JP6520166B2 - Infrared detection element, method for manufacturing the same, and infrared detector - Google Patents

Description

  The present invention relates to an infrared detection device in which semiconductor quantum dots are formed in a light absorption layer, a method of manufacturing the same, and an infrared detector.

  In recent years, an infrared detection element has attracted attention as a sensor for detecting a heat source, measuring a temperature, detecting a specific gas, or a camera for night vision. In addition, an image sensor (infrared detector) configured by arranging the infrared detection elements in a one-dimensional or two-dimensional manner is also attracting attention.

  Many proposals have been made for the structure and materials of such infrared detection elements. The quantum dot infrared detection element (QDIP: Quantum Dot Infrared Photodetector) by which the semiconductor quantum dot was formed in the light absorption layer is the example.

  The QDIP has a structure in which the quantum dot is three-dimensionally surrounded by a semiconductor material having a band gap larger than that of the quantum dot constituent material. As a result, electrons and holes are strongly confined in the quantum dot, and discrete energy levels (subbands) are formed. Then, when an infrared ray having a wavelength corresponding to the energy difference between the sub-bands is incident, an inter-band transition in which carriers are transitioned from a low energy level to a high energy level occurs, and an excitation current can be detected. Since this excitation current is dependent on the wavelength of incident light, QDIP has discrete spectral sensitivity.

  Therefore, in order to perform temperature-dependent spectrum identification and gas detection with high accuracy, the spectral sensitivity of QDIP needs to be generated in the spectrum in order to perform extraction of the spectrum depending on the gas substance with high accuracy.

の式１で表される。ここで、Ｒ_ｐは検知波長λ_ｐに対する受光感度、Ａは赤外線検出素子の受光面積、Δｆは赤外線検出素子の帯域幅、ｉ_ｎはノイズ電流である。 As described above, QDIP is an infrared detection element whose electric conductivity changes due to light absorption, and the relative detectability D ^* , which is a performance index thereof, is

It is expressed by Equation 1. Here, R _p is the light reception sensitivity with respect to detecting the wavelength lambda _p, A light-receiving area of the infrared detection element, Delta] f is the bandwidth of the infrared detection element, i _n is the noise current.

の式２で表される。ここでｅは素電荷、Ｉは暗電流である。 The main cause of the noise current i _n is dark current,

Is expressed by Equation 2. Here, e is an elementary charge and I is a dark current.

Formula 1, from Equation 2, in order to constitute an infrared detecting element having a high specific detectivity D ^* for the desired wavelength, as well as increase the light receiving sensitivity R _p at a particular wavelength lambda _p, reduce the dark current I It turns out that doing is effective.

の式３で表される。ここで、ηは量子効率、ｇは光伝導利得ｇ、ｅは素電荷、ｈはプランク定数、ｃは暗電流である。 In addition, the light reception sensitivity R _{p of} QDIP, which is a photoconductive infrared detection device, is

It is expressed by Equation 3. Here, η is a quantum efficiency, g is a photoconductive gain g, e is an elementary charge, h is a Planck constant, and c is a dark current.

From Equation 3, it is understood that it is effective to increase the quantum efficiency η and the photoconductive gain g in order to have a large light receiving sensitivity R _p with respect to the desired wavelength λ _p .

の式４で表される。ここで、τ_Ｔは赤外線検出素子を流れるキャリア走行時間、τ_Ｒはキャリアの再結合時間である。 The photoconductive gain g is

It is represented by Formula 4. Here, τ _T is a carrier transit time flowing through the infrared detection element, and τ _R is a carrier recombination time.

Therefore, in order to have a large photoconductive gain g, it is necessary to shorten the carrier transit time τ _T and to lengthen the recombination time τ _R.

の式５で表される。 Here, assuming that the length of the infrared detection element is L, the applied voltage is V, and the electric conductivity is μ, the carrier traveling time τ _T is

Is expressed by Equation 5.

As described above, the higher the electric conductivity μ, the shorter the carrier transit time τ _{T and the} larger the photoconductive gain g. Then, the larger the photoconductive gain g, the higher the light receiving sensitivity and the relative detection ability of the infrared detecting element.

