JPH0677130A - Lateral superlattice device - Google Patents

Abstract

PURPOSE:To provide a lateral superlattice device in which a voltage applied to an electrode can effectively contribute to potential modulation. CONSTITUTION:A lateral superlattice device consists of a conductive substrate 51, a quantum well structure layer 50 formed on the substrate 51 and having a quantum well structure in the thickness direction, and layers 55 and 56 to which voltages to confine carriers in the quantum well structure layer 50 in the lateral direction are applied. The voltage application layers include impurity- doped semiconductor layers 55 and a plurality of thin-line Schottky electrodes 56. The semiconductor layers 55 are provided only between the plurality of Schottky electrodes that are formed on the quantum well structure layer 50.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a quantum well structure, and more particularly to a lateral superlattice device having a carrier confinement structure in the film thickness direction and the lateral direction.

[0002]

2. Description of the Related Art In a conductive structure in which carrier motion is restricted to a low-dimensional space, carrier scattering is suppressed and effective mobility is greatly increased. This is applied to a laser diode. It has been pointed out that if this is done, it is possible to expect a decrease in the oscillation threshold and an improvement in characteristics due to the rapid spectrum.
Therefore, until now, various methods have been used to form quantum wires having one-dimensional freedom of motion.
A typical fabrication method uses a fine processing technique using an electron beam, an X-ray, or a charged particle beam. By forming an electrode on the upper part of a two-dimensional carrier system and applying in-plane potential modulation, 1 A method for realizing a three-dimensional carrier system has been proposed. Here, the method of realizing low-dimensional carriers by the voltage applied to the electrodes is less affected by surface processing damage than the method of fine processing, and the voltage can change the dimension of carrier confinement on the same element. It is unique and has advantages in developing devices that apply low-dimensional carriers.

A one-dimensional confinement potential is added to free carriers in the bulk to form carriers having two-dimensional freedom of movement, which can be realized by stacking semiconductor thin films having different band gaps. In order to make the difference between carrier energy levels due to quantization significant, the thickness of the semiconductor layer in which carriers are confined needs to be equal to or less than the de Broglie wavelength. The thin film structure that requires dimensional accuracy of this level is a metal organic chemical vapor deposition (MOCVD) method that can control the growth film thickness at the atomic layer level,
It can be prepared by a method such as molecular beam growth method (MBE).

For a carrier having this two-dimensional degree of freedom,
As a typical structure for forming a carrier having a one-dimensional freedom of motion by adding one dimension of confinement by applying a voltage, Applied Physics Letters No. 52, Vol. 13 (198).
8 years) The element described in pages 1071 to 1073 is known. The structure of this element is shown in FIG. In this device, a carrier structure having a two-dimensional degree of freedom is formed on a substrate 21 by a modulation doping structure layer 20 of an impurity, and then a cap layer 25 highly doped with an impurity is formed on the structure, and a Schottky. Electrode 2
6 is provided and the shut key electrode 26 is finely processed into a grating shape. Modulation doped structure layer 20
Is composed of an n-type doped layer 24, a spacer layer 23, and a channel layer 22. Further, an ohmic electrode 27 is provided on the back surface of the substrate 21. This element is
By applying a voltage between the Schottky electrode 26 and the ohmic electrode 27, the potential of the channel layer 22 is modulated to restrain the carriers in the in-plane direction. When a voltage is applied to the Schottky electrode, the potential in the channel layer 22 changes. However, the cap layer 2 heavily doped with impurities
The variation in the region immediately below 5 is suppressed by the carriers in the cap layer 25, and the variation is smaller than that in the region immediately below the Schottky electrode 26. Therefore, the two-dimensional electron gas by modulation doping can be confined in the in-plane direction by the grating-shaped Schottky electrode 26 provided on the cap layer 25. Since this structure is not a structure that defines the region for confining carriers by processing, it is hardly affected by processing damage, and the quantum confining effect of carriers can be clearly seen.

[0005]

However, the device having the structure shown in FIG. 2 is not always efficient in generating potential modulation for confining in-plane direction by voltage. This is because in this structure, the potential modulation in the in-plane direction cannot be obtained in the channel layer 22 until the cap layer 25 immediately below the Schottky electrode 26 is completely depleted, and the absolute value of the voltage is increased to cause depletion. The potential modulation in the in-plane direction occurs in the channel layer 22 only after the layer penetrates the cap layer. Therefore, since the voltage from 0 V to the potential modulation of the channel layer appears in balance with the carriers expelled from within the cap layer 25 under the electrode, it cannot contribute to the increase of the potential modulation of the channel layer.

The present invention provides a lateral superlattice device having a structure in which the voltage applied to the electrodes efficiently contributes to potential modulation.

