JPH04320068A - Infrared ray image sensor - Google Patents

Abstract

PURPOSE:To provide a planar type infrared ray image sensor in which an optical transition is allowed even if an infrared ray is incident perpendicularly to a main surface or a rear surface of a semiconductor device. CONSTITUTION:A high resistance semiconductor layer 2, a spacer layer 3 of a high resistance semiconductor layer having smaller electron affinity than that of the layer 2, and a carrier supply layer 4 are sequentially laminated on a semi-insulating GaAs substrate 1, and an electron storage layer is formed in one dimensional manner only near the bottom of a recess of the layer 3 near a boundary between the layers 2 and 3. Thus, an optical transition occurs even by an infrared ray incident perpendicularly to detect the ray.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in the field of electronics, relates to an infrared imaging device that responds to infrared rays, particularly in the wavelength band of 8 to 12 μm.

0002

[Prior Art] Infrared imaging devices, especially infrared imaging devices that respond to infrared rays in the wavelength range of 8 to 12 μm, which is the window into the atmosphere, are being considered for application in satellite communications, remote sensing technology, and even disaster prevention management systems. In recent years, it has been attracting widespread attention. Common challenges for infrared imaging devices used in these applications include increasing the number of pixels, increasing density, and establishing manufacturing technology including mounting technology, and many research institutes are actively researching and developing these issues. . Until now, mercury cadmium telluride (HgCd) has been the main material for infrared imaging devices.
Since Te) is a highly volatile material, it is difficult to handle and unsuitable for increasing the number of pixels, and problems in manufacturing still remain. In contrast, recently, multiple quantum wells (Mu
An MQW-type infrared detection device that applies the inter-subband transition of a quantum well (hereinafter referred to as MQW) has been proposed, and is attracting attention as a device that opens up new possibilities.

[0003] Figure 5 shows, for example, Applied Physics Letters 1988, vol. 53, 296-29.
Page 8 (Applied Physics Letter
s, Vol. 53 (1988) pp. 296 ~2
98) is a cross-sectional structural diagram showing the structure of the MQW type infrared detection device shown in FIG. In the figure, 1 is semi-insulating GaAs
Substrate, 5 and 52 are n+ -GaAs layers, 7 and 8 are bias electrodes, 13 is an infrared ray, and 51 is an Al layer with a thickness of 1.73 μm.
A GaAs-GaAs MQW layer (hereinafter referred to as an MQW layer at the end), 53 is an infrared incident window. Here, MQW layer 5
1 is, for example, Alx Ga1-x As with a thickness of 30 nm
(x=0.31) It has a multiple quantum well structure constructed by alternately stacking barrier layers and GaAs well layers with a thickness of 4 nm, and 50 quantum wells are formed in the MQW layer 51. Further, the infrared incident window 53 is formed by obliquely polishing the semi-insulating GaAs substrate 1 at an angle of 45° with respect to the main surface.

Next, the principle of operation of this MQW type infrared detection device will be explained. FIG. 6 is a diagram showing a bandgap diagram of the MQW layer 51, and here shows a state in which an electric field is applied. In the figure, 61 is a conduction band, 62
is a valence band, 63 is a GaAs quantum well layer, 64 is an AlG
This is an aAs barrier layer. Electrons mainly exist in GaAs and AlG
It is confined within the GaAs quantum well layer 63 due to the difference in electron affinity with aAs, and forms discrete energy levels due to quantum mechanical effects. At this time, the energy difference from the ground level takes a certain value mainly determined by the thickness of the GaAs quantum well layer 63, the thickness of the AlGaAs barrier layer 64, the composition ratio of Al in the AlGaAs barrier layer 64, and the band shape. , in the structure shown in FIG. 5, is approximately 0.15 eV. This energy is approximately 8.3 μm in terms of the wavelength of light, and when infrared rays of this wavelength are incident, the incident infrared rays are absorbed and an optical transition from the normal level to the first excited level occurs. Furthermore, as shown in FIG. 6, the first excited level is the conduction band 6 of AlGaAs.
1, and electrons excited by the incidence of infrared rays can be conducted through the MQW layer 51. The MQW type infrared detection device shown in FIG. 5 detects infrared rays by utilizing this change in conductivity due to infrared absorption.