  There are Patent Document 1 and Non-Patent Document 1 as a technique related to an infrared detection element in which the light reception sensitivity is improved in QDIP. For example, in Non-Patent Document 1, a quantum dot, which is one of QDIPs, has a DWELL (Dot-in-Well) structure in a quantum well to improve the transition probability of electrons in the quantum dot, whereby an infrared detection element To increase the sensitivity of

Patent No. 4066002

S. Krishna et al., APPLIEDPHYSICSLETTERS 83, 14, No. 2745-2747 (issued in 2003)

  As described above, in order to improve the light reception sensitivity of QDIP, it is necessary to improve the quantum efficiency η and the photoconductive gain g.

  However, in the method of improving the quantum efficiency according to Non-Patent Document 1, there is a problem that there is a high probability that electrons conducted out of the quantum dot due to light absorption and conducted are captured by another quantum dot. This means that the photoconduction gain is reduced due to the short recombination time, and the light reception sensitivity can not be improved.

As described above, in order to improve the light receiving sensitivity R _p , it is necessary to increase the photoconductive gain g. However, since the photoconductive gain g is proportional to the dark current I, and noise current i _n Increasing the photoconductive gain g increases, the ratio detectability D ^* a can not be efficiently improved.

  Accordingly, the main object of the present invention is to provide an infrared detection device having high specific detectability, a method of manufacturing the same, and an infrared detector.

  In order to solve the above problems, the invention relating to an infrared detection device including a semiconductor quantum dot includes a carrier supply layer including an energy level of a quantum level that captures electrons conducting in the infrared detection device, and a semiconductor quantum dot Coulomb interaction with the first quantum level of the energy level at which the semiconductor quantum dot captures electrons from the carrier supply layer, the energy level lower than the first quantum level, and electrons trapped in the first quantum level And a light absorption layer having at least three quantum levels of a second quantum level whose energy level changes to the fourth quantum level, and a third quantum level whose energy level is lower than the second quantum level, and a carrier And a carrier conduction layer having a subband level substantially equal in energy level to the quantum level in the supply layer, and the light absorption layer absorbs light of a predetermined wavelength to The fourth quantum level is a quantum level in the carrier supply layer by the fact that the electrons trapped in the child level are excited to the third quantum level and the number of electrons trapped in the first quantum level decreases. When the energy level of the carrier supply layer is approximately equal to the energy level of the sub-band level, electrons trapped in the quantum level in the carrier supply layer conduct the sub-band level via the fourth quantum level.

  The invention according to the infrared detection device is characterized in that the infrared detection elements are arranged in one or two dimensions.

  Furthermore, the invention according to the method of manufacturing an infrared detection device including a semiconductor quantum dot forms a carrier supply layer including an energy level of a quantum level that captures electrons conducted through the infrared detection device, and includes a semiconductor quantum dot Coulomb interaction with the first quantum level of the energy level at which the semiconductor quantum dot captures electrons from the carrier supply layer, the energy level lower than the first quantum level, and electrons trapped in the first quantum level Supply the light absorption layer with at least three quantum levels, the second quantum level whose energy level changes to the fourth quantum level, and the third quantum level whose energy level is lower than that of the second quantum level And forming a carrier conduction layer having a subband level substantially equal to the quantum level in the carrier supply layer with respect to the quantum level in the carrier supply layer. The features.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the infrared detection element which improved ratio detection ability efficiently, its manufacturing method, and an infrared detector.

It is sectional drawing of the infrared detection element concerning 1st Embodiment. It is the figure which showed the band structure when a positive bias voltage is applied to a function part. It is a band structure which shows a mode at the time of the electron of a 1st quantum level transitioning to a 3rd quantum level. It is the figure which showed the detailed structure of the carrier supply layer in a infrared detection element, a light absorption layer, and a carrier conduction layer. It is a figure showing energy band structure in a section which does not contain columna quantum dots when positive bias voltage is impressed. It is the schematic of the molecular beam epitaxial device used when manufacturing an infrared detector. It is a figure which shows the energy band structure of the infrared detection element concerning 2nd Embodiment. It is the figure which showed the energy band structure of the infrared detection element concerning 3rd Embodiment.

First Embodiment
Hereinafter, the first embodiment of the present invention will be described in detail. FIG. 1 is a schematic view showing a cross section of the infrared detection element 2 according to the first embodiment. The infrared detector is configured by arranging the infrared detection elements 2 one-dimensionally or two-dimensionally.