[0007]

In order to achieve the above object, according to a first aspect of the present invention, a substrate having conductivity and a quantum well structure formed on the substrate and having a quantum well structure in a thickness direction are formed. A lateral superlattice device having a well structure layer and a voltage application layer for confining carriers of the quantum well structure layer in a lateral direction, wherein the voltage application layer is provided in order on the quantum well structure layer. A semiconductor layer having a semiconductor layer doped with impurities and a plurality of Schottky electrodes in the form of thin wires, and the semiconductor layer below the Schottky electrode has a number of carriers per unit volume of the semiconductor layer that is a layer of the semiconductor layer. The value obtained by multiplying the thickness is smaller than the value obtained by multiplying the number of carriers per unit volume of the semiconductor layer by the layer thickness of the semiconductor layer in the semiconductor layer between the Schottky electrodes. Le superlattice device is provided.

In order to achieve the above object, according to a second aspect of the present invention, a substrate having conductivity and a quantum well structure layer having a quantum well structure in a thickness direction on the substrate. A lateral superlattice device having a voltage application layer for confining carriers of the quantum well structure layer in a lateral direction, wherein the voltage application layer is a semiconductor layer doped with impurities, and a plurality of thin line-shaped A Schottky electrode, the Schottky electrode is provided on the quantum well structure layer, and the semiconductor layer is provided only between the Schottky electrodes on the quantum well structure layer. A lateral superlattice device is provided.

According to a third aspect of the present invention, a substrate having conductivity, a quantum well structure layer having a quantum well structure in the thickness direction on the substrate, and a carrier of the quantum well structure layer. Is a lateral superlattice element for confining the quantum well structure layer in a lateral direction, wherein the voltage applying layer is a plurality of thin linear first layers for applying different voltages to the quantum well structure layer. A lateral having a Schottky electrode and a plurality of second linear Schottky electrodes, wherein the first Schottky electrodes and the second Schottky electrodes are alternately arranged. A superlattice device is provided.

[0010]

In the lateral superlattice according to the first aspect of the present invention, the quantum well structure layer formed on the substrate has a quantum well structure in the thickness direction and has two-dimensional freedom in the in-plane direction. Realize your career. When a voltage is applied between the Schottky electrode and the conductive substrate, the semiconductor layer immediately below the Schottky electrode (hereinafter referred to as the cap layer) is depleted, and the potential of the quantum well structure layer changes. To do.
Since the semiconductor layer between the Schottky electrodes is highly doped with impurities, the fluctuation of the potential of the quantum well layer immediately below the cap layer between the Schottky electrodes is suppressed. As a result, a high potential portion and a low potential portion are formed in the quantum well structure layer, and carriers are confined in the lateral direction.

In this case, in the first aspect of the present invention, the number of carriers contained in the cap layer doped with impurities is
The area under the Schottky electrode is smaller than the area between the Schottky electrodes. Therefore, of the voltage of the Schottky electrode, the voltage consumed for depleting the cap layer below the Schottky electrode is smaller than in the conventional case, and the voltage efficiently contributes to potential modulation.

In the lateral superlattice element according to the second aspect of the present invention, the cap layer is provided only between the Schottky electrodes, so that the Schottky electrode voltage is not consumed for depleting the cap layer. , Contributes directly to the potential modulation of the quantum well structure layer. Therefore, the fluctuation range of the potential in the in-plane direction becomes larger than that of the conventional structure, and a more ideal one-dimensional carrier system can be formed.

In the lateral superlattice device according to the third aspect of the present invention, different voltages are applied to the quantum well structure layer between the first Schottky electrode and the second Schottky electrode which are alternately arranged. . Therefore, in the third aspect, since the cap layer is not used as in the conventional case, the displacement of the applied voltage is not limited by the impurity concentration of the cap layer, and an arbitrary voltage can be applied. Thereby, the potential modulation can be efficiently formed.

[0014]

An embodiment of the present invention will be described with reference to the drawings.

First, as a first embodiment of the present invention, a latertell superlattice device having a single quantum well structure is shown in FIG. As shown in FIG. 5, the lateral superlattice device according to the present embodiment is
A quantum well structure layer 5 having a quantum well structure in the thickness direction on a substrate 51 made of n-GaAs having a thickness of 400 μm.
It has 0. Further, on the quantum well structure layer 50, in order to confine carriers of the quantum well structure layer 50 in the lateral direction, a Ni film having a thickness of 300 angstrom (hereinafter, angstrom is indicated by A) is processed into a Schottky. Electrode 56 and n + with a thickness of 200A
And a cap layer 55 made of a GaAs film (impurity concentration 1 × 10 ¹⁸ cm ³ ). On the back surface of the substrate 51, an ohmic electrode 5 composed of an Au—Ge alloy film is formed.
7 are arranged.

The Schottky electrode 56 is formed on the quantum well structure layer 50 with a period of 1000 A and one electrode width of 500 A. The cap layer 55 is the quantum well structure layer 50.
It is arranged only between the electrodes of the upper Schottky electrode 56. The quantum well structure layer 50 is, in order from the substrate 51 side, a barrier layer 5 formed of an i-AlGaAs film having a thickness of 500A.
2. Well layer 5 made of i-GaAs film with a thickness of 50A
3. A barrier layer 54 made of an i-AlGaAs film having a thickness of 300 A is laminated.

