JP2015142110A - Image sensor and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow for detection of only an optical signal having a wavelength corresponding to only one MQW layer out of a lower MQW layer and an upper MQW layer, and easy and reliable separation of two optical signals each having a different wavelength, by a relatively simple configuration.SOLUTION: In each pixel 10, a first photoconductor type element is constituted to include a lower MQW layer 2 and a lower contact layer 4 and an intermediate contact layer 5 sandwiching the same, and a second photoconductor type element is constituted to include an upper MQW layer 3 and an intermediate contact layer 5 and an upper contact layer 6 sandwiching the same. The first photoconductor type element includes a first barrier layer 7, i.e., a semiconductor layer of a material having a forbidden band wider than the lower MQW layer 2 between the lower MQW layer 2 and the intermediate contact layer 5, and the second photoconductor type element includes a second barrier layer 8, i.e., a semiconductor layer of a material having a forbidden band wider than the upper MQW layer 3 between the intermediate contact layer 5 and the upper MQW layer 3.

Description

  The present invention relates to an image sensor and a manufacturing method thereof.

  An infrared image sensor includes an image sensor (hereinafter referred to as a two-wavelength infrared image sensor) configured by a sensor unit that converts optical signals in two different wavelength ranges into electrical signals (photocurrent signals) and a drive circuit. . In general, the sensor unit is composed of a large number of pixels, and each pixel has a photoelectric conversion element. As a photoelectric conversion element, for example, there is a quantum well infrared detector (QWIP: Quantum Well Infrared Photodetector). The QWIP includes a contact layer connected to an external circuit and a multi-quantum well (MQW) layer that converts an optical signal into an electric signal.

As a two-wavelength infrared image sensor, for example, there is an image sensor in which each pixel is configured by two QWIPs having different detection wavelength ranges.
A schematic configuration of a pixel of a typical two-wavelength infrared image sensor is shown in FIG.
Each pixel 100 includes a lower MQW layer 102 and an upper MQW layer 103, a lower contact layer 104, an intermediate contact layer 105, and an upper contact layer 106 on a GaAs substrate 101. Electrodes 109 a, 109 b, and 109 c are electrically connected to the lower contact layer 104, the intermediate contact layer 105, and the upper contact layer 106 through wirings 108 a, 108 b, and 108 c, and are connected to the drive circuit 110. The wirings 108 a and 108 b have necessary electrical insulation by the insulating layer 107. The wiring 108 c is connected to the upper contact layer 106 through the opening 107 a formed in the insulating layer 107.

  In this two-wavelength infrared image sensor, photocurrent signals from the lower MQW layer 102 or the upper MQW layer 103 are individually read out through the three electrodes 109a, 109b, and 109c. In this case, a bias voltage is applied to the lower MQW layer 103 and the upper MQW layer 103 via the electrode 109b and the intermediate contact layer. The first switch 110a is turned on, the second switch 110b is turned off, and the photocurrent signal from the lower MQW layer 102 is read through the electrode 109a. Further, the first switch 110a is turned off and the second switch 110b is turned on, so that the photocurrent signal from the upper MQW layer 103 is read out through the electrode 109c.

  In the above two-wavelength infrared image sensor, there is a demand for increasing the number of pixels so that a higher-definition image can be acquired. In order to keep the overall size at a certain level, the area occupied by each pixel is reduced. However, since each pixel has three electrodes for connection to the drive circuit, it is difficult to miniaturize each pixel.

FIG. 7 shows a schematic configuration of a two-wavelength infrared image sensor that is devised to reduce the size of each pixel.
Each pixel 200 includes a lower MQW layer 202 and an upper MQW layer 203 on a GaAs substrate 201, and a lower contact layer 204, an intermediate contact layer 205, and an upper contact layer 206 common to all the pixels 200. Yes.

An output electrode 211 is electrically connected to the intermediate contact layer 205 via a wiring 208 and is connected to the drive circuit 210. A first common electrode 212 is electrically connected to the lower contact layer 204 common to all the pixels 200 via a wiring 209 a formed in an end structure 200 a provided at one end of the plurality of pixels 200, and the driving circuit 210. A bias voltage V _B is applied to the first common electrode 212. A second common electrode 213 is electrically connected to each upper contact layer 206 via a wiring 209 b formed in an end structure 200 b provided at the other end of the plurality of pixels 200, and is connected to the drive circuit 210. ing. _A bias voltage V _A is applied to the second common electrode 213. The wirings 208, 209 a, and 209 b are provided with necessary electrical insulation by the insulating layer 207. The wiring 208 is connected to the intermediate contact layer 205 through an opening 207 b formed in the insulating layer 207. The wiring 209 b is connected to the upper contact layer 206 through the opening 207 a formed in the insulating layer 207.