  The infrared detection element 2 includes a substrate unit 10, a functional unit 20, and a contact unit 30 provided to sandwich the functional unit 20.

  The substrate unit 10 is formed of a semiconductor substrate 11 and a buffer layer 13 provided on the semiconductor substrate 11.

  The functional unit 20 is formed by sequentially laminating the lower layer 21, the carrier supply layer 23, the light absorption layer 25, and the carrier conductive layer 27. The light absorption layer 25 includes a plurality of quantum dots 25aa.

  The contact portion 30 includes a lower contact layer 31 provided between the lower layer 21 and the buffer layer 13, a lower electrode 33 joined to the lower contact layer 31, and an upper contact layer provided on the carrier conductive layer 27. 35 is formed by the upper electrode 37 joined to the upper contact layer 35.

The buffer layer 13 is formed of the same material as the semiconductor substrate 11. The lower contact layer 31 is a semiconductor doped in n ⁺ -type.

  In FIG. 1, the power supply 4 and the ammeter 6 are connected in series between the lower electrode 33 and the upper electrode 37. As a result, a predetermined voltage is applied to the functional unit 20. In this state, when the quantum dots 25aa of the light absorption layer 25 absorb infrared light, the electric conductivity of the functional unit 20 changes, and electrons are conducted. Therefore, the size of the conduction electron is proportional to the amount of infrared radiation absorbed by the quantum dot 25aa. The ammeter 6 detects an amount of infrared radiation as a current by detecting a current due to conduction electrons.

  FIG. 2 is a diagram showing a band structure of the functional unit 20 when a positive bias voltage is applied to the functional unit 20. As shown in FIG. The left and right direction in FIG. 2 corresponds to the vertical direction in FIG. 1, the left side corresponds to the lower contact layer 31 side, and the right side corresponds to the upper contact layer 35 side. Moreover, in the same figure, "(circle)" mark has shown the electron.

  The carrier supply layer 23 has a quantum level La with a large density of states. For this reason, most of the electrons conducted from the lower contact layer 31 are captured by the quantum level La. However, due to thermal excitation, a few electrons transition to the interlayer continuous state level Lb and reach the light absorption layer 25.

  The light absorption layer 25 has at least three or more discrete quantum levels. In FIG. 2, three quantum levels in which the energy decreases in the order of the first quantum level L1, the second quantum level L2, and the third quantum level L3 are shown.

  The carrier conduction layer 27 has, for example, a subband level Lm formed of a plurality of quantum structures and an intermediate layer continuous state level Lb. Then, most of the electrons having reached the carrier conductive layer 27 conduct the subband level Lm lower than the intermediate layer continuous state level Lb to reach the upper contact layer 35. As a result, the electrical conductivity of the subband level Lm is higher than that of the intermediate layer continuous state level Lb.

(Operating principle)
Next, the operation of the infrared detection element 2 configured as described above will be described. FIG. 3 is a band structure showing a state when an electron of the first quantum level L1 transitions to the third quantum level L3.

  When an electron of the first quantum level L1 absorbs light (infrared ray) having energy equal to the energy difference between the first quantum level L1 and the third quantum level L3, this electron transitions to the third quantum level L3. Do.

  The energy level of the second quantum level L2 changes according to the number of electrons present in the first quantum level L1. Therefore, when the electron of the first quantum level L1 transitions to the third quantum level L3 and the number of electrons of the first quantum level L1 decreases, the Coulomb interaction weakens and the energy of the second quantum level L2 The level goes down. The second quantum level L2 whose energy level is lowered is referred to as a fourth quantum level L4. At this time, the energy difference between the second quantum level L2 and the fourth quantum level L4 may be higher than the energy levels of the quantum level La and the subband level Lm.

  Then, when the fourth quantum level L4 matches the quantum level La of the carrier supply layer 23 and the subband level Lm of the carrier conductive layer 27, the electrons of the carrier supply layer 23 form the fourth quantum level L4 and the subband Conducting with the level Lm causes conduction to the upper contact layer 35 side.

  That is, in the infrared detection element 2 according to the structure of the first embodiment, when electrons of the first quantum level L1 absorb infrared rays of energy equal to the energy difference between the first quantum level L1 and the third quantum level L3. The electrons of the quantum level La are conducted to the fourth quantum level L4 and the subband level Lm. This conduction can be regarded as a change in the electrical conductivity of the functional unit 20 as the infrared detection element 2 absorbs the infrared light.

