JP2012109434A - Quantum-dot infrared detector and infrared image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quantum-dot infrared detector having an increased sensitivity and an infrared image sensor.SOLUTION: The quantum-dot infrared detector comprises: quantum dots; a first barrier layer that covers the quantum dots and that has an energy gap broader than that of the quantum dots; an intermediate layer that is provided above the first barrier layer and below the quantum dots, and that has an energy gap broader than that of the quantum dots and narrower than that of the first barrier; a photoelectric conversion layer that is provided in the first barrier layer and that has an energy gap broader than that of the quantum dots and narrower than that of the first barrier; and electrode layers provided on two sides of the photoelectric conversion layer.

Description

  The present invention relates to a quantum dot infrared detector and an infrared image sensor.

  The quantum dot infrared detector is an infrared photodetector that utilizes intersubband transition of quantum dots. When the quantum dot is irradiated with infrared rays, the electrons bound to the transition source level of the quantum dot are photoexcited, and the intersubband transitions to the transition destination level. The electrons photoexcited in the subband are released from the quantum dot binding by thermal excitation or tunnel effect, and are collected on the electrode by the applied voltage to form a photocurrent. Infrared light can be detected by detecting this photocurrent with an external circuit. There are also quantum well infrared detectors that utilize intersubband transitions in quantum wells. However, quantum well infrared detectors have limited applicability because they do not respond to normal incidence light.

  The quantum dot infrared detector has a photoelectric conversion layer and electrode layers provided on the upper surface and the lower surface of the photoelectric conversion layer. Furthermore, the photoelectric conversion layer has a quantum dot and an intermediate layer surrounding the quantum dot. Here, the energy gap of the intermediate layer (the energy difference between the bottom of the conduction band and the top of the valence band) is wider than that of the quantum dots. Therefore, the intermediate layer becomes an energy barrier against electrons in the conduction band of the quantum dot, and generates a quantum level in the quantum dot.

  A basic quantum dot infrared detector consisting of a quantum dot and a photoelectric conversion layer having only an intermediate layer cannot generate a sufficient photocurrent and has a problem of low sensitivity (corresponding to a signal). It was.

  In order to solve this problem, a quantum dot photodetector has been developed in which a quantum dot is surrounded by a semiconductor layer (hereinafter referred to as a barrier layer) having a wider energy gap than the intermediate layer. This barrier layer enhances the quantum confinement effect in the quantum dots and facilitates the transition of electrons excited by light, resulting in improved sensitivity of the quantum dot infrared detector.

  As characteristics of the infrared detector, it is important that the sensitivity is high and the signal-to-noise ratio (S / N) is small.

JP 2009-65141 A

  However, it is not easy to further improve the sensitivity of the quantum dot infrared detector. For example, if the barrier layer is made thick in order to enhance the quantum confinement effect of the excited level, the sensitivity is decreased. This is because the thicker barrier layer suppresses escape of electrons that have transitioned to the excited level (hereinafter referred to as “excited electrons”) through a tunnel to the intermediate layer.

  Therefore, an object of the present invention is to provide a quantum dot infrared detector that facilitates escape of electrons to the intermediate layer and enhances sensitivity.

  In order to achieve the above object, according to a first aspect of the present apparatus, a quantum dot, a first barrier layer that covers the quantum dot and has a wider energy gap than the quantum dot, and the first barrier An intermediate layer provided above the quantum dot and below the quantum dot and having an energy gap wider than the quantum dot and narrower than the first barrier layer; and an energy gap provided in the first barrier layer; There is provided a quantum dot infrared detector comprising a photoelectric conversion layer having a quantum well layer wider than a quantum dot and narrower than the first barrier layer, and electrode layers provided on both sides of the photoelectric conversion layer.

  According to the present quantum dot infrared detector, the sensitivity of a quantum dot infrared detector having a barrier layer can be improved.