Next, the manufacturing process of the lateral superlattice of the first embodiment will be described with reference to FIG. First, FIG. 9 (a)
As shown in, a n-type GaAs film is prepared as the substrate 51,
As shown in FIG. 9B, an AlGaAs film not added with an impurity as a barrier layer 52, a GaAs film as a well layer 53, and an AlGaAs film as a barrier layer 54 are laminated on a substrate by a molecular beam epitaxy method (MBE method). Form a single quantum well. A ohmic electrode 57 is formed on the rear surface of the substrate.
The u-Ge alloy film is formed by vapor deposition.

Further, n-type GaAs is formed on the AlGaAs film.
The films are laminated to form a cap layer. A photoresist (PMMA: polymethylmethacrylate) is applied to the entire surface of the n-type GaAs film, and a grating pattern is formed by direct writing with an electron beam (FIG. 9C).
As shown in FIG. 9D, n of the cap layer 55 is formed by an alkaline etchant using this photoresist as a mask.
The type GaAs layer is etched. Then, a Ni film to be the Schottky electrode 56 is vapor-deposited, and by a lift-off method,
The element is completed by patterning the Ni film into a grating shape.

Next, as comparative examples, FIGS.
The lateral superlattice element of (a) will be described. The lateral superlattice device of the comparative example has a cap layer 15 as in the conventional case.
5 is provided on the entire surface of the quantum well structure layer 50. Board 5
1. The quantum well structure layer 50 and the ohmic electrode 57 are the first
Since the structure is similar to that of the lateral superlattice of the above embodiment, description thereof will be omitted. On the quantum well structure layer 50, in order to confine the carriers of the quantum well structure layer 50 in the lateral direction, an n + -GaAs film (impurity concentration 1 ×
A cap layer 155 composed of 10 ¹⁸ cm ~ ³ ) and a thickness of 3
A Schottky electrode 156 obtained by processing a Ni film of 00A into a grating shape is sequentially laminated.

Here, taking the example of FIG. 3, the cap layer 155.
Consider the effects of. FIG. 4 shows the magnitude of the potential modulation in the single quantum well with respect to the voltage applied to the electrode, obtained by simulation using the impurity concentration of the cap layer as a parameter. 5x10 ¹⁷ cm ~ ³
With the following impurity concentrations, almost no potential modulation occurs even with an applied voltage of −2V. Impurity concentration is 1 × 10 ¹⁸ c
It can be seen that when the impurity concentration is m ³ or more, a modulation of about 25 mV can be obtained at a voltage of −2.0V. At this time, the change in the magnitude of modulation is not linear with respect to the applied voltage,
The change in modulation is relatively small up to -1.0V, and the slope becomes slightly larger when the absolute value is larger than -1.0V. In this way, by providing the cap layer with a high impurity concentration,
When a voltage is applied, the potential modulation right under the cap layer is suppressed, and the potential modulation can be effectively applied.

Next, the operation of the lateral superlattice element of the first embodiment will be described with reference to FIG. 6 in comparison with the operation of the lateral superlattice element of the comparative example. As shown in FIGS. 6A and 6B, the cap layer 155 of the lateral superlattice element of the comparative example is formed on the entire surface of the barrier layer 54. The Schottky electrode 156 is formed on the cap layer 155. On the other hand, the cap layer 56 of the lateral superlattice element of the first embodiment is formed only between the Schottky electrodes 56 on the barrier layer 54. The potential modulation in the well layer 53 when -2 V is applied to the Schottky electrodes 156 and 56 is shown in FIG.
Shown in (c) and (d). The positions of the electrodes 156 and 56 and the cap layer 55 are shown in the figure. In the lateral superlattice element of the comparative example, the magnitude of potential modulation is about 40 mV, whereas in the lateral superlattice element of the first embodiment, a potential amplitude of about 70 mV is obtained. Due to this large potential amplitude, the carriers in the well layer 53 are effectively confined in the in-plane direction, and the degree of freedom is limited to one dimension.

As described above, in the lateral superlattice device of the first embodiment, the large potential amplitude is obtained firstly by the cap layer 55 having a high impurity concentration disposed between the Schottky electrodes 56. The fluctuation of the potential immediately below is suppressed. Secondly, the high-concentration impurity layer is removed from under the Schottky electrode, so that the modulation of the potential directly below the electrode 56 is emphasized.
It is due to one action.

FIG. 6E shows the applied voltage dependence of the potential modulation in the quantum well layer 53. In the lateral superlattice element of the first embodiment, large potential modulation is obtained even in the range where the absolute value of the voltage applied to the Schottky electrode 56 is small. Further, in the lateral superlattice element according to the first embodiment, the potential modulation even when a positive voltage is applied is due to the Schottky potential generated between the electrode 56 and the barrier layer 54. In the lateral superlattice element of the comparative example, the rate of increase in potential modulation is small in a region where the absolute value of the negative applied voltage to the Schottky electrode 156 is small, and the rate of increase in potential modulation increases as the absolute value increases. In the region where the voltage applied to the Schottky electrode 156 is small and the cap layer is not depleted, the resistance in the in-plane direction of the cap layer is low, and in the region where the absolute value of the applied voltage is large,
Since the cap layer directly below the electrode is depleted, the rate of change in potential increases. Although not shown in FIG. 6 (e),
In the conventional structure, when the absolute value of the applied voltage is increased in the negative direction, the increase rate of the potential modulation increases. The absolute value is the magnitude of the potential modulation in the structure of the lateral superlattice element of the first embodiment. Never exceeds.

