insulating film 57 to the bottom surface of the opening of the first insulating film 57, through the side surface of the opening of the first insulating film 57, and to the upper surface of the first insulating film 57; The thin film portion 56a of the surface electrode 56 is formed. The thin film portion 56a of the surface electrode 56 is made of a thin metal having a thickness of about 5 to 10 nm, and a portion of the thin film portion 56a where the Schottky contact of the AlN layer 54 in the opening is an electron emission portion. The thick film portion 56b of the surface electrode 56 is formed of a metal having a thickness of 100 nm or more provided on the first insulating film 57, and the thick film portion 56b is connected to the thin film portion 56a to form a wiring connection pad. Functions as a unit. The above structure is
The structure is basically common to the NEA electron-emitting device described in the above embodiment.

Here, in this embodiment, on the first insulating film 57, a cylindrical second insulating film having a part with an inner diameter larger than the opening diameter of the first insulating film 57 is partially omitted. 58
And an upper electrode 59 made of metal for closing the upper end surface of the second insulating film 58. This second insulating film 58
Is also generally made of silicon oxide or the like. Also,
On the first insulating film 57, a sidewall 63 made of silicon oxide or silicon nitride surrounding the periphery of the second insulating film 58 is formed. And the surface electrode 5
6, the electron traveling chamber 60 surrounded by the second insulating film 58, the side wall 63 and the upper electrode 59 has an inner diameter of about 1
At 0 μm, the pressure is reduced to about 10 ⁻⁵ Torr (about 1.33 mPa).

In this embodiment, Al _x Ga _{1 -x}
The N layer 53 has a gradient composition in which the Al content ratio with respect to Ga is approximately 0 (x = 0) at the lower end portion, and conversely, the Al content ratio is approximately 1 at the upper end portion.

In the above structure, the semiconductor layer 52 and the electron transfer layer 53 form a solid layer functioning as an electron control layer, the upper electrode 59 functions as an external electrode, and the second insulating film 58 and the side The wall 63 forms a sealing member.

The present vacuum transistor accelerates electrons emitted in response to a signal applied between the surface electrode 56 and the lower electrode 55 in the decompressed electron traveling chamber 60 and receives the electrons at the upper electrode 59. In addition, since the electron transit area is set to a vacuum, it functions as an amplifying element or a switching element having high insulating properties, low internal loss, and low temperature dependence.

The micro vacuum transistor of this embodiment uses the structure of the NEA electron-emitting device similar to the ninth embodiment. However, the present invention is not limited to this, and any one of the first to eleventh embodiments may be used. The NEA electron-emitting device described in the embodiment can also be used.

Here, a method for manufacturing the vacuum transistor of the present embodiment will be described. FIGS. 21 (a) to 21 (d)
It is a figure showing a manufacturing process of a vacuum transistor in this embodiment.

First, an n-GaN 52 serving as an electron supply layer and an Al _x Ga serving as an electron transfer layer are provided on a sapphire substrate 51.
_{A 1-x} N layer 53 and an AlN layer 54 as a surface layer are formed. This step is as described in the first embodiment.

Next, in a step shown in FIG. 20A, after depositing a silicon oxide film as the first insulating film 57, an opening for an electron emission portion is formed, and thereafter, an upper electrode is formed on the entire surface of the substrate. Thickness of 5 to 10 n for forming the thin film portion 56 a of 56
An m-thick titanium film 56x is deposited. Furthermore, after depositing an aluminum film thereon, this aluminum film is patterned to be substantially concentric with the opening of the first insulating film 57 and having a diameter larger than that of the opening of the first insulating film 57. A core 65 composed of a cylindrical portion and a rod-shaped portion extending in four directions from the bottom of the cylindrical portion is formed. The core 65 forms a water wheel-shaped pattern including a cylindrical portion having a vertical axis and a vertical wall portion of the same thickness extending radially in all directions from the cylindrical portion by the first patterning of the aluminum film. , First
It is easily formed by reducing the thickness of the vertical wall portion by the second patterning. The core 65 may be made of a photoresist. Depending on the material of the sidewall 63 to be formed later, the thickness of the vertical wall portion may be reduced only slightly or may not be reduced at all.

Next, in the step shown in FIG.
After depositing a silicon oxide film 58x to be the second insulating film 59 on the entire surface of the substrate by the VD method, the silicon oxide film 58x is planarized by, for example, the CMP method until the core 65 of the aluminum film is exposed. Thereafter, a tungsten film 59x to be the upper electrode 59 is deposited on the entire surface of the substrate by sputtering.