2 is a schematic diagram illustrating a structure of a quantum dot infrared detector according to Embodiment 1. FIG. 4 is a cross-sectional view illustrating the structure of a photoelectric conversion layer of the quantum dot infrared detector according to Embodiment 1. FIG. FIG. 3 is a partially enlarged view of FIG. 2. FIG. 4 is an energy band diagram of the photoelectric conversion layer taken along line IV-IV in FIG. 3. It is the elements on larger scale of the photoelectric converting layer in which the quantum well layer is not provided in the 1st barrier layer. FIG. 6 is an energy band diagram of the photoelectric conversion layer taken along line VI-VI in FIG. 5. It is a figure explaining the relationship between the thickness of a quantum well layer, and the sensitivity of the quantum dot type infrared detector of Embodiment 1. It is a figure explaining the relationship between the thickness of a quantum well layer, and the S / N ratio of the quantum dot type infrared detector of Embodiment 1. FIG. 4 is an energy band diagram of the photoelectric conversion layer along the line IX-IX in FIG. 3. 6 is a schematic diagram illustrating a cross section of an infrared image sensor according to Embodiment 2. 6 is a partially enlarged view illustrating a photoelectric conversion layer of a quantum dot infrared detector according to Embodiment 3. FIG. FIG. 12 is an energy band diagram of the photoelectric conversion layer taken along line XII-XII in FIG. 11. 6 is a schematic diagram illustrating a photoelectric conversion layer of a quantum dot infrared detector according to Embodiment 4. FIG. 6 is a partially enlarged view illustrating a photoelectric conversion layer of a quantum dot infrared detector according to Embodiment 5. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof. In addition, the same code | symbol is attached | subjected to the corresponding part even if drawings differ, The description is abbreviate | omitted.

(Embodiment 1)
(1) Structure and operation-Overall structure-
FIG. 1 is a schematic diagram illustrating the structure of the quantum dot infrared detector 2 of the present embodiment. In FIG. 1, a power source 10 and a current detector 12 are also illustrated in order to explain the operation of the quantum dot infrared detector 2.

  As shown in FIG. 1, the quantum dot infrared detector 2 of the present embodiment includes a photoelectric conversion layer 4 and electrode layers 6 a and 6 b provided on both sides of the photoelectric conversion layer 4. The electrode layers 6a and 6b are, for example, n-type low-resistance semiconductor layers. Here, the lower electrode layer 6 a, the photoelectric conversion layer 4, and the upper electrode layer 6 b are stacked on the semiconductor substrate 9 in this order.

  The lower electrode layer 6a and the upper electrode layer 6b are provided with metal electrodes 8a and 8b, respectively. A power supply 10 for supplying a constant voltage is connected between the electrode layers 6a and 6b via the metal electrodes 8a and 8b. Accordingly, a constant voltage is applied to the photoelectric conversion layer 4.

  The infrared rays 12 to be detected are incident from the back surface of the semiconductor substrate 9. Next, the infrared rays 12 reach the photoelectric conversion layer 4 and a part thereof is absorbed by the photoelectric conversion layer 4. Thereafter, the infrared rays 12 are reflected by the upper metal electrode 8b. Thereby, the infrared rays 12 reenter the photoelectric conversion layer 4 and are absorbed again by the photoelectric conversion layer 4.

  Infrared rays absorbed by the photoelectric conversion layer 4 generate photocarriers. Due to the voltage applied to the photoelectric conversion layer 4, this photocarrier becomes a photocurrent and is taken out to the outside. This photocurrent is detected by the current detector 12 to detect infrared rays.

―Photoelectric conversion layer―
FIG. 2 is a cross-sectional view illustrating the structure of the photoelectric conversion layer 4 of the quantum dot infrared detector 2. FIG. 3 is a partially enlarged view of FIG. In FIG. 2, electrode layers 6a and 6b are also shown for reference.

  As shown in FIGS. 2 and 3, the photoelectric conversion layer 4 includes a plurality of quantum dots 14, a first barrier layer 16 covering the quantum dots 14, and a quantum well provided in the first barrier layer 16. It has a layer 18. Here, the quantum well layer 18 is in contact with the quantum dots 14.

  Furthermore, the photoelectric conversion layer 4 has a second barrier layer 20 that is in contact with the bottom surface of the quantum dots 14. In addition, the photoelectric conversion layer 4 includes an intermediate layer 22 (that is, one side of the first barrier layer 16) above the first barrier layer 16 and the lower side (opposite side of the one side) of the quantum dots 14 (ie, the one side). And an intermediate layer 22) provided on both sides of the first barrier layer 16.