  On the other hand, when the electrons of the first quantum level L1 do not absorb infrared rays, a few electrons of the electrons of the quantum level La are thermally excited and transition to the energy level of the interlayer continuous state level Lb having low electrical conductivity. Then, the upper contact layer 35 is reached. The conduction of electrons at this time is detected as dark current.

  Therefore, only when the electron of the first quantum level L1 absorbs infrared light, the electron of the quantum level La passes the fourth quantum level L4, conducts the subband level Lm, and this is detected as a photocurrent . The conduction at this time continues until it is captured again in the first quantum level L1 after the recombination time.

As described above, the infrared detection element 2 changes its electrical conductivity due to absorption of infrared light, and the electrical conductivity of the current (photocurrent) flowing when the infrared detection element 2 absorbs infrared light in the light absorption layer is high. Indicates On the other hand, when the infrared ray is not absorbed, the infrared detection element 2 exhibits low electric conductivity. The current flowing at this time is a dark current. The carrier transit time τ _T when the dark current flows is reduced from Equations 5 and 4. As a result, the photoconductive gain of the photocurrent with respect to the dark current is increased, and the relative detectability of the infrared detection element 2 is improved.

(Example of configuration)
Next, a configuration example of the infrared detection element 2 will be described in detail. FIG. 4 is a view showing a detailed configuration of the carrier supply layer 23, the light absorption layer 25, and the carrier conductive layer 27 in the infrared detection element 2 shown in FIG.

  The carrier supply layer 23 includes a first intermediate layer 23a with a thickness of several tens of nm, a quantum well layer 23b with a thickness of several nm formed on the first intermediate layer 23a, and a thickness of several tens with a thickness of The second intermediate layer 23c of nm is formed.

  The quantum well layer 23 b is formed of a material having a smaller band gap than the first intermediate layer 23 a and the second intermediate layer 23 c. The band gap of the second intermediate layer 23c is larger than that of the first intermediate layer 23a.

  The first intermediate layer 23a may be, for example, AlGaAs, the quantum well layer 23b may be, for example, GaAs, and the second intermediate layer 23c may be, for example, AlGaAs having an Al component ratio higher than that of the first intermediate layer 23a.

  The upper and lower portions of the quantum well layer 23 b are quantum wells formed by being covered with a material having a band gap larger than that of the quantum well layer 23 b. Based on quantum mechanics, electrons bound to the quantum well form discrete levels. This level is the quantum level La in FIG.

  The light absorption layer 25 is a quantum dot layer 25a including a plurality of quantum dots 25aa planarly formed on the second intermediate layer 23c and a quantum dot embedded layer 25ab surrounding and under the quantum dots 25aa. The third intermediate layer 25b having a thickness of several tens of nm stacked on the dot layer 25a is formed. The quantum dot layer 25a may be, for example, an InAs quantum dot formed in a GaAs quantum dot buried layer, and the third intermediate layer 25b may be, for example, AlGaAs.

  Based on quantum mechanics, electrons bound to quantum dots can only take discrete energy levels. Then, three of the plurality of levels in the quantum dot layer correspond to the first quantum level L1, the second quantum level L2, and the third quantum level L3. In addition, discrete quantum levels of the conduction band of the quantum dot are generally equal to the energy of infrared rays with a wavelength of several μm to several tens of μm.

  The carrier conductive layer 27 includes columna quantum dots 27a formed by connecting a plurality of quantum dots in the longitudinal direction, and the periphery of the columna quantum dots 27a is covered with a fourth intermediate layer 27b.

  Most columna quantum dots 27 a are stacked directly on the quantum dots 25 aa of the light absorption layer 25. The fourth intermediate layer 27b is, for example, AlGaAs, and the columnar quantum dots 27a can be exemplified by InGaAs. In columner quantum dots 27a, discrete energy levels of a plurality of quantum dots forming the quantum dots are vertically coupled in the figure, and form coupling levels corresponding to subband levels Lm in FIG.

FIG. 5 is a diagram showing the energy band structure of the infrared detection element which does not include the columner quantum dots 27a. As in the case of FIG. 2, the horizontal direction of FIG. 5 corresponds to the vertical direction of FIG. 4, the left side of FIG. 5 corresponds to the lower contact layer 31 side, and the right side corresponds to the upper contact layer 35 side.
However, no quantum level is formed in the carrier conduction layer because columner quantum dots 27a are not included, and therefore no subband level is also formed.

