JP6213808B2 - Infrared detector manufacturing method and wavelength spectrum measuring apparatus manufacturing method - Google Patents

Description

  The present invention relates to an infrared detector formed in an array and having a plurality of infrared detection pixels that detect infrared rays of different wavelengths, and in particular, a quantum dot infrared detection element (Quantum) including semiconductor quantum dots as the infrared detection pixels. The present invention relates to an infrared detector having a Dot Infrared Photodetector (hereinafter also referred to as “QDIP”) in a light absorption layer.

  In recent years, there has been an increasing demand for infrared detectors for the purpose of detecting heat over a wide range from around room temperature to about 1000 ° C., and measuring concentrations of carbon dioxide and air pollutants. There are a plurality of candidates for the material and structure of the infrared detector, one of which is QDIP, which includes semiconductor quantum dots in the light absorption layer.

  QDIP has a structure in which the periphery of a quantum dot is three-dimensionally surrounded by a semiconductor having a larger band gap than the material constituting the quantum dot. In addition, electrons and holes are strongly confined in the quantum dot region. As a result, discrete energy levels are formed in the quantum dots. Among these levels, infrared rays having a detection wavelength corresponding to the energy difference between subbands can be detected using a plurality of electronic subband levels in the conduction band.

  As described above, since QDIP uses discrete intersubband transitions, the infrared detection band is theoretically a narrow band. In addition, since electrons and holes are strongly confined in the quantum dots, dark current can be suppressed and a high signal-to-noise ratio can be expected.

  QDIP is not a single element but an array detector in which a plurality of elements are arranged one-dimensionally or two-dimensionally to acquire an infrared image, and further, an infrared detector is combined with a spectroscope. There is also a method of using such as acquiring a spectrum.

  In particular, in the latter case, the wavelength to be detected changes depending on the position of the sensor array. Broadband infrared sensors with sensitivity in all wavelength bands covered by the spectrometer may be arrayed. However, if stray light from a spectrometer or other spectroscopic device including an optical system is taken into account, only the wavelength that has been separated is detected. In some cases, narrowband operation QDIP is desirable. At this time, the detection wavelength of the sensor array must also change in accordance with the wavelength of the split light.

  In this specification, the parameter such as the detection wavelength “changes” means that the parameter “differs gradually depending on the array position”. That is, it does not mean that the parameter “changes with time”.

  As a prior art for realizing such a sensor array in which the detection wavelength is changed, FIG. 6 of Patent Document 1 discloses a sensor array including a plurality of quantum dots having different heights. The technique disclosed in Patent Document 1 realizes a sensor array in which the energy level of electrons or holes changes due to the change in the height of the quantum dots, and as a result, the detection wavelength changes. ing.

  As another conventional technique, Patent Document 2 discloses a method of changing a detection wavelength by mixing quantum dots and an intermediate layer covering the quantum dots by thermal annealing to change an energy level. In the technique disclosed in Patent Document 2, the temperature of thermal annealing is changed depending on the position of the substrate, and the amount of change in the energy level varies depending on the degree of mixing. As a result, the detection wavelength is changed depending on the position of the sensor array. be able to.

JP 2009-210474 A JP 2012-109420 A

  By the way, in the technique disclosed in Patent Document 1, the quantum dot structure is formed by etching after forming the quantum well structure. Thus, the quantum dot formed by an etching process has a physical or chemical damage in the etching cross section, which causes an increase in dark current and a decrease in detection sensitivity. As a result, there is a problem that the performance as an infrared detector deteriorates.

  On the other hand, in the technique disclosed in Patent Document 2, the quantum dots and the intermediate layer are mixed by thermal annealing. This is because the confinement potential of the quantum dots becomes shallow as the detection wavelength changes, and the dark current increases. There are also side effects. Therefore, it is difficult to increase the amount of change in the detection wavelength from the viewpoint of minimizing the increase in dark current.

  Therefore, an object of the present invention is to provide an infrared detector having a small dark current and an excellent S / N ratio.

  According to the present invention, there is provided a semiconductor substrate and a plurality of infrared detection pixels that are formed in an array along the X axis and the Y axis on the semiconductor substrate and detect infrared rays incident from the semiconductor substrate side. Each of the plurality of infrared detection pixels includes a semiconductor intermediate layer and a plurality of quantum dots arranged in an array, and includes at least one quantum dot layer formed in the intermediate layer. And an infrared ray having a detection wavelength corresponding to an energy difference between a first electronic level that is a ground level formed by quantum confinement of the quantum dot layer and a second electronic level that is an excitation level. An infrared detector for detecting the plurality of infrared detection pixels, wherein at least one of a size and a material composition of a quantum dot included in the quantum dot layer is the X axis and the Y axis. The detection wavelength corresponding to the energy difference between the first electron level and the second electron level is gradually different along the axial direction by being gradually different along at least one axial direction. An infrared detector is obtained.