As described above, according to the first embodiment of the present invention, since the cap layer 55 is not disposed immediately below the Schottky electrode 56, the applied voltage contributes to the potential modulation of the quantum well portion efficiently. be able to. Therefore, even when a low voltage is applied to the Schottky electrode 56, a large potential amplitude can be formed in the quantum well structure layer 50. This makes it possible to effectively confine the carriers in the well layer 53 in the lateral direction with a low applied voltage, and realize a lateral superlattice with a narrow quantum well width at a low applied voltage.

Further, in the lateral superlattice element of the first embodiment shown in FIG. 5, the Schottky electrode 56 and the cap layer 5 are included.
From between 5 and 5, the barrier layer 54 is exposed. Barrier layer 54
Is composed of an Al _x Ga _1-x As layer having a large Al composition, so that oxidation easily proceeds. Therefore, in the structure of the lateral superlattice element of the first embodiment as shown in FIG. 5, the entire element is packaged in order to prevent the characteristics of the element from changing with time due to the oxidation of the barrier layer 54. By providing a protective film, a structure for protecting the barrier layer 54 can be formed.

For example, FIG. 7A shows the structure of the lateral superlattice element of the first embodiment in which the protective film 59 is provided below the Schottky electrode 56 and the cap layer 55.
As the protective film 59, a SiO ₂ film having a film thickness of 100 A was used. Since the SiO ₂ film has a high resistance, different potentials can be applied to the quantum well structure layer 50 even if it is provided below the cap layer 55 and the Schottky electrode 56. When manufacturing the lateral superlattice element of FIG. 7A, after forming the barrier layer 54 in FIG.
₂ film is formed by CVD method, and then Schottky electrode 5
6 and the cap layer 55 are formed. In this structure, the material of the protective film is SiO ₂ if it is a high resistance film.
The material is not limited to the film, and various materials can be used. For example, an Al ₂ O ₃ film or a Si ₃ N ₄ film can be used.

Further, for example, the structure of another element in which a protective film is provided on the lateral superlattice element of the first embodiment is shown in FIG. 7 (b).
Shown in. This structure has a thickness of 100 A of S as the protective film 58 after the cap layer 55 is formed in the manufacturing process.
An iO ₂ film is formed. Next, the SiO ₂ film is removed by photolithography only in the portion where the Schottky electrode 56 is in contact with the barrier layer 54. After that, the Schottky electrode 56 is formed similarly to the manufacturing process described above. As a result, the barrier layer 5 between the cap layer 55 and the Schottky electrode 56 is formed.
Since the protective film 58 is disposed on the surface 4, the barrier layer 54 is not exposed, and deterioration of the lateral superlattice element over time can be prevented.

Next, a lateral superlattice according to the second embodiment of the present invention will be described with reference to FIG.

The lateral superlattice of the second embodiment is an element characterized in that the cap layer immediately below the Schottky electrodes is formed thinner than the cap layer between the Schottky electrodes. As shown in FIG. 13, the lateral superlattice device according to the second embodiment includes a quantum well structure layer 70 having a quantum well structure in the thickness direction on a substrate 71 made of n-GaAs having a thickness of 400 μm. There is. In addition, the quantum well structure layer 70
Cap layers 75a and 75b and a Schottky electrode 76 obtained by processing a Ni film having a thickness of 300 A into a grating shape are arranged on the upper side in order to confine carriers in the quantum well structure layer 70 in the lateral direction. On the back surface of the substrate 71, the ohmic electrode 7 made of an Au—Ge alloy film is formed.
7 are arranged.

The cap layer 75 is a low impurity concentration n + -GaAs film (impurity concentration 1 × 10 ¹⁷ cm
³ ) low-concentration cap layer 75a and a thickness of 200A
High impurity concentration n + -GaAs film (impurity concentration 1 × 1
The high-concentration cap layer 75b is made of 0 ¹⁸ cm ³ ). The low-concentration cap layer 75 a is formed on the entire surface of the quantum well structure layer 70. This low concentration cap layer 7
Grating-shaped Schottky electrode 76 on 5a
And the high-concentration cap layer 75b is disposed only between the Schottky electrodes 76. Therefore, between the Schottky electrodes 76, the cap layer 75 is thick because it is composed of the two layers of the low-concentration cap layer 75a and the high-concentration cap layer 75b. Immediately below the Schottky electrode 75,
The cap layer is thin because it is composed only of the low-concentration cap layer 75a. The Schottky electrode 76 has a cycle of 10
00A, one electrode width 500A is formed.

