JP2019125698A - Infrared detection element - Google Patents

Abstract

To provide an infrared detection element capable of adjusting a peak wavelength of a sensitivity spectrum to 8 μm to 10 μm where light reception sensitivity is high.SOLUTION: The infrared detection element includes at least one light absorption layer having a quantum dot layer. The quantum dot layer includes quantum dots represented by InGaAs(0.43≤x≤0.51). A peak wavelength of a sensitivity spectrum is 8 μm or more and 10 μm or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an infrared detection element.

  The infrared detection element is used for heat detection, concentration measurement of carbon dioxide and air pollutants, remote sensing using an artificial satellite, and the like. As one of infrared detectors, a quantum dot infrared detector using intersubband transition of quantum dots is known.

  The quantum dot infrared detection device has a structure in which the periphery of the quantum dot is three-dimensionally surrounded by a semiconductor having a band gap larger than that of the material constituting the quantum dot. Electrons or holes are strongly confined within the quantum dot, and discrete energy levels are formed. Among these levels, a plurality of electronic subband levels in the conduction band are used to detect an infrared ray having an energy corresponding to an intersubband energy difference.

  Patent Document 1 describes a quantum dot infrared detector including an intermediate layer between the quantum dot and the barrier layer. By facilitating the escape of electrons from the quantum dots by the interlayer, the sensitivity of the infrared detector is increased.

JP 2012-109434 A

  However, the above-mentioned infrared detector uses InAs for the quantum dots, and does not have the peak wavelength of the sensitivity spectrum in a wavelength band of 8 μm to 14 μm where infrared absorption by the atmosphere hardly occurs.

  An object of the present invention is to provide an infrared detecting element capable of adjusting the peak wavelength of the sensitivity spectrum to 8 μm to 10 μm where the light receiving sensitivity is high, in view of the above-mentioned problems.

The infrared detection element according to one aspect of the present invention includes at least one light absorption layer including a quantum dot layer, and the quantum dot layer is an In _x Ga _1-x As (0.43 ≦ x ≦ 0.51). And the peak wavelength of the sensitivity spectrum is 8 μm or more and 10 μm or less.

  According to the present invention, it is possible to provide an infrared detecting element capable of adjusting the peak wavelength of the sensitivity spectrum to 8 μm to 10 μm where the light receiving sensitivity is high.

It is the figure which showed typically the cross section of the infrared detection element concerning this embodiment. It is the cross-sectional schematic diagram which expanded the principal part of the element part of the infrared detection element concerning this embodiment. It is the figure which showed typically the conduction band structure of the infrared detection element shown in FIG. It is the figure which showed typically the relationship between the light reception wavelength of the infrared detection element concerning this embodiment, and the light reception sensitivity in a light reception wavelength. It is the figure which showed typically the conduction band structure of the infrared detection element which used InAs for the quantum dot. It is the figure which showed typically the relationship between the light reception wavelength of the infrared detection element which used InAs for the quantum dot, and the light reception sensitivity in a light reception wavelength. Is a diagram showing the relationship between the light-receiving sensitivity of the _{In x Ga 1-x As (} 0.43 ≦ x ≦ 0.51) peak wavelength and the infrared detection element formed quantum dots. The relationship between the light receiving sensitivity of infrared light detected in the examination in FIG. 7, the In composition ratio x of In _x Ga _{1 -x} As, and the peak wavelength λp is summarized in one graph.

  Hereinafter, an infrared detection element according to an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings used in the following description, in order to make the features easy to understand, the features that are the features may be enlarged and shown for convenience, and the dimensional ratio of each component is not necessarily the same as the actual.

  FIG. 1 is a schematic cross-sectional view of the infrared detection element according to the present embodiment. The infrared detection element 100 shown in FIG. 1 includes an element portion 20, a semiconductor substrate 21, a buffer layer 22, a lower contact layer 23, an upper contact layer 24, an upper electrode 25, a lower electrode 26, and a voltage source 27. And an ammeter 28.

