JP2021077804A - Infrared detector - Google Patents

Abstract

To provide an infrared detector that can improve an S/N ratio.SOLUTION: An infrared detector includes a first light receiving layer that absorbs a first infrared ray, a second light receiving layer that absorbs a second infrared ray, a barrier layer provided between the first light receiving layer and the second light receiving layer, a first electrode layer disposed to have the first light receiving layer held between the barrier layer and the first electrode layer and provided in contact with the first light receiving layer, a second electrode layer disposed to have the second light receiving layer held between the barrier layer and the second electrode layer and provided in contact with the second light receiving layer. The band gap of the first light receiving layer is larger than the band gap of the second light receiving layer. The band gap of the second electrode layer is larger than the band gap of the second light receiving layer. The band gap of the second electrode layer is less than or equal to the band gap of the first light receiving layer.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an infrared detector.

Type II Superlattice (T2SL) is expected to be a material for next-generation infrared detectors that will replace Mercury Cadmium Telluride (MCT). In recent years, infrared detection using the Type II superlattice has been expected. There is a lot of research on vessels. An example of an infrared detector using a type II superlattice has a light receiving layer provided on a GaSb substrate containing a superlattice of a material such as GaSb, InAs, AlSb.

Research is also being conducted on a two-wavelength infrared detector capable of detecting two-wavelength infrared rays. The dual wavelength infrared detector includes two light receiving layers having different band gaps and a barrier layer provided between them. The barrier layer blocks the flow of either electrons or holes. A two-wavelength infrared detector whose hole flow is blocked by a barrier layer is sometimes called a pBp type, and a two-wavelength infrared detector whose electron flow is blocked by a barrier layer is sometimes called an nBn type.

Japanese Unexamined Patent Publication No. 2011-211019 JP-A-2018-107277

SPIE Proceedings. Vol. 8155, pp.815507 (2011)

With a conventional two-wavelength infrared detector, a sufficient signal / noise ratio (S / N ratio) cannot be obtained.

An object of the present disclosure is to provide an infrared detector capable of improving the signal-to-noise ratio.

According to one embodiment of the present disclosure, a first light receiving layer that absorbs a first infrared ray, a second light receiving layer that absorbs a second infrared ray, the first light receiving layer, and the second light receiving layer. A first electrode layer that is arranged so as to sandwich the first light receiving layer between the barrier layer provided between the two and the barrier layer and is in contact with the first light receiving layer, and the barrier layer. It has a second electrode layer that is arranged so as to sandwich the second light receiving layer between them and is in contact with the second light receiving layer, and the band gap of the first light receiving layer is the second light receiving layer. The band gap of the second electrode layer is larger than the band gap of the light receiving layer, the band gap of the second electrode layer is larger than the band gap of the second light receiving layer, and the band gap of the second electrode layer is the band gap of the first light receiving layer. An infrared detector that is less than or equal to the bandgap of

According to the present disclosure, the S / N ratio can be improved.

It is sectional drawing which shows the infrared ray detector which concerns on 1st Embodiment. It is a figure which shows the energy band in the infrared detector which concerns on 1st Embodiment. It is a figure which shows the energy band in the infrared detector which concerns on 1st Embodiment in 1st operation example. It is a figure which shows the energy band in the infrared detector which concerns on 1st Embodiment in 2nd operation example. It is sectional drawing (the 1) which shows the manufacturing method of the infrared detector which concerns on 1st Embodiment. It is sectional drawing (the 2) which shows the manufacturing method of the infrared detector which concerns on 1st Embodiment. It is sectional drawing (the 3) which shows the manufacturing method of the infrared detector which concerns on 1st Embodiment. It is sectional drawing (the 4) which shows the manufacturing method of the infrared detector which concerns on 1st Embodiment. It is sectional drawing which shows the infrared ray detector which concerns on 2nd Embodiment. It is a figure which shows the energy band in the infrared detector which concerns on 2nd Embodiment. It is a figure which shows the energy band in the infrared detector which concerns on 2nd Embodiment in 1st operation example. It is a figure which shows the energy band in the infrared detector which concerns on 2nd Embodiment in 2nd operation example. It is sectional drawing which shows the infrared ray detector which concerns on 3rd Embodiment. It is a figure which shows the energy band in the infrared detector which concerns on 3rd Embodiment. It is a perspective view which shows the infrared imaging element which concerns on 4th Embodiment. It is sectional drawing which shows the part of the infrared image pickup element which concerns on 4th Embodiment enlarged. It is a schematic diagram which shows the infrared imaging system which concerns on 5th Embodiment.

By reducing the dark current, which is noise, the S / N ratio of the infrared detector can be improved. In an infrared detector capable of detecting infrared rays of two wavelengths, carriers heat generated in an electrode layer provided adjacent to a light receiving layer cause an increase in dark current. In particular, of the two electrode layers, carriers that generate heat in the electrode layer provided adjacent to the light receiving layer that receives infrared rays on the long wavelength side are more likely to cause an increase in dark current. The heat generation of the carrier can be suppressed by making the band gap of the electrode layer larger than the band gap of the light receiving layer. From these viewpoints, in order to improve the S / N ratio, it is conceivable to make the band gap of the electrode layer adjacent to the light receiving layer larger than the band gap of the light receiving layer that receives infrared rays on the long wavelength side. However, when the band gap of the electrode layer is excessively large, it becomes difficult for the photocurrent to flow out through the electrode layer. Since a decrease in photocurrent leads to a decrease in signal, a sufficient S / N ratio cannot be obtained. The inventor of the present application has conducted a diligent study based on these findings. As a result, it became clear that it is important that an appropriate relationship is established between the bandgap of the two light receiving layers and the bandgap of the two electrode layers included in the infrared detector capable of detecting infrared rays of two wavelengths. It was. Further, according to the simulation performed by the inventor of the present application, the dark current is ignored when the difference in the band gap between the electrode layer and the light receiving layer adjacent to each other is 0.03 eV or more in order to establish the above-mentioned appropriate relationship. It was also revealed that it was suppressed to the extent possible.

Hereinafter, embodiments of the present disclosure will be specifically described with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration may be designated by the same reference numerals to omit duplicate explanations.

(First Embodiment)
First, the first embodiment will be described. The first embodiment relates to a pBp type infrared detector. FIG. 1 is a cross-sectional view showing an infrared detector according to the first embodiment. FIG. 2 is a diagram showing an energy band in the infrared detector according to the first embodiment when no bias is applied. Ef in FIG. 2 indicates the Fermi level.

As shown in FIG. 1, the infrared detector 100 according to the first embodiment includes a substrate 101, a buffer layer 102, an etching stopper layer 103, a first electrode layer 110, and a first light receiving layer 120. It has a barrier layer 150, a second light receiving layer 130, and a second electrode layer 140. The infrared detector 100 further includes an insulating film 160, a first electrode 170, and a second electrode 180.

The substrate 101 is, for example, an n-type GaSb substrate. For example, the Miller index on the surface of the substrate 101 is (100). The buffer layer 102 is provided on the substrate 101. The buffer layer 102 is, for example, a GaSb layer. The thickness of the buffer layer 102 is, for example, about 90 nm to 110 nm. The etching stopper layer 103 is provided on the buffer layer 102. The etching stopper layer 103 is, for example, an InAsSb layer. The thickness of the etching stopper layer 103 is, for example, about 280 nm to 320 nm. The mixed crystal composition of the InAsSb layer is preferably a mixed crystal composition lattice-matched to GaSb, and the InAsSb layer is preferably an InAs _0.91 Sb _0.09 layer.