The quantum well structure layer 70 comprises an i-Al _x Ga _{1 -x} As film (0≤x≤) having a thickness of 500A in order from the substrate 71 side.
Barrier layer 72 was formed in 1), a thickness of 50A i-Al _y G
a _1-y As film (0 ≦ y ≦ 1, y ≦ x), i-Al _x Ga _1-x As film (0 ≦ x) having a thickness of 300A
The barrier layer 74 formed by ≦ 1) is laminated.

Next, a method of manufacturing the lateral superlattice element of the second embodiment will be described. The method of manufacturing the lateral superlattice element of the second embodiment is substantially the same as the method of manufacturing the first lateral superlattice element shown in FIG.
In (b), n + -GaAs to be the cap layer 75
The film is divided into two layers, an n + -GaAs film having a low impurity concentration and an n + -GaAs film having a high impurity concentration. Then, in FIG. 9D, when the cap layer 75 is etched, only the upper n + -GaAs film having a high impurity concentration is used by using an etchant whose etching rate varies depending on the impurity concentration of the n + -GaAs film. Etching. The other steps are the same as those in the first embodiment, and the description thereof will be omitted.

Next, the operation of the lateral superlattice of the second embodiment will be described. When a voltage is applied between the Schottky electrode 76 and the ohmic electrode 77, the Schottky electrode 76
The low concentration cap layer 75a immediately below is depleted, and the electrode 56
The potential of the quantum well structure layer 70 immediately below is modulated. At this time, since the cap layer 75 immediately below the Schottky electrode 76 is formed to have a smaller film thickness and a lower impurity concentration than the space between the Schottky electrodes 76, the voltage required for depletion. Is smaller than the comparative example shown in FIG. Further, since the high concentration cap layer 75b having a high impurity concentration is disposed between the Schottky electrodes 76,
The fluctuation of the potential immediately below the high-concentration cap layer 75b is suppressed. Therefore, the modulation of the potential directly under the electrode 76 is emphasized, and the modulation can be formed more effectively than before with a low applied voltage.

Further, in the lateral superlattice element of the second embodiment, since the low concentration cap layer 75 of the cap layer 75 covers the entire surface of the barrier layer 74, there is no risk of the barrier layer 74 being oxidized. As a result, even when Al _x Ga _1-x As is used for the barrier layer, a change in the characteristics of the device can be prevented without exposing a layer having a large Al composition on the surface.
Further, the manufacturing process of the lateral superlattice element of the second embodiment uses the etchant whose etching rate depends on the impurity concentration, so that it can be manufactured in the same manner as the first embodiment without increasing the number of times of etching. You can Therefore, it is possible to realize a lateral superlattice device in which deterioration over time is prevented and potential modulation efficiency is improved without lowering manufacturing efficiency.

Next, a lateral superlattice device according to a third embodiment of the present invention will be described with reference to FIG.

The lateral superlattice element of the third embodiment has a thickness of 400 as in the lateral superlattice element of the first embodiment.
A quantum well structure layer 10 having a quantum well structure in a thickness direction is provided on a substrate 11 composed of μm n-GaAs. Further, on the quantum well structure layer 10, a Schottky electrode 16 obtained by processing a Ni film having a thickness of 300 A into a grating shape and n + having a thickness of 200 A in order to confine carriers in the quantum well structure layer 10 in the lateral direction. And a cap layer 15 made of a GaAs film (impurity concentration 1 × 10 ¹⁸ cm ³ ). On the back surface of the substrate 11, Au-
An ohmic electrode 17 composed of a Ge alloy film is arranged. The Schottky electrode 16 is the quantum well structure layer 10.
On the top, a period of 1000 A and one electrode width of 500 A are formed. The cap layer 15 is arranged only between the respective electrodes of the Schottky electrode 16 on the quantum well structure layer 10.

Thirdly, in the embodiment, the quantum well structure layer 1
0 is i-Ga with a thickness of 5000 A in order from the substrate 11 side.
Channel layer 12 formed of As film, i-thickness of 100 A
Spacer layer 13 made of AlGaAs film, thickness 500
It has a modulation doping structure in which an n-type doped layer 14 formed of the n-AlGaAs film of A is laminated.

When a voltage is applied to the Schottky electrode 16, a potential amplitude is formed in the quantum well structure layer 10 and carriers in the channel layer 12 are confined in the lateral direction. The operations of the Schottky electrode 16 and the cap layer 15 are the same as those of the lateral superlattice device of the first embodiment, so the description thereof will be omitted.

Next, a lateral superlattice device according to a fourth embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 12, the lateral superlattice element of the fourth embodiment has a quantum well structure layer 120 having a quantum well structure in the thickness direction on a substrate 121 made of n-GaAs having a thickness of 400 μm. Is equipped with. Further, on the quantum well structure layer 120, in order to confine the carriers of the quantum well structure layer 120 in the lateral direction, a Ni film having a thickness of 300 A is processed into a grating shape, and the same thickness as the first Schottky electrode 126. A second Schottky electrode 125 formed by processing 300 A of Ni into a grating shape is arranged. The first Schottky electrode 126 has a period of 1000 A and one electrode width 50 on the quantum well structure layer 120.
It is formed at 0A. Second Schottky electrode 125
Are alternately arranged between the first Schottky electrodes 126 on the quantum well structure layer 120 and the first Schottky electrodes 126. The first Schottky electrode 126 and the second Schottky electrode 125 are electrically non-contact with each other. An ohmic electrode 127 made of an Au—Ge alloy film is arranged on the back surface of the substrate 121.

