JP2006228994A - Photodetector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the light including a plurality of wavelengths using only a kind of quantum dot structure. <P>SOLUTION: A plurality of quantum dot layers 12 having quantum dot 13 are provided, and a plurality of barrier layers 14 are also provided which are alternately stacked with a plurality of quantum dot layers 12 to embed the same layers. A pair of first electrodes 16, 17 are provided perpendicularly to a plurality of barrier layers 14, and a pair of second electrodes 18, 19 are provided horizontally to a plurality of barrier layers 14. Accordingly, since electron energy potential of the quantum dot 13 which emits the carrier by absorbing the light may be varied in accordance with the electric field applied to a pair of first electrodes 16, 17, the wavelength of the detected light can also be varied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light detector that detects light, and more particularly to a light detector that detects a plurality of lights using quantum dots.

  At present, in a photodetector that detects light by capturing a current that flows when incident light is absorbed, a quantum well photodetector (QWIP) that cannot absorb vertically incident light is three-dimensional. A quantum dot photodetector (Quantum Dot Infrared Photodetector, QDIP) that can absorb vertically incident light using a quantum dot capable of confining carriers in the field is drawing attention. In this QDIP, the optical coupling structure required in QWIP is unnecessary, and the formation process is simplified (for example, Non-Patent Document 1, Patent Documents 1 and 2).

Hereinafter, a case where light of two types of wavelengths is detected by the conventional QDIP will be described. FIG. 3 is a schematic cross-sectional view of a main part of a conventional QDIP element.
As illustrated in FIG. 3, the QDIP element 30 includes a plurality of contact layers 31, 33, and 35 and a plurality of quantum dot structures 32 and 34. The contact layers 31, 33, and 35 are epitaxial layers that extract carriers emitted by absorbing infrared rays as current. Each of the quantum dot structures 32 and 34 absorbs infrared rays having a predetermined wavelength and emits carriers.

Here, in the conventional QDIP element 30, a plurality of quantum dot structures 32 and 34 are stacked in accordance with the number of light to be detected. For example, when having sensitivity to light of two types of wavelengths, two types of quantum dot structures 32 and 34 are stacked.
L Chu, A Zrenner, G Bohm, G Abstreiter, Lateral intersubband photocurrent spectroscopy on InAs / GaAs quantum dots, February 8, 2000 JP-A-10-326906 JP 2003-218366 A

  However, the conventional QDIP element 30 can detect only one type of light with one type of quantum dot structure. Therefore, since a plurality of different quantum dot structures 32 and 34 are stacked in order to detect light having a plurality of wavelengths, the manufacturing process of the QDIP element 30 is complicated.

  This invention is made | formed in view of such a point, and it aims at providing the photodetector which can detect the light of several wavelengths using only one kind of quantum dot structure.

  In the present invention, in order to solve the above-described problem, as illustrated in FIG. 1, in the photodetector that detects light, a plurality of quantum dot layers 12 having quantum dots 13 and a plurality of quantum dot layers 12 are alternately arranged. A plurality of barrier layers 14 embedded in the plurality of quantum dot layers 12, a first pair of electrodes 16, 17 provided perpendicular to the plurality of barrier layers 14, and a plurality of barrier layers 14 And a second pair of electrodes 18 and 19 provided in parallel to each other.

  According to such a light detector, the electron energy potential of the quantum dot 13 that absorbs light and emits carriers can be changed according to the electric field applied to the first pair of electrodes 16, 17. The wavelength of can be changed. Therefore, by applying a predetermined electric field to the first pair of electrodes 16 and 17, light having a predetermined wavelength can be detected.

In the present invention, the first pair of electrodes is provided perpendicular to the plurality of barrier layers.
In this way, the electron energy potential of the quantum dot that absorbs light and emits carriers can be changed according to the electric field applied to the first pair of electrodes, so that the wavelength of the detected light can be changed. Therefore, light having a predetermined wavelength can be detected by applying a predetermined electric field to the first pair of electrodes. That is, light of a plurality of wavelengths can be detected using only one type of quantum dot structure.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, it demonstrates taking the case of the infrared rays in light. FIG. 1 is a schematic cross-sectional view of an essential part of a QDIP element.
The photodetector has a plurality of QDIP elements 10. The quantum dots 13 are formed on the surface of the quantum dot layer 12, and the quantum dot layers 12 and the quantum dots 13 are embedded with a barrier layer 14. In order to increase the infrared absorption sensitivity, these layers are laminated several times. The first pair of electrodes 16, 17 are provided perpendicular to the plurality of barrier layers 14, the second pair of electrodes 18, 19 are provided in parallel to the plurality of barrier layers 14, and the QDIP element 10 Is formed.