The first electrode layer 110 is provided on the etching stopper layer 103. The first electrode layer 110 includes a type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.0 nm, and the thickness of the GaSb layer is 1.2 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.0 nm and GaSb layers having a thickness of 1.2 nm are alternately laminated is about 0.177 eV. For example, the first electrode layer 110 ^{is doped with Be so that the hole concentration is about 1 × 10 18} cm ^-3 , and the first electrode layer 110 has a p-type conductive type. The thickness of the first electrode layer 110 is, for example, about 340 nm to 380 nm.

The first light receiving layer 120 is provided on the first electrode layer 110. The first light receiving layer 120 includes a type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.4 nm and the thickness of the GaSb layer is 1.2 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.4 nm and GaSb layers having a thickness of 1.2 nm are alternately laminated is about 0.146 eV. For example, the first light receiving layer 120 ^{is doped with Be so that the hole concentration is about 1 × 10 16} cm ^-3 , and the first light receiving layer 120 has a p-type conductive type. The thickness of the first light receiving layer 120 is, for example, about 1200 nm to 1400 nm.

The barrier layer 150 is provided on the first light receiving layer 120. The barrier layer 150 includes a Type II superlattice in which InAs layers and AlSb layers are alternately laminated. For example, the thickness of the InAs layer is 4.6 nm, and the thickness of the AlSb layer is 1.2 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 4.6 nm and AlSb layers having a thickness of 1.2 nm are alternately laminated is about 0.485 eV. For example, the barrier layer 150 ^{is doped with Be so that the hole concentration is about 1 × 10 16} cm ^-3 , and the barrier layer 150 has a p-type conductive type. The barrier layer 150 functions as a unipolar barrier layer that blocks only holes. The thickness of the barrier layer 150 is, for example, about 90 nm to 110 nm.

The second light receiving layer 130 is provided on the barrier layer 150. The second light receiving layer 130 includes a type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 4.8 nm and the thickness of the GaSb layer is 2.1 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 4.8 nm and GaSb layers having a thickness of 2.1 nm are alternately laminated is about 0.091 eV. For example, the second light receiving layer 130 ^{is doped with Be so that the hole concentration is about 1 × 10 16} cm ^-3 , and the second light receiving layer 130 has a p-type conductive type. The thickness of the second light receiving layer 130 is, for example, about 1200 nm to 1400 nm.

The second electrode layer 140 is provided on the second light receiving layer 130. The second electrode layer 140 includes a type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 4.2 nm and the thickness of the GaSb layer is 2.1 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 4.2 nm and GaSb layers having a thickness of 2.1 nm are alternately laminated is about 0.127 eV. For example, the second electrode layer 140 ^{is doped with Be so that the hole concentration is about 1 × 10 18} cm ^-3 , and the second electrode layer 140 has a p-type conductive type. The thickness of the second electrode layer 140 is, for example, about 340 nm to 380 nm.

As described above, the superlattice material contained in the first electrode layer 110, the superlattice material contained in the first light receiving layer 120, the superlattice material contained in the second light receiving layer 130, and the second electrode. The superlattice material contained in layer 140 is common. Further, the hole concentration of the first light receiving layer 120 and the hole concentration of the second light receiving layer 130 are about the same, and the hole concentration of the first electrode layer 110 and the holes of the second electrode layer 140 It is about the same as the concentration. The hole concentration of the first electrode layer 110 is higher than the hole concentration of the first light receiving layer 120, and the hole concentration of the second electrode layer 140 is higher than the hole concentration of the second light receiving layer 130.

The second electrode layer 140, the second light receiving layer 130, the barrier layer 150 and the first light receiving layer 120 are etched in a mesa shape, and the insulating film 160 is the second electrode layer 140 and the second light receiving layer. It covers the sides of 130, the barrier layer 150, and the first light receiving layer 120. The insulating film 160 is, for example, a silicon oxide film. The thickness of the insulating film 160 is, for example, about 480 nm to 520 nm. The insulating film 160 also covers the upper surface of the first electrode layer 110 and the upper surface of the second electrode layer 140.

The insulating film 160 is formed with an opening 167 that exposes a part of the upper surface of the first electrode layer 110 and an opening 168 that exposes a part of the upper surface of the second electrode layer 140. A first electrode 170 is formed inside the opening 167, and a second electrode 180 is provided inside the opening 168. The first electrode 170 has, for example, a Ti film in contact with the first electrode layer 110, a Pt film on the Ti film, and an Au film on the Pt film. The first electrode 170 is ohmic-bonded to the first electrode layer 110. The second electrode 180 has, for example, a Ti film in contact with the second electrode layer 140, a Pt film on the Ti film, and an Au film on the Pt film. The second electrode 180 is ohmic-bonded to the second electrode layer 140.

As described above, in the infrared detector 100, the bandgap Eg1 of the first electrode layer 110 is about 0.177 eV, and the bandgap Eg2 of the first light receiving layer 120 is about 0.146 eV. Further, the bandgap Eg3 of the second light receiving layer 130 is about 0.091 eV, the bandgap Eg4 of the second electrode layer 140 is about 0.127 eV, and the bandgap Eg5 of the barrier layer 150 is about 0.485 eV. Is. Since the bandgap Eg2 and the bandgap Eg3 are different, the wavelength of the first infrared ray absorbed by the first light receiving layer 120 and the wavelength of the second infrared ray absorbed by the second light receiving layer 130 are different. The barrier layer 150 is provided between the first light receiving layer 120 and the second light receiving layer 130. The first electrode layer 110 is arranged so as to sandwich the first light receiving layer 120 with the barrier layer 150, and is in contact with the first light receiving layer 120. The second electrode layer 140 is arranged so as to sandwich the second light receiving layer 130 with the barrier layer 150, and is in contact with the second light receiving layer 130.

As shown in FIG. 2, the bandgap Eg2 of the first light receiving layer 120 is larger than the bandgap Eg3 of the second light receiving layer 130. Therefore, the wavelength of the second infrared ray received by the second light receiving layer 130 is longer than the wavelength of the first infrared ray absorbed by the first light receiving layer 120. The bandgap Eg4 of the second electrode layer 140 is larger than the bandgap Eg3 of the second light receiving layer 130. The bandgap Eg1 of the first electrode layer 110 is larger than the bandgap Eg2 of the first light receiving layer 120. The bandgap Eg4 of the second electrode layer 140 is equal to or less than the bandgap Eg2 of the first light receiving layer 120.

The infrared detector 100 is irradiated with infrared Ir from the substrate 101 side. The infrared Ir irradiated to the infrared detector 100 enters the inside of the infrared detector 100 through the substrate 101 and is absorbed by the first light receiving layer 120 or the second light receiving layer 130 according to the wavelength. When infrared Ir is absorbed by the first light receiving layer 120 or the second light receiving layer 130, electron-hole pairs are generated in the first light receiving layer 120 or the second light receiving layer 130 that has absorbed the infrared Ir. To. The electrons and holes generated in the first light receiving layer 120 or the second light receiving layer 130 diffuse according to the electric field applied between the first electrode layer 110 and the second electrode layer 140. And an electric current is generated. Then, this current can be detected externally as a signal current (photocurrent).