  In the plurality of infrared detection pixels, at least one of the size and the material composition of the quantum dots included in the quantum dot layer may be gradually different linearly along the axial direction.

  The intermediate layer may be made of GaAs or AlGaAs, and the quantum dot layer may be made of InAs.

  Each of the light absorption layers of the plurality of infrared detection pixels is made of a semiconductor, further includes a cap layer formed on the quantum dot layer in the intermediate layer, and the second layer along the x-axis direction. The energy of the electron level of the plurality of infrared detection pixels is different from that of the energy of the first electron level, so that the plurality of infrared detection pixels has the energy of the first electron level and the energy of the first electron level. The energy of the second electron level is gradually different with different signs along the axial direction, so that the first electron level and the second electron level detected by the infrared detection pixel are The energy difference may be gradually different along the axial direction. In this case, in the plurality of infrared detection pixels, at least one of the size and the material composition of the quantum dots included in the quantum dot layer is gradually different along the axial direction, and the material composition of the cap layer However, the energy of the first electron level and the energy of the second electron level are gradually different with different signs along the axial direction. Also good.

  The cap layer may be made of InGaAs.

  In addition, according to the present invention, the infrared detector and a spectroscopic device that demultiplexes the light according to the wavelength of incident infrared light, the detection wavelength of each of the plurality of infrared detection pixels and the demultiplexed by the spectroscopic device. Thus, a wavelength spectrum measuring apparatus is obtained in which the wavelengths incident on the infrared detection pixels are equal. In this case, the detection wavelengths of the plurality of infrared detection pixels may be gradually different along the axial direction according to the inverse dispersion of the spectroscopic device.

  Furthermore, according to the present invention, there is provided a method for manufacturing the infrared detector, wherein the quantum dot layer is formed on the surface of the intermediate layer on which the quantum dot layer is to be formed in the quantum dot layer forming step. Included in the quantum dot layer of each infrared detection pixel by setting a relative angle in the supply direction and gradually changing the supply rate of the raw material of the quantum dot layer with respect to the surface of the intermediate layer along the axial direction The method for producing an infrared detector is characterized in that at least one of the size of the quantum dots and the material composition is gradually varied along the axial direction.

  The infrared detector according to the present invention has a small dark current and an excellent S / N ratio.

It is sectional drawing which shows the structure of the infrared detector by Example 1 of this invention. It is the upper surface and expanded sectional view which show the structure of the infrared detector by Example 1 of this invention. It is a figure explaining operation | movement of the infrared detector by Example 1 of this invention. It is a figure explaining the manufacturing method of the infrared detector by Examples 1-3 of this invention. It is the upper surface and expanded sectional view which show the structure of the infrared detector by Example 2 of this invention. It is a figure explaining operation | movement of the infrared detector by Example 2 of this invention. It is the upper surface and expanded sectional view which show the structure of the infrared detector by Example 3 of this invention. It is a figure explaining operation | movement of the infrared detector by Example 3 of this invention. It is a figure which shows the outline of the wavelength spectrum measuring apparatus which has an infrared detector by Example 4 of this invention. It is a figure explaining operation | movement of the wavelength spectrum measuring apparatus contained in Example 4 of this invention. It is a figure explaining operation | movement of the spectroscopy apparatus contained in Example 4 of this invention.

  An infrared detector according to the present invention includes a semiconductor substrate and a plurality of infrared detection pixels formed on the semiconductor substrate in an array along the X-axis and the Y-axis, each detecting infrared rays incident from the semiconductor substrate side. doing.

  Each of the plurality of infrared detection pixels has a light absorption layer. The light absorption layer includes at least a semiconductor intermediate layer and at least one quantum dot layer formed in the intermediate layer, including a plurality of quantum dots arranged in an array.

  Further, each of the plurality of infrared detection pixels has a detection wavelength corresponding to an energy difference between a first electronic level that is a ground level formed by quantum confinement of the quantum dot layer and a second electronic level that is an excitation level. Detect infrared rays.

  In particular, in the present invention, in the plurality of infrared detection pixels, at least one of the size and the material composition of the quantum dots included in the quantum dot layer is gradually different along the axial direction of at least one of the X axis and the Y axis. . Thereby, the detection wavelength corresponding to the energy difference between the first electron level and the second electron level gradually differs along the axial direction.

  In the present invention, since at least one of the size and the material composition of the quantum dots included in the quantum dot layer is gradually changed along the axial direction, the etching process and the thermal annealing process are not performed. Therefore, the infrared detector according to the present invention has a small dark current and an excellent S / N ratio.

  Hereinafter, the present invention will be described in more detail with reference to the drawings.

[Constitution]
FIG. 1 is a cross-sectional view illustrating the structure of an infrared detector 200 according to an embodiment of the present invention.