FIG. 4 is an energy band diagram of the photoelectric conversion layer 4 along the line IV-IV in FIG. The vertical axis 24 is the energy of electrons. The horizontal axis 26 corresponds to the position in the direction perpendicular to the semiconductor substrate 9 (the same applies hereinafter). 4 shows an energy E _C at the bottom of the conduction band, such as quantum dots 14, the top of the energy E _V of the valence band is shown. In addition, the positions of the quantum dots 14 and the like are shown in the upper part of FIG.

  As shown in FIG. 4, the energy gap Eg of the first barrier layer 16 is wider than the energy gap of the quantum dots 14. Similarly, the energy gap of the second barrier layer 20 is wider than that of the quantum dots 14. On the other hand, the energy gap of the intermediate layer 22 is wider than that of the quantum dots 14 and narrower than that of the first barrier layer 16 and the second barrier layer 20. The energy gap of the quantum well layer 18 is wider than that of the quantum dots 14 and narrower than that of the first barrier layer 16 and the second barrier layer 20.

  That is, the bottom of the conduction band of the first barrier layer 16 is higher than the bottom of the conduction band of the quantum dots 14. Similarly, the bottom of the conduction band of the second barrier layer 20 is higher than the bottom of the conduction band of the quantum dots 14. On the other hand, the bottom of the conduction band of the intermediate layer 22 is higher than the quantum dots 14 and lower than the first barrier layer 16 and the second barrier layer 20. The bottom of the conduction band of the quantum well layer 18 is higher than the quantum dots 14 and lower than the first barrier layer 16 and the second barrier layer 20.

  When infrared rays are incident on the photoelectric conversion layer 4, the electrons 30 bound to the transition source level 28 of the quantum dots 14 absorb the infrared rays and transition to the quantum level of the quantum well layer 18. Next, the electrons 32 excited in the quantum well layer escape from the quantum well layer 18 by the tunnel effect or thermal excitation and become photocarriers 34. Thereafter, the photocarrier 34 becomes a photocurrent by a voltage applied to the photoelectric conversion layer 4 and is taken out to the outside.

  FIG. 5 is a partially enlarged view of a photoelectric conversion layer in which the quantum well layer 18 is not provided in the first barrier layer 16. 6 is an energy band diagram of the photoelectric conversion layer taken along line VI-VI in FIG. When infrared rays are incident on the photoelectric conversion layer, the electrons 30 bound to the transition source level 28 of the quantum dots 14 absorb the infrared rays and transition to the excitation level 36 of the quantum dots 14. Next, a part of the excited electrons 38 escapes from the quantum dots 14 by the tunnel effect or thermal excitation, and becomes photocarriers. However, many excited electrons 38 are relaxed to the transition source level 28 and cannot escape to the intermediate layer. For this reason, as shown in FIG. 5, with the structure in which the quantum dots 14 are simply covered with the first barrier layer 16, the excited electrons 38 are difficult to escape to the intermediate layer 22, and the sensitivity of the quantum dot infrared detector is sufficiently high. It cannot be increased.

  On the other hand, in the present quantum dot infrared detector 2, as shown in FIG. 4, electrons 32 that have absorbed infrared rays transition to the quantum well layer 18 that is spatially separated from the quantum dots 14 (or the quantum dots 14. After the transition to the excited level of the quantum well 18). Therefore, the excited electrons 32 are not easily relaxed to the transition source level 28 of the quantum dot 14. For this reason, the residence time of the excited electrons in the quantum well becomes longer, and the excited electrons easily escape to the intermediate layer. Therefore, the sensitivity of the present quantum dot infrared detector 2 is increased.

  FIG. 7 is a diagram for explaining the relationship between the thickness of the quantum well layer 18 and the sensitivity of the quantum dot infrared detector 2 of the present embodiment. The horizontal axis represents the thickness (arbitrary unit) of the quantum well layer 18. The vertical axis represents the sensitivity (arbitrary unit) of the quantum dot infrared detector 2. As shown in FIG. 7, the sensitivity of the quantum dot infrared detector 2 does not change so much while the quantum well layer 18 is thin, but increases as the quantum well layer 18 becomes thick and eventually reaches a maximum value. Thereafter, the sensitivity of the quantum dot infrared detector 2 decreases.