Here, the details of the operation of the infrared detector 100 will be described. FIG. 3 is a diagram showing an energy band in the infrared detector 100 in the first operation example. FIG. 4 is a diagram showing an energy band in the infrared detector 100 in the second operation example.

In the first operation example, the infrared Ir absorbed by the second light receiving layer 130 is detected. In the first operation example, as shown in FIG. 3, the first electrode 170 is such that the lower end Ec2 of the conduction band of the first light receiving layer 120 is equal to or less than the lower end Ec3 of the conduction band of the second light receiving layer 130. A positive voltage is applied to the second electrode 180, and a negative voltage is applied to the second electrode 180. The bandgap Eg4 of the second electrode layer 140 is larger than the bandgap Eg3 of the second light receiving layer 130. Therefore, the heat generation of the carrier in the second electrode layer 140 is suppressed, and the dark current can be reduced. In particular, in the present embodiment, since the bandgap Eg4 is 0.03 eV or more larger than the bandgap Eg3, the dark current generated by the carriers heat-generated in the second electrode layer 140 can be suppressed to a negligible extent.

When the infrared Ir that can be absorbed by the second light receiving layer 130 enters the inside of the infrared detector 100 through the substrate 101, the infrared Ir is absorbed by the second light receiving layer 130 and the second light receiving layer 130 that has absorbed the infrared Ir. Electrons 10 and holes 20 are generated at. The electrons 10 pass through the barrier layer 150 and diffuse to the first light receiving layer 120 according to the electric field applied between the first electrode layer 110 and the second electrode layer 140.

For the electrons 10 diffused into the first light receiving layer 120, a potential barrier of the first electrode layer 110 exists on the first electrode layer 110 side, and a barrier layer exists on the second electrode layer 140 side. There is a potential barrier of 150, the second light receiving layer 130 and the second electrode layer 140. In the present embodiment, the difference ΔEg12 (= Eg1-Eg2) between the bandgap Eg1 of the first electrode layer 110 and the bandgap Eg2 of the first light receiving layer 120 is 0.031 eV, and the difference between the band gap Eg1 and the band gap Eg2 of the first light receiving layer 120 is 0.031 eV. The difference ΔEg43 (= Eg4-Eg3) between the bandgap Eg4 and the bandgap Eg3 of the second light receiving layer 130 is 0.036 eV. That is, the difference ΔEg12 is smaller than the difference ΔEg43, and the potential barrier of the first electrode layer 110 is smaller than the potential barrier of the barrier layer 150, the second light receiving layer 130, and the second electrode layer 140. Therefore, the electrons 10 diffused into the first light receiving layer 120 reach the first electrode 170 via the first electrode layer 110, and the signal current (photocurrent) Is sufficiently flows out to the outside. This is the same even when the lower end Ec2 of the conduction band of the first light receiving layer 120 is equal to the lower end Ec3 of the conduction band of the second light receiving layer 130.

As shown in FIG. 2, in the infrared detector 100, the difference ΔEv12 (= Ev1-) between the upper end Ev1 of the valence band of the first electrode layer 110 and the upper end Ev2 of the valence band of the first light receiving layer 120. Ev2) is about the same as the difference ΔEv43 (= Ev4-Ev3) between the upper end Ev4 of the valence band of the second electrode layer 140 and the upper end Ev3 of the valence band of the second light receiving layer 130. Therefore, the difference between the difference ΔEg43 and the difference ΔEg12 is the difference between the lower end Ec4 of the conduction band of the second electrode layer 140 and the lower end Ec3 of the conduction band of the second light receiving layer 130 ΔEc43 (= Ec4-Ec3) and the first. The difference between the lower end Ec1 of the conduction band of the electrode layer 110 and the lower end Ec2 of the conduction band of the first light receiving layer 120 is about the same as the difference ΔEc12 (= Ec1-Ec2).

In the second operation example, the infrared Ir absorbed by the first light receiving layer 120 is detected. In the second operation example, as shown in FIG. 4, a negative voltage is applied to the first electrode 170, and a positive voltage is applied to the second electrode 180. The upper end Ev2 of the valence band of the first light receiving layer 120 is equal to or higher than the upper end Ev3 of the valence band of the second light receiving layer 130. The bandgap Eg1 of the first electrode layer 110 is larger than the bandgap Eg2 of the first light receiving layer 120. Therefore, the heat generation of the carrier in the first electrode layer 110 is suppressed, and the dark current can be reduced. In particular, in the present embodiment, since the bandgap Eg1 is 0.03 eV or more larger than the bandgap Eg2, the dark current generated by the carriers heat-generated in the first electrode layer 110 can be suppressed to a negligible extent.

When the infrared Ir that can be absorbed by the first light receiving layer 120 enters the inside of the infrared detector 100 through the substrate 101, the infrared Ir is absorbed by the first light receiving layer 120 and the infrared Ir is absorbed by the first light receiving layer 120. Electrons 10 and holes 20 are generated at. The electrons 10 pass through the barrier layer 150 and diffuse to the second light receiving layer 130 according to the electric field applied between the first electrode layer 110 and the second electrode layer 140.

For the electrons 10 diffused into the second light receiving layer 130, the barrier layer 150, the first light receiving layer 120, and the potential barrier of the first electrode layer 110 exist on the first electrode layer 110 side. On the side of the second electrode layer 140, there is a potential barrier of the second electrode layer 140. In the present embodiment, the bandgap Eg4 of the second electrode layer 140 is equal to or less than the bandgap Eg2 of the first light receiving layer 120, and the potential barrier of the second electrode layer 140 is the barrier layer 150 and the first light receiving layer. It is smaller than the potential barrier of 120 and the first electrode layer 110. Therefore, the electrons 10 diffused into the second light receiving layer 130 reach the second electrode 180 via the second electrode layer 140, and the signal current (photocurrent) Is sufficiently flows out to the outside.

As described above, according to the infrared detector 100 according to the first embodiment, the dark current generated by the carriers heat-generated in the second electrode layer 140 and the carriers generated by the heat-generated carriers in the first electrode layer 110 are generated. Dark current can be suppressed. Further, the signal current (photocurrent) Is sufficiently flows out to the outside. Therefore, according to the infrared detector 100, the S / N ratio can be improved.

The p-type impurities contained in the first electrode layer 110, the first light receiving layer 120, the barrier layer 150, the second light receiving layer 130, and the second electrode layer 140 are not limited to Be. For example, Zn may be used as the p-type impurity.

Next, a method of manufacturing the infrared detector 100 according to the first embodiment will be described. 5A to 5D are cross-sectional views showing a method of manufacturing the infrared detector 100 according to the first embodiment. In this manufacturing method, the buffer layer 102, the etching stopper layer 103, the first electrode layer 110, the first light receiving layer 120, the barrier layer 150, the second light receiving layer 130, and the second electrode layer 140 are placed on the substrate 101. Epitaxially grow. In the following description, these semiconductor layers will be epitaxially grown by the Molecular Beam Epitaxy (MBE) method.