  In such a configuration, a case is considered where infrared light of energy equal to the energy difference between the first quantum level L1 and the third quantum level L3 is absorbed in the light absorption layer 25. At this time, electrons of the first quantum level L1 transition to the third quantum level L3. As a result, it is assumed that the energy level of the second quantum level L2 is lowered to coincide with or close to the quantum level La.

  Even if electrons of the second quantum level L2 are to conduct in such a state, the transition to the interlayer continuous state level Lb can not be made because the energy difference between the second quantum level L2 and the interlayer continuous state level Lb is large. Therefore, the electrons of the second quantum level L2 can not be conducted. Therefore, even if absorption of infrared radiation occurs in the light absorption layer 25, it becomes difficult to detect the photocurrent. It goes without saying that there are no electrons that transition to the interlayer continuous state level Lb due to thermal excitation, but it is needless to say that the number is very small.

  Therefore, by forming the columner quantum dots 27a, the photocurrent can be conducted efficiently through the subband level Lm.

(Production method)
Next, a method of manufacturing the infrared detection element 2 will be described. FIG. 6 schematically shows a molecular beam epitaxial (MBE) apparatus used when manufacturing the infrared detection element 2.

  A semiconductor substrate 11 of semi-insulating non-doped GaAs of plane orientation (001) is mounted on the substrate holder 51 in the vacuum chamber 50. The substrate holder 51 is provided with an electric heater for adjusting the temperature of the semiconductor substrate 11. Further, the substrate holder 51 is provided with a rotation mechanism for rotating the semiconductor substrate 11 so that the supplied raw material has a uniform thickness regardless of the positions of the raw material supply sources 52 to 53.

  The first source supply source 52 is set as In, the second source supply source 53 is Ga, the third source supply source 54 is As, which is a group V element, as a target material. . In the following, the semiconductor substrate 11 is manufactured while rotating unless otherwise specified.

  Subsequently, the temperature of the semiconductor substrate 11 is raised by irradiating the semiconductor substrate 11 made of GaAs with As, which is a V-group element, from the third raw material supply source 54, thereby forming a natural oxide film on the semiconductor substrate 11 Remove. After removing the oxide film, the substrate temperature is set to about 580 ° C., and the buffer layer 13 having a thickness of 500 nm is formed. The buffer layer 13 is made of the same non-doped GaAs as the semiconductor substrate 11.

Next, an n-type lower contact layer 31 made of GaAs doped with Si atoms at a concentration of about 2 × 10 ¹⁸ cm ⁻³ is formed to a thickness of 500 nm.

  Further, an i-type lower layer 21 composed of non-doped GaAs and an i-type first intermediate layer 23a composed of AlGaAs are stacked with a thickness of 50 nm, and then a quantum well layer 23b composed of GaAs doped with Si atoms With a thickness of 5 nm as a representative value. Thereafter, an i-type second intermediate layer 23c made of non-doped AlGaAs is stacked.

  Subsequently, after forming GaAs with a thickness of 2 nm on the second intermediate layer 23c, the substrate temperature is lowered to about 490.degree. Then, while irradiating As from the third raw material supply source 54, In is supplied from the first raw material supply source 52 by an amount corresponding to a thickness equivalent to two atomic layers, to form quantum dots 25aa made of InAs.

  At this time, the InAs layer grows into an island-like three-dimensional shape instead of a two-dimensional thin film due to a strain generated due to a difference in lattice constant between InAs and GaAs. This growth mode is called SK (Stranski-Krastanov) mode.

In this manner, the quantum dots are formed in high density on the plane side by side and become a layer of the quantum dots 25aa. The typical diameter of the quantum dot is about 20 to 30 nm and the height is about 3 to 7 nm, and the number density per square centimeter is about 1 × 10 ¹¹ .

Subsequently, doping is performed on the top of the quantum dot 25aa. The dopant is, for example, a Si atom, and by irradiating this Si atom, quantum dots are formed in a scattered state on the surface of the layer. The scattering surface density of Si atoms is made approximately the same as the surface density of quantum dots. That is, when the surface density ^{Ncm -2} quantum dots, spread side the density of Si atoms also about ^{Ncm -2} (N is a natural number of positive properties).