By the way, the electrons confined within the quantum well form discrete energy levels, and the confined state of each level is a standing wave standing in the direction perpendicular to the MQW layer 51. It is in a state of confinement. Therefore, only the electric field component of the incident infrared rays in the direction in which the standing wave stands, that is, in the direction perpendicular to the MQW layer 51, interacts with the electrons in the quantum well and causes an optical transition. Since the direction of the electric field vector of the infrared rays 13 is in the in-plane direction perpendicular to the traveling direction of the infrared rays, in order to interact with the electrons in the quantum well, the infrared rays 13 are incident on the MQW layer 51 obliquely. There is a need. For this reason, Figure 5
In the MQW type infrared detection device shown in FIG. It is configured to allow

[0006]

[Problems to be Solved by the Invention] Since the conventional MQW type infrared detection device is constructed as described above, it is possible to
3 had to be incident obliquely from the polished surface, which made it difficult to integrate a plurality of elements to construct an infrared imaging device. Furthermore, since the MQW structure is a vertical device with a thickness of about 2 μm, it is a planar type element.
For example, there are problems such as poor compatibility with the manufacturing process with GaAsFETs, and the difficulty of constructing an infrared imaging device by monolithically forming an infrared detection device and external circuits such as a bias circuit on the same substrate. there were.

The present invention has been made to solve the above-mentioned problems, and in the first invention, even when infrared rays are perpendicularly incident on the main surface or the back surface of a semiconductor device, the optical The purpose of this invention is to obtain a new planar type infrared imaging device that allows transitions. Furthermore, the second
An object of the invention is to provide a band structure in which electrons excited by optical transition efficiently contribute to electrical conduction in the infrared imaging device according to the first invention.

[0008]

[Means for Solving the Problems] An infrared imaging device according to a first aspect of the present invention includes a first type of high-resistance semiconductor layer on a semiconductor substrate, and an electron affinity higher than that of the first type of high-resistance semiconductor layer. In an infrared imaging device having a layered structure in which a small second type high resistance semiconductor layer and an n-type doped second type semiconductor layer are sequentially laminated, the first type high resistance semiconductor layer and the second type doped semiconductor layer are stacked in sequence. A pair of outputs including means for forming a plurality of one-dimensional electron storage layers at the heterojunction interface with two types of high-resistance semiconductor layers, and provided in regions facing each other with the region having the one-dimensional electron storage layer interposed therebetween. It is configured to include electrodes.

Furthermore, in the infrared imaging device according to the second invention, in the infrared imaging device according to the first invention, the one-dimensional electron storage layer has at least two layers in the in-plane direction of the first type high-resistance semiconductor layer. The energy level of the second of the two confinement states overlaps the energy level of the barrier.

0010

[Operation] In the infrared imaging device of the present invention, by forming a one-dimensional electron storage layer at the heterojunction interface of a semiconductor, an optical transition occurs even with infrared rays incident perpendicularly to the heterojunction interface, and the infrared rays are detected. can do. In addition, since it is a planar infrared imaging device that uses a heterojunction, the manufacturing process is compatible with many semiconductor devices such as field effect transistors, so the infrared detection device and photocurrent amplification circuit described above have good compatibility. An infrared imaging device can be easily configured by integrating a plurality of infrared rays on the same substrate and arranging a plurality of them.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing the structure of an embodiment of the infrared imaging device of the present invention. In the figure, 1 is semi-insulating GaAs
The substrate, 2 is a high resistance GaAs layer (hereinafter referred to as i-GaAs layer), 3 is a high resistance Alx Ga1-x As (x=0
．． 3) Spacer layer (hereinafter referred to as spacer layer), 4 is n
-Alx Ga1-x As (x=0.3) carrier supply layer (hereinafter referred to as carrier supply layer), 5 is n+ -G
6 is a Schottky metal, 7 and 8 are bias electrodes, 9 and 10 are n+ regions, 11 is a one-dimensional electron storage layer, 12 is an antireflection film, and 13 is an infrared ray. As shown in the figure, in a semiconductor stacked structure in which an i-GaAs layer 2, a spacer layer 3, and a carrier supply layer 4 are sequentially stacked on a semi-insulating GaAs substrate 1, the spacer layer 3 has a concave portion whose shape is an inverted triangle. The upper end surface of the carrier supply layer 4 formed on the insulating Ga layer has an uneven periodic structure in its cross section.
It is formed to be a plane parallel to the upper end surface of the As substrate 1. Here, the thickness of the spacer layer 3 is 15 nm at the concave portion,
The thickness of the convex portion is 50 nm, and the carrier supply layer 4 is formed above the convex portion so that the total thickness of the spacer layer 3 and the carrier supply layer 4 is 90 nm. In such a structure, electrons are one-dimensionally distributed only in the region near the interface between the i-GaAs layer 2 and the spacer layer 3, near the bottom of the recess in the spacer layer 3, that is, in the very close region near the apex of the inverted triangle. An accumulation layer is formed. When the width of this one-dimensional electron storage layer 11 was experimentally investigated, it was confirmed that an electron storage layer having a width of approximately 8 nm was formed.