First, a substrate 101 such as an n-type GaSb (100) substrate is introduced into the substrate introduction chamber of the MBE apparatus. Next, the substrate 101 is conveyed to the growth chamber held in the ultra-high vacuum. Then, for example, the substrate 101 is heated in an Sb atmosphere. By this heating, the oxide film on the surface of the substrate 101 is removed. Subsequently, as shown in FIG. 5A, the buffer layer 102 is formed on the substrate 101 and the etching stopper layer 103 is formed on the buffer layer 102 by the MBE method. The temperature of the substrate 101 is, for example, about 480 ° C to 520 ° C. The formation of the buffer layer 102 improves the flatness of the surface of the base of the etching stopper layer 103.

Then, as shown in FIG. 5B, the first electrode layer 110, the first light receiving layer 120, the barrier layer 150, the second light receiving layer 130, and the second electrode layer 140 are placed on the etching stopper layer 103 by the MBE method. To form. The temperature of the substrate 101 is, for example, about 350 ° C. to 520 ° C.

Then, as shown in FIG. 5C, the second electrode layer 140, the second light receiving layer 130, the barrier layer 150, and the first light receiving layer 120 are exposed so that a part of the surface of the first electrode layer 110 is exposed. Is selectively etched into a mesa shape.

Subsequently, as shown in FIG. 5D, the side surfaces of the second electrode layer 140, the second light receiving layer 130, the barrier layer 150 and the first light receiving layer 120, and the first electrode layer 110 and the second electrode layer. An insulating film 160 is formed so as to cover the upper surface of the 140. The insulating film 160 can be formed by, for example, a chemical vapor deposition (CVD) method. When a silicon oxide film is formed as the insulating film 160, for example, silane and nitrous oxide may be used as the reaction gas.

Next, an opening 167 that exposes a part of the upper surface of the first electrode layer 110 and an opening that exposes a part of the upper surface of the second electrode layer 140 by selective etching of the insulating film 160 using a mask. It forms a portion 168 (see FIG. 1). Further, the first electrode 170 is formed inside the opening 167, and the second electrode 180 is formed inside the opening 168 (see FIG. 1).

In this way, the infrared detector 100 according to the first embodiment can be manufactured.

(Second embodiment)
Next, the second embodiment will be described. The second embodiment relates to an nBn type infrared detector. The second embodiment differs from the first embodiment mainly in the conductive type of the first electrode layer, the first light receiving layer, the barrier layer, the second light receiving layer and the second electrode layer. .. FIG. 6 is a cross-sectional view showing an infrared detector according to the second embodiment. FIG. 7 is a diagram showing an energy band in the infrared detector according to the second embodiment when no bias is applied. Ef in FIG. 7 indicates the Fermi level.

As shown in FIG. 6, the infrared detector 200 according to the second embodiment includes a substrate 101, a buffer layer 102, an etching stopper layer 103, a first electrode layer 210, and a first light receiving layer 220. It has a barrier layer 250, a second light receiving layer 230, and a second electrode layer 240. The infrared detector 200 further includes an insulating film 160, a first electrode 170, and a second electrode 180.

The first electrode layer 210 is provided on the etching stopper layer 103. The first electrode layer 210 includes a type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.0 nm, and the thickness of the GaSb layer is 3.6 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.0 nm and GaSb layers having a thickness of 3.6 nm are alternately laminated is about 0.246 eV. For example, the first electrode layer 210 ^{is doped with Si so that the electron concentration is about 1 × 10 18} cm ^-3 , and the first electrode layer 210 has an n-type conductive type. The thickness of the first electrode layer 210 is, for example, about 340 nm to 380 nm.

The first light receiving layer 220 is provided on the first electrode layer 210. The first light receiving layer 220 includes a type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.3 nm, and the thickness of the GaSb layer is 3.6 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.3 nm and GaSb layers having a thickness of 3.6 nm are alternately laminated is about 0.212 eV. For example, the first light receiving layer 220 ^{is doped with Si so that the electron concentration is about 1 × 10 16} cm ^-3 , and the first light receiving layer 220 has an n-type conductive type. The thickness of the first light receiving layer 220 is, for example, about 1200 nm to 1400 nm.

The barrier layer 250 is provided on the first light receiving layer 220. The barrier layer 250 is, for example, an Al _0.2 Ga _0.8 Sb layer. The _{bandgap of the Al 0.2} Ga _0.8 Sb layer is about 1.083 eV. For example, the barrier layer 250 ^{is doped with Si so that the electron concentration is about 1 × 10 16} cm ^-3 , and the barrier layer 250 has an n-type conductive type. The barrier layer 250 functions as a unipolar barrier layer that blocks only electrons. The thickness of the barrier layer 250 is, for example, about 90 nm to 110 nm.

The second light receiving layer 230 is provided on the barrier layer 250. The second light receiving layer 230 includes a type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 4.2 nm and the thickness of the GaSb layer is 2.1 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 4.2 nm and GaSb layers having a thickness of 2.1 nm are alternately laminated is about 0.127 eV. For example, the second light receiving layer 230 ^{is doped with Si so that the electron concentration is about 1 × 10 16} cm ^-3 , and the second light receiving layer 230 has an n-type conductive type. The thickness of the second light receiving layer 230 is, for example, about 1200 nm to 1400 nm.

The second electrode layer 240 is provided on the second light receiving layer 230. The second electrode layer 240 includes a Type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.6 nm and the thickness of the GaSb layer is 2.1 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.6 nm and GaSb layers having a thickness of 2.1 nm are alternately laminated is about 0.171 eV. For example, the second electrode layer 240 ^{is doped with Si so that the electron concentration is about 1 × 10 18} cm ^-3 , and the second electrode layer 240 has an n-type conductive type. The thickness of the second electrode layer 240 is, for example, about 340 nm to 380 nm.

As described above, the superlattice material contained in the first electrode layer 210, the superlattice material contained in the first light receiving layer 220, the superlattice material contained in the second light receiving layer 230, and the second electrode. The superlattice material contained in layer 240 is common. Further, the electron concentration of the first light receiving layer 220 and the electron concentration of the second light receiving layer 230 are about the same, and the electron concentration of the first electrode layer 210 and the electron concentration of the second electrode layer 240 are the same. Degree. The electron concentration of the first electrode layer 210 is higher than the electron concentration of the first light receiving layer 220, and the electron concentration of the second electrode layer 240 is higher than the electron concentration of the second light receiving layer 230.

The second electrode layer 240, the second light receiving layer 230, the barrier layer 250, and the first light receiving layer 220 are etched in a mesa shape, and the insulating film 160 is the second electrode layer 240 and the second light receiving layer. It covers the side surfaces of 230, the barrier layer 250, and the first light receiving layer 220. The insulating film 160 also covers the upper surface of the first electrode layer 210 and the upper surface of the second electrode layer 240.

An opening 167 and an opening 168 are formed in the insulating film 160, a first electrode 170 is formed inside the opening 167, and a second electrode 180 is provided inside the opening 168. The first electrode 170 has, for example, a Ti film in contact with the first electrode layer 210, a Pt film on the Ti film, and an Au film on the Pt film. The first electrode 170 is ohmic-bonded to the first electrode layer 210. The second electrode 180 has, for example, a Ti film in contact with the second electrode layer 240, a Pt film on the Ti film, and an Au film on the Pt film. The second electrode 180 is ohmic-bonded to the second electrode layer 240.