  As shown in FIG. 1, the infrared detector 200 has a structure in which infrared detection pixels 100 corresponding to one pixel of an infrared image to be acquired are arranged on a plane (FIG. 1 is a cross-sectional view and can only be seen one-dimensionally. Note that there is no). The infrared detector 200 includes a semiconductor substrate 1, a buffer layer 2, a lower contact layer 3, a light absorbing layer 4, an upper contact layer 5, a protective film 6, a lower electrode 7, an upper electrode 8, and the like.

  Specifically, the buffer layer 2 is formed on the semiconductor substrate 1. The buffer layer 2 is made of the same semiconductor material as that of the semiconductor substrate 1. A lower contact layer 3 is formed on the buffer layer 2. The lower contact layer 3 is composed of an n-type semiconductor as a main material. The lower contact layer 3 may be directly formed on the semiconductor substrate 1 without the buffer layer 2 interposed therebetween. Further, the light absorption layer 4 and the lower electrode 7 are formed on the lower contact layer. Further, an upper contact layer 5 is formed on the light absorption layer 4. The upper contact layer 5 is composed of an n-type semiconductor as a main material. When the semiconductor substrate 1 is n-type, the lower electrode 7 may be directly formed thereon.

  The light absorption layer 4 and the upper contact layer 5 are partially removed by an etching process or the like, the side wall portion of the light absorption layer 4 and a part of the upper contact layer 5 are covered with the protective film 6, and the upper contact layer 5 is covered with the upper electrode 8. Infrared detection pixels 100 including the light absorption layer 4, the upper contact layer 5, the protective film 6, and the upper electrode 8 are arranged in a plane.

  Under the condition that an appropriate voltage is applied between the upper electrode 8 and the lower electrode 7, when the infrared ray X is incident from the lower side of the semiconductor substrate 1, the light absorption layer 4 emits infrared rays having a wavelength corresponding to the structure. As a result, a photocurrent flows between the upper electrode 8 and the lower electrode 7. Although not shown in FIG. 1, conductive bumps are formed on the upper electrode 8, and a readout circuit is attached to the conductive bumps so that photocurrents from a large number of infrared detection pixels 100 are collectively read out. be able to.

  In order to increase the detection efficiency of the incident infrared ray X, an antireflection film may be formed on the lower side of the semiconductor substrate 1 or the thickness may be reduced by polishing to avoid absorption by the semiconductor substrate 1.

  The light absorption layer 4 includes a quantum dot layer 42 and an intermediate layer 41. Specifically, each layer is repeatedly formed in the order of the intermediate layer 41 and the quantum dot layer 42 on the lower contact layer 3. By repeating such lamination 10 times or more, the infrared absorption efficiency in the light absorption layer 4 can be increased. In FIG. 1, three times of repeated lamination are shown for the sake of brevity.

  FIG. 2 is a top view and an enlarged sectional view showing the structure of the infrared detector 200 according to the first embodiment. Infrared detection pixels 100 are arranged on a plane on the semiconductor substrate 1 and a lower electrode 7 is formed. For the sake of space, only 8 × 8 detection pixels are shown, but the number of detection pixels is not limited to this and may be larger. Further, in practice, only a necessary part is cut out and used as a detector instead of a circular substrate, but it is shown as in FIG. 2 for easy understanding that it is formed on the semiconductor substrate 1. Yes.

  The feature of this embodiment is that the size of the quantum dots contained in the quantum dot layer 42 changes substantially linearly along the direction of at least one axis (in this example, the x-axis). FIG. 2 also shows enlarged cross-sectional views of the infrared detection pixels 100A and 100B for easy understanding of the change. As shown in FIG. 2, when comparing the size of the quantum dots contained in the quantum dot layer 42A of the infrared detection pixel 100A and the quantum dots contained in the quantum dot layer 42B of the infrared detection pixel 100B, the latter is more than the former. Is also big. As a result, the infrared wavelengths that can be detected by the infrared detection pixel 100A and the infrared detection pixel 100B are different. The infrared wavelength that can be detected by pixels between these infrared detector pixels is the wavelength between the infrared detection pixel 100A and the infrared detection pixel 100B.

[Operation]
Next, the operation of the infrared detector 200 will be described with reference to FIG.

  FIG. 3 is a diagram for explaining the operation of the infrared detector 200 according to the first embodiment, and shows an electron energy band diagram of the conduction band of the infrared detection pixels 100A and 100B shown in FIG. The left-right direction in FIG. 3 corresponds to the lower upper direction in FIGS. 1 and 2, that is, when FIG. 3 is rotated 90 degrees counterclockwise, it coincides with the directions in FIGS. Strictly speaking, the electron energy band of the quantum dot has a three-dimensional structure, but is represented by one dimension as an approximation.