Next, the principle of operation of this infrared storage device will be explained. FIG. 2(a) is a cross-sectional structural diagram showing the structure of an infrared storage device according to an embodiment of the present invention, and FIG.
) is a diagram showing a band diagram in the vicinity of the interface between the i-GaAs layer 2 and the spacer layer 3, that is, in the region where the one-dimensional electron storage layer 11 is formed, and here shows a state where an electric field is applied. In the figure, 21 is a conduction band, 22 is a valence band, 23 is an electron pocket, 24 is a potential barrier, and 25 is a Fermi level. Figure 2(b)
), the conduction band 21 is formed by the one-dimensional electron storage layer 11.
Only the region in which electrons are formed penetrates below the Fermi level 25, forming periodic electron pockets 23 in the conduction band 21. The electrons in this electron pocket 23 are confined in two directions: a direction parallel to the main surface of the semiconductor (x direction) and a direction perpendicular to the main surface of the semiconductor (z direction). Of these, the energy of the confined state in the direction horizontal to the semiconductor main surface (x direction) is:
Forms discrete energy levels through quantum mechanical effects. At this time, the energy difference between the ground level and the first excited level is determined by the crystallographic thickness of the spacer layer 3 and carrier supply layer 4, the shape and period of the periodic structure, and the band structure. A specific value. In the first embodiment, the energy difference between the ground level and the first excited level was experimentally investigated and found to be approximately 0.1
It was confirmed that it was eV. This energy is 12μ
This corresponds to the energy of the m-band infrared ray 13, and when the infrared ray 13 of this wavelength is incident, the incident infrared ray is absorbed, and an optical transition from the ground level to the first excited level occurs. Further, the second excited level is designed to overlap with the conduction band 21 of the potential barrier 24, and the excited electrons can be conducted in the direction of the bias electrode 8 by the electric field. Here, the confinement state of electrons due to confinement in the direction horizontal to the main surface of the semiconductor (x direction) is a confinement state like a standing wave standing in the x direction. Optical transitions are also allowed by infrared rays 13, and the device operates as an infrared detection device. In the manner described above, an infrared imaging device with sufficient sensitivity even to vertically incident infrared rays was realized.

FIG. 3 is a circuit diagram showing an example of the configuration of one pixel unit of an infrared imaging device according to a second embodiment of the present invention. In the figure, 31 is the infrared detection device shown in the first embodiment, 32 is a GaAs field effect transistor (hereinafter referred to as GaAsFET), 33, 34, and 35 are resistors, and 36 is an operational amplifier transmission circuit. Since the infrared detecting device 31 shown in the first embodiment generates a weak photocurrent due to the incidence of infrared rays, it is preferable to configure the infrared detecting device 31 by combining a current amplifying circuit. Figure 3(a) shows the infrared detection device 3.
This is the simplest photocurrent amplification circuit constructed by combining 1 and 1 GaAsFET 32. Since the infrared detection device 31 according to the first embodiment has a planar structure,
It has good process compatibility with other semiconductor devices, such as GaAsFET32, and is easy to integrate on the same substrate.The circuit shown in FIG. The imaging device can be easily configured. Furthermore, it is also possible to monolithically configure the shift register including the GaAsFET 32. FIG. 3B shows a modified example of the photocurrent amplification circuit shown in FIG. This makes it possible to amplify only the photocurrent change with good linearity. With this circuit as well, a monolithic infrared imaging device can be constructed relatively easily, as in the case of FIG. 3(a).