As described above, in the infrared detector 200, the bandgap Eg1 of the first electrode layer 210 is about 0.246 eV, and the bandgap Eg2 of the first light receiving layer 220 is about 0.212 eV. Further, the bandgap Eg3 of the second light receiving layer 230 is about 0.127 eV, the bandgap Eg4 of the second electrode layer 240 is about 0.171 eV, and the bandgap Eg5 of the barrier layer 250 is about 1.083 eV. Is. Since the bandgap Eg2 and the bandgap Eg3 are different, the wavelength of the first infrared ray absorbed by the first light receiving layer 220 and the wavelength of the second infrared ray absorbed by the second light receiving layer 230 are different. The barrier layer 250 is provided between the first light receiving layer 220 and the second light receiving layer 230. The first electrode layer 210 is arranged so as to sandwich the first light receiving layer 220 with the barrier layer 250, and is in contact with the first light receiving layer 220. The second electrode layer 240 is arranged so as to sandwich the second light receiving layer 230 with the barrier layer 250, and is in contact with the second light receiving layer 230.

As shown in FIG. 7, the bandgap Eg2 of the first light receiving layer 220 is larger than the bandgap Eg3 of the second light receiving layer 230. Therefore, the wavelength of the second infrared ray received by the second light receiving layer 230 is longer than the wavelength of the first infrared ray absorbed by the first light receiving layer 220. The bandgap Eg4 of the second electrode layer 240 is larger than the bandgap Eg3 of the second light receiving layer 230. The bandgap Eg1 of the first electrode layer 210 is larger than the bandgap Eg2 of the first light receiving layer 220. The bandgap Eg4 of the second electrode layer 240 is equal to or less than the bandgap Eg2 of the first light receiving layer 220.

Other configurations are the same as in the first embodiment.

The infrared detector 200 is irradiated with infrared Ir from the substrate 101 side. The infrared Ir irradiated to the infrared detector 200 enters the inside of the infrared detector 200 through the substrate 101 and is absorbed by the first light receiving layer 220 or the second light receiving layer 230 according to the wavelength. When infrared Ir is absorbed by the first light receiving layer 220 or the second light receiving layer 230, electron-hole pairs are generated in the first light receiving layer 220 or the second light receiving layer 230 that has absorbed the infrared Ir. To. The electrons and holes generated in the first light receiving layer 220 or the second light receiving layer 230 diffuse according to the electric field applied between the first electrode layer 210 and the second electrode layer 240. And an electric current is generated. Then, this current can be detected externally as a signal current (photocurrent).

Here, the details of the operation of the infrared detector 200 will be described. FIG. 8 is a diagram showing an energy band in the infrared detector 200 in the first operation example. FIG. 9 is a diagram showing an energy band in the infrared detector 200 in the second operation example.

In the first operation example, the infrared Ir absorbed by the second light receiving layer 230 is detected. In the first operation example, as shown in FIG. 8, the first operation is such that the upper end Ev2 of the valence band of the first light receiving layer 220 is equal to or higher than the upper end Ev3 of the valence band of the second light receiving layer 230. A negative voltage is applied to the electrode 170, and a positive voltage is applied to the second electrode 180. The bandgap Eg4 of the second electrode layer 240 is larger than the bandgap Eg3 of the second light receiving layer 230. Therefore, the heat generation of the carrier in the second electrode layer 240 is suppressed, and the dark current can be reduced. In particular, in the present embodiment, since the bandgap Eg4 is 0.03 eV or more larger than the bandgap Eg3, the dark current generated by the carriers heat-generated in the second electrode layer 240 can be suppressed to a negligible extent.

When the infrared Ir that can be absorbed by the second light receiving layer 230 enters the inside of the infrared detector 200 through the substrate 101, the infrared Ir is absorbed by the second light receiving layer 230 and the second light receiving layer 230 that has absorbed the infrared Ir. Electrons 10 and holes 20 are generated at. The holes 20 pass through the barrier layer 250 and diffuse to the first light receiving layer 220 according to the electric field applied between the first electrode layer 210 and the second electrode layer 240.

With respect to the holes 20 diffused into the first light receiving layer 220, a potential barrier of the first electrode layer 210 exists on the first electrode layer 210 side, and a barrier exists on the second electrode layer 240 side. There is a potential barrier between the layer 250, the second light receiving layer 230 and the second electrode layer 240. In the present embodiment, the difference ΔEg12 (= Eg1-Eg2) between the bandgap Eg1 of the first electrode layer 210 and the bandgap Eg2 of the first light receiving layer 220 is 0.034 eV, and that of the second electrode layer 240. The difference ΔEg43 (= Eg4-Eg3) between the bandgap Eg4 and the bandgap Eg3 of the second light receiving layer 230 is 0.044 eV. That is, the difference ΔEg12 is smaller than the difference ΔEg43, and the potential barrier of the first electrode layer 210 is smaller than the potential barrier of the barrier layer 250, the second light receiving layer 230, and the second electrode layer 240. Therefore, the holes 20 diffused into the first light receiving layer 220 reach the first electrode 170 via the first electrode layer 210, and the signal current (photocurrent) Is sufficiently flows out to the outside. This is the same even when the upper end Ev2 of the valence band of the first light receiving layer 220 is equal to the lower end Ev3 of the valence band of the second light receiving layer 230.

As shown in FIG. 7, in the infrared detector 200, the difference between the lower end Ec1 of the conduction band of the first electrode layer 210 and the lower end Ec2 of the conduction band of the first light receiving layer 220 ΔEc12 (= Ec1-Ec2). Is about the same as the difference ΔEc43 (= Ec4-Ec3) between the lower end Ec4 of the conduction band of the second electrode layer 240 and the lower end Ec3 of the conduction band of the second light receiving layer 230. Therefore, the difference between the difference ΔEg43 and the difference ΔEg12 is the difference ΔEv43 (= Ev4-Ev3) between the upper end Ev4 of the valence band of the second electrode layer 240 and the upper end Ev3 of the valence band of the second light receiving layer 230. The difference between the upper end Ev1 of the valence band of the first electrode layer 210 and the upper end Ev3 of the first light receiving layer 220 valence band is about the same as the difference ΔEv12 (= Ev1-Ev2).

In the second operation example, the infrared Ir absorbed by the first light receiving layer 220 is detected. In the second operation example, as shown in FIG. 9, a positive voltage is applied to the first electrode 170, and a negative voltage is applied to the second electrode 180. The lower end Ec2 of the conduction band of the first light receiving layer 220 is equal to or less than the lower end Ec3 of the conduction band of the second light receiving layer 230. The bandgap Eg1 of the first electrode layer 210 is larger than the bandgap Eg2 of the first light receiving layer 220. Therefore, the heat generation of the carrier in the first electrode layer 210 is suppressed, and the dark current can be reduced. In particular, in the present embodiment, since the bandgap Eg1 is 0.03 eV or more larger than the bandgap Eg2, the dark current generated by the carriers heat-generated in the first electrode layer 210 can be suppressed to a negligible extent.

When the infrared Ir that can be absorbed by the first light receiving layer 220 enters the inside of the infrared detector 200 through the substrate 101, the infrared Ir is absorbed by the first light receiving layer 220 and the infrared Ir is absorbed by the first light receiving layer 220. Electrons 10 and holes 20 are generated at. The holes 20 pass through the barrier layer 250 and diffuse to the second light receiving layer 230 according to the electric field applied between the first electrode layer 210 and the second electrode layer 240.