The quantum well structure layer 120 comprises, in order from the substrate 121 side, a barrier layer 122 formed of an i-AlGaAs film having a thickness of 500A, a well layer 123 formed of an i-GaAs film having a thickness of 50A, and a thickness of 300A. The barrier layer 124 is formed by laminating an i-AlGaAs film.

When operating the lateral superlattice of the fourth embodiment, different potentials are applied to the first Schottky electrode 126 and the second Schottky electrode 125, and the quantum well structure layer 120 is applied. Form a potential modulation.

In this embodiment, since the cap layer is not used, it is not necessary to deplete the cap layer as in the conventional case, and the potential difference does not depend on the impurity concentration of the cap layer. A potential modulation of the amplitude of can be formed.

Next, a method for measuring the optical characteristics of the lateral superlattice elements of the above-mentioned first, second, third and fourth embodiments will be described with reference to FIG. FIG. 8 shows the lateral superlattice device of the first embodiment as an example. First, the substrate 5
A quantum well structure layer 50 is formed on top of the substrate 1, and an ohmic electrode 57 is formed on the back surface of the substrate 51 as shown in FIG. In the central region of the quantum well structure layer 50, a graded cap layer 55 and a Schottky electrode 56 are formed as shown in FIG. A portion other than the region where the electrode 56 and the cap layer 55 are formed is covered with a conductive light shielding film 81 as shown in FIG. 8C. The light shielding film 81 and the Schottky electrode 56 are brought into electrical contact with each other to be electrically connected. Here, as the conductive light shielding film 81, a metal or a metal oxide film is used. Finally, the conductive light shielding film 81 and the ohmic electrode 57 are packaged so that a voltage can be applied to the ohmic electrode 57, and the wires are connected by bonding or the like.

Here, the light shielding film 81 and the ohmic electrode 57.
When a voltage is applied between and, potential modulation is formed in the quantum well structure. As a result, quantum wells are formed also in the lateral direction, and discrete levels different from the normal conduction band and valence band are formed. When the device is irradiated with light from the Schottky electrode 56 side as shown in FIG. 8D, the light is absorbed in the quantum well structure layer between the Schottky electrodes 56. The electrons are excited by the levels formed in the quantum well and emit light when they recombine. The band gap due to the level formed in the quantum well is wider than the normal band gap, and the wavelength of emitted light is shorter. In the lateral superlattice element of this example, the potential amplitude is large even at a low applied voltage, so that the well width is small and more discrete levels are formed. Therefore, the wavelength of the light emitted from the lateral superlattice device of this embodiment is shorter than that of the light emitted from the conventional lateral superlattice device when the voltages of equal magnitude are applied. Therefore, after manufacturing the lateral superlattice of each of the above-described examples, by examining the wavelength of the emitted light, it is possible to confirm whether or not the potential is efficiently formed and the quantum well having a narrow well width is formed. it can.

Regarding the conventional one-dimensional carrier system,
For example, the state of carrier confinement is often evaluated by light emission from the sample such as photoluminescence, but in the structure as shown in FIG. 8 (4), only the place where a one-dimensional conduction system is formed by the Schottky gate 56 shields light. Since it is not covered with a film, the optical characteristics can be evaluated without being affected by the surrounding two-dimensional carrier system.

A switching element according to the fifth embodiment of the present invention will be described with reference to FIGS. 10 and 11. The switching element of the present embodiment is similar to the lateral superlattice element of the first embodiment in that the quantum well structure layer 50 and the substrate 5 are provided on the substrate 51.
As shown in FIG. 10A, an ohmic electrode 57 is provided on the back surface of the first electrode. A cap layer 5 is formed on the quantum well structure layer 50.
5 is arranged, and the central region of the cap layer 55 is grayed.
The Schottky electrodes 56 are formed into a grating shape and are alternately arranged with the cap layer in a grating shape. At both ends of the Schottky electrode 56 in the direction along the line of the grating, Si is diffused into the cap layer and the quantum well structure layer at positions not in contact with the Schottky electrode 56 to provide a source 101 and a drain 102. ing.

Schottky electrode 56 and ohmic electrode 5
7, when a voltage is applied, a sharper potential is formed in the quantum well structure layer 50 along the direction of current flow, as in the first embodiment, as in the first embodiment. , A quantum wire is formed in the lateral direction. Therefore, the energy that the carrier can take in the lateral direction is quantized. In this state, when the cap layer 55 between the Schottky electrodes 56 is irradiated with modulated light, the source 10
2. The current flowing between the drain 101 is controlled. Since the potential is steep, the size of the quantum well for confining the carriers in the lateral direction becomes small, and the carriers are confined in the well to form discrete levels. As the quantized level spacing increases, the change in state due to the allowed scattering is limited and the probability of carrier scattering is reduced. The substantial mobility of electrons is improved, and the switching speed is higher than that of a switching device using a conventional lateral superlattice device.