  The semiconductor substrate 21, the buffer layer 22, and the lower contact layer 23 are bases of the element unit 20. For the semiconductor substrate 21, a III-V group semiconductor compound can be used. For example, GaAs or the like can be used.

  The buffer layer 22 is stacked on one surface of the semiconductor substrate 21. The buffer layer 22 is generally made of the same material as that of the semiconductor substrate 21. However, other materials that are lattice matched with the semiconductor substrate 21 may be used if the crystal quality is sufficient.

The lower contact layer 23 is stacked on the surface of the buffer layer 22 opposite to the semiconductor substrate 21. The lower contact layer 23 is in charge of electrical connection between the element portion 20 and the lower electrode 26. The lower contact layer 23 is configured mainly of an n-type semiconductor. The lower contact layer 23 can be made of, for example, GaAs doped with Si atoms at a concentration of about 2 × 10 ¹⁸ cm ⁻³ .

  The element portion 20 and the lower electrode 26 are stacked on one surface of the lower contact layer 23. The lower electrode 26 can be made of a conductive material.

  The lower electrode 26 is connected to the upper electrode 25 via a voltage source 27 and an ammeter 28. The upper electrode 25 can be made of a conductive material. The voltage source 27 applies an appropriate voltage between the upper electrode 25 and the lower electrode 26. Electrons are injected into the element unit 20 by applying a voltage. The ammeter 28 measures the photocurrent flowing between the upper electrode 25 and the lower electrode 26. The photocurrent is generated by absorbing the infrared ray L incident on the element unit 20.

The upper electrode 25 is connected to the upper contact layer 24. The upper contact layer 24 is formed on the top surface of the element unit 20. The upper contact layer 24 is in charge of electrical connection between the element portion 20 and the upper electrode 25. The upper contact layer 24 is mainly composed of an n-type semiconductor. The upper contact layer 24 can be made of, for example, GaAs doped with Si atoms at a concentration of about 2 × 10 ¹⁸ cm ⁻³ .

  The element portion 20 is provided between the lower contact layer 23 and the upper contact layer 24. The element unit 20 absorbs the infrared light L and generates a photocurrent. In the element unit 20, the light absorption layer 10 and the intermediate layer 11 are sequentially stacked. The light absorbing layer 10 may be a single layer, but in order to enhance the absorption efficiency of the incident infrared light L, it is preferable that a plurality of layers be stacked. Specifically, it is preferable that ten or more light absorption layers 10 be stacked.

  FIG. 2 is a schematic cross-sectional view of an enlarged main part of the element portion 20 of the infrared detection element 100 according to the present embodiment, and is an enlarged view in the vicinity of one quantum dot 12A.

  As shown in FIG. 2, the light absorption layer 10 includes a lower barrier layer 15, an underlayer 14, a quantum dot layer 12, a quantum well layer 13, a cap layer 16, and an upper barrier layer 17.

  The quantum dot layer 12 captures electrons injected into the element unit 20 by the voltage source 27 (see FIG. 1). FIG. 3 is a view schematically showing the conduction band structure of the infrared detection element 100 shown in FIG. As shown in FIG. 3, the quantum dot layer 12 has the lowest energy level. Therefore, the electrons injected into the element unit 20 fall into the quantum dot layer 12.

Quantum dot layer 12 _includes quantum dots 12A, denoted by _{In x Ga 1-x As (} 0.43 ≦ x ≦ 0.51). In _x Ga _1-x As quantum dot 12A composed of (0.43 ≦ x ≦ 0.51) is higher minimum energy E1 compared to quantum dots using InAs. Therefore, in this example, only the ground state u ₁ exists.

  In the above composition formula, the In composition ratio x is preferably 0.43 ≦ x ≦ 0.51, and more preferably 0.45 <x <0.50. The composition of the quantum dot 12A greatly affects the conduction band structure that the quantum dot 12A can have.