  Electron ground level EL1 and excitation level EL2 are formed by quantum confinement by quantum dot layer 42A or 42B. Infrared light corresponding to the intersubband transition energy difference between the ground level EL1 and the excitation level EL2 (the length of the arrow in the figure) can be absorbed and detected.

  As described above, when comparing the size of the quantum dots included in the quantum dot layer 42A of the infrared detection pixel 100A and the quantum dots included in the quantum dot layer 42B of the infrared detection pixel 100B, the latter is larger than the former. This corresponds to the latter having a wider electron confinement potential. As a result, the energy of the ground level EL1 and the level EL2 of the infrared detection pixel 100B is lower than that of the infrared detection pixel 100A, and the difference between them is reduced (the arrow is shorter in the latter case). Since the wavelength is the reciprocal of the energy difference, the detection wavelength of the infrared detection pixel 100B is longer than that of the infrared detection pixel 100A.

  There are many detection pixels between the infrared detection pixel 100A and the infrared detection pixel 100B, but the size of the quantum dots contained in the quantum dot layer 42 changes substantially linearly along the x-axis direction. The detection wavelength changes almost linearly from the infrared detection pixel 100A to the infrared detection pixel 100B.

  In this way, in the infrared detector in which the infrared detection pixels are arranged on the plane, the size of the quantum dot included in the quantum dot layer is changed in at least one axial direction. It is possible to provide an infrared detector in which has changed.

[Production method]
Next, a manufacturing method of the infrared detector 200 according to the first embodiment of the present invention will be described.

[1: Crystal growth process including quantum dots]
FIG. 4 is a diagram for explaining a method of manufacturing an infrared detector according to the first embodiment of the present invention, and shows an outline of a molecular beam epitaxial (MBE) apparatus. FIG. 4 shows only the portions necessary for explaining the manufacturing method characteristic of the present invention.

  As the semiconductor substrate 1, a GaAs substrate having a (001) plane orientation is prepared, and this substrate is mounted on the substrate holder 301 in the vacuum chamber 300 of the MBE apparatus. The substrate holder 301 can heat the semiconductor substrate 1 through a heater and rotate the semiconductor substrate 1 in a rotational direction so that the raw material has a uniform thickness on the substrate regardless of the position of the raw material supply source. A rotation mechanism for rotating r301 is provided. In is supplied from the first raw material supply source 302, Ga is supplied from the second raw material supply source 303, and As is supplied from the third raw material supply source 304. Hereinafter, the substrate is rotated unless otherwise specified.

  After the natural oxide film is removed from the semiconductor substrate 1, the temperature of the substrate is set to about 580 ° C., and the buffer layer 2 is stacked with a thickness of 500 nm. The buffer layer 2 is made of the same GaAs as the semiconductor substrate 1.

Next, an n-type lower contact layer 3 having a thickness of 500 nm is stacked. The lower contact layer 3 is made of GaAs doped with Si atoms at a concentration of about 2 × 10 ¹⁸ cm ⁻³ .

  Next, an i-type first intermediate layer 41 having a thickness of about 50 nm is stacked. The intermediate layer 41 is made of GaAs.

  Then, after lowering the substrate temperature to about 490 ° C. and stopping the substrate rotation, that is, in a state where the raw material has a non-uniform thickness on the substrate, the thickness is about 2 to 3 atomic layers, In is supplied from the first raw material supply source 302 and As is supplied from the third raw material supply source 304.

At this time, InAs grows in an island shape three-dimensionally due to the strain generated from the difference in lattice constant between InAs and GaAs. This growth mode is called an SK (Stranski-Krastanov) mode, and quantum dots are formed according to this mode. As a result, a quantum dot layer 42 in which quantum dots are arranged in a plane at high density is formed. The typical diameter of the quantum dot is 20 to 30 nm, the height is 5 nm, and the number density per square centimeter is about 5 × 10 ¹⁰ .

  In the material supply source arrangement shown above, the In supply rate is higher on the right side of FIG. 4 than on the left side, and as a result, the InAs quantum dots are larger on the right side than on the left side. The quantum dots 42B and 42A having different sizes shown in FIG. 2 are formed in this way.

  When the quantum dot layer 42 is formed, Si atoms are doped with a number density similar to that of the quantum dots, if necessary. This is because the ground level EL1 is preliminarily doped with one electron.

  Next, substrate rotation is started, the substrate temperature is raised again, and an intermediate layer 41 made of GaAs is laminated.

  According to the above procedure, the lamination of the intermediate layer 41 and the quantum dot layer 42 is repeated 10 times or more. Thereby, the light absorption layer 4 can be formed.

Finally, an n-type upper contact layer 5 having a thickness of 200 nm is stacked. The n-type upper contact layer 5 is made of GaAs doped with Si atoms at a concentration of about 2 × 10 ¹⁸ cm ⁻³ .