For the holes 20 diffused into the second light receiving layer 230, there are potential barriers of the barrier layer 250, the first light receiving layer 220, and the first electrode layer 210 on the first electrode layer 210 side. On the side of the second electrode layer 240, there is a potential barrier of the second electrode layer 240. In the present embodiment, the band gap Eg4 of the second electrode layer 240 is equal to or less than the band gap Eg2 of the first light receiving layer 220, and the potential barrier of the second electrode layer 240 is the barrier layer 250 and the first light receiving layer. It is smaller than the potential barrier of 220 and the first electrode layer 210. Therefore, the holes 20 diffused into the second light receiving layer 230 reach the second electrode 180 via the second electrode layer 240, and the signal current (photocurrent) Is sufficiently flows out to the outside.

As described above, according to the infrared detector 200 according to the second embodiment, the dark current generated by the carriers heat-generated in the second electrode layer 240 and the carriers generated by the heat-generated carriers in the first electrode layer 210 are generated. Dark current can be suppressed. Further, the signal current (photocurrent) Is sufficiently flows out to the outside. Therefore, according to the infrared detector 200, the S / N ratio can be improved.

The n-type impurities contained in the first electrode layer 210, the first light receiving layer 220, the barrier layer 250, the second light receiving layer 230, and the second electrode layer 240 are not limited to Si. For example, Te may be used as the n-type impurity.

The infrared detector 200 according to the second embodiment can be manufactured by the same method as the manufacturing method of the infrared detector 100 according to the first embodiment. For example, instead of the first electrode layer 110, the first light receiving layer 120, the barrier layer 150, the second light receiving layer 130, and the second electrode layer 140, the first electrode layer 210 and the first light receiving layer 220 , The barrier layer 250, the second light receiving layer 230 and the second electrode layer 240 can be epitaxially grown by the MBE method.

(Third Embodiment)
Next, a third embodiment will be described. A third embodiment relates to an nBn type infrared detector. The third embodiment differs from the second embodiment mainly in the configuration of the first electrode layer and the second electrode layer. FIG. 10 is a cross-sectional view showing an infrared detector according to a third embodiment. FIG. 11 is a diagram showing an energy band in the infrared detector according to the third embodiment when no bias is applied. Ef in FIG. 11 indicates the Fermi level.

As shown in FIG. 10, the infrared detector 300 according to the third embodiment includes a substrate 101, a buffer layer 102, an etching stopper layer 103, a first electrode layer 310, and a first light receiving layer 220. It has a barrier layer 250, a second light receiving layer 230, and a second electrode layer 340. The infrared detector 200 further includes an insulating film 160, a first electrode 170, and a second electrode 180. That is, the first electrode layer 310 is provided in place of the first electrode layer 210 in the second embodiment, and the second electrode layer 340 is provided in place of the second electrode layer 240 in the second embodiment. Has been done.

The first electrode layer 310 is provided on the etching stopper layer 103. The first electrode layer 310 has a first sub-electrode layer 311 and a second sub-electrode layer 312, and a third sub-electrode layer 313. The thickness of the first electrode layer 310 is, for example, about 340 nm to 380 nm. The first to third sub-electrode layers 311 to 313 are examples of the first semiconductor layer.

The first sub-electrode layer 311 is provided on the etching stopper layer 103. The first sub-electrode layer 311 includes a Type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.0 nm, and the thickness of the GaSb layer is 3.6 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.0 nm and GaSb layers having a thickness of 3.6 nm are alternately laminated is about 0.246 eV. For example, the first sub-electrode layer 311 ^{is doped with Si so that the electron concentration is about 1 × 10 18} cm ^-3 , and the first sub-electrode layer 311 has an n-type conductive type.

The second sub-electrode layer 312 is provided on the first sub-electrode layer 311. The second sub-electrode layer 312 includes a Type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.1 nm, and the thickness of the GaSb layer is 3.6 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.1 nm and GaSb layers having a thickness of 3.6 nm are alternately laminated is about 0.235 eV. For example, the second sub-electrode layer 312 ^{is doped with Si so that the electron concentration is about 1 × 10 18} cm ^-3 , and the second sub-electrode layer 312 has an n-type conductive type.

The third sub-electrode layer 313 is provided on the second sub-electrode layer 312. The third sub-electrode layer 313 includes a Type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.2 nm, and the thickness of the GaSb layer is 3.6 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.2 nm and GaSb layers having a thickness of 3.6 nm are alternately laminated is about 0.223 eV. For example, the third sub-electrode layer 313 ^{is doped with Si so that the electron concentration is about 1 × 10 18} cm ^-3 , and the third sub-electrode layer 313 has an n-type conductive type.

The second electrode layer 340 is provided on the second light receiving layer 230. The second electrode layer 340 includes a first sub-electrode layer 341, a second sub-electrode layer 342, a third sub-electrode layer 343, a fourth sub-electrode layer 344, and a fifth sub-electrode layer. It has 345 and a sixth sub-electrode layer 346. The thickness of the second electrode layer 340 is, for example, about 340 nm to 380 nm. The first to sixth sub-electrode layers 341 to 346 are examples of the second semiconductor layer.

The first sub-electrode layer 341 is provided on the second light receiving layer 230. The first sub-electrode layer 341 includes a Type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 4.1 nm and the thickness of the GaSb layer is 2.1 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 4.1 nm and GaSb layers having a thickness of 2.1 nm are alternately laminated is about 0.135 eV. For example, the first sub-electrode layer 341 ^{is doped with Si so that the electron concentration is about 1 × 10 18} cm ^-3 , and the first sub-electrode layer 341 has an n-type conductive type.

The second sub-electrode layer 342 is provided on the first sub-electrode layer 341. The second sub-electrode layer 342 includes a Type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 4.0 nm and the thickness of the GaSb layer is 2.1 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 4.0 nm and GaSb layers having a thickness of 2.1 nm are alternately laminated is about 0.141 eV. For example, the second sub-electrode layer 342 ^{is doped with Si so that the electron concentration is about 1 × 10 18} cm ^-3 , and the second sub-electrode layer 342 has an n-type conductive type.

The third sub-electrode layer 343 is provided on the second sub-electrode layer 342. The third sub-electrode layer 343 includes a Type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.9 nm, and the thickness of the GaSb layer is 2.1 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.9 nm and GaSb layers having a thickness of 2.1 nm are alternately laminated is about 0.148 eV. For example, the third sub-electrode layer 343 ^{is doped with Si so that the electron concentration is about 1 × 10 18} cm ^-3 , and the third sub-electrode layer 343 has an n-type conductive type.

The fourth sub-electrode layer 344 is provided on the third sub-electrode layer 343. The fourth sub-electrode layer 344 includes a Type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.8 nm and the thickness of the GaSb layer is 2.1 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.8 nm and GaSb layers having a thickness of 2.1 nm are alternately laminated is about 0.155 eV. For example, the fourth sub-electrode layer 344 ^{is doped with Si so that the electron concentration is about 1 × 10 18} cm ^-3 , and the fourth sub-electrode layer 344 has an n-type conductive type.