  By setting the composition formula of the quantum dot 12A in the above range, the peak wavelength of the sensitivity spectrum can be adjusted to 8 μm to 10 μm where the light receiving sensitivity is high.

In the quantum dot layer 12, a plurality of quantum dots 12A exist. The density of the quantum dots 12A in the quantum dot layer 12 is preferably 1 × 10 ¹⁰ / cm ² or more and 1 × 10 ¹² / cm ² or less, and is 5 × 10 ¹⁰ / cm ² or more 5 × 10 ¹¹ It is more preferable that it is / cm < ² > or less, and it is more preferable that it is 1 * 10 < ¹¹ > piece / cm < ² >. The number of quantum dots 12A, which are infrared absorbers, is preferably larger in terms of increasing the total volume of the absorption medium. On the other hand, when the number of quantum dots 12A increases too much, the distance between adjacent quantum dots 12A becomes too close to affect each other. As a result, the three-dimensional confinement effect of the quantum dots 12A is reduced. Therefore, the absorption efficiency of the infrared rays L is enhanced by the presence of the quantum dots 12A in a predetermined density range.

  The upper surface 12a in the stacking direction of the quantum dots 12A is preferably planarized. That is, the heights of the plurality of quantum dots 12A are preferably substantially constant. Here, “substantially constant” means that the deviation is within 20% of the average value of the heights of the 50 quantum dots 12A measured by observing the cross section of the wafer including the quantum dots 12A with a transmission electron microscope.

When the heights of the plurality of quantum dots 12A are aligned, the ground state u ₁ in each quantum dot 12A becomes constant. In the infrared detection element 100, the absorption wavelength is determined by the energy level difference between the ground state u ₁ and the excited state. That is, as the ground state u ₁ in each quantum dot 12 A becomes constant, the energy level difference becomes constant, and the sensitivity of the infrared detection element 100 to infrared light of a specific wavelength increases.

  The height of the quantum dot 12A is preferably 3 nm or more and 6 nm or less, more preferably 4 nm or more and 5 nm or less, and still more preferably 4.5 nm.

  The shape of the quantum dot 12A is preferably cylindrical or truncated cone. The size of the quantum dot 12A is preferably 10 nm or more and 30 nm or less, more preferably 15 nm or more and 25 nm or less, and still more preferably 20 nm. Here, the size of the quantum dot 12A refers to the diameter of the lower surface of the quantum dot 12A in the stacking direction. The upper surface of the quantum dot 12A is preferably 10 nm or more and 20 nm or less, more preferably 12 nm or more and 18 nm or less, and still more preferably 14 nm or more and 15 nm or less.

  The size and height of the quantum dots 12 A change the conduction band structure of the quantum dot layer 12. For example, if the size and height of the quantum dot 12A are too large, the number of electrons captured in the quantum dot layer 12 increases. As the number of electrons captured increases, each may interact and the sensitivity of infrared detection may be reduced.

  Preferably, the quantum dots 12A are doped with Si. When the quantum dots 12A are doped with Si, electrons serving as carriers increase. The infrared detection element 100 reads out the movement of electrons as photocurrent. That is, when the number of carriers increases, the detection sensitivity of the infrared detection element 100 is improved. In particular, when the lower barrier layer 15 and the upper barrier layer 17 described later are provided, it is preferable to dope Si. These barrier layers inhibit the flow of electrons. Therefore, by increasing the number of carriers in the infrared detection element 100, a decrease in detection sensitivity can be further prevented.

The quantum well layer 13 covers at least a part of the quantum dot 12A. The shape of the upper surface of the quantum well layer 13 preferably reflects the shape of the quantum dot 12A, and the quantum well layer 13 preferably covers the upper surface 12a of the quantum dot 12A. When the quantum well layer 13 covers the upper surface 12a of the quantum dot 12A, an intermediate level is provided at the energy level, and the photocurrent easily flows. The quantum well layer 13 contains a substance having a lower In composition ratio x than the quantum dot 12A. For example, In _0.1 Ga _0.9 As or the like can be used.