  In this case, the electrodes 212 and 213 connected to the lower contact layer 204 and the upper contact layer 206 are common electrodes that connect all the pixels 200 arranged in large numbers. With such a configuration, it is only necessary to form one output electrode 211 for each pixel 200, and miniaturization of each pixel is realized.

JP 2011-211019 A Special table 2008-211019 gazette JP 2000-188407 A JP 2010-192815 A

Proc. Of SPIE vol.5783, 804

  In the two-wavelength infrared image sensor of FIG. 7, an appropriate bias voltage is applied to the first and second common electrodes 212 and 213, and a photocurrent signal is read from the output electrode 211. For example, a voltage is applied between the first common electrode 212 and the output electrode 211, and a potential is applied to the second common electrode 213 so as to be the same potential as the output electrode 211. Then, the lower MQW layer 202 is biased to generate a photocurrent signal, but the upper MQW layer 203 is not biased and therefore does not generate a photocurrent signal. Therefore, only the photocurrent signal from the lower MQW layer 202 can be read out via the output electrode 211 by the transistor 210a.

Conversely, a voltage is applied between the second common electrode 213 and the output electrode 211, and a potential is applied to the first common electrode 212 so as to be the same potential as the output electrode 211. Then, the upper MQW layer 203 is biased to generate a photocurrent signal, but the lower MQW layer 202 is not biased and therefore does not generate a photocurrent signal. Therefore, only the photocurrent signal from the upper MQW layer 203 can be read out via the output electrode 211 by the transistor 210a.
As described above, the photocurrent signals from the respective MQW layers can be individually read out. If each MQW layer is configured to be sensitive to light in different wavelength bands, it is possible to individually detect optical signals of two wavelengths having different wavelength ranges.

  Here, in order to bias one MQW layer to generate a photocurrent signal and not bias the other MQW layer to generate a photocurrent signal, the output electrode and the common electrode through the other MQW layer Must match. If this potential does not match, the device current due to the generated potential difference is added to the photocurrent signal as noise, and the other MQW layer responds to light incidence in a wavelength band with sensitivity, and light of two wavelengths The signal cannot be separated sufficiently.

Generally, a potential cannot be directly applied to an output electrode for reading a photocurrent signal. FIG. 8 is a schematic circuit diagram of a two-wavelength infrared image sensor. The potential Vs of the output electrode is indirectly determined by the gate potential VIG of the transistor in the driver circuit and the drain current flowing through the transistor. Potentials that can be arbitrarily set from outside are the potentials V _A and V _{B of the} two common electrodes, and the gate potential VIG of the transistor.

For a large number of arranged pixels included in a two-wavelength infrared image sensor, the characteristics of the MQW layer of each pixel are not exactly the same, and there are generally some differences between the pixels. In this case, even if the same potentials V _A , V _B , and VIG are applied to each pixel, the current that flows due to the difference in the characteristics of the MQW layer differs, and the potential Vs of the output electrode varies from pixel to pixel. Also, even if the characteristics of all the pixels are exactly the same, when driving as a two-wavelength infrared image sensor, it is common that the amount of light incident on each pixel is different, and the photocurrent signal generated for each pixel Is different. Since the potential V _S depends on the amount of current, the potential V _S is also different for each pixel.

As described above, in the conventional two-wavelength infrared image sensor, the settings of the potentials V _A , V _B , and VIG for generating the photocurrent signal from only one of the lower and upper MQW layers are different for each pixel. . Therefore, there is a problem that only one MQW layer cannot be driven at the same time for all pixels, and optical signals of two different wavelengths cannot be sufficiently separated.

  The present invention has been made in view of the above problems, and detects only an optical signal having a wavelength corresponding to only one of the lower MQW layer and the upper MQW layer with a relatively simple configuration. An object of the present invention is to provide a highly reliable image sensor that can easily and reliably separate optical signals of two different wavelengths and a method of manufacturing the same.

  One aspect of the image sensor is an image sensor including a plurality of pixels, wherein the pixels are a first active layer having sensitivity to one wavelength region and a first active layer having sensitivity to another wavelength region. Two active layers, an output electrode electrically connected to the first active layer and the second active layer, and a first common electrically connected to the first active layer included in each of the pixels An electrode; a second common electrode electrically connected to the second active layer included in each of the pixels; a first contact layer sandwiching the first active layer; and sandwiching the second active layer A first semiconductor layer that is disposed between one of the first contact layers and the first active layer and has a material having a larger forbidden band than the first active layer; , Disposed between one of the second contact layers and the second active layer. Than said second active layer and a second semiconductor layer having a width greater material bandgap.