  After growing the quantum dots 25aa, the supply of In and Ga is stopped, and the substrate temperature is lowered to about 50 ° C. to form the quantum dot embedded layer 25ab. The quantum dot embedded layer 25ab has a thickness of 5 nm, and the material is GaAs.

  After that, while keeping the substrate temperature at least 30 ° C. or more again, the state where only As is irradiated is maintained for several minutes. The substrate temperature at this time is set to a temperature at which the quantum dots 25aa and the quantum dot embedded layer 25ab are not damaged (thermally not affected).

  Since the heights of the quantum dots 25aa have variations, the tops of some quantum dots may protrude from the quantum dot embedded layer 25ab. And, there are also variations in the height of the projecting portion. However, by performing this step, the top of the quantum dot 25 aa protruding from the quantum dot embedded layer 25 ab evaporates or is diffused and flattened in the horizontal direction. Thereby, the heights of the quantum dots 25aa are made uniform, and become approximately equal to the thickness of the quantum dot embedded layer 25ab.

  Subsequently, after forming the lower layer of the fourth intermediate layer 27b, the substrate temperature is lowered to about 490 ° C., As is irradiated from the third raw material supply source 54, and In from the first raw material supply source 52 is Ga is supplied from the raw material supply source 53 by an amount corresponding to the thickness of the two atomic layers to form quantum dots made of InGaAs.

  Columnar quantum dots in which AlGaAs quantum dots are connected in the growth direction by repeating the lamination step of the InGaAs quantum dots and the buried layer made of AlGaAs a plurality of times in the same procedure as the formation procedure of the quantum dots 25aa and the quantum dot buried layer 25ab. 27a and a fourth intermediate layer 27b are formed.

  Since distortion due to the formation of the quantum dots 25aa is accumulated on the surface of the second intermediate layer 23c, the columnar quantum dots 27a are formed only immediately above the quantum dots 25aa.

Next, on the fourth intermediate layer 27b, an n-type upper contact layer 35 of 200 nm thick composed of GaAs doped with Si atoms at a concentration of about 2 × 10 ¹⁸ cm ⁻³ is stacked, and an infrared detection element The manufacturing process of the second substrate (wafer for infrared detector) is completed.

  Then, the process of manufacturing the wafer for infrared detectors manufactured and manufacturing the infrared detection element 2 is described.

  For processing of the wafer for infrared detectors, photolithography, dry etching or wet etching is used. First, a resist is applied to a wafer by spin coating, and a pattern (for example, a square pattern) for separating infrared detection elements is formed by photolithography.

  Using this pattern as a mask, the upper contact layer 35, the carrier conductive layer 27, the light absorption layer 25, the carrier supply layer 23, and the lower contact layer 31 are etched halfway by dry etching or wet etching as shown in FIG. , Part of the surface of the lower contact layer 31 is exposed.

  In this process, the plurality of infrared detection elements 2 are separately formed on the infrared detector wafer. The diameter of the light receiving surface of the infrared detection element 2 varies depending on the application, but is typically 20 μm to 300 μm.

  Next, an alloy ohmic electrode made of AuGe / Ni / Au is formed to form an electrode of the upper contact layer 35 and the lower contact layer 31, and the upper electrode 37 and the lower electrode 33 as shown in FIG. 4 are formed. The upper electrode 37 and the lower electrode 33 are respectively formed by a lift-off method including steps of lithography, metal deposition, resist peeling and the like, and an infrared ray transmitting window structure and an electrode structure are formed in desired shapes and in desired positions.

  Thus, the infrared detection element 2 shown in FIG. 4 is completed.

  In addition, in the said manufacturing method, although the light absorption layer containing quantum dot 25aa and those periphery structures are formed by MBE method, the growth method is not limited to this method. For example, these structures may be formed using other crystal growth methods such as metal organic chemical vapor deposition (MOCVD).

  The material composition, thickness, and material configuration of the carrier conductive layer 27, the light absorption layer 25, the carrier supply layer 23 and the like are not limited to the above as long as the effects of the present invention are satisfied.

Second Embodiment
Next, a second embodiment will be described. In addition, regarding the same configuration as the first embodiment, the same reference numeral is used, and the description is appropriately omitted. FIG. 7 is a view showing an electron energy band structure of the infrared detection element 2 according to the second embodiment.