Next, in the step shown in FIG. 20C, the entire tungsten film 59x, silicon oxide film 58x, core 65, and titanium film 56x are patterned into a vertical cylindrical shape by photolithography and dry etching. Thus, the dimensions of the first insulating film 58, the upper electrode 59, and the thin film portion 56a of the surface electrode 56 are substantially determined.

Next, in the step shown in FIG. 20D, the entire substrate is immersed in a sulfated water solution (a mixed solution of sulfuric acid and hydrogen peroxide solution). At this time, since the upper end surface of the rod of the core 65 is exposed, the core 65 made of aluminum is etched from this portion by the sulfated water solution, and the core 65 is finally removed. Then, the thin film portion 56 of the second insulating film 58, the upper electrode 59, and the surface electrode 56
An electron traveling chamber 60 surrounded by a is formed.

Next, when a thick silicon oxide film is deposited on the substrate, the lateral hole formed after the rod-shaped portion of the core 65 is removed is closed by the thick silicon oxide film. At this time, the pressure of the internal electron traveling chamber 60 is set to, for example, 10 ⁻⁵ Torr by depositing SiO ₂ on the substrate from above using the MBE method, the sputtering method, the vacuum evaporation method, or the like.
While the pressure is reduced to a low pressure of r (about 1.33 mPa) or less, the side hole can be easily closed with the silicon oxide film.

In particular, after the majority of the lateral holes are initially closed by using the CVD method or the like, finally, the lateral holes are completely closed by an insulating material by MBE, sputtering, vacuum deposition, or the like. By doing so, the vacuum state of the internal electron traveling chamber 60 can be ensured while increasing the opening size of the lateral hole to facilitate the process.

Thereafter, the thick silicon oxide film is anisotropically etched to form the upper electrode 59, the second insulating film 58, and the side wall 63 surrounding the side surface of the thin film portion 56a of the surface electrode 56.

Although illustration of subsequent steps is omitted, after removing the sidewall 63, the upper electrode 59, and one end of the second insulating film 58, a metal film (for example, a Pt film) is deposited on the substrate. By patterning this,
The thick film portion 56b of the surface electrode 56 is formed. Thereafter, a hole reaching a part of the n-GaN layer 52 is formed in the substrate, and the lower electrode 55 is formed.

Through the above steps, a vacuum transistor can be easily obtained.

It is to be noted that not only the present embodiment but also the above first to first embodiments
It goes without saying that a vacuum transistor can be formed using the structure of any one of the NEA electron-emitting devices disclosed in the eleventh embodiment. Therefore,
A superlattice layer may be provided instead of the Al _x Ga _1-x N layer 53,
Al _x Ga having a high Al content ratio x without providing the 1N layer 54
It is possible to provide a surface electrode that makes direct Schottky contact with the _1-xN layer.

Fourteenth Embodiment Next, a fourteenth embodiment, which is a modification of the thirteenth embodiment, will be described.
The vacuum transistor according to the embodiment will be described.

FIG. 22 is a sectional view showing the structure of a vacuum transistor according to this embodiment. The present embodiment has a structure in which the NEA electron-emitting device is housed in a closed container.

As shown in FIG. 22, the vacuum transistor of this embodiment has a sealing cap 70, a cap 70, and a NEA in addition to the structure substantially similar to that of the thirteenth embodiment shown in FIG. A jig 71 for attaching an electron-emitting device, a lower electrode 55, a surface electrode 56,
Terminals 72 to 74 electrically connected to the upper electrode 59 are provided. However, in the present embodiment, the electron traveling chamber 60 is not necessarily sealed by the second insulating film 58, the upper electrode 59, and the like, and the second insulating film 58 is formed in a bridge shape. The side wall 63 shown in FIG. 20 does not exist. In the present embodiment, the sealing member is constituted by the cap 70 and the jig 71, and the inside of the electron traveling chamber 60 is 10 ^-5 Torr (about 1.3).
It is maintained at a high vacuum of 3 mPa) or less.

According to this embodiment, the same effects as in the thirteenth embodiment can be exhibited. In particular, in the present embodiment, the degree of vacuum (degree of pressure reduction) of the electron traveling chamber 60 is set.
Is easily reduced to 10 ⁻⁵ Torr (about 1.33 mPa) or less.

-Other Embodiments- In the structures of the above-described first to eleventh embodiments, various configuration examples have been described. By using a structure obtained by combining those configurations, the respective effects can be reduced. It is also possible to combine.