  One aspect of a method for manufacturing an image sensor is a method for manufacturing an image sensor including a plurality of pixels, and when forming the pixels, a first active layer having sensitivity to one wavelength region is formed. Forming a second active layer having sensitivity to other wavelength ranges, connecting an output electrode to the first active layer and the second active layer, and including the first active layer included in each of the pixels; Forming a first common electrode electrically connected to the layer; forming a second common electrode electrically connected to the second active layer included in each of the pixels; and A first contact layer is formed so as to be sandwiched, a second contact layer is formed so as to sandwich the second active layer, and a first semiconductor layer having a material having a forbidden band larger than that of the first active layer Formed between one of the first contact layers and the first active layer. The second semiconductor layer having a width greater material bandgap than the second active layer is formed between one and the second active layer of the second contact layer.

  According to the above aspects, it is possible to detect only an optical signal having a wavelength corresponding to only one of the lower MQW layer and the upper MQW layer with a relatively simple configuration. A highly reliable image sensor capable of easily and reliably separating optical signals is realized.

It is a schematic sectional drawing which shows the structure of the 2 wavelength infrared image sensor by 1st Embodiment. It is a figure which shows the energy state about the periphery of each MQW layer in the 2 wavelength infrared image sensor of 1st Embodiment. It is a circuit diagram explaining the selective detection of the optical signal in the 2 wavelength infrared image sensor of 1st Embodiment. It is a schematic sectional drawing shown in order of a process about the manufacturing method of the 2 wavelength infrared image sensor by 1st Embodiment. It is a schematic sectional drawing which shows the structure of the 2 wavelength infrared image sensor by 2nd Embodiment. It is a schematic sectional drawing which shows the structure of the conventional 2 wavelength infrared image sensor. It is a schematic sectional drawing which shows the structure of the conventional 2 wavelength infrared image sensor. FIG. 8 is a circuit diagram of the two-wavelength infrared image sensor of FIG. 7.

  In the following embodiments, a two-wavelength infrared image sensor is exemplified as an image sensor, and the configuration and manufacturing method thereof are disclosed.

(First embodiment)
First, the first embodiment will be described.
FIG. 1 is a schematic cross-sectional view showing the configuration of the two-wavelength infrared image sensor according to the first embodiment. In FIG. 1, for convenience of illustration, only two pixels among a plurality of pixels are illustrated.
In the two-wavelength infrared image sensor according to the present embodiment, a plurality of pixels 10 are arranged in a matrix, for example, and an end structure 10a is provided at one end of the plurality of pixels 10 and an end structure 10b is provided at the other end. Configured. A drive circuit 20 is connected to each pixel 10 via an output electrode 14, and to the end structures 10 a and 10 b via a first common electrode 15 and a second common electrode 16.

Each pixel 10 has a lower MQW layer 2 and an upper MQW layer 3 on a GaAs substrate 1, a lower contact layer 4 below the lower MQW layer 2 common to all the pixels 10, and an intermediate contact above the lower MQW layer 2. A layer 5 and an upper contact layer 6 on the upper MQW layer 3.
The lower MQW layer 2 and the upper MQW layer 3 are each a multiple quantum well (MQW) layer that converts an optical signal into an electrical signal. The lower MQW layer 2 is an active layer having sensitivity to a predetermined one wavelength region. The upper MQW layer 3 is an active layer having sensitivity to other wavelength ranges different from the wavelength range of the lower MQW layer 2. A lower MQW layer 2 and a lower contact layer 4 and an intermediate contact layer 5 sandwiching the lower MQW layer 2 constitute a first photoconductor element that is QWIP. The upper MQW layer 3 and the intermediate contact layer 5 and the upper contact layer 6 sandwiching the upper MQW layer 3 constitute a second photoconductor element that is QWIP.

  A diffraction grating having an uneven surface is formed on the upper contact layer 6. This diffraction grating becomes an optical coupling structure 9 necessary for QWIP.

  In the present embodiment, the first photoconductor-type element is a first barrier layer 7, which is a semiconductor layer made of a material having a wider forbidden band than the lower MQW layer 2 between the lower MQW layer 2 and the intermediate contact layer 5. It has. Similarly, the second photoconductor element includes a second barrier layer 8, which is a semiconductor layer made of a material having a larger forbidden band width than the upper MQW layer 3, between the intermediate contact layer 5 and the upper MQW layer 3. ing.