  When the quantum well layer 18 becomes thicker, the excited electrons 32 easily stay in the quantum well layer 18, and the sensitivity increases. On the other hand, when the quantum well layer 18 is further thickened, the first barrier layer 16 is too far from the quantum dot 14 and the quantum confinement effect of the excitation level of the quantum dot by the first barrier layer 16 is reduced. For this reason, the infrared absorptivity of the photoelectric conversion layer 4 is lowered, and the sensitivity is lowered.

  FIG. 8 is a diagram for explaining the relationship between the thickness of the quantum well layer 18 and the S / N ratio (signal to noise ratio) of the quantum dot infrared detector 2 of the present embodiment. The horizontal axis represents the thickness (arbitrary unit) of the quantum well layer 18. The vertical axis represents the S / N ratio (arbitrary unit) of the quantum dot infrared detector 2. The S / N ratio in FIG. 8 is linearly displayed.

  As shown in FIG. 8, the S / N ratio of the quantum dot infrared detector 2 increases with the thickness of the quantum well layer 18 and eventually reaches a maximum value, and then decreases. Such a change in the S / N ratio coincides with the sensitivity change in FIG. However, the S / N ratio is larger than the sensitivity of FIG. This is considered because the quantum well layer 18 not only promotes the generation of the photocarriers 34 (see FIG. 4), but also suppresses dark current that becomes noise.

  Next, the influence of the barrier layers 16 and 20 on the S / N ratio of the present quantum dot infrared detector 2 will be described. FIG. 9 is an energy band diagram of the photoelectric conversion layer 4 along the line IX-IX in FIG. That is, it is an energy band diagram along a path (IX-IX line) that does not cross the quantum dot 14 vertically. Dark current that causes noise flows along such a path.

  Electrons 40 (hereinafter referred to as dark current electrons) that form a dark current first pass through the barrier 17 in which the second barrier layer 20 and a part 16a of the first barrier layer are integrated by a tunnel effect or thermal excitation. Pass through and enter the quantum well layer 14. Thereafter, the dark current electrons 40 further pass through the remaining portion 16b of the first barrier layer 16 by the tunnel effect or thermal excitation, and move to the intermediate layer 22 on the opposite side. At this time, the barrier layers 16 and 20 inhibit the flow of the dark current electrons 40 and reduce the dark current.

  On the other hand, as apparent from FIGS. 3 and 4, the only barrier layer through which the electrons 32 excited by infrared rays must pass is a portion 16 b of the first barrier layer 16. Therefore, the number of excited electrons that are prevented from escaping to the intermediate layer 22 by the barrier layers 16 and 20 is smaller than that of dark current electrons. Excited electrons that have become a photocurrent travel on the intermediate layer and are blocked by the next barrier layers 16 and 20. Of the blocked electrons, those trapped in the well layer are relaxed to quantum dots. Will be caused. Electrons relaxed to the transition source level are reused for absorption and excitation of infrared rays to generate a photocurrent, so that the photocurrent decrease due to such inhibition is smaller than the dark current. On the other hand, there is an effect that excited electrons increase due to the quantum confinement effect of the barrier layers 16 and 20 and the photocarriers 34 that escape to the intermediate layer 22 also increase. As a result, the photocurrent increases.

  As described above, the barrier layers 16 and 20 increase the photocurrent while decreasing the dark current. For this reason, the S / N ratio is improved.

(2) Manufacturing Method Next, the structure of the quantum dot infrared detector 2 will be described in more detail according to the manufacturing method.

-Lower electrode layer formation process (see Figs. 1 and 2)-
First, an n-type GaAs layer to be the lower electrode layer 6a is grown on the semi-insulating GaAs substrate 9. The thickness of this n-type GaAs layer is, for example, 1000 nm. The n-type dopant is, for example, Si. The concentration of this n-type dopant is, for example, 2 × 10 ¹⁸ cm ⁻³ . The growth method is, for example, a molecular beam epitaxy method (hereinafter the same). The substrate temperature during growth (hereinafter referred to as substrate temperature) is, for example, 600 ° C.

Next, an i-type (insulating) Al _x Ga _1-x As layer (0 <x <1; hereinafter the same) is grown as the lowermost intermediate layer 22a. The composition x of Al is, for example, 0.2. The thickness is, for example, 50 nm.