  The energy band structure of electrons of the infrared detection element according to the second embodiment is different from the energy band structure of electrons of the infrared detection element of the first embodiment in that a resonance level Lc is formed. . The energy level of this resonance level Lc is equal to the energy level of the third quantum level L3.

  Then, as in the first embodiment, the electrons in the first quantum level L1 of the light absorption layer 25 absorb infrared rays of energy equal to the energy difference between the first quantum level L1 and the third quantum level L3. It transitions to the third quantum level L3.

  At this time, electrons of the quantum level La of the carrier supply layer 23 conduct the subband level Lm with high electrical conductivity via the fourth quantum level L4 to reach the upper contact layer 35.

  On the other hand, the electrons transited to the third quantum level L3 have a higher probability than the probability of relaxing to the second quantum level L2 and the first quantum level L1 between the light absorption layer 25 and the carrier conduction layer 27. The potential barrier is tunneled to move to the resonance level Lc. The resonance level Lc can be generated by changing the growth conditions of the columna quantum dots 27a (for example, changing the growth temperature).

Since the electron transited to the third quantum level L3 tunnels to the resonance level Lc with high probability, the probability of relaxation from the third quantum level L3 to the first quantum level L1 decreases. That is, it becomes possible to efficiently conduct electrons excited by absorption of infrared light to the carrier conduction layer. Therefore, as compared with the first embodiment, the carrier recombination time τ _R in Equation 4 is increased, and there is an advantage that the photoconductive gain of the infrared detection element 2 is increased.

Third Embodiment
Next, a third embodiment will be described. In addition, regarding the same configuration as the first embodiment and the second embodiment, the same reference numerals are used, and the description will be appropriately omitted.

  FIG. 8 is a diagram showing an energy band structure of electrons of the infrared detection element according to the third embodiment. The energy band structure of the infrared detection element according to the third embodiment is the same as the energy band structure of the infrared detection element according to the first embodiment in terms of the wave function W1 of the first quantum level L1 and the second quantum level L2. The difference is that the evenness and oddity with the wave function W2 are formed to be equal.

  According to quantum mechanics, light emission between quantum levels and optical transition accompanied by absorption are permitted only between wave functions with different evenness and oddity, so the case where the evenness between the wave function W1 and the wave function W2 is equal In addition, the electrons do not cause relaxation with light emission and excitation with light excitation between the first quantum level L1 and the second quantum level L2. Therefore, the wave function W1 of the first quantum level L1 and the wave function W2 of the second quantum level L2 are configured to have symmetrical wave functions (that is, even parity).

  In such a configuration, when an electron of the first quantum level L1 absorbs an infrared ray having an energy equal to the energy difference between the first quantum level L1 and the third quantum level L3 of the light absorption layer 25, the electron is It transitions only to the quantum level L3. Then, electrons of the quantum level La of the carrier supply layer 23 preferentially conduct through the second quantum level L2 to the subband level Lm having high electrical conductivity to reach the upper contact layer 35.

  In the first embodiment, after the electrons transited to the third quantum level L3 are relaxed to the second quantum level L2 (level is lowered), they are relaxed to the first quantum level. However, in the third embodiment, since the wave function W1 of the first quantum level L1 and the wave function W2 of the second quantum level L2 are equal in evenness, relaxation due to light emission does not occur. Since the lifetime of the electrons of the quantum level L2 is extended, the probability of conduction to the subband level Lm is improved. That is, the second quantum level by light absorption is efficiently changed to the fourth quantum level, and the detection sensitivity of infrared rays is improved.

Further, since the probability of relaxation from the second quantum level L2 to the first quantum level L1 decreases, the carrier recombination time τ _R in Equation 4 increases, and the photoconductive gain of the infrared detection element 2 increases. There is.

  The infrared detection element described in each of the above embodiments can be applied to a high sensitivity infrared detection device or a phototransistor in the mid-infrared and mid-far infrared regions.

  In addition, it is added that it is applicable to the application such as a light receiver for communication in which it is necessary to selectively receive a specific wavelength.

  Although the present invention has been described above with reference to the embodiment (and the example), the present invention is not limited to the above embodiment (and the example). The configurations and details of the present invention can be modified in various ways that can be understood by those skilled in the art within the scope of the present invention.