In each of the above embodiments, the surface layer is made of Al
Although the surface layer is made of N or Al _x Ga ₁ -xN, the surface layer may be made of another NEA material such as diamond.

Also, AlN, Al _x Ga ₁ -xN, or a plurality of these NEA material films can be laminated. For example, a very thin coating layer such as a diamond layer may be provided on the surface layer in each of the above embodiments to protect the surface layer. In particular, when the surface layer is opened without providing a metal film on the electron-emitting portion, the AlN layer or Al _x
It is preferable to provide a coating layer for protection of the Ga _1-x N layer.

In the first to eleventh embodiments, the Al
_The xGa ₁ -xN layer may be doped with an n-type impurity to function as an n-type semiconductor.

A plurality of electron-emitting portions in the first to eleventh embodiments may be provided in one element.

[0186] The Al in the embodiment using the _x Ga _1-x N layer, Al _x is Ga _1-x N layer of Al content ratio x is a continuously varying structure, Al _x Ga _1-x For example, the Al content ratio x of the N layer may change stepwise.

[0187]

According to the electron-emitting device of the present invention, the surface layer is made of a material having a negative electron affinity or a nearly negative electron affinity, and electrons can be smoothly moved from the electron supply layer to the surface layer. Since the composition gradient layer and the superlattice layer are provided, it is possible to provide an electron emission which can be driven at a low voltage and has a function of emitting electrons with high efficiency.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a structure of a NEA electron-emitting device using AlN as an example of a NEA material.

FIGS. 2A and 2B are energy band diagrams respectively showing the energy band states of a semiconductor having a negative electron affinity and a semiconductor having a positive electron affinity.

FIG. 3 is a view showing measured data of electron affinity of Al _x Ga ₁ -xN.

FIGS. 4A and 4B are energy band diagrams showing an energy band state of each layer in a no-load state and when a voltage V is applied between a surface electrode and an electron supply layer.

FIG. 5 is a diagram showing the dependence of the band gap of Al _x Ga ₁ -xN on the Al content ratio.

FIGS. 6A and 6B show a single barrier type NEA.
FIG. 4 is an energy band diagram showing an energy band state when the electron-emitting device is not loaded and when a voltage is applied.

FIG. 7 schematically shows the structure of an electron-emitting device having a superlattice laminated portion in which two superlattice layers represented by Al _x Ga ₁ -xN and having different Al contents are alternately laminated as an electron transfer layer. FIG.

FIGS. 8A and 8B are energy band diagrams showing the energy band structure of a superlattice stacked NEA electron-emitting device when no load is applied and when a voltage is applied.

FIG. 9 is a sectional view showing the structure of the NEA electron-emitting device according to the first embodiment of the present invention.

FIG. 10 is a sectional view showing the structure of a NEA electron-emitting device according to a second embodiment of the present invention.

FIG. 11 is a cross-sectional view illustrating a structure of a NEA electron-emitting device according to a third embodiment of the present invention.

FIG. 12 is a sectional view showing a structure of a NEA electron-emitting device according to a fifth embodiment of the present invention.

FIG. 13 is a cross-sectional view illustrating a structure of a NEA electron-emitting device according to a sixth embodiment of the present invention.

FIG. 14 is a sectional view showing the structure of a NEA electron-emitting device according to a seventh embodiment of the present invention.

FIG. 15 is a sectional view showing the structure of a NEA electron-emitting device according to an eighth embodiment of the present invention.

FIG. 16 is a sectional view showing a structure of a NEA electron-emitting device according to a ninth embodiment of the present invention.

FIG. 17 is a sectional view showing a structure of a NEA electron-emitting device according to a tenth embodiment of the present invention.

FIG. 18 is a sectional view showing a structure of a microvacuum transistor according to an eleventh embodiment of the present invention.

FIGS. 19A and 19B are diagrams illustrating a configuration of a surface electrode portion of a NEA electron-emitting device applicable to each embodiment.

FIG. 20 is a cross-sectional view illustrating a structure of a micro vacuum transistor according to a thirteenth embodiment.

FIGS. 21A to 21D are cross-sectional views illustrating a manufacturing process of the microvacuum transistor according to the thirteenth embodiment.

FIG. 22 is a sectional view showing a structure of a microvacuum transistor according to a fourteenth embodiment of the present invention.

FIGS. 23A and 23B are a cross-sectional view showing a structure of a junction type NEA device reported so far and an energy band diagram showing an energy band state when a voltage is applied thereto.