In the above embodiment, the one-dimensional electron storage layer 11 is formed by providing the spacer layer 3 with an uneven periodic structure.
However, the shape of this periodic structure of unevenness is not limited to an inverted triangular cross-sectional shape. For example, as shown in FIG. 4(a), a periodic structure of unevenness having a rectangular cross-sectional shape may be adopted. . Further, as shown in FIG. 4(b), an n+ -GaAs cap layer 4 is formed in stripes on the carrier supply layer 4.
1, or by providing the carrier supply layer 4 with a periodic structure of recesses and recesses as shown in FIG. 4(c). That is, any structure may be used as long as it allows the formation of the one-dimensional electron storage layer 11 at the semiconductor hetero interface, and the structure is not limited to the structure shown in the above embodiment. Furthermore, in the above embodiment,
Although no electric field is applied to the Schottky metal 6, the width of the one-dimensional electron storage layer 11 is effectively changed by applying an electric field, so that the response wavelength can be changed. For this purpose, an electric field may be applied to the Schottky metal 6. Further, in the above embodiment, an example was explained in which GaAs was used for the channel layer and AlGaAs was used for the spacer layer 3 and the carrier supply layer 4, but the semiconductor material used for the spacer layer 3 and the carrier supply layer 4 was the semiconductor material used for the channel layer. The same objective can be achieved with any combination of materials, as long as the conditions that the material has a smaller electron affinity and a larger energy gap than the other materials are met. However, in practical terms, it is desirable that the lattice constants of both are similar and that a combination is used that will yield a high-quality heterojunction.

[0015]

As explained above, according to the first invention, a first type of high resistance semiconductor layer is provided on a semiconductor substrate, and a second type of high resistance semiconductor layer having a lower electron affinity than the first type of high resistance semiconductor layer is formed on a semiconductor substrate. In the infrared detection device, the infrared detection device has a layer structure in which a high-resistance semiconductor layer of 1 and a second type of n-type doped semiconductor layer are sequentially laminated. It includes means for forming a plurality of one-dimensional electron storage layers at the heterojunction interface with the resistive semiconductor layer, and includes a pair of output electrodes provided in regions facing each other across the region having the one-dimensional electron storage layers. With this configuration, optical transition is allowed even by infrared rays incident from a direction perpendicular to the heterojunction interface, and an infrared imaging device that operates under normal incidence can be obtained.

Furthermore, according to the second invention, in the infrared imaging device according to the first invention, the one-dimensional electron storage layer has at least two confinement states in the in-plane direction of the first type high-resistance semiconductor layer. The second of these two confinement states is
Since the energy level of the confined state of the barrier overlaps with the energy level of the barrier, the electrons excited by the optical transition efficiently contribute to electrical conduction, resulting in an infrared imaging device with high sensitivity and operating at normal incidence. It has the effect of being

[0017] The infrared detection device and the photocurrent amplification circuit according to the first invention are integrated on the same substrate as one pixel unit, and the pixel units may be arranged in a line or in an array. For example, a monolithically integrated infrared imaging device can be easily constructed.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the structure of an infrared imaging device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional structural diagram showing the structure of an infrared imaging device according to an embodiment of the present invention, and a diagram showing a band diagram in a region where a one-dimensional electron storage layer is formed.

FIG. 3 is a circuit diagram showing an example of the configuration of one pixel unit of an infrared imaging device according to a second example of the present invention.

FIG. 4 is a cross-sectional structural diagram showing a modification of the infrared imaging device according to an embodiment of the present invention.

FIG. 5 is a cross-sectional structural diagram showing the structure of a conventional MQW type infrared imaging device.

FIG. 6 is a band diagram for explaining the operating principle of a conventional MQW type infrared imaging device.

[Explanation of symbols]

1 Semi-insulating GaAs substrate 2 i-GaAs layer 3 Spacer layer 4 Carrier supply layer 5 n+ -GaAs layer 6 Schottky metal 7 Bias electrode 8 Bias electrode 9 n+ area 10 n+ area 11 One-dimensional electron storage layer 12 Anti-reflection film 13 Infrared rays 21 Conduction band 22 Valence band 23 Electronic pocket 24 Potential barrier 25 Fermi level

Claims (2)

[Claims] 1. A first type of high-resistance semiconductor layer on a semiconductor substrate, a second type of high-resistance semiconductor layer having a lower electron affinity than the first type of high-resistance semiconductor layer, and an n-type doped second type of high-resistance semiconductor layer. A plurality of one-dimensional semiconductor layers having a layer structure in which two types of semiconductor layers are sequentially laminated, and arranged in parallel to the heterojunction interface between the first type of high-resistance semiconductor layer and the second type of high-resistance semiconductor layer. An infrared imaging device comprising an electron storage layer and a pair of output electrodes in regions facing each other with a region having the one-dimensional electron storage layer in between. 2. The one-dimensional electron storage layer has at least two confinement states in the in-plane direction of the first type of high-resistance semiconductor layer,
2. The infrared imaging device according to claim 1, wherein the energy level of the second confinement state of the two confinement states overlaps with the energy level of the barrier.