-Growth process of underlying barrier layer (see Fig. 3)-
Next, the substrate temperature is lowered to 470.degree. After that, 1ML (molecular layer) is grown as AlAs which becomes the second barrier layer 20 (hereinafter referred to as a base barrier layer).

-Quantum dot growth process (see Figure 3)-
The underlying barrier layer 20 is irradiated with In molecular beams and As molecular beams to grow InAs corresponding to 2.0 ML. The supply rate of In and As is 0.2 ML / s in terms of the growth rate of the InAs layer. As a result, the InAs layer exceeds the critical thickness, and the InAs layer becomes the quantum dots 14. That is, self-assembled quantum dots are formed. The height of this quantum dot 14 is about 1.5 nm. The diameter of the quantum dot 14 is about 15 nm. The density of the quantum dots 14 is about 2 × 10 ¹¹ cm ⁻² .

-Growth process of lower buried barrier layer (see Fig. 3)-
Next, 3 ML of AlAs which becomes a part 16a of the first barrier layer 16 (hereinafter referred to as a lower buried barrier layer) is grown.

-Growth process of quantum well layer (see Fig. 3)-
Next, Al _x Ga _1-x As having a thickness of 6 ML, which becomes the quantum well layer 18, is grown. The composition x of Al is, for example, 0.2.

-Growth process of upper buried barrier layer (see Fig. 3)-
Next, AlAs having a thickness of 6 ML, which becomes the remaining portion 16b (hereinafter referred to as an upper buried barrier layer) of the first barrier layer 16, is grown.

-Intermediate layer growth process (see Fig. 3)-
Next, the substrate temperature is raised to 600 ° C. Thereafter, an i-type Al _x Ga _1-x As layer having a thickness of 50 nm is grown as the intermediate layer 22. The composition x of Al is, for example, 0.2.

  Next, the above-described “underlying barrier layer growth step” to “intermediate layer growth step” are sequentially repeated 29 times to form the photoelectric conversion layer 4 (see FIG. 2).

-Upper electrode layer formation process (see Figs. 1 and 2)-
Next, an n-type GaAs layer to be the upper electrode layer 6b is grown (see FIGS. 1 and 2). The thickness of this n-type GaAs layer is, for example, 1000 nm. The n-type dopant is, for example, Si. The concentration of this n-type dopant is, for example, 2 × 10 ¹⁸ cm ⁻³ . The substrate temperature is 600 ° C., for example.

-Element fabrication process-
Next, an etching mask corresponding to the upper electrode layer 6b and the photoelectric conversion layer 4 is formed by lithography on the surface of the growth layer formed by the above steps (see FIG. 1). At this time, etching masks are arranged at regular intervals in two orthogonal directions in the surface of the growth layer. Thereafter, using this etching mask, the upper electrode layer 6b and the photoelectric conversion layer 4 are etched to expose the lower electrode layer 6a.

  As described above, a plurality of stacked structures in which the photoelectric conversion layer 4 and the upper electrode layer 6b are stacked are formed on the lower electrode layer 6a. This laminated structure is two-dimensionally arranged and becomes a pixel of an infrared image sensor described later. This pixel is a square with one side of, for example, 25 μm. The pixel pitch is, for example, 30 μm.

  Next, metal electrodes 8a and 8b are formed on the lower electrode layer 6a and the upper electrode layer 6b, respectively. The metal electrodes 8a and 8b are metal films having high reflectivity, such as metal films such as gold, silver, and aluminum, or composite films such as AuGe / Au. Therefore, the metal electrode 8 b on the upper electrode layer 6 b also functions as an infrared reflective film that has passed through the photoelectric conversion layer 4. One metal electrode 8a on the lower electrode layer 6a may be provided for each pixel, or one or several metal electrodes may be provided as a common metal electrode shared by each pixel.

  Next, the entire processed surface excluding the metal electrodes 8a and 8b is covered with a SiN (or SiON) protective film. Thereafter, the GaAs substrate 9 is cut into a predetermined size.

  As described above, a plurality of infrared detectors 2 arranged two-dimensionally are formed on a common substrate. Here, the plurality of infrared detectors 2 and the semiconductor substrate 9 form an infrared sensor array.