[Explanation of symbols]

1 electron supply layer 2 electron moving layer 3 surface layer 4 surface electrode 11 sapphire substrate 12 n-GaN layer 13 Al _x Ga _1-x N layer 14 AlN layer 15 lower electrode 16 surface electrode 16a first region (electron-emitting portion) 16b second region 17 anode electrode 18 upper (surface layer) 19 lower 20 buried insulating layer (buried p-type layer) 21 surface electrode 21a first region (electron emission portion) 21b second region 22 surface electrode 22a first (Electron emitting portion) 22b second region 23 insulator film 24 surface electrode 24a first region (electron emitting portion) 24b second region 25 insulator film 26 control electrode 27 superlattice layer 28 first region (Electron Emitting Portion) 29 Second Region 30 Surface Electrode 51 Sapphire Substrate 52 n-GaN Layer 53 Al _x Ga _{1 -x} N Layer 54 AlN Layer 55 Lower Electrode 56 Surface electrode 56a Thin film portion 56b Thick film portion 57 First insulating film 58 Second insulating film 59 Upper electrode 60 Electron traveling chamber 61 High frequency signal source 62 Wiring 63 Sidewall 65 Core 70 Cap 71 Jig 72 to 74 Terminal

Continuation of front page (72) Inventor Masahiro Exit 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Person Kentaro Seto 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term (reference) 5C035 BB01 BB03

Claims (37)