Since a steep potential is formed, holes and electrons are spatially separated. Therefore, when one photon is incident, the current flowing between the source 102 and the drain 101 becomes large. This makes it possible to realize a high-speed and highly sensitive switching element by photoexcitation. Further, in the lateral superlattice used in this example, the quantum confinement potential of carriers can be efficiently formed in the in-plane direction of the substrate with a low applied voltage. As a result, the confinement potential can be formed with a small voltage. Therefore, by applying this structure to a switching element, a switching element with high speed and low power consumption can be realized.

In the manufacturing process shown in the above-mentioned first embodiment, the electron beam direct writing method is used to expose the photoresist, but it is of course possible to use the ultraviolet ray irradiation method through the photomask. is there. Further, although the MBE method is used to form the semiconductor layers such as the quantum well structure layer and the cap layer in the above description, the metal organic chemical vapor deposition method (MOCVD method) can also be used for the growth.

Further, in each of the above embodiments, after the lateral superlattice element and the switching element are completed, a protective film, a light shielding film, an antireflection film, or the like is further deposited depending on the application of the element. use.

Further, in the second embodiment, the cap layer 75
The number of carriers to be depleted under the Schottky electrode is reduced by forming the film thickness of the film under the Schottky electrode and thickly between the Schottky electrodes, but the thickness of the cap layer is not limited to this. The same effect can be obtained by disposing a constant carrier layer having a low impurity concentration under the Schottky electrode.

[0053]

In the lateral superlattice device of the present invention, a quantum confining potential of carriers can be efficiently formed in the in-plane direction of the substrate by a low applied voltage.

[Brief description of drawings]

FIG. 1 is a sectional view of a lateral superlattice device according to a third embodiment of the present invention.

FIG. 2 is a cross-sectional view of a lateral superlattice device according to a conventional example.

FIG. 3 is a cross-sectional view of a lateral superlattice device to which a single quantum well is applied according to a conventional technique.

FIG. 4 is a graph showing the dependence of the potential modulation in the structure of FIG. 3 on the impurity concentration of the cap layer.

FIG. 5 is a sectional view of a lateral superlattice device using a single quantum well according to the first embodiment of the present invention.

6A and 6B are cross-sectional views for comparing the configurations of the comparative example using the conventional technique shown in FIG. 3 and the element of the present example of FIG. (C) (d) Graph comparing the efficiency of potential modulation formation in the in-plane direction of the substrate between the comparative example and the present example. (E) A graph comparing the potential modulation with respect to the applied voltage in the comparative example and the present embodiment.

7A and 7B are cross-sectional views of a device in which a protective film is provided on the lateral superlattice device according to the first embodiment of the present invention.

FIG. 8 is an explanatory view showing a measuring method for measuring optical characteristics of the elements of the first, second and third embodiments.

9A and 9B are explanatory views showing a manufacturing process of the lateral superlattice element shown in FIG.

FIG. 10A is a perspective view of a switching element using the lateral superlattice element of the first embodiment. (B) b of FIG.
FIG.

11 is an explanatory view showing potential modulation in the in-plane direction of the substrate in the quantum well structure layer of the switching element of FIG.

FIG. 12 is a sectional view of a lateral superlattice device according to a fourth embodiment of the present invention.

FIG. 13 is a sectional view of a lateral superlattice device according to a second embodiment of the present invention.

[Explanation of symbols]

10, 50, 70, 120 ... Quantum well structure layer, 11, 2
1, 51, 71, 101, 121 ... Substrate, 12, 52,
72, 122 ... Barrier layer, 13, 53, 73, 123 ... Well layer, 14, 54, 74, 124 ... Barrier layer, 15, 2
5, 55, 75, 155 ... Cap layer, 16, 26, 5
6, 76, 156 ... Schottky electrodes, 17, 57, 7
7, 127 ... Ohmic electrodes, 58, 59 ... Protective film, 1
01 drain, 102 ... Source, 126 ... First Schottky electrode, 125 ... Second Schottky electrode.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01L 29/812 29/804 29/88 S

Claims (12)