Reference Signs List 2 infrared detecting element 10 substrate portion 11 semiconductor substrate 13 buffer layer 20 functional portion 21 lower layer 23 carrier supply layer 23a first intermediate layer 23b quantum well layer 23c second intermediate layer 25 light absorption layer 25a quantum dot layer 25aa quantum dot 25ab quantum Dot buried layer 25b Third intermediate layer 27 Carrier conductive layer 27a Columnar quantum dot 27b Fourth intermediate layer 30 Contact portion 31 Lower contact layer 33 Lower electrode 35 Upper contact layer 37 Upper electrode

Claims (10)

An infrared detection device comprising a semiconductor quantum dot,
A carrier supply layer including energy levels of quantum levels that capture electrons conducted through the infrared detection element;
The first quantum level of the energy level at which the semiconductor quantum dot captures the electrons from the carrier supply layer, the energy level is lower than the first quantum level, and the first quantum level includes the semiconductor quantum dot. The second quantum level whose energy level changes to the fourth quantum level by Coulomb interaction with electrons trapped in the second quantum level, and at least three quantum levels of the third quantum level whose energy level is lower than that of the second quantum level A light absorption layer having a level,
A carrier conduction layer having a subband level substantially equal in energy level to the quantum level in the carrier supply layer;
The light absorption layer absorbs light of a predetermined wavelength, and the electrons trapped in the first quantum level are excited to the third quantum level, and the number of electrons trapped in the first quantum level is The fourth quantum level is captured by the quantum level in the carrier supply layer when the fourth quantum level has an energy level substantially equal to that of the quantum level in the carrier supply layer and the sub-band level. An infrared detection element characterized in that electrons conduct the sub-band level via the fourth quantum level. The infrared detection device according to claim 1, wherein
The carrier supply layer is formed of a laminate of a first intermediate layer, a quantum well layer, and a second intermediate layer, and the band gap of the quantum well layer is the band gap of the first intermediate layer and the second intermediate layer. An infrared detection device characterized in that the quantum level in the carrier supply layer is formed in the quantum well layer by using a smaller material. The infrared detection device according to claim 1 or 2, wherein
The carrier conducting layer, an infrared detection element which comprises a column Na quantum dots plurality of quantum dots in the direction is connected to stack from the light absorbing layer. The infrared detection device according to claim 3,
The column Na quantum dots, infrared detecting device characterized by being formed directly on the quantum dot in the light-absorbing layer. The infrared detection element according to any one of claims 1 to 4, wherein
An infrared detection element characterized in that a resonance level of substantially the same energy level as the third quantum level is formed in a region near the carrier conduction layer in contact with the light absorption layer. The infrared detection device according to any one of claims 1 to 5, wherein
An infrared detection element characterized in that the even function of the wave function with respect to the crystal growth direction of the first quantum level and the wave function with respect to the crystal growth direction of the second quantum level are equal.   An infrared detection apparatus characterized in that the infrared detection element according to any one of claims 1 to 6 is arranged in one dimension or two dimensions. A method of manufacturing an infrared detection element including a semiconductor quantum dot, comprising:
Forming a carrier supply layer including energy levels of quantum levels that capture electrons conducted through the infrared detection element;
The first quantum level of the energy level at which the semiconductor quantum dot captures the electrons from the carrier supply layer, the energy level is lower than the first quantum level, and the first quantum level includes the semiconductor quantum dot. The second quantum level whose energy level changes to the fourth quantum level by Coulomb interaction with electrons trapped in the second quantum level, and at least three quantum levels of the third quantum level whose energy level is lower than that of the second quantum level Forming a light absorption layer having a level with the carrier supply layer;
3. A method of manufacturing an infrared detection device, comprising: forming a carrier conduction layer having a subband level substantially equal to the quantum level in the carrier supply layer with an energy level. It is a manufacturing method of the infrared detection element according to claim 8.
The carrier supply layer is formed of a laminate of a first intermediate layer, a quantum well layer, and a second intermediate layer, and the band gap of the quantum well layer is the same as that of the first intermediate layer and the second intermediate layer. A manufacturing method of an infrared detection element characterized by forming with a material smaller than a band gap. A method of manufacturing an infrared detection element according to claim 8 or 9, wherein
Wherein in forming the carrier conduction layer, method for manufacturing an infrared detecting element, wherein a plurality of quantum dots in a direction to stack from the light-absorbing layer forms a column Na quantum dots linked.

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