Specifically, the lower MQW layer 2, the upper MQW layer 3, the first barrier layer 7, and the second barrier layer 8 each have, for example, AlGaAs as a compound semiconductor containing aluminum. Here, the compound semiconductor of the first barrier layer 7 has a higher aluminum composition ratio than the compound semiconductor of the lower MQW layer 2. For example, the first barrier layer 7 is made of Al _0.4 GaAs, and the lower MQW layer 2 is made of Al _0.3 GaAs. The compound semiconductor of the second barrier layer 8 has a higher aluminum composition ratio than the compound semiconductor of the upper MQW layer 3. For example, the second barrier layer 8 is made of Al _0.4 GaAs, and the upper MQW layer 3 has Al _0.25 GaAs.

The output electrode 14 is electrically connected to the intermediate contact layer 5 through the wiring 12 and is connected to the transistor 20 a of the drive circuit 20. A first common electrode 15 is electrically connected to the lower contact layer 4 common to all the pixels 10 via a wiring 13 a formed in an end structure 10 a provided at one end of the plurality of pixels 10. 20 is connected. A bias voltage V _B is applied to the first common electrode 15 by the drive circuit 20. A second common electrode 16 is electrically connected to each upper contact layer 6 via a wiring 13 b formed in an end structure 10 b provided at the other end of the plurality of pixels 10, and is connected to the drive circuit 20. ing. _A bias voltage V _A is applied to the second common electrode 16 by the drive circuit 20. The wirings 12, 13 a, and 13 b are provided with necessary electrical insulation by the insulating layer 11. The wiring 12 is connected to the intermediate contact layer 5 through the opening 11 b formed in the insulating layer 11. The wiring 13 b is connected to the upper contact layer 6 through the opening 11 a formed in the insulating layer 11.

  In the two-wavelength infrared image sensor according to the present embodiment, the first barrier layer 7 and the second barrier layer 8 are provided as described above. As a result, rectification is imparted to the lower MQW layer 2 and the upper MQW layer 3. Hereinafter, this rectification will be described.

  FIG. 2 is a diagram showing an energy state around each MQW layer in the two-wavelength infrared image sensor according to the first embodiment. FIG. 2A shows a state in which no barrier voltage is applied, and FIG. When it is on the emitter side, (c) shows the case where the barrier layer is on the collector side. In FIG. 2, the intermediate contact layer 5 is a “contact layer”, and one of the lower MQW layer 2 and the upper MQW layer 3 is taken as an “MQW layer” as an example, and one of the first barrier layer 7 and the second barrier layer 8 is used. Is illustrated as a “barrier layer”.

  In the situation where a voltage is applied to the MQW layer, when a barrier layer made of a material having a larger forbidden band than the MQW layer is on the emitter side, no current flows because the barrier layer blocks the inflow of carriers (flow). hard). When the barrier layer is on the collector side, carriers flow into the MQW layer, and some carriers that are not subjected to energy dissipation due to inelastic scattering in the MQW layer cross the barrier layer and reach the collector-side contact layer. . For this reason, a current flows relatively easily.

  Consider driving only the upper MQW layer and detecting only the optical signal of the corresponding wavelength. In this case, it is necessary that no current flows in the lower MQW layer. For example, in the conventional two-wavelength infrared image sensor as shown in FIG. 7, there is a potential difference between the second common electrode and the output electrode, and it is necessary to apply each potential so that the output electrode and the first common electrode have the same potential. was there. On the other hand, in the two-wavelength infrared image sensor of the present embodiment, the lower MQW layer has a rectifying property. Therefore, even if the output electrode and the first common electrode are not set to the same potential, the current relationship does not flow due to the rectifying property. I just need it. Such a potential relationship exists as a region having a certain range as a potential setting. Therefore, even if the potentials of the output electrodes are different among the pixels, all the pixels can have a potential relationship that prevents current from flowing due to rectification at the same time. With this configuration, only an optical signal having a wavelength corresponding to the upper MQW layer can be detected.

  Consider driving only the lower MQW layer and detecting only the optical signal of the corresponding wavelength. In this case, it is necessary that no current flows in the upper MQW layer. In the two-wavelength infrared image sensor of this embodiment, since the upper MQW layer has a rectifying property, even if the output electrode and the second common electrode are not set to the same potential, the potential relationship may be such that no current flows due to the rectifying property. Such a potential relationship exists as a region having a certain range as a potential setting. Therefore, even if the potentials of the output electrodes are different among the pixels, all the pixels can have a potential relationship that prevents current from flowing due to rectification at the same time. With this configuration, only an optical signal having a wavelength corresponding to the lower MQW layer can be detected.

The above-described selective detection of the optical signal will be specifically described with reference to FIG.
In the two-wavelength infrared image sensor of this embodiment, the photocurrent signal flows in a direction in which electrons flow from the first common electrode or the second common electrode through the transistor toward the signal readout circuit.