  In order to operate these infrared detectors 2, a voltage of 1 V, for example, is applied between the lower electrode layer 6a and the upper electrode layer 6b via the metal electrodes 8a and 8b. Thereby, the infrared detector 2 comes to detect infrared rays having a wavelength of 8 to 10 μm. The infrared detection sensitivity is about 1.2 times that in the case where the quantum barrier layer 18 is not provided in the first barrier layer 16. Further, the S / N ratio is about 1.7 times. Thus, according to the present embodiment, both the sensitivity and S / N ratio of the quantum dot infrared detector are improved.

(Embodiment 2)
FIG. 10 is a schematic diagram illustrating a cross section of the infrared image sensor 41 of the present embodiment.

  Hereinafter, according to the manufacturing method, the structure of the infrared image sensor 41 of the present embodiment will be described.

  First, an optical signal processing device 46 is prepared. The optical signal processing device 46 processes the optical signal (that is, photocurrent) detected by the infrared sensor array 42 of the first embodiment, and generates image data of an infrared image projected on the back surface of the infrared sensor array 42. Integrated circuit device (read circuit: for example, CMOS circuit). For example, the optical signal processing device 46 generates a digital signal corresponding to the photocurrent intensity generated by each pixel, and outputs the digital signal according to the pixel arrangement order. Here, the optical signal processing device 46 has a plurality of electrodes 44 corresponding to the metal electrodes 8 a and 8 b of the infrared sensor array 42.

  Next, In bumps 48 are placed on the metal electrodes 8 a and 8 b of the infrared sensor array 42.

  Next, the infrared sensor array 42 and the optical signal processing device 46 are overlapped so that the metal electrodes 8a and 8b of the infrared sensor array 42 and the electrode 44 of the optical signal processing device 46 face each other through bumps.

  Finally, the metal electrodes 8a and 8b and the electrode 44 are connected by a reflow process. The infrared image sensor 41 is completed through the above steps.

  When the infrared image sensor 41 is operated, the optical signal processing device 46 supplies a drive voltage (for example, 1 V) to each pixel of the infrared sensor array 42. Each pixel of the infrared sensor array 42 receives the infrared ray 12, generates a photocurrent, and supplies it to the optical signal processing device 46. The optical signal processing device 46 performs analog-digital conversion on the photocurrent and sequentially outputs it in accordance with the pixel arrangement order. At this time, in this embodiment, since the sensitivity of each pixel (quantum dot infrared detector) is improved, a clear image can be obtained.

(Embodiment 3)
FIG. 11 is a partially enlarged view illustrating the photoelectric conversion layer of the quantum dot infrared detector according to the present embodiment. In the first embodiment, the quantum well layer 18 is in contact with the quantum dots 14 as shown in FIG. However, in the present embodiment, as shown in FIG. 11, the quantum well layer 18 a is not in contact with the quantum dots 14. Except for this point, the structure of the infrared detector is substantially the same as the infrared detector of the first embodiment.

FIG. 12 is an energy band diagram of the photoelectric conversion layer taken along line XII-XII in FIG.
In the present embodiment, as shown in FIG. 12, the quantum well layer 18a is spatially separated from the quantum dots 14 by the lower buried barrier layer 16a. Therefore, it is difficult for the excited electrons 32 to relax to the transition source level 28 of the quantum dot 14 as compared with the first embodiment. Therefore, the excited electrons are easily escaped to the intermediate layer 22.

  As described above, even if the quantum well layer 18a is not in contact with the quantum dots 14, the sensitivity of the quantum dot infrared detector can be improved.

(Embodiment 4)
FIG. 13 is a schematic diagram illustrating a photoelectric conversion layer of the quantum dot infrared detector according to the present embodiment. In the first embodiment, as shown in FIG. 3, the quantum well layer 18 is a single layer. However, in this embodiment, as shown in FIG. 13, two quantum well layers are provided. Further, the buried barrier layer 16 of the present embodiment has three barrier layers 16c, 16d, and 16e corresponding to the two quantum well layers 18b and 18c. Except for the above points, the structure of the quantum dot infrared detector is substantially the same as that of the quantum dot infrared detector of the first embodiment. Here, the thickness of the quantum well layers 18b and 18c is 2ML. The thicknesses of the barrier layers 16c, 16d, and 16e are 3ML, 2ML, and 6ML, respectively.