  The energy level of the quantum well layer 13 is located between the cap layer 16 and the quantum dot layer 12. That is, the quantum well layer 13 functions as an intermediate level when the confined electron is excited. When the intermediate level exists, the photocurrent easily flows, and the sensitivity of the infrared detection element 100 is improved.

  The thickness of the quantum well layer 13 is preferably 4 nm or more and 7 nm or less, more preferably 5 nm or more and 6 nm or less, and still more preferably 5.7 nm. Here, the thickness of the quantum well layer 13 refers to the thickness of the quantum well layer 13 in the portion where the quantum dot 12A does not exist. When the width of the quantum well layer 13 is too thick, the quantum confinement effect by the quantum dots 12A is reduced. As a result, dark current increases, which causes the sensitivity of the infrared detection element 100 to decrease.

The lower barrier layer 15 is located below the stacking direction of the quantum dot layer 12. The conduction band edge of the lower barrier layer 15 has a higher energy level than the energy level of GaAs as a reference. As a material having such a conduction band offset, for example, GaAs doped with Al can be mentioned. More specifically, Al _0.2 Ga _0.8 As can be used for the lower barrier layer 15.

  On the other hand, the upper barrier layer 17 is located above the stacking direction of the quantum dot layer 12. The conduction band edge of the upper barrier layer 17 has a higher energy level than the energy level of GaAs as a reference. The same material as the lower barrier layer 15 can be used for the upper barrier layer 17.

  Electrons bound to the quantum dot layer 12 pass through the lower barrier layer 15 and the upper barrier layer 17 by tunneling or thermal excitation. In other words, the lower barrier layer 15 and the upper barrier layer 17 inhibit the flow of electrons. The lower barrier layer 15 and the upper barrier layer 17 suppress the dark current of the infrared detection element 100.

  The thickness of the lower barrier layer 15 and the upper barrier layer 17 is preferably 2 nm or less, and more preferably 1 nm or less. If their thickness is too thick, it will be difficult for electrons to pass through these barriers. That is, not only the dark current of the infrared detection element 100 but also the flow of necessary photocurrent may be hindered. As a result, the sensitivity of the infrared detection element 100 may be reduced.

  The underlayer 14 is located between the lower barrier layer 15 and the quantum dot layer 12. The underlayer 14 is made of GaAs in the same manner as the intermediate layer 11. It is difficult to stack the quantum dot layer 12 on the lower barrier layer 15 doped with Al. By providing the underlayer 14, the crystallinity of the quantum dot layer 12 is enhanced.

  The cap layer 16 is located between the upper barrier layer 17 and the quantum dot layer 12. The cap layer 16 is also made of GaAs in the same manner as the intermediate layer 11.

  The energy levels of the underlayer 14 and the cap layer 16 are located between the quantum dot layer 12 and the lower barrier layer 15 or the upper barrier layer 17. That is, the underlayer 14 and the cap layer 16 function as intermediate levels when the confined electrons are excited. When the intermediate level exists, the photocurrent easily flows, and the sensitivity of the infrared detection element 100 is improved.

  The thickness of the underlayer 14 and the cap layer 16 is preferably 0.5 nm or more and 2 nm or less, and more preferably 1.0 nm or more and 1.5 nm or less. If the width of the quantum well formed by the underlayer 14 and the cap layer 16 is too thick, the quantum confinement effect by the quantum dot 12A decreases. Therefore, dark current increases, which causes the sensitivity of the infrared detection element 100 to decrease.

  It is the quantum dot layer 12 that absorbs the infrared light L (see FIG. 1) in the light absorption layer 10. Therefore, the essential layer is the quantum dot layer 12. On the other hand, it is preferable that the infrared detection element 100 also include the other layers described above, since the other layers also contribute significantly to light absorption.