  When the upper MQW layer is driven, as shown in FIG. 3A, the photocurrent signal electrons flow from the second common electrode to the signal readout circuit via the transistor. At this time, the potential barrier of the upper MQW layer does not disturb the electron flow. Here, the potential of the first common electrode is made sufficiently lower than the potential Vs of the output electrode. At this time, the lower MQW layer does not flow current due to the potential barrier. Further, even if the resistance of the upper MQW layer has fluctuation in the plane, if the first common electrode is set lower than the potential Vs of the output electrode in all pixels, the lower MQW layer Current does not flow through.

When driving the lower MQW layer, as shown in FIG. 3B, photocurrent signal electrons flow from the first common electrode to the signal readout circuit via the transistor. At this time, the potential barrier of the lower MQW layer does not disturb the electron flow. Here, the potential of the second common electrode is made sufficiently lower than the potential Vs of the output electrode. At this time, the upper MQW layer does not flow current due to the potential barrier. Even if the resistance of the lower MQW layer has fluctuation in the plane, if the second common electrode is set lower than the potential Vs of the output electrode in all pixels, the upper MQW layer Current does not flow through.
As described above, the two-wavelength infrared image sensor according to the present embodiment can reliably separate and detect optical signals having two different wavelengths.

Hereinafter, the manufacturing method of the two-wavelength infrared image sensor according to the present embodiment will be described.
FIG. 4 is a schematic cross-sectional view illustrating the manufacturing method of the two-wavelength infrared image sensor according to the first embodiment in the order of steps. In FIG. 4, for convenience of illustration, only one pixel is illustrated from among a plurality of pixels.

  First, as shown in FIG. 4A, each compound semiconductor layer 4, 2, 7, 5, 8, 3, 6 is sequentially stacked on a semi-insulating GaAs substrate 1 and optically coupled at the top. Structure 9 is formed. For example, a metal organic vapor phase epitaxy (MOVPE) method is used for crystal growth of each compound semiconductor layer. Instead of the MOVPE method, a molecular beam epitaxy (MBE) method or the like may be used.

Specifically, first, n-GaAs is grown on the GaAs substrate 1 as a compound semiconductor layer to be the lower contact layer 4 to a thickness of about 2000 nm, for example. As the n-type dopant, for example, Si is ^{added at} a density of about 1 × 10 ¹⁸ cm ⁻³ .

Next, a compound semiconductor layer to be the lower MQW layer 2 is formed. Specifically, (1) an Al _x Ga _1-x As layer is grown to a thickness of about 30 nm, for example. The Al composition x is, for example, 0.3. (2) An In _y Ga _1-y As layer is grown to a thickness of about 2.5 nm, for example. The In composition y is, for example, 0.3. After the steps (1) and (2) are repeated 10 times, an Al _x Ga _1-x As layer is grown to a thickness of about 30 nm, for example. As a result, the compound semiconductor layer to be the lower MQW layer 2 is formed.

Next, an Al _z Ga _1-z As layer is grown to a thickness of, for example, about 50 nm as a compound semiconductor layer to be the first barrier layer 7. The Al composition z is higher than the Al composition x, for example, 0.4. Since the Al composition z is higher than the Al composition x, the first barrier layer 7 has a larger forbidden band width than the lower MQW layer 2.
Next, as a compound semiconductor layer serving as an intermediate contact layer, an n-GaAs layer is grown to a thickness of about 1000 nm, for example.

Next, an Al _m Ga _1-m As layer is grown to a thickness of, for example, about 50 nm as a compound semiconductor layer to be the second barrier layer 8. The Al composition m is higher than the Al composition n described later, for example, 0.4.

Next, a compound semiconductor layer to be the upper MQW layer 3 is formed. Specifically, (3) an Al _n Ga _1-n As layer is grown to a thickness of about 40 nm, for example. The Al composition n is 0.25, for example. (4) A GaAs layer is grown to a thickness of about 5 nm, for example. After the steps (3) and (4) are repeated 10 times, an Al _n Ga _1-n As layer is grown to a thickness of about 50 nm, for example. As described above, the compound semiconductor layer to be the upper MQW layer 3 is formed. Here, since the Al composition m is higher than the Al composition n, the second barrier layer 8 has a larger forbidden band width than the upper MQW layer 3.

Next, an n-GaAs layer is grown to a thickness of, for example, about 1500 as a compound semiconductor layer to be the upper contact layer 6.
Next, the upper layer portion of the upper contact layer 6 is processed by lithography and etching to form irregularities having a diffraction grating structure on the surface of the upper contact layer 6. A metal film, such as an AuGe / Au film, is formed by embedding irregularities in the surface of the upper contact layer 6 by lithography, etching, and metal vapor deposition. Thus, the optical coupling structure 9 is formed on the upper contact layer 6.