  As described above, even if a plurality of quantum well layers are provided, the sensitivity of the quantum dot infrared detector can be improved.

(Embodiment 5)
FIG. 14 is a partially enlarged view illustrating the photoelectric conversion layer of the quantum dot infrared detector according to the present embodiment. As shown in FIG. 3, the quantum dot infrared detector 2 of Embodiment 1 has a base barrier layer 20 in contact with the bottom surface of the quantum dots. However, the quantum dot infrared detector of the present embodiment does not have such an underlying barrier layer 20 as shown in FIG. Except for this point, the structure of the present quantum dot infrared detector is substantially the same as the infrared detector of the first embodiment.

  The absence of the underlying barrier layer 20 weakens the quantum confinement effect of the excited level by the barrier layer. However. Since the side surface and the top of the quantum dot 14 are covered with the barrier layer 16, the quantum confinement effect is exhibited. Therefore, the sensitivity of the quantum dot infrared detector is higher due to the barrier layer 16. This increased sensitivity is further enhanced by the quantum well layer 18.

  In the above embodiment, the quantum dots, the first barrier layer, the second barrier layer, the quantum well layer, the intermediate layer, and the like are formed of InAs, AlAs, or AlGaAs. However, these semiconductor structures can be formed from various materials. For example, a quantum dot, a first barrier layer, a second barrier layer, a quantum well layer, and an intermediate layer are respectively made of InAs, GaAs, AlAs, InP, GaP, AlP, InSb, GaSb, AlSb, InN, GaN, You may form by the semiconductor selected from the group which consists of AlN, or the mixed crystal of these semiconductors.

2 ... Quantum dot infrared detector 4 ... Photoelectric conversion layers 6a, 6b ... Electrode layer 14 ... Quantum dot 16 ... First barrier layer 18 ... Quantum well layer 20 ... Second barrier layer 22, 22a ... intermediate layer 41 ... infrared image sensor 42 ... infrared sensor array

Claims (7)

A quantum dot; a first barrier layer that covers the quantum dot and has a wider energy gap than the quantum dot; and an energy gap that is provided above the first barrier layer and below the quantum dot and wider than the quantum dot. A photoelectric conversion layer having an intermediate layer narrower than the first barrier layer, and a quantum well layer provided in the first barrier layer and having an energy gap wider than the quantum dots and narrower than the first barrier layer; ,
Electrode layers provided on both sides of the photoelectric conversion layer,
Equipped with a quantum dot infrared detector. In the quantum dot type infrared detector according to claim 1,
The quantum well layer is in contact with the quantum dots,
Quantum dot infrared detector. In the quantum dot type infrared detector according to claim 1,
The quantum well layer is not in contact with the quantum dots,
Quantum dot infrared detector. In the quantum dot type infrared detector according to any one of claims 1 to 4,
A plurality of the quantum well layers are provided.
Quantum dot infrared detector. In the quantum dot type infrared detector according to any one of claims 1 to 3,
Furthermore, the photoelectric conversion layer has a second barrier layer that is in contact with the bottom surface of the quantum dot and has an energy gap wider than that of the quantum well layer and the intermediate layer.
Quantum dot infrared detector. In the quantum dot type infrared detector according to any one of claims 1 to 5,
The quantum dots, the first barrier layer, the second barrier layer, the quantum well layer, and the intermediate layer are respectively InAs, GaAs, AlAs, InP, GaP, AlP, InSb, GaSb, AlSb, InN. A semiconductor selected from the group consisting of GaN, AlN, or a mixed crystal of the semiconductor,
Quantum dot infrared detector. A quantum dot; a first barrier layer that covers the quantum dot and has a wider energy gap than the quantum dot; and an upper side of the first barrier layer and a lower side of the quantum dot; A photoelectric layer having an intermediate layer that is wider and narrower than the first barrier layer, and a quantum well layer that is provided in the first barrier layer and has an energy gap wider than that of the quantum dots and narrower than that of the first barrier layer. An infrared sensor array in which two-dimensionally arranged quantum dot infrared detectors including a conversion layer and electrode layers provided on both sides of the photoelectric conversion layer;
An optical signal processing device that processes optical signals detected by the respective quantum dot infrared detectors and generates image data of an infrared image projected on the infrared sensor array;
Infrared image sensor.

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