  The quantum dot layer 42 made of InAs may be InGaAs. The intermediate layer 41 may be AlGaAs. However, as the Al composition ratio increases, the crystal quality decreases, so the Al composition ratio is desirably 30% or less.

  In the above manufacturing method, the light absorption layer 4 including the quantum dot layer 42 and the peripheral structure thereof are formed by the MBE method, but the present invention is not limited to this method. For example, other crystal growth methods such as metal organic chemical vapor deposition (MOCVD) may be used for these structures.

[2: Detector structure processing and electrode process]
Subsequently, the upper contact layer 5, the light absorbing layer 4 and a part of the lower contact layer 3 are etched using ultraviolet lithography, dry etching, or wet etching technology. Thereby, a part of the surface of the lower contact layer 3 is exposed.

  By this etching, the separated structure becomes one of the infrared detection pixels 100. The size of one side of the light receiving surface of the infrared detection pixel 100 varies depending on the application, but is typically about 20 μm to 100 μm.

  Next, a protective film 6 made of SiNx (silicon nitride) is formed using a chemical vapor deposition (CVD) apparatus or the like. As a result, the upper contact layer 5 and the lower contact layer 3 are also covered with the protective film 6 in addition to the side walls of each infrared detection pixel 100. In order to form electrodes on the upper contact layer 5 and the lower contact layer 3, a part of the protective film 6 is first removed by etching. Thereafter, an alloy ohmic electrode made of AuGe / Ni / Au is formed to form the upper electrode 7 and the lower electrode 6. The upper electrode 7 and the lower electrode 6 are each formed by a lift-off method. The lift-off method includes processes such as lithography, metal deposition, and resist stripping.

  Through the above steps, the basic configuration of the infrared detector 200 according to the first embodiment is completed.

  FIG. 5 is a top view and an enlarged sectional view for explaining the structure of the infrared detector 201 according to the second embodiment of the present invention.

  As shown in FIG. 5, the difference between Example 2 and Example 1 is that the material composition of the quantum dots contained in the quantum dot layer 42 changes almost linearly along the x-axis direction. . That is, the material composition is different between the quantum dot layers 42A and 42C. Since other than that is the same, detailed description of a structure is abbreviate | omitted.

  Next, the operation of the infrared detector 201 will be described with reference to FIG.

  FIG. 6 is a diagram for explaining the operation of the infrared detector 201 according to the second embodiment, and shows an electron energy band diagram of the conduction band of the infrared detection pixels 100A and 100C shown in FIG. When FIG. 6 is rotated 90 degrees counterclockwise, it corresponds to the direction of FIG.

  As in the first embodiment, the electron ground level EL1 and the excitation level EL2 are formed by quantum confinement by the quantum dot layer 42A or 42C.

  The quantum dot layer 42A and the quantum dot layer 42C of the infrared detection pixel 100A and the infrared detection pixel 100C have the same size but different material composition. In FIG. 6, this is expressed as that the energy of the bottom of the conduction band of the quantum dot layer 42C is smaller than that of the quantum dot layer 42A. In other words, the latter corresponds to a deeper electron confinement potential. As a result, the energy of the ground level EL1 and level EL2 of 100C is reduced as compared with the infrared detection pixel 100A, and the difference between them is reduced (the arrow is shorter in the latter case). Therefore, the detection wavelength of 100C is longer than that of infrared detection pixel 100A.

  The feature of this embodiment is that the material composition of the quantum dot layer 42 changes substantially linearly along the direction of at least one axis (in this example, the x-axis). There are a large number of detection pixels between the infrared detection pixel 100A and the infrared detection pixel 100C, but since the material composition of each quantum dot layer 42 changes substantially linearly along the x-axis direction, the detection wavelength is It changes substantially linearly from the infrared detection pixel 100A to the infrared detection pixel 100C.

  Next, as for the manufacturing method, only a method for stacking the quantum dot layers 42 different from that in Example 1 will be described. In Example 2, the quantum dot layer 42 is made of InGaAs.

  In FIG. 4, In is supplied from the first raw material supply source 302, Ga is supplied from the fourth raw material supply source 305, and As is supplied from the third raw material supply source 304.

  The substrate rotation is stopped and the quantum dot layer 42 is stacked, but since In and Ga are supplied at a shallow angle with respect to the substrate, In is more on the right side than on the left side, and Ga is more on the left side than on the right side. Will be supplied. As a result, in the quantum dot layer 42 composed of InGaAs, the In composition ratio increases from the left side to the right side. InGaAs has a lower conduction band energy as the In composition ratio increases. This is a method for producing a structure in which the material composition of the quantum dot layer 42 shown in FIGS. 5 and 6 is changed in the x-axis direction.

  In this way, in the infrared detector in which the infrared detection pixels are arranged on the plane, the material composition of the quantum dot layer is changed in at least one axial direction, so that the detection wavelength is changed in the axial direction. Can be provided.