  Subsequently, as shown in FIG. 4B, the compound semiconductor layers 4, 2, 7, 5, 8, 3, 6 are processed by lithography and etching. Thereby, the compound semiconductor layers 4, 2, 7, 5, 8, 3, and 6 are divided into the pixel 10 and the end structures 10a and 10b. In the pixel 10, the compound semiconductor layers 8, 3, 6 are further processed by lithography and etching to expose part of the surface of the intermediate contact layer 5.

Subsequently, as shown in FIG. 4C, an insulating layer 11 is formed.
Specifically, an insulating film, for example, a SiON film is deposited on the entire surface by a CVD method or the like to form the insulating layer 11. The insulating layer 11 is processed by lithography and etching. As a result, the insulating layer 11 has an opening 11a exposing a part of the surface of the optical coupling structure 9, an opening 11b exposing a part of the surface of the intermediate contact layer 5, and a part of the surface of the lower contact layer 4. Is formed.

Subsequently, as shown in FIG. 4D, the wirings 12, 13a, and 13b are formed.
Specifically, a metal film such as an AuGe / Au film is formed on the entire surface by sputtering or the like. The AuGe / Au film is processed by lithography and etching. As described above, the wiring 12 electrically connected to the intermediate contact layer 5, the wiring 13 a electrically connected to the lower contact layer 4, and the upper contact layer 6 are electrically connected via the optical coupling structure 9. Wiring 13b is formed.

Subsequently, as shown in FIG. 4E, an output electrode 14, which is, for example, an In bump, a first common electrode 15, and a second common electrode 16 are formed on the wirings 12, 13a and 13b, respectively, and the drive circuit 20 Connect with.
As described above, the two-wavelength infrared image sensor according to the present embodiment is manufactured.

  As described above, according to the present embodiment, it is possible to detect only an optical signal having a wavelength corresponding to only one of the lower MQW layer 2 and the upper MQW layer 3 with a relatively simple configuration. Thus, a highly reliable two-wavelength infrared image sensor capable of easily and reliably separating optical signals having two different wavelengths can be realized.

(Second Embodiment)
Next, the second embodiment will be described. The second embodiment discloses a two-wavelength infrared image sensor as in the first embodiment, but differs from the first embodiment in that the formation positions of the first barrier layer and the second barrier layer are different. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 5 is a schematic cross-sectional view showing the configuration of the two-wavelength infrared image sensor according to the second embodiment. In FIG. 5, for convenience of illustration, only two pixels of the plurality of pixels are illustrated.
In the two-wavelength infrared image sensor according to the present embodiment, as in the first embodiment, a plurality of pixels 30 are arranged in a matrix, for example, and an end structure 30a is provided at one end of the plurality of pixels 30 and the other end. Is provided with an end structure 30b. The drive circuit 20 is connected to each pixel 30 via the output electrode 14, and to the end structures 30 a and 30 b via the first common electrode 15 and the second common electrode 16.

Each pixel 30 has a lower MQW layer 2 and an upper MQW layer 3 on a GaAs substrate 1, a lower contact layer 4 below the lower MQW layer 2 common to all the pixels 10, and an intermediate contact above the lower MQW layer 2. A layer 5 and an upper contact layer 6 on the upper MQW layer 3.
The lower MQW layer 2 and the upper MQW layer 3 are each a multiple quantum well (MQW) layer that converts an optical signal into an electrical signal. The lower MQW layer 2 is an active layer having sensitivity to a predetermined one wavelength region. The upper MQW layer 3 is an active layer having sensitivity to other wavelength ranges different from the wavelength range of the lower MQW layer 2. A lower MQW layer 2 and a lower contact layer 4 and an intermediate contact layer 5 sandwiching the lower MQW layer 2 constitute a first photoconductor element that is QWIP. The upper MQW layer 3 and the intermediate contact layer 5 and the upper contact layer 6 sandwiching the upper MQW layer 3 constitute a second photoconductor element that is QWIP.

  A diffraction grating having an uneven surface is formed on the upper contact layer 6. This diffraction grating becomes an optical coupling structure 9 necessary for QWIP.

  In the present embodiment, the first photoconductor element is a first barrier layer 7, which is a semiconductor layer made of a material having a wider forbidden band than the lower MQW layer 2 between the lower contact layer 4 and the lower MQW layer 2. It has. Similarly, the second photoconductor element includes a second barrier layer 8, which is a semiconductor layer made of a material having a larger band gap than the upper MQW layer 3, between the upper MQW layer 3 and the upper contact layer 6. ing.