  In the QDIP element 10, by changing the electric field applied between the electrode 16 and the electrode 17, it is possible to change the wavelength of infrared rays to be detected, and to detect infrared rays having a plurality of wavelengths. The quantum dots 13 absorb infrared rays and emit carriers. Carriers emitted from the quantum dots 13 flow through the quantum dot layer 12 and the barrier layer 14 in accordance with an electric field applied between the electrode 18 via the contact layer 11 and the electrode 19 via the contact layer 15.

  Here, for example, InGaAs or InAs is used as the material of the quantum dots 13, GaAs is used as the material of the barrier layer 14, and Au—Ge— is used as the material of the electrodes 16, 17, 18, and 19. Ni / Au is used.

Next, a process for forming the QDIP element 10 will be described.
Each epitaxial layer of the QDIP element 10 is formed by an MBE (molecular beam epitaxial) method, and the quantum dots 13 of the QDIP element 10 are formed by a self-assembled quantum dot forming method.

First, a GaAs substrate (not shown) having a (100) surface is introduced into an ultrahigh vacuum chamber.
Next, the contact layer 11 having a thickness of about 50 nm is grown by doping with an n-type impurity of about 1 × 10 ¹⁸ cm ⁻³ . Next, a barrier layer 14 made of i-GaAs having a thickness of about 50 nm and not doped with impurities is grown. Next, InAs having a thickness of about 2 ML to 3 ML (molecular layer) that is not doped with impurities is uniformly supplied. Here, in the initial supply of InAs, InAs grows flat two-dimensionally to form the quantum dot layer 12, but in the subsequent supply of InAs, the InAs is caused by strain generated from the difference in lattice constant between GaAs and InAs. Grows three-dimensionally in an island shape to form quantum dots 13. The quantum dots 13 have a diameter of about 20 nm to 50 nm, a height of about 5 to 7 nm, and are present at about 10 ¹⁰ pieces / cm ² to 10 ¹¹ pieces / cm ² . Next, a barrier layer 14 made of i-GaAs having a thickness of about 50 nm and not doped with impurities is grown. Here, the quantum dot layer 12, the quantum dot 13, and the barrier layer 14 are repeated 10 to 20 times, and the last barrier layer 14 is grown. Next, the contact layer 15 having a thickness of about 50 nm is grown by doping with an n-type impurity of about 1 × 10 ¹⁸ cm ⁻³ .

Next, in a predetermined place, the space between the contact layer 15 and the contact layer 11 is ground to form electrodes 16, 17, 18, 19 made of Au or the like.
Next, the operation of the QDIP element 10 will be described.

Here, when an electric field is not applied between the electrode 16 and the electrode 17 by a CMOS circuit (not shown), an infrared wavelength based on the original quantum dot structure is detected.
First, an electric field is applied between the electrode 18 and the electrode 19 so that the emitted carriers are taken out by the CMOS circuit. Next, infrared rays are absorbed by the quantum dots 13 of the QDIP element 10, and carriers bound to the quantum levels formed in the quantum dots 13 are excited to the bottom of the conduction band of the barrier layer. Next, the excited and emitted carriers flow between the contact layer 11 and the contact layer 15 in accordance with an electric field applied through the electrode 18 and the electrode 19. Next, the CMOS circuit captures the current and detects infrared light as the current.

  In addition, when an electric field is applied between the electrode 16 and the electrode 17 by the CMOS circuit, the wavelength of infrared rays due to the original quantum dot structure and the applied electric field is detected using the quantum confined Stark effect.

  First, an electric field is applied between the electrode 18 and the electrode 19 so that the emitted carriers are taken out by the CMOS circuit. Next, an electric field is applied between the electrode 16 and the electrode 17 so that a predetermined infrared ray can be detected by the CMOS circuit. Next, infrared rays are absorbed by the quantum dots 13 of the QDIP element 10, and carriers bound to the quantum levels formed in the quantum dots 13 are excited to the bottom of the conduction band of the barrier layer. Next, the excited and emitted carriers flow between the contact layer 11 and the contact layer 15 according to the electric field applied through the electrode 18 and the electrode 19. Next, the CMOS circuit captures the current and detects infrared light as the current.