  The material composition of the quantum dot layer shown here is merely an example, and any combination realized by the arrangement of the material supply source may be used.

  FIG. 7 is a top view and an enlarged cross-sectional view illustrating the structure of the infrared detector 203 according to the third embodiment of the present invention.

  As shown in FIG. 7, the difference of Example 3 from Examples 1 and 2 is that a cap layer 44 having a material composition different from that of the intermediate layer 41 is formed immediately above the quantum dot layer 42. More specifically, in addition to the fact that the size of the quantum dots contained in the quantum dot layer 42 changes substantially linearly along the x-axis direction, the material composition of the cap layer 44 also changes substantially linearly. Yes. That is, the quantum dot layers 42F and 42G have different quantum dot sizes, and the cap layer 44F and the cap layer 44G have different material compositions. The rest of the configuration is the same as that already described, and a detailed description of the configuration is omitted.

  Next, the operation of the infrared detector 203 will be described with reference to FIG.

  FIG. 8 illustrates the operation of the infrared detector 203 according to the third embodiment, and shows an electron energy band diagram of the conduction band of the infrared detection pixels 100F and 100G shown in FIG. When FIG. 8 is rotated 90 degrees counterclockwise, it coincides with the direction of FIG.

  Similar to the first and second embodiments, the electron ground level EL1 and the excitation level EL2 are caused by quantum confinement including the quantum dot layer 42F (or quantum dot layer 42G) and the cap layer 44F (or cap layer 44G). It is formed.

  First, in the quantum dot layer 42A and the quantum dot layer 42D of the infrared detection pixels 100F and 100G, the latter has a smaller quantum dot size. This corresponds to the fact that the latter has a narrower electron confinement potential. At this time, as described in the explanation of the operation of the first embodiment using FIG. 3, the energy of the ground level EL1 of 100G is increased as compared with the infrared detection pixel 100F.

  Further, when comparing the cap layer 44F and the cap layer 44G, the energy at the bottom of the conduction band is lower in the latter than in the former, reflecting the difference in material composition. As a result, the energy of the excitation level EL2 of 100G decreases as compared with the infrared detection pixel 100F. The reason for this is as described in the explanation of the operation of the first embodiment using FIG.

  Therefore, the energy difference between EL2 and EL1 is smaller in 100G than in the infrared detection pixel 100F (the arrow is shorter in the latter). As a result, the detection wavelength of 100G is longer than that of infrared detection pixel 100F.

  At this time, the change in the x-axis direction of FIG. 7 of EL1 and EL2 caused by the change in the size of the quantum dots contained in the quantum dot layer 42 and the material composition of the cap layer is different in sign, so that Example 1 Compared with (2) and (2), the infrared detection wavelength can be changed in a wider range in Example 3.

  There are a large number of detection pixels between the infrared detection pixels 100F and 100G, but the size of the quantum dots contained in the quantum dot layer 42 and the material composition of the cap layer 44 change substantially linearly along the x-axis direction. Therefore, the detection wavelength changes almost linearly from the infrared detection pixels 100F to 100G.

  Next, as for the manufacturing method, only the method of laminating the quantum dot layer 42 and the cap layer 44 will be described. The cap layer 44 is made of InGaAs.

  In FIG. 4, In is supplied from the first raw material supply source 302, Ga is supplied from the fourth raw material supply source 305, and As is supplied from the third raw material supply source 304.

  Although the substrate rotation is stopped and the InAs quantum dot layer 42 is stacked, the amount of In supplied is larger on the right side than on the left side, and as described in Example 1, the right side has larger quantum dots than the left side ( Corresponding to FIG. Thereafter, when the substrate is rotated 180 degrees, the left and right are interchanged, and the quantum dots are larger on the left side than on the right side (corresponding to FIG. 7).

  Next, the cap layer 44 made of InGaAs is stacked by raising the temperature of the substrate. Since In and Ga are supplied at a shallow angle with respect to the substrate, In is supplied more on the right side than on the left side, and As is supplied on the left side more than on the right side. As a result, in the cap layer 44 made of InGaAs, the In composition ratio increases from the left side to the right side. InGaAs has a lower conduction band energy as the In composition ratio increases. This is a manufacturing method of the structure shown in FIGS.

  In this way, in the infrared detector in which the infrared detection pixels are arranged on the plane, the size of the quantum dots included in the quantum dot layer and the material composition of the cap layer formed immediately above are in at least one axial direction. By changing at the same time, it is possible to provide an infrared detector in which the detection wavelength is changed in the axial direction. At this time, if the changes in the excitation level EL2 and the ground level EL1 in the axial direction are different from each other, the detection wavelength can be changed in a wider range than in the first and second embodiments.

  FIG. 9 is a diagram showing an outline of a wavelength spectrum measuring apparatus having an infrared detector according to Embodiment 4 of the present invention.