Specifically, the lower MQW layer 2, the upper MQW layer 3, the first barrier layer 7, and the second barrier layer 8 each have, for example, AlGaAs as a compound semiconductor containing aluminum. Here, the compound semiconductor of the first barrier layer 7 has a higher aluminum composition ratio than the compound semiconductor of the lower MQW layer 2. For example, the first barrier layer 7 is made of Al _0.4 GaAs, and the lower MQW layer 2 is made of Al _0.3 GaAs. The compound semiconductor of the second barrier layer 8 has a higher aluminum composition ratio than the compound semiconductor of the upper MQW layer 3. For example, the second barrier layer 8 is made of Al _0.4 GaAs, and the upper MQW layer 3 has Al _0.25 GaAs.

The output electrode 14 is electrically connected to the intermediate contact layer 5 through the wiring 12 and is connected to the transistor 20 a of the drive circuit 20. A first common electrode 15 is electrically connected to the lower contact layer 4 common to all the pixels 30 via a wiring 13 a formed in an end structure 30 a provided at one end of the plurality of pixels 30. 20 is connected. A bias voltage V _B is applied to the first common electrode 15 by the drive circuit 20. A second common electrode 16 is electrically connected to each upper contact layer 6 via a wiring 13 b formed in an end structure 30 b provided at the other end of the plurality of pixels 30, and is connected to the drive circuit 20. ing. _A bias voltage V _A is applied to the second common electrode 16 by the drive circuit 20. The wirings 12, 13 a, and 13 b are provided with necessary electrical insulation by the insulating layer 11. The wiring 12 is connected to the intermediate contact layer 5 through the opening 11 b formed in the insulating layer 11. The wiring 13 b is connected to the upper contact layer 6 through the opening 11 a formed in the insulating layer 11.

In the two-wavelength infrared image sensor according to the present embodiment, the first barrier layer 7 and the second barrier layer 8 are provided as described above. As a result, rectification is imparted to the lower MQW layer 2 and the upper MQW layer 3. In the present embodiment, contrary to the first embodiment, the photocurrent signal flows in a direction in which electrons flow from the signal readout circuit through the transistor toward the first common electrode or the second common electrode.
In the two-wavelength infrared image sensor according to the present embodiment, optical signals having two different wavelengths can be reliably separated and detected.

  As described above, according to the present embodiment, it is possible to detect only an optical signal having a wavelength corresponding to only one of the lower MQW layer 2 and the upper MQW layer 3 with a relatively simple configuration. Thus, a highly reliable two-wavelength infrared image sensor capable of easily and reliably separating optical signals having two different wavelengths can be realized.

  Hereinafter, various aspects of the image sensor and the manufacturing method thereof will be collectively described as additional notes.

(Appendix 1) An image sensor including a plurality of pixels,
The pixel is
A first active layer sensitive to one wavelength region;
A second active layer having sensitivity to other wavelength ranges;
An output electrode electrically connected to the first active layer and the second active layer;
A first common electrode electrically connected to the first active layer included in each of the pixels;
A second common electrode electrically connected to the second active layer included in each of the pixels;
A first contact layer sandwiching the first active layer;
A second contact layer sandwiching the second active layer;
A first semiconductor layer disposed between one of the first contact layers and the first active layer and having a material having a larger forbidden band width than the first active layer;
And a second semiconductor layer disposed between one of the second contact layers and the second active layer and having a material having a larger forbidden band width than the second active layer. Image sensor.

(Appendix 2) The first active layer, the second active layer, the first semiconductor layer, and the second semiconductor layer each include a compound semiconductor containing aluminum,
The compound semiconductor of the first semiconductor layer has a higher aluminum composition ratio than the compound semiconductor of the first active layer,
The image sensor according to appendix 1, wherein the compound semiconductor of the second semiconductor layer has a higher aluminum composition ratio than the compound semiconductor of the second active layer.

(Appendix 3) One of the first contact layers is a common contact layer electrically connected to the first active layer included in each of the pixels,
The supplementary note 1 or 2, wherein the first common electrode is electrically connected to the first first active layer included in each of the pixels via the common contact layer. Image sensor.

  (Supplementary note 4) Any one of Supplementary notes 1 to 3, further comprising a drive circuit that is capable of independently applying a variable voltage to the first common electrode and the second common electrode. The image sensor according to item.

  (Additional remark 5) The diffraction grating formed on one side of the said 2nd contact layer provided on the said 2nd active layer was further provided, The additional remark 1-4 characterized by the above-mentioned Image sensor.