The fifth sub-electrode layer 345 is provided on the fourth sub-electrode layer 344. The fifth sub-electrode layer 345 includes a Type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.7 nm, and the thickness of the GaSb layer is 2.1 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.7 nm and GaSb layers having a thickness of 2.1 nm are alternately laminated is about 0.163 eV. For example, the fifth sub-electrode layer 345 ^{is doped with Si so that the electron concentration is about 1 × 10 18} cm ^-3 , and the fifth sub-electrode layer 345 has an n-type conductive type.

The sixth sub-electrode layer 346 is provided on the fifth sub-electrode layer 345. The sixth sub-electrode layer 346 includes a Type II superlattice in which InAs layers and GaSb layers are alternately laminated. For example, the thickness of the InAs layer is 3.6 nm and the thickness of the GaSb layer is 2.1 nm. The bandgap of the Type II superlattice in which InAs layers having a thickness of 3.6 nm and GaSb layers having a thickness of 2.1 nm are alternately laminated is about 0.171 eV. For example, the sixth sub-electrode layer 346 ^{is doped with Si so that the electron concentration is about 1 × 10 18} cm ^-3 , and the sixth sub-electrode layer 346 has an n-type conductive type.

As described above, the first electrode layer 310 is provided in place of the first electrode layer 210, and the second electrode layer 340 is provided in place of the second electrode layer 240. Other configurations are the same as in the second embodiment.

As shown in FIG. 11, in the infrared detector 300, among the first to third sub-electrode layers 31 to 313, the closer to the first light receiving layer 220, the smaller the band gap. That is, the band gap changes stepwise from the first light receiving layer 220 to the first sub-electrode layer 311 with a difference of about the thermal energy. Therefore, when detecting the infrared Ir absorbed by the second light receiving layer 230, the signal current Is can be easily drawn.

Similarly, among the first to sixth sub-electrode layers 341 to 346, the closer to the second light receiving layer 230, the smaller the band gap. That is, the band gap changes stepwise from the second light receiving layer 230 to the sixth sub-electrode layer 346 depending on the difference in thermal energy. Therefore, when detecting the infrared Ir absorbed by the first light receiving layer 220, the signal current Is can be easily drawn.

The bandgap of the first to fifth sub-electrode layers 341 to 345 is smaller than the bandgap of the second electrode layer 240 of the second embodiment, but larger than the bandgap of the second light receiving layer 230. Therefore, the effect of reducing the dark current can be obtained. Similarly, the bandgap of the second to third sub-electrode layers 312-313 is smaller than the bandgap of the first electrode layer 210 of the second embodiment, but smaller than the bandgap of the first light receiving layer 220. Since it is large, the effect of reducing the dark current can be obtained.

In the second electrode layer 340, the first sub-electrode layer 341, the second sub-electrode layer 342, and the third sub-electrode layer 343 have a band gap difference of less than 0.03 eV from the second light receiving layer 230. And it is preferable to make the fourth sub-electrode layer 344 thin. In the first electrode layer 310, it is preferable to thin the second sub-electrode layer 312 and the third sub-electrode layer 313 having a bandgap difference of less than 0.03 eV from the first light receiving layer 220.

In the present disclosure, the wavelength of the second infrared ray received by the second light receiving layer is longer than the wavelength of the first infrared ray received by the first light receiving layer. Therefore, in order to sufficiently improve the S / N ratio, it is important to suppress the dark current generated by the heat-generated carriers in the second electrode layer. Therefore, if the band gap of the second electrode layer is larger than the band gap of the second light receiving layer, the band gap of the first electrode layer does not need to be larger than the band gap of the first light receiving layer, and the first The band gap of the electrode layer 1 may be about the same as the band gap of the first light receiving layer.

In the superlattice contained in the first light receiving layer and the second light receiving layer, the thickness of the InAs layer and the GaSb layer is not limited to that of the above embodiment, and is appropriately changed according to the wavelength of infrared rays to be absorbed. You may.

In the superlattice contained in the first electrode layer, the first light receiving layer, the second light receiving layer, and the second electrode layer, the InSb layer is lattice-aligned with the GaSb substrate between the InAs layer and the GaSb layer. May be provided. The material of the superlattice is not limited to InAs and GaSb. For example, two or more of InAs, InSb, GaSb and AlSb may be used as the material of the superlattice. As long as the material responds to the infrared region, a mixed crystal of two or more of InAs, InSb, GaSb and AlSb may be used as the material of the superlattice. For _{example, InAs 1-a Sb a (} 0 ≦ a ≦ 1) may be used in the material of the superlattice.

The method for forming the first electrode layer, the first light receiving layer, the barrier layer, the second light receiving layer, and the second electrode layer is not limited to the MBE method. For example, a first electrode layer, a first light receiving layer, a barrier layer, a second light receiving layer, and a second electrode layer are formed by an organometallic chemical vapor deposition (CVD) method or the like. May be good. The method for forming the insulating film is not limited to the CVD method. For example, an insulating film may be formed by an atomic layer deposition (ALD) method, a sputtering method, or the like.

The etching stopper layer may not be used. Further, the substrate, the buffer layer and the etching stopper layer may be removed after the formation of the first electrode and the second electrode.

The wavelength of infrared rays detected by the infrared detector according to the present disclosure is not limited. For example, mid-infrared rays having a wavelength of 3 μm to 5 μm may be detected, and far-infrared rays having a wavelength of 8 μm to 12 μm may be detected. The infrared detector according to the present disclosure can be applied to, for example, the field of security and the field of infrastructure inspection.

(Fourth Embodiment)
Next, a fourth embodiment will be described. The fourth embodiment relates to an infrared image pickup device including the infrared detector 100 according to the first embodiment. FIG. 12 is a perspective view showing an infrared imaging element according to a fourth embodiment. FIG. 13 is an enlarged cross-sectional view showing a part of the infrared imaging element according to the fourth embodiment.

The infrared image pickup element 400 according to the fourth embodiment includes an infrared image pickup panel 41 and a drive circuit 42, and the infrared image pickup panel 41 and the drive circuit 42 are electrically connected by bumps 43.

In the infrared imaging panel 41, for example, a plurality of infrared detectors 100 according to the first embodiment are two-dimensionally arranged in a plane in a matrix. Each infrared detector 100 becomes a pixel. In the infrared imaging panel 41, the substrate 101, the buffer layer 102, the etching stopper layer 103, the first electrode layer 110, and the first electrode 170 are common to each infrared detector 100. A surface wiring 44 is formed on the insulating film 160 of each infrared detector 100, and a bump 43 is formed on each surface wiring 44. The bump 43 is, for example, an In bump. A part of the bump 43 is a common electrode 43a of each infrared detector 100. Each surface wiring 44 is electrically connected to the first electrode 170 or the second electrode 180 at one end.

The drive circuit 42 is a drive unit of each infrared detector 100, and has a plurality of transistors 45 and a power supply line 46 to which a power _{supply voltage VA is applied.} Each transistor 45 is electrically connected to the bump 43, and the power supply line 46 is electrically connected to the common electrode 43a. By applying the power supply voltage _VA , the output current I flows through each infrared detector 100.

According to the present embodiment, a highly reliable infrared imaging element 400 including an infrared detector 100 having a superlattice structure capable of improving infrared absorption efficiency is realized.

When manufacturing the infrared imaging element 400, for example, after forming the first electrode 170 and the second electrode 180, a metal film for the surface wiring 44 is formed to form a bump 43. Next, the drive circuit 42 is bonded. In this way, the infrared imaging device 400 can be manufactured.