The infrared detector 200 and the spectroscopic device 400 shown in the first embodiment are configured. When the infrared ray X indicated by a large arrow enters the spectroscopic device 400, the spectroscopic device demultiplexes the light according to the incident wavelength. As a typical example in FIG. 8, those demultiplexed infrared X _A and X _B in the x-direction is shown. Wavelength of X _A and X _B is to match each detection wavelength of infrared detection pixels 100A and the infrared detection pixel 100B, the spectroscopic apparatus is designed.

  Next, FIG. 10 is a diagram for explaining the operation of the wavelength spectrum measuring apparatus. (A) is a two-dimensional region 500 in which a spectrum is to be measured, and a spectroscopic device 400 is incident on a one-dimensional region 501 that is partially cut out in the x direction through a condenser lens or the like. (B) is a top view of the infrared detector 200, and is demultiplexed by the spectroscopic device 400 in the x direction according to the incident wavelength.

  Therefore, what is projected onto each infrared detection pixel 100 on the infrared detector 200 is the one in which the spatial distribution of the one-dimensional region 501 is unchanged in the y direction and the wavelength component is decomposed in the x direction. By scanning the entire two-dimensional area in which the one-dimensional area 501 is desired to be imaged, spectrum measurement of the two-dimensional area becomes possible. At this time, the detection wavelength of the infrared detector 200 changes only in the y direction, and the detection wavelength does not change in the x direction.

  FIG. 11 is a diagram for explaining the operation of the spectroscopic device 400 of FIG. 9, and is a diagram for explaining the operation of the diffraction grating 410 provided in the spectroscopic device for changing the optical path for each incident wavelength. The diffraction grating has N grooves per unit length. When the incident infrared ray 412 is incident on the normal line 411 of the diffraction grating at an angle α, the incident infrared ray 412 is diffracted in the direction of the angle β with respect to the normal line. α and β are positive when they are on the right side of the normal in the figure. Assuming that the wavelength of infrared rays is λ and first-order diffraction, the following formula 1 is satisfied.

  Here, assuming that the incident angle α is constant, the following formula 2 is obtained by differentiating both sides of the formula 1 by λ.

  Expression 2 is an expression representing how much the diffraction angle β changes per unit wavelength. The inverse dispersion D = dλ / dx of the diffraction grating, that is, the wavelength resolution per unit length, is expressed as dx = f · dβ using the focal length f of the spectroscopic device, and using Equation 2 below. Equation 3 is obtained.

  For example, a spectroscopic device having a number of engravings of the diffraction grating N = 50 (/ mm) and f = 130 mm is used. When an infrared ray having a wavelength of 7.5 μm is incident from the direction of α = −7.1 degrees, it is diffracted in the direction of β = 30 degrees. At this time, the inverse dispersion D in the vicinity of 7.5 μm = 0.133 μm / mm. Therefore, if there is an infrared detector having a size of 15 mm in the x direction at the above-mentioned position of β = 30 degrees, the wavelength is demultiplexed in the range of 2 μm in width, ie, 6.5 μm to 8.5 μm with 7.5 μm as the center. (From the calculation formula 0.133 × 15 = 2.00 μm).

  Since the size in the x direction is 15 mm, when the size of one side of one pixel is 30 μm (= 0.03 mm), the number of pixels in the x direction may be set to 15 / 0.03 = 500.

  It should be noted here that the inverse dispersion is not constant in the x direction. In the above example, D = 0.137 and 0.129 nm / mm at wavelengths of 6.5 μm and 8.5 μm, respectively. Therefore, the wavelength change in the x direction of the infrared detector 200 is more preferably a value corresponding to the inverse dispersion D.

  As described above, it is most preferable that the wavelength changes in the x direction in accordance with the change in the inverse dispersion, but the wavelength may be linearly changed as the first approximation. The reason is as follows. In the above example, the change of D is about 6% (difference between 0.137 and 0.129), whereas the typical wavelength detection width Δλ / λ is about 10% (full width at half maximum Δλ of spectrum, center) Wavelength λ). Therefore, the change in D falls within the range of the detection wavelength band spread Δλ / λ.

  The spectroscopic device ideally diffracts incident infrared rays only in a specific direction according to the wavelength, but there is actually a component that does not follow this law, that is, a stray light component. This is based on imperfections such as irregular reflection inside the apparatus and cannot be completely removed. In this embodiment, since each pixel detects only infrared rays corresponding to the diffraction wavelength, stray light components deviating from the diffraction wavelength, which are noise factors, are not detected. On the other hand, an infrared detector having a wide wavelength band is used in many conventional examples, and stray light components deviating from the diffraction wavelength are also detected.

  In this way, by combining an infrared detector in which infrared detection pixels are arranged on a plane and whose detection wavelength is changed in at least one axial direction with a spectroscopic device, a wavelength spectrum measurement device with reduced noise can be provided.