[Claims] 1. A semiconductor layer functioning as an electron supply layer, a surface layer provided apart from the semiconductor layer, and made of a material having a negative or near zero electron affinity, a semiconductor layer, and the surface layer And a composition gradient layer whose composition is changed so that the electron affinity decreases in a direction from the semiconductor layer toward the surface layer; and a composition gradient layer provided on the surface layer, and An electron-emitting device comprising: a surface electrode for applying a voltage so as to supply electrons to the surface. 2. The electron-emitting device according to claim 1, wherein the composition gradient layer is made of an undoped semiconductor material. 3. The electron-emitting device according to claim 1, wherein the composition gradient layer has a band gap that extends almost continuously from the semiconductor layer to the surface layer at least in part. element. 4. The electron-emitting device according to claim 1, wherein the surface layer contains aluminum nitride (AlN). 5. The electron-emitting device according to claim 1, further comprising a coating layer provided on the surface layer and made of a material different from the surface layer. 6. The electron-emitting device according to claim 5, wherein the coating layer contains a material having an electron affinity of negative or close to zero. 7. The electron-emitting device according to claim 6, wherein the coating layer contains aluminum nitride (AlN). 8. The electron-emitting device according to claim 1, wherein the area including the composition gradient layer and the surface layer changes such that the proportion of Al increases as approaching the outermost surface. Al _x Ga
An electron-emitting device comprising _1-xN (0 ≦ x ≦ 1). 9. The electron-emitting device according to claim 1, wherein said surface electrode is in Schottky contact with said surface layer. 10. The electron-emitting device according to claim 1, wherein the surface electrode has an energy barrier between the first region and the surface layer. An electron-emitting device having a second region larger than an energy barrier between the first region and the second region. 11. The electron-emitting device according to claim 1, wherein the surface electrode has a pattern for controlling the distribution of emitted electrons. Electron emitting device. 12. The electron-emitting device according to claim 1, wherein an insulator layer is provided on the surface electrode so as to open at least a part of the surface electrode. And an external electrode provided on the insulator layer for accelerating and controlling electrons emitted from the surface layer to the outside. 13. A semiconductor layer functioning as an electron supply layer, a surface layer provided apart from the semiconductor layer and made of a material having an electron affinity of negative or close to zero, a semiconductor layer and the surface layer And a superlattice layer in which a plurality of layers for resonantly transmitting electrons supplied in a direction from the semiconductor layer toward the surface layer are stacked, and a superlattice layer provided on the surface layer, A surface electrode for applying a voltage so as to supply electrons to the outermost surface of the surface layer. 14. The electron-emitting device according to claim 13, wherein the superlattice layer is composed of two mixed crystals represented by Al _x Ga ₁ -xN (0 ≦ x ≦ 1) and has a component ratio of each other. An electron-emitting device comprising different layers alternately stacked. 15. The electron-emitting device according to claim 13, wherein the surface layer contains aluminum nitride (AlN). 16. One of claims 13 to 15
The electron-emitting device according to any one of claims 1 to 3, further comprising a coating layer provided on the surface layer and made of a material different from the surface layer. 17. The electron-emitting device according to claim 16, wherein the coating layer includes a material having an electron affinity of negative or close to zero. 18. The electron-emitting device according to claim 16, wherein the coating layer contains aluminum nitride (AlN). 19. A semiconductor layer functioning as an electron supply layer, a surface layer provided apart from the semiconductor layer, and made of a material having a negative or near zero electron affinity, a semiconductor layer and the surface layer And an electron transfer layer for supplying electrons in a direction from the semiconductor layer toward the surface layer; and an electron transfer layer provided so as to make a Schottky contact with at least a part of the surface layer, from the semiconductor layer to the surface. A surface electrode for applying a voltage so as to supply electrons to the outermost surface of the layer. 20. The electron-emitting device according to claim 19, wherein the composition of the electron transfer layer is changed such that the electron affinity decreases in a direction from the semiconductor layer toward the surface layer. Electron-emitting device. 21. The electron-emitting device according to claim 19, wherein the composition of the electron transfer layer changes such that a band gap increases in a direction from the semiconductor layer toward the surface layer. Electron-emitting device. 22. The electron-emitting device according to claim 19, wherein the electron transfer layer is formed by stacking a plurality of layers for resonantly transmitting electrons supplied from the semiconductor layer toward the surface layer. An electron-emitting device comprising a lattice layer. 23. The electron-emitting device according to claim 19, wherein the surface layer contains aluminum nitride (AlN). 24. A electron emission device according to claim 19, the region including the electron transfer layer and the surface layer, Al _x Ga which changes as the proportion of Al closer to the outermost surface is increased
An electron-emitting device comprising _1-xN (0 ≦ x ≦ 1). 25. The electron-emitting device according to claim 19, wherein the surface electrode has a first region having a smaller area than the semiconductor layer provided in contact with only a part of the surface layer; An electron-emitting device provided continuously with the first region and having an energy barrier between the surface layer and the surface layer, the second region being larger than the energy barrier between the surface layer and the first region. 26. The electron-emitting device according to claim 25, wherein the second region has a larger area than the first region and is more resistant to ion bombardment than a material forming the first region. An electron-emitting device comprising a material having a large size. 27. The electron-emitting device according to claim 25, further comprising: an insulator layer formed on a region of the surface layer other than a first region that is in contact with the surface electrode. The second region of the electrode is provided from the side surface to the upper surface of the insulator layer. 28. The electron-emitting device according to claim 25, wherein the second region of the surface electrode has a larger thickness than the first region. . 29. A solid layer functioning as an electronic control layer, and provided on the solid layer and having a negative or zero electron affinity.
A surface layer made of a material close to the surface layer, a surface electrode provided in contact with the surface layer, for applying a voltage between the solid layer and the outermost surface of the surface layer, and the surface electrode sandwiches a space. An electron-emitting device comprising: an external electrode provided; and a sealing member for keeping a space between the surface electrode and the external electrode in a reduced pressure state. 30. The electron-emitting device according to claim 29, wherein the solid layer is interposed between the semiconductor layer functioning as an electron supply layer and the semiconductor layer and the surface layer. A composition gradient layer in which the composition is changed such that the electron affinity decreases in the direction toward. 31. The electron-emitting device according to claim 30, wherein the composition gradient layer changes in composition such that a band gap increases in a direction from the semiconductor layer toward the surface layer. Electron-emitting device. 32. A electron emission device according to claim 29 or 30, wherein a region including the composition gradient layer and a surface layer, Al _x G which varies as the percentage of Al closer to the outermost surface is increased
An electron-emitting device comprising a _1-x N (0 ≦ x ≦ 1). 33. The electron-emitting device according to claim 29, wherein the solid layer is interposed between the semiconductor layer functioning as an electron supply layer and the semiconductor layer and the surface layer. A superlattice layer in which a plurality of layers for resonantly transmitting electrons supplied in a direction toward the substrate are stacked. 34. The electron-emitting device according to claim 29, wherein the surface layer contains aluminum nitride (AlN). 35. The electron-emitting device according to claim 29, wherein the surface electrode has a smaller area than the semiconductor layer provided in contact with only a part of the surface layer. A first region having an energy barrier between the surface layer and the first region, the second region being provided continuously with the first region and having an energy barrier between the surface layer and the first region. An electron-emitting device comprising: 36. The electron-emitting device according to claim 35, wherein the second region has a larger area than the first region, and is more ion bombarded than a material forming the first region. An electron-emitting device comprising a material having a high resistance to light. 37. The electron-emitting device according to claim 35, further comprising an insulator layer formed on a region of the surface layer other than a first region that is in contact with the surface electrode. An electron-emitting device, wherein the second region is provided from a side surface to an upper surface of the insulator layer.