  In the element portion 20, the light absorption layer 10 is stacked via the intermediate layer 11. The intermediate layer 11 is preferably made of GaAs. The intermediate layer 11 flattens the lamination surface in which the unevenness is formed by the quantum dots 12A. Therefore, the thickness of the intermediate layer 11 is preferably 30 nm or more and 60 nm or less, more preferably 40 nm or more and 50 nm or less, and still more preferably 46 nm.

  The specific configuration of the infrared detection element 100 has been described above. Next, the operation of the infrared detection element 100 will be described using the drawings.

  As shown in FIG. 1, the infrared ray L is incident on the infrared detection element 100. The incident infrared light L is absorbed by the light absorption layer 10. The light absorbing layer 10 absorbs the infrared light L and generates a photocurrent. The generated photocurrent is detected by the ammeter 28. A process of absorbing the infrared light L and generating a photocurrent in the light absorption layer 10 will be described.

  As shown in FIG. 3, the quantum dot layer 12 has the lowest energy level. Therefore, the electrons injected into the element unit 20 by the voltage source 27 (see FIG. 1) are captured by the quantum dot layer 12. The electrons captured by the quantum dot layer 12 are excited by the infrared ray L (see FIG. 1). The excited electrons pass through the lower barrier layer 15 or the upper barrier layer 17 by tunneling or thermal excitation to generate a photocurrent.

When an electron is excited, a transition (first transition) from the ground state u ₁ of the quantum dot layer 12 to the excited state w _k (1 ≦ k <500) having a magnetic quantum number of 3 mainly occurs. Of the energy required for excitation process, the energy E1 of the ground state u _1, the energy difference between the binding energy Ec of the underlayer 14 and the cap layer 16 in the excited state wk is, matches the infrared energy 8 to 10 [mu] m.

On the other hand, when the composition and configuration of the quantum dot layer 12 change, the transition process of electrons also changes. For example, a transition (second transition) from the ground state u ₁ of the quantum dot layer 12 to another excited state w _{k ′} occurs. Excited state w _{k 'is} spread wide wave function in the substrate growth axis direction from the excited state w _k. Therefore, the overlap of the wave functions of the excited state w _{k ′} and the ground state u ₁ is smaller than in the case of the excited state w _k, and the transition dipole moment is small.

FIG. 4 is a view schematically showing the relationship between the light reception wavelength of the infrared detection element 100 according to the present embodiment and the light reception sensitivity at the light reception wavelength. As shown in FIG. 4, the sensitivity spectrum is discrete with respect to the light receiving wavelength. This is because the quantum dot 12A composed of In _x Ga _1-x As (0.43 ≦ x ≦ 0.51) has a level that can be taken in the quantum dot layer 12 fixed to the ground state u ₁ It is.

  The first sensitivity spectrum QD1 is generated by the first transition when the quantum dot 12A has a predetermined composition. The first transition is caused by infrared light of a wavelength corresponding to the energy difference between the minimum energy E1 and the binding energy Ec. The infrared wavelength corresponds to the peak wavelength λ1 of the first sensitivity spectrum QD1.

  The energy required for the first transition process is minimal in the excitation process. Therefore, the peak wavelength λ1 is the shortest wavelength among the generated sensitivity spectrum.

Infrared detector 100 according to this embodiment includes quantum dots quantum dot layer is denoted by _{In x Ga 1-x As (} 0.43 ≦ x ≦ 0.51). Therefore, the peak wavelength λ1 is 8 μm or more and 10 μm or less.

  On the other hand, the second sensitivity spectrum QD2 is generated by the second transition when the composition of the quantum dot 12A or the configuration of the surroundings is changed. The second transition requires more energy than the first transition. Therefore, the maximum light receiving sensitivity of the second sensitivity spectrum QD2 is smaller than the first sensitivity spectrum QD1. The peak wavelength λ2 is longer than the peak wavelength λ1.