[Claims] 1. A substrate having conductivity, a quantum well structure layer formed on the substrate and having a quantum well structure in a thickness direction, and a voltage application for confining carriers in the quantum well structure layer in a lateral direction. A lateral superlattice element having a layer, wherein the voltage application layer is provided on the quantum well structure layer in order, an impurity-doped semiconductor layer, and a plurality of thin line Schottky electrodes. A value obtained by multiplying the number of carriers per unit volume of the semiconductor layer by the layer thickness of the semiconductor layer with respect to the semiconductor layer under the Schottky electrode, A lateral superlattice device characterized by being smaller than a value obtained by multiplying the number of carriers per unit volume by the layer thickness of the semiconductor layer. 2. The lateral superstructure according to claim 1, wherein the layer thickness of the semiconductor layer below the Schottky electrode is formed thinner than the layer thickness of the semiconductor layer between the Schottky electrodes. Lattice element. 3. The semiconductor layer according to claim 1, wherein the semiconductor layer is the first
Semiconductor layer and a first semiconductor layer laminated on the first semiconductor layer
A second semiconductor layer having an impurity concentration higher than that of the semiconductor layer, wherein the second semiconductor layer is arranged only between the Schottky electrodes. 4. A substrate having conductivity, a quantum well structure layer having a quantum well structure in the thickness direction on the substrate, and a voltage application layer for confining carriers in the quantum well structure layer in the lateral direction. A lateral superlattice device having, wherein the voltage application layer is a semiconductor layer doped with impurities,
A plurality of Schottky electrodes in the form of thin lines, the Schottky electrode is provided on the quantum well structure layer, and the semiconductor layer is provided only between the Schottky electrodes on the quantum well structure layer. Lateral superlattice device characterized by being used. 5. The lateral superlattice device according to claim 4, further comprising a protective layer for covering the quantum well structure layer in the gap between the Schottky electrode and the semiconductor layer. 6. The lateral superlattice according to claim 4, further comprising a high resistance layer between the quantum well structure layer and the voltage application layer. 7. A substrate having conductivity, a quantum well structure layer having a quantum well structure in a thickness direction on the substrate, and a voltage application layer for confining carriers in the quantum well structure layer in a lateral direction. A lateral superlattice element having: a voltage applying layer, wherein the voltage applying layer has a plurality of thin line-shaped first Schottky electrodes for applying two different voltages to the quantum well structure layer; Lateral Schottky electrodes, wherein the first Schottky electrodes and the second Schottky electrodes are alternately arranged. 8. The quantum well structure layer according to claim 1, 4 or 7, wherein the quantum well layer sandwiches the quantum well layer.
A lateral superlattice device comprising a barrier layer having a bandgap larger than that of the quantum well layer. 9. The lateral superlattice according to claim 1, 4 or 7, wherein the quantum well structure layer has a modulation-doped structure in which a non-doped semiconductor layer and a semiconductor layer doped with impurities are stacked. element. 10. A source region, a drain region, and a channel region, which is formed between a semiconductor and disposed between the source region and the drain region, in which the conductivity of carriers changes according to the light intensity. An optical conductivity modulator having, wherein the channel region has a conductive substrate layer, a quantum well structure layer having a quantum well structure in a thickness direction provided on the substrate layer, and the quantum well. A voltage application layer for confining carriers of the structure layer in the lateral direction, wherein the voltage application layer is provided in order on the quantum well structure layer, an impurity-doped semiconductor layer, and a plurality of thin wires. A Schottky electrode in the shape of a Schottky electrode, and a value obtained by multiplying the number of carriers per unit volume of the semiconductor layer by the layer thickness of the semiconductor layer is the Schottky For the semiconductor layer between the electrodes, than the value obtained by multiplying the thickness of the semiconductor layer to the number of carriers per unit volume of the semiconductor layer, the optical conductivity modulation element, characterized in that small. 11. An optical communication system comprising a light source, an optical fiber for transmitting an optical signal emitted by the light source, and a light receiving element for receiving the optical signal transmitted by the optical fiber, wherein the light receiving element is conductive. Substrate layer, a quantum well structure layer having a quantum well structure in the thickness direction, which is provided on the substrate layer, and a voltage application layer for confining carriers in the quantum well structure layer in the lateral direction. The voltage application layer includes an impurity-doped semiconductor layer and a plurality of thin line-shaped Schottky electrodes, which are sequentially provided on the quantum well structure layer, and the semiconductor under the Schottky electrode. For a layer, the value obtained by multiplying the number of carriers per unit volume of the semiconductor layer by the layer thickness of the semiconductor layer is the value of the number of carriers per unit volume of the semiconductor layer between the Schottky electrodes. An optical communication system, characterized in that from the value obtained by multiplying the thickness of the semiconductor layer A number of small. 12. A plurality of electronic circuit parts for processing input data, a light emitting element for converting an electric signal into an optical signal, for transmitting and receiving a signal between the plurality of electronic circuit parts, In an optical computer having an optical fiber for transmitting an optical signal and a light receiving element for receiving the optical signal transmitted by the optical fiber, the light receiving element is provided on a conductive substrate layer and the substrate layer, A quantum well structure layer having a quantum well structure in the thickness direction, and a voltage application layer for confining carriers of the quantum well structure layer in the lateral direction, the voltage application layer, on the quantum well structure layer. Sequentially provided, having a semiconductor layer doped with impurities, and a plurality of Schottky electrodes in the form of thin lines, for the semiconductor layer under the Schottky electrode, per unit volume of the semiconductor layer The value obtained by multiplying the number of carriers by the layer thickness of the semiconductor layer is smaller than the value obtained by multiplying the number of carriers per unit volume of the semiconductor layer by the layer thickness of the semiconductor layer for the semiconductor layer between the Schottky electrodes. Characteristic lateral superlattice device.