If necessary, the substrate 101, the buffer layer 102, and the etching stopper layer 103 may be removed.

In the fourth embodiment, the infrared detector 200 or 300 may be used instead of the infrared detector 100.

(Fifth Embodiment)
Next, a fifth embodiment will be described. A fifth embodiment relates to an infrared imaging system including the infrared imaging element 400 according to the fourth embodiment. FIG. 14 is a schematic view showing an infrared imaging system according to a fifth embodiment.

The infrared imaging system 500 according to the fifth embodiment includes a sensor unit 51, a control calculation unit 52, and a display unit 53.

The sensor unit 51 includes a lens 54 that collects incident light, an infrared image pickup device 400 according to a fourth embodiment, and a cooling section 55 for cooling the infrared image pickup element 400. The control calculation unit 52 controls the drive circuit 42 of the infrared image pickup element 400. The display unit 53 displays an infrared image captured by the infrared image sensor 400 based on the image pickup signal transmitted from the control calculation unit 52.

According to this embodiment, a highly reliable infrared imaging system 500 including an infrared imaging element 400 having a superlattice structure capable of improving infrared absorption efficiency is realized.

Although the preferred embodiments and the like have been described in detail above, the embodiments are not limited to the above-described embodiments and the like, and various embodiments and the like described above are used without departing from the scope of the claims. Modifications and substitutions can be added.

Hereinafter, various aspects of the present disclosure will be described together as an appendix.

(Appendix 1)
A first light receiving layer that absorbs the first infrared ray,
A second light receiving layer that absorbs the second infrared ray,
A barrier layer provided between the first light receiving layer and the second light receiving layer,
A first electrode layer arranged so as to sandwich the first light receiving layer with the barrier layer and in contact with the first light receiving layer, and
A second electrode layer arranged so as to sandwich the second light receiving layer with the barrier layer and in contact with the second light receiving layer, and
Have,
The bandgap of the first light receiving layer is larger than the bandgap of the second light receiving layer.
The bandgap of the second electrode layer is larger than the bandgap of the second light receiving layer.
An infrared detector characterized in that the band gap of the second electrode layer is equal to or smaller than the band gap of the first light receiving layer.
(Appendix 2)
The infrared detector according to Appendix 1, wherein the bandgap of the first electrode layer is larger than the bandgap of the first light receiving layer.
(Appendix 3)
The difference between the band gap of the first electrode layer and the band gap of the first light receiving layer is smaller than the difference between the band gap of the second electrode layer and the band gap of the second light receiving layer. The infrared detector according to Appendix 2, characterized by the above.
(Appendix 4)
The difference between the band gap of the first electrode layer and the band gap of the first light receiving layer is 0.03 eV or more.
The infrared detector according to Appendix 2 or 3, wherein the difference between the band gap of the second electrode layer and the band gap of the second light receiving layer is 0.03 eV or more.
(Appendix 5)
The first electrode layer includes a plurality of first semiconductor layers arranged in the thickness direction of the first electrode layer.
The second electrode layer includes a plurality of second semiconductor layers arranged in the thickness direction of the second electrode layer.
The band gap of the plurality of first semiconductor layers is so large that it is separated from the first light receiving layer.
The infrared detector according to any one of Supplementary note 2 to 4, wherein the band gap of the plurality of second semiconductor layers is increased so as to be separated from the second light receiving layer.
(Appendix 6)
Item 1 of Appendix 1 to 5, wherein the first light receiving layer, the second light receiving layer, the barrier layer, the first electrode layer, and the second electrode layer include a superlattice. Infrared detector described in.
(Appendix 7)
The infrared detector according to Appendix 6, wherein the superlattice is a type II superlattice.
(Appendix 8)
The superlattice material contained in the first light receiving layer, the superlattice material contained in the second light receiving layer, the superlattice material contained in the first electrode layer, and the second electrode layer. The infrared detector according to Appendix 6 or 7, wherein the materials of the superlattice are common.
(Appendix 9)
The infrared detector according to any one of Supplementary note 1 to 8, wherein the band gap of the barrier layer is larger than the band gap of the first light receiving layer and the band gap of the second light receiving layer. ..
(Appendix 10)
With multiple infrared detectors
A drive unit that drives the plurality of infrared detectors,
Have,
An image pickup device, wherein each of the plurality of infrared detectors is the infrared detector according to any one of Supplementary Provisions 1 to 9.
(Appendix 11)
Infrared sensor and
A control unit that controls the infrared sensor unit and
A display unit that displays the captured infrared image and
Have,
The infrared sensor unit
The image sensor according to Appendix 10 and
A cooling unit that cools the image sensor and
A lens for injecting infrared rays into the image sensor and
An imaging system characterized by having.

10: Electrons 20: Holes 100, 200, 300: Infrared detectors 110, 210, 310: First electrode layer 120, 220: First light receiving layer 130, 230: Second light receiving layer 140, 240, 340 : Second electrode layer 150, 250: Barrier layer 311: First sub electrode layer 312: Second sub electrode layer 313: Third sub electrode layer 341: First sub electrode layer 342: Second sub Electrode layer 343: Third sub-electrode layer 344: Fourth sub-electrode layer 345: Fifth sub-electrode layer 346: Sixth sub-electrode layer 400: Infrared imaging element 500: Infrared imaging system

Claims (6)

A first light receiving layer that absorbs the first infrared ray,
A second light receiving layer that absorbs the second infrared ray,
A barrier layer provided between the first light receiving layer and the second light receiving layer,
A first electrode layer arranged so as to sandwich the first light receiving layer with the barrier layer and in contact with the first light receiving layer, and
A second electrode layer arranged so as to sandwich the second light receiving layer with the barrier layer and in contact with the second light receiving layer, and
Have,
The bandgap of the first light receiving layer is larger than the bandgap of the second light receiving layer.
The bandgap of the second electrode layer is larger than the bandgap of the second light receiving layer.
An infrared detector characterized in that the band gap of the second electrode layer is equal to or smaller than the band gap of the first light receiving layer. The infrared detector according to claim 1, wherein the band gap of the first electrode layer is larger than the band gap of the first light receiving layer. The difference between the band gap of the first electrode layer and the band gap of the first light receiving layer is smaller than the difference between the band gap of the second electrode layer and the band gap of the second light receiving layer. The infrared detector according to claim 2. The difference between the band gap of the first electrode layer and the band gap of the first light receiving layer is 0.03 eV or more.
The infrared detector according to claim 2 or 3, wherein the difference between the band gap of the second electrode layer and the band gap of the second light receiving layer is 0.03 eV or more. The first electrode layer includes a plurality of first semiconductor layers arranged in the thickness direction of the first electrode layer.
The second electrode layer includes a plurality of second semiconductor layers arranged in the thickness direction of the second electrode layer.
The band gap of the plurality of first semiconductor layers is so large that it is separated from the first light receiving layer.
The infrared detector according to any one of claims 2 to 4, wherein the band gap of the plurality of second semiconductor layers is increased so as to be separated from the second light receiving layer. Any one of claims 1 to 5, wherein the first light receiving layer, the second light receiving layer, the barrier layer, the first electrode layer, and the second electrode layer include a superlattice. Infrared detector as described in the section.

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