  In addition, changing the composition or the like of the quantum dot 12A changes the position at which the peak of the sensitivity spectrum is obtained. For example, depending on the excitation process, a third sensitivity spectrum QD3 or the like is also generated. These excitation processes require more energy than the first and second transitions. Therefore, the maximum light receiving sensitivity of the sensitivity spectrum after the third sensitivity spectrum QD3 is reduced, and the peak wavelength is also shifted to a long wavelength.

  The infrared ray transmittance of the atmosphere is also shown in FIG. 4 (symbol A). The atmosphere absorbs infrared rays, but the transmittance of infrared rays in the wavelength band of 8 μm to 14 μm is high. This zone is called the window of the atmosphere. The infrared detection element is also used, for example, for remote sensing using a satellite. Therefore, the influence of infrared absorption by the atmosphere can not be ignored. Therefore, it is preferable to use the window of the atmosphere in the detection of infrared radiation under the atmospheric environment. The infrared detection element 100 according to the present embodiment has a peak wavelength λp of 8 μm or more and 10 μm or less, and utilizes a window of the atmosphere.

  On the other hand, FIG. 5 is a view schematically showing the conduction band structure of the infrared detection device using InAs for the quantum dots. FIG. 6 is a view schematically showing the relationship between the light receiving wavelength of an infrared detecting element using InAs for quantum dots and the light receiving sensitivity at the light receiving wavelength. In FIG. 6, the transmittance of infrared rays of the atmosphere is also shown (symbol A).

As shown in FIG. 5, the energy level of the quantum dot layer 12 ′ using InAs for the quantum dots is lower than when using In _x Ga _{1 -x} As for the quantum dots. Therefore, there are a plurality of possible states (state u ₁ , state v ₁ , state _{w 1} ) in the quantum dot layer 12 ′. That is, there are many electron excitation processes. As a result, the sensitivity spectrum shown in FIG. 6 is obtained by superimposing a plurality of peaks.

Further, since the energy level of the quantum dot layer 12 'is low, the energy difference between the minimum energy E1 and the bound energy Ec by the intermediate layer 11' becomes large. That is, the energy required for the transition from the state u ₁ , the state v ₁ , the state _{w 1} to the state u _k , the state v _k , and the state _wk is increased. Therefore, the peak wavelength λp of the sensitivity spectrum of the infrared detection element is shorter than the window of the atmosphere.

As described above, the infrared detection element according to the present embodiment includes the quantum dots represented by In _x Ga _1-x As (0.43 ≦ x ≦ 0.51), and the peak wavelength of the sensitivity spectrum is 8 μm or more 10 μm or less. That is, the infrared detection element according to the present embodiment has the peak wavelength of the sensitivity spectrum in the shortest wavelength region of the atmospheric window. Therefore, it is possible to detect infrared rays particularly at high sensitivity even in the atmospheric window.

  Next, an example of a method of manufacturing the infrared detection element according to the present embodiment will be described based on FIGS. 1 and 2.

  A GaAs substrate having a (001) plane orientation is prepared as the semiconductor substrate 21. Then, the semiconductor substrate 21 is introduced into a molecular beam epitaxial (MBE) apparatus. After removing the natural oxide film, the temperature of the semiconductor substrate 21 is maintained at about 580.degree. Thereafter, a buffer layer made of GaAs which is the same as the semiconductor substrate 21 is stacked to a thickness of 500 nm.

Next, the lower contact layer 23 is stacked on the buffer layer 22. The lower contact layer 23 is doped with Si atoms at a concentration of about 2 × 10 ¹⁸ cm ⁻³ after stacking GaAs.

  Then, the element unit 20 is stacked on the lower contact layer 23 obtained. First, GaAs is stacked as the intermediate layer 11. The light absorbing layer 10 is laminated on the intermediate layer 11.