(Appendix 6) A method for manufacturing an image sensor having a plurality of pixels,
In forming the pixel,
Forming a first active layer sensitive to one wavelength region;
Forming a second active layer sensitive to other wavelength ranges;
Forming an output electrode connected to the first active layer and the second active layer;
Forming a first common electrode electrically connected to the first active layer included in each of the pixels;
Forming a second common electrode electrically connected to the second active layer included in each of the pixels;
Forming a first contact layer to sandwich the first active layer;
Forming a second contact layer so as to sandwich the second active layer;
Forming a first semiconductor layer having a material having a larger forbidden band width than the first active layer between one of the first contact layers and the first active layer;
A second semiconductor layer having a material having a larger forbidden band width than that of the second active layer is formed between one of the second contact layers and the second active layer. Method.

(Appendix 7) The first active layer, the second active layer, the first semiconductor layer, and the second semiconductor layer each include a compound semiconductor containing aluminum,
The compound semiconductor of the first semiconductor layer has a higher aluminum composition ratio than the compound semiconductor of the first active layer,
The image sensor manufacturing method according to claim 6, wherein the compound semiconductor of the second semiconductor layer has a higher aluminum composition ratio than the compound semiconductor of the second active layer.

(Appendix 8) One of the first contact layers is a common contact layer electrically connected to the first active layer included in each of the pixels,
The image sensor manufacturing method according to appendix 6 or 7, wherein the first common electrode is electrically connected to the first active layer included in each of the pixels via the common contact layer. Method.

1, 101, 201 GaAs substrate 2, 102, 202 Lower MQW layer 3, 103, 203 Upper MQW layer 4, 104, 204 Lower contact layer 5, 105, 205 Intermediate contact layer 6, 106, 206 Upper contact layer 7 First Barrier layer 8 Second barrier layer 9 Optical coupling structure 10, 30, 100, 200 Pixel 10a, 10b, 30a, 30b, 200a, 200b End structure 11, 107, 207 Insulating layer 11a, 11b, 107a, 207a, 207b Opening 12, 13a, 13b, 108a, 108b, 108c, 208, 209a, 209b Wiring 14, 211 Output electrode 15, 212 First common electrode 16, 213 Second common electrode 20, 110, 210 Drive circuit 20a, 210a Transistor 109a, 109b, 109c electrode 110a first switch 11 b the second switch

Claims (6)

An image sensor having a plurality of pixels,
The pixel is
A first active layer sensitive to one wavelength region;
A second active layer having sensitivity to other wavelength ranges;
An output electrode electrically connected to the first active layer and the second active layer;
A first common electrode electrically connected to the first active layer included in each of the pixels;
A second common electrode electrically connected to the second active layer included in each of the pixels;
A first contact layer sandwiching the first active layer;
A second contact layer sandwiching the second active layer;
A first semiconductor layer disposed between one of the first contact layers and the first active layer and having a material having a larger forbidden band width than the first active layer;
And a second semiconductor layer disposed between one of the second contact layers and the second active layer and having a material having a larger forbidden band width than the second active layer. Image sensor. The first active layer, the second active layer, the first semiconductor layer, and the second semiconductor layer each have a compound semiconductor containing aluminum,
The compound semiconductor of the first semiconductor layer has a higher aluminum composition ratio than the compound semiconductor of the first active layer,
2. The image sensor according to claim 1, wherein the compound semiconductor of the second semiconductor layer has a higher aluminum composition ratio than the compound semiconductor of the second active layer. One of the first contact layers is a common contact layer electrically connected to the first active layer included in each of the pixels,
3. The first common electrode according to claim 1, wherein the first common electrode is electrically connected to the first first active layer included in each of the pixels via the common contact layer. Image sensor.   4. The driving circuit according to claim 1, further comprising a drive circuit that is capable of independently applying a variable voltage to the first common electrode and the second common electrode. 5. Image sensor.   The image sensor according to claim 1, further comprising a diffraction grating formed on one of the second contact layers provided on the second active layer. A method of manufacturing an image sensor having a plurality of pixels,
In forming the pixel,
Forming a first active layer sensitive to one wavelength region;
Forming a second active layer sensitive to other wavelength ranges;
Forming an output electrode connected to the first active layer and the second active layer;
Forming a first common electrode electrically connected to the first active layer included in each of the pixels;
Forming a second common electrode electrically connected to the second active layer included in each of the pixels;
Forming a first contact layer to sandwich the first active layer;
Forming a second contact layer so as to sandwich the second active layer;
Forming a first semiconductor layer having a material having a larger forbidden band width than the first active layer between one of the first contact layers and the first active layer;
A second semiconductor layer having a material having a larger forbidden band width than that of the second active layer is formed between one of the second contact layers and the second active layer. Method.

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