  The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention.

  Needless to say, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the technical scope described in the claims.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Buffer layer 3 Lower contact layer 4 Light absorption layer 41 Intermediate layer 42, 42A, 42B, 42C, 42F, 42G Quantum dot layer 44F, 44G Cap layer 5 Upper contact layer 6 Protective film 7 Lower electrode 8 Upper electrode 100 , 100A, 100B, 100C, 100F, 100G Infrared detection pixels 200, 201, 203 Infrared detector 300 Vacuum chamber 301 Substrate holder 302 First raw material supply source 303 Second raw material supply source 304 Third raw material supply source 305 First 4 raw material supply source 400 spectroscopic device 410 diffraction grating 411 normal line 412 incident infrared ray 413 diffracted infrared ray 500 two-dimensional region 501 one-dimensional region

Claims (8)

A plurality of infrared detection pixels formed on the semiconductor substrate in an array along the X-axis and the Y-axis, each detecting infrared rays incident from the semiconductor substrate side;
Each of the plurality of infrared detection pixels is
A light absorption layer including an intermediate layer made of a semiconductor and a plurality of quantum dots arranged in an array, and at least one quantum dot layer formed in the intermediate layer;
Infrared detector for detecting an infrared ray having a detection wavelength corresponding to an energy difference between a first electronic level which is a ground level formed by quantum confinement of the quantum dot layer and a second electronic level which is an excitation level A manufacturing method of
In the formation step of the quantum dot layer, a relative angle of a supply direction of the raw material of the quantum dot layer with respect to the surface of the intermediate layer where the quantum dot layer is to be formed is set, and the quantum dot with respect to the surface of the intermediate layer by varying progressively along the feed rate of the raw material layer in the axial direction, at least one of the size and material composition of the quantum dots included in the quantum dot layer of each of said infrared detection pixels, along the axial direction gradually as a result of varying the manufacture of an infrared detector, wherein the detection wavelength corresponding to the energy difference between the first electron level and the second electron level varying progressively along the axis Te Way . Method for manufacturing an infrared detector according to claim 1, at least one of the size and material composition of the quantum dots included in the prior SL quantum dot layer, gradually varied linearly along the axial direction. 3. The method of manufacturing an infrared detector according to claim 1, wherein the intermediate layer is made of GaAs or AlGaAs, and the quantum dot layer is made of InAs. Each of the plurality of the light absorption layer of the infrared detection pixel is made of a semiconductor, the method for manufacturing a infrared detector to further have a cap layer formed on the quantum dot layer of the intermediate layer,
By varying progressively the energy of the previous SL first electron level of energy and the second electron level opposite sign along the axial direction, the first electron level of the infrared detection pixels to detect position and the energy difference between the second electron level, method for manufacturing an infrared detector according to any one of claims 1 to 3 varied progressively along the axial direction. Especially addition, the material composition of the cap layer varying gradually along said axis to at least one of the size and material composition of the quantum dots included in the prior SL quantum dot layer differ progressively along the axial direction Accordingly, the first electron level of energy and the second electron level of energy, the method for manufacturing an infrared detecting device of claim 4 gradually varied opposite sign along the axial direction. 6. The method of manufacturing an infrared detector according to claim 5, wherein the cap layer is made of InGaAs. Comprises a infrared detector, and a spectroscopic device for demultiplexing according to the wavelength of incident infrared rays,
The infrared detector includes a semiconductor substrate and a plurality of infrared detection pixels that are formed in an array along the X axis and the Y axis on the semiconductor substrate and detect infrared rays incident from the semiconductor substrate side. And
Each of the plurality of infrared detection pixels includes an intermediate layer made of a semiconductor and a plurality of quantum dots arranged in an array, and is made of at least one quantum dot layer formed in the intermediate layer and a semiconductor, A first electron that has a light absorption layer including a cap layer formed on the quantum dot layer in the intermediate layer and is a ground level formed by quantum confinement between the quantum dot layer and the cap layer An infrared detector that detects infrared rays having a detection wavelength corresponding to an energy difference between a second electron level that is a level and an excitation level,
Wherein a plurality of infrared detection pixels each detection wavelength, in the manufacturing method of the spectroscopic apparatus the demultiplexed by each of said infrared detection pixels and the wavelength to be incident on the equal have wavelength spectrometer,
The said infrared detector is manufactured by the manufacturing method of the infrared detector as described in any one of Claim 1 thru | or 6. The manufacturing method of the wavelength spectrum measuring apparatus characterized by the above-mentioned . The method for manufacturing a wavelength spectrum measuring apparatus according to claim 7, wherein the plurality of infrared detection pixels have detection wavelengths that gradually vary along the axial direction according to the inverse dispersion of the spectroscopic device.

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