The light absorption layer 10 is laminated in the following procedure. First, on the intermediate layer 11, the lower barrier layer 15 represented by Al _x Ga _1-x As having a thickness of 1 nm or less and the underlayer 14 made of GaAs having a thickness of about 1 nm are sequentially stacked.

Thereafter, the temperature of the semiconductor substrate 21 was lowered to 500 ° C. before and after, the thickness is laminated _In x _{Ga 1-x} As of 2-3 atomic layers.

At this time, In _x Ga _1-x As is three-dimensionally grown like an island due to a strain generated from a difference in lattice constant. This is a mode called SK (Stranski-Krastanov) mode growth, and this method provides a quantum dot layer 12 in which a plurality of quantum dots 12A are arranged in a plane. The height of the quantum dot 12A, size, density, etc., can be adjusted by an amount of the growth temperature, growth rate, and supplies _In x _{Ga 1-x} As.

  It is preferable to perform flushing after producing the quantum dots 12A. Flushing refers to equalizing the heights of the plurality of quantum dots 12A. Flushing can be performed according to the following procedure. First, after the quantum dots 12A are grown, a buried layer made of a material that is less likely to evaporate than the material constituting the quantum dots 12A is formed around the quantum dots 12A at a height lower than that of the quantum dots 12A. As a result, the quantum dots 12A are embedded in the embedded layer. Then, the semiconductor substrate 21 is heated to evaporate the quantum dots 12A not covered by the embedded layer. Through such a procedure, the heights of the plurality of quantum dots 12A become uniform. In contained in the quantum dot 12A is easier to sublime than Ga. Therefore, by heating, a part of In contained in the quantum dot 12A is sublimated, and the upper surface 12a of the quantum dot 12A is flattened.

  Further, it is preferable to dope the quantum dots 12A with Si. The Si doping is performed by irradiating a Si molecular beam on the quantum dot layer 12 for a predetermined time by molecular beam epitaxy (MBE).

  Then, on the quantum dot layer 12, a quantum well layer 13 in which the In composition ratio x is smaller than that of the quantum dot layer 12 is stacked. The quantum dot layer 12 is covered with the quantum well layer 13 by stacking the quantum well layer 13 about 5 to 6 nm. The quantum well layer 13 reflects the shape of the quantum dot 12A.

Thereafter, a cap layer 16 of GaAs having a thickness of about 1 nm and an upper barrier layer 17 represented by Al _x Ga _{1 -x} As having a thickness of 1 nm or less are sequentially stacked. Thereby, the light absorption layer 10 is formed. Then, the element portion 20 is obtained by repeatedly laminating the intermediate layer 11 and the light absorption layer 10 a plurality of times.

Finally, the upper contact layer 24 is stacked on the element unit 20. The upper contact layer 24 is doped with Si atoms at a concentration of about 2 × 10 ¹⁸ cm ⁻³ after stacking GaAs. Here, an example of manufacturing using the MBE method has been described, but other crystal growth methods such as metal organic chemical vapor deposition (MOCVD method) may be used.

  Then, a part of the obtained laminate is selectively etched to expose the lower contact layer 23. Selective etching is performed by dry etching or wet etching after performing ultraviolet lithography.

  Each structure separated by etching constitutes an infrared detection element. An infrared detector can be obtained by arranging a plurality of these infrared detection elements.

  The upper electrode 25 and the lower electrode 26 can be formed by the lift-off method, respectively. The lift-off method includes the steps of lithography, metal deposition, resist stripping and the like.

  Although the preferred embodiments of the present invention have been described above in detail, the present invention is not limited to the specific embodiments, and various modifications may be made within the scope of the present invention as set forth in the appended claims. It is possible to change and change

Example 1
As Example 1, the infrared detection element of the structure of FIG. 1 was prepared. The number of laminated light absorbing layers 10 was ten. Moreover, the structure of the light absorption layer 10 used the thing of the structure of FIG. The lower barrier layer 15 and the upper barrier layer 17 are made of Al _0.2 Ga _0.8 As and have a thickness of 1 nm. The underlayer 14 and the cap layer 16 are made of GaAs and have a thickness of 1 to 1.5 nm. The quantum dot 12A is a truncated cone having a lower diameter of 20 nm, an upper diameter of 14 nm, and a height of 4.5 nm. The composition of the quantum dot 12A was In _x Ga _1-x As, and the range of x was changed. Furthermore, the quantum well layer 13 has a thickness of 5.7 nm using In _0.1 Ga _0.9 As.