Next, changes in the quantum level of the quantum dots when an electric field is applied to the first pair of electrodes 16 and 17 will be described. FIG. 2 is a diagram illustrating an example of a change in quantum level.
First, as illustrated in FIG. 2A, the electron energy potential necessary for the quantum dots 13 to absorb infrared rays and emit carriers is that electrons are bound from the bottom of the conduction band of the barrier layer 14. This is the difference in the quantum level in the quantum dots 13 that are present.

Thereafter, when an electric field is applied to the first pair of electrodes 16 and 17, the electron energy potential necessary for emitting carriers is changed by the quantum confined Stark effect, as illustrated in FIG. 2B. . For example, when a voltage of 10 V is applied between the electrode 16 and the electrode 17, the wavelength of the infrared ray to be detected is changed from 10 μm to 9.3 μm. The amount of change in the quantum level of this quantum dot is defined by the following equation.
ΔE = E1-E2 = −0.0022 × m * × e ² F ⁴ L ⁴ / h ²
Here, ΔE is the amount of change in the quantum level, E1 is the quantum level before applying the electric field, and E2 is the quantum level after applying the electric field. Further, m * is an effective mass, e is an elementary charge amount, F is an electric field strength, L is a constant defined by the size of the quantum dot, and h is a Planck constant.

  In addition, when detecting several infrared rays, the detection time with respect to each infrared rays becomes short. For example, when detecting infrared rays of one kind of wavelength with one kind of quantum dot structure, a time of about 30 msec is required. Further, when detecting infrared rays having two types of wavelengths with one type of quantum dot structure, a time of about 15 msec is required for each infrared ray. Further, when detecting infrared rays having three types of wavelengths with one type of quantum dot structure, a time of about 10 msec is required for each infrared ray.

  The photodetector includes such a QDIP element 10 as one pixel. For example, many QDIP elements 10 are arranged on a single GaAs substrate. Since each QDIP element 10 absorbs a large amount of infrared rays, a larger amount of carriers are emitted. Therefore, by using this, an image corresponding to the temperature of the object is generated by the photodetector.

  In this way, the electron energy potential of the quantum dot 13 that absorbs infrared rays and emits carriers can be changed according to the electric field applied to the first pair of electrodes 16 and 17, so that the wavelength of infrared rays to be detected is changed. it can. Therefore, by applying a predetermined electric field to the first pair of electrodes 16 and 17, infrared light having a predetermined wavelength can be detected. That is, infrared rays having a plurality of wavelengths can be detected using only one type of quantum dot structure.

  Further, since infrared rays with a plurality of wavelengths can be detected with one type of quantum dot structure, a plurality of quantum dot structures do not have to be stacked even when detecting infrared rays with a plurality of wavelengths. Therefore, the manufacturing process can be simplified.

  In addition, since one kind of quantum dot structure is stacked more, sensitivity to infrared rays can be increased.

It is a principal part cross-sectional schematic diagram of a QDIP element. It is a figure which shows the example of a change of a quantum level. It is a principal part cross-sectional schematic diagram of the conventional QDIP element.

Explanation of symbols

10 QDIP element 11, 15 Contact layer 12 Quantum dot layer 13 Quantum dot 14 Barrier layer 16, 17, 18, 19 Electrode

Claims (5)

In the light detector that detects light,
A plurality of quantum dot layers having quantum dots;
A plurality of barrier layers that are alternately stacked with the plurality of quantum dot layers and embed the plurality of quantum dot layers;
A first pair of electrodes provided perpendicular to the plurality of barrier layers;
A second pair of electrodes provided in parallel to the plurality of barrier layers;
An optical detector comprising:   The light detector according to claim 1, wherein the light is an infrared ray.   2. The wavelength of light to be detected is changed in accordance with an electric field applied to the first pair of electrodes, and the second pair of electrodes takes out carriers emitted from the quantum dots. The described photodetector.   2. The photodetector according to claim 1, wherein there is one kind of quantum dot structure having each quantum dot layer and each barrier layer. 2. The photodetector according to claim 1, wherein the barrier layer is made of GaAs, and the quantum dots are made of InAs or InGaAs.

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