And the light reception sensitivity with respect to the light reception wavelength of the produced infrared detector was measured. FIG. 7 is a diagram showing the relationship between the peak wavelength λ _{p of a} quantum dot formed of In _x Ga _1-x As and the light receiving sensitivity of the infrared detection element.

  As shown in FIG. 7, it has been confirmed that the light receiving sensitivity decreases as the peak wavelength λp of the quantum dot increases. That is, in the window of the atmosphere, as the peak wavelength λp approaches 8 μm, the light receiving sensitivity of the infrared detection element 100 is increased.

  The infrared detection element 100 according to the present embodiment sets the peak wavelength λp of the sensitivity spectrum to 8 μm or more and 10 μm or less by optimizing the In composition ratio x and the structure. That is, the infrared detection element 100 can use the region having the highest light receiving sensitivity among the windows of the atmosphere having high infrared transmittance.

FIG. 8 is a graph showing the relationship between the light receiving sensitivity of infrared light detected in the study in FIG. 7, the In composition ratio x of In _x Ga _{1 -x} As, and the peak wavelength λp.

  As shown in FIG. 8, when the In composition ratio x is 0.45 ≦ x ≦ 0.50, the peak wavelength λp satisfies 8.1 μm ≦ λp ≦ 9.4 μm. The light receiving sensitivity R at this time showed a high light receiving sensitivity as 16.9 (40%) ≦ R ≦ 41.8%.

10: light absorption layer 11: intermediate layer 12: quantum dot layer 12A: quantum dot 13: quantum well layer 14: base layer 15: lower barrier layer 16: cap layer 17: upper barrier layer 20: element portion 21: semiconductor substrate 22 : Buffer layer 23: Lower contact layer 24: Upper contact layer 25: Upper electrode 26: Lower electrode 27: Voltage source 28: Ammeter 100: Infrared detector L: Infrared λp: Peak wavelength

Claims (10)

At least one light absorbing layer comprising a quantum dot layer,
The quantum dot layer includes quantum dots represented by In _x Ga _1-x As (0.43 ≦ x ≦ 0.51),
The infrared detection element whose peak wavelength of a sensitivity spectrum is 8 micrometers or more and 10 micrometers or less.   The infrared detection device according to claim 1, wherein at least a part of the quantum dots is covered with a quantum well layer having an In ratio lower than that of the quantum dots.   The infrared detection device according to claim 2, wherein the quantum well layer covers an upper surface in a stacking direction of the quantum dots.   The infrared detection element according to any one of claims 1 to 3, wherein the quantum dot is doped with Si.   The infrared detection element according to any one of claims 1 to 4, wherein the upper surface in the stacking direction of the quantum dots is flattened.   The infrared detection element according to any one of claims 1 to 5, wherein the diameter of the lower surface of the quantum dot in the stacking direction is 10 nm or more and 30 nm or less.   The light absorption layer further comprises an upper barrier layer located above the stacking direction of the quantum dot layer, and a lower barrier layer located below the stacking direction of the quantum dot layer. The infrared detection element as described in any one.   The infrared detection device according to claim 7, wherein a thickness of the upper barrier layer and the lower barrier layer is 1 nm or less.   The infrared detection device according to claim 7, further comprising an underlayer made of GaAs between the lower barrier layer and the quantum dot layer.   The infrared detection element according to any one of claims 1 to 9, wherein a plurality of the light absorption layers are stacked via an intermediate layer.

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