JP2013161876A - Light detecting semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light detecting semiconductor device capable of selectively increasing a response current to be detected.SOLUTION: A light detecting semiconductor device includes: a first semiconductor layer 2; a second semiconductor layer 3 formed on the first semiconductor layer 2, having an energy band gap greater than that of the first semiconductor layer 2, and having a channel formed on the first semiconductor layer 2 side of the interface with the first semiconductor layer 2; a third semiconductor layer 4 formed on the second semiconductor layer 3, and having an energy band gap smaller than that of the second semiconductor layer 3; quantum dots 5 formed on the third semiconductor layer 4 by being doped with an impurity, and having an energy band gap smaller than that of the first semiconductor layer 2; fourth semiconductor layers 6 and 7 formed on the third semiconductor layer 4 and the quantum dots 5, and composed of the same material as the third semiconductor layer 4; a first electrode 10 formed on the fourth semiconductor layers 6 and 7; and second and third electrodes 8 and 9 formed on the first semiconductor layer 2 on both sides of the first electrode 10, respectively.

Description

  The present invention relates to a light detection semiconductor device.

  Since the intensity of the electromagnetic wave spontaneously radiated from the object is strong in the infrared band, the infrared light is used as an electromagnetic wave for recognizing the image of the object. The amount of infrared light emitted from an object increases mainly as the temperature of the object increases.

  An example of an object that emits infrared rays is the human body, but the amount of infrared light emitted from a human body having a temperature higher than room temperature is greater than the amount of infrared light emitted from the surrounding environment having a temperature comparable to room temperature. .

  Therefore, it is possible to display the human body as an image on the screen by using the infrared detecting device whose response output changes depending on the amount of light.

  As an infrared detection device, an image detection device having a MOS structure and a HEMT structure is known. For example, in an image sensing device having a MOS structure, a source electrode and a drain electrode are formed on an upper impurity diffusion layer in a semiconductor substrate, and a gate electrode is formed on the impurity diffusion layer between these electrodes via a gate insulating film. Has a formed structure. Further, quantum dots are formed in the gate insulating film, and the gate electrode is formed from a semiconductor layer.

  According to the image sensing device, application of a positive voltage to the gate electrode aligns the quantum level of the quantum dot and the Fermi level of the channel region, so that electrons in the channel of the impurity diffusion layer cause the quantum mechanical action on the gate insulating film. Slips through and moves into the quantum dot.

  The electrons confined in the quantum dots move away the electrons in the channel due to the Coulomb potential and reduce the current flowing through the channel. Thereafter, when the gate insulating film is irradiated with infrared rays, the electrons in the quantum dots are photoexcited and separated, thereby reducing the electrons in the plurality of quantum dots and increasing the current in the channel. Infrared irradiation is detected by observing such an increase in current, and the current in the channel increases at approximately the same rate as the amount of light increases.

JP 2006-210620 A

  When an image of a human body is detected by the image detection device described above, the human body and its surrounding environment are the detection targets. In a situation where no human body exists in the surrounding environment, only the surrounding environment is detected by the image detection device. In this case, in the image detection apparatus, a current that responds to the amount of light corresponding to the temperature of the surrounding environment, for example, a temperature that is about the same as room temperature flows.

  When a human body enters the surrounding environment, a current corresponding to the amount of infrared light corresponding to the body temperature of the human body, which is higher than room temperature, flows in a pixel that receives light from the human body. Therefore, it is possible to select and detect an image of the human body by taking a difference between current values corresponding to the temperatures of the surrounding environment and the human body.

  However, the response current in the image detection apparatus at the time of detecting the surrounding environment is excessive when the human body is used as a detection target, and the detection efficiency is thereby lowered.

  In general, in an image detection apparatus, the dynamic range of response current is limited, and adjustment is performed so that the response current at the time of human body detection is just within the dynamic range. However, it is most ideal that the response current in the surrounding environment is eliminated, only the response current for detecting the human body is detected, and the dynamic range at the time of image detection is occupied only by the human body detection.

  Therefore, the photodetection semiconductor device is required to reduce the response current derived from the environment other than the detection target.

  An object of the present invention is to provide a photodetection semiconductor device capable of selectively increasing a response current to be detected.

According to one aspect of the present embodiment, the first semiconductor layer is formed on the first semiconductor layer and has a larger energy band gap than the first semiconductor layer. A second semiconductor layer in which a channel is formed on the first semiconductor layer side in an interface with the layer, and an energy band gap formed on the second semiconductor layer, as compared with the second semiconductor layer. A third semiconductor layer having a small size, a quantum dot formed by doping impurities on the third semiconductor layer, and having an energy band gap smaller than that of the first semiconductor layer, and the third semiconductor layer And a fourth semiconductor layer formed on the quantum dot and made of the same material as the third semiconductor layer, a first electrode formed on the fourth semiconductor layer, and On each side of one electrode The second is formed on the serial first semiconductor layer, a third electrode, a light sensing semiconductor device including a is provided.
The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention.

  According to the present invention, the quantum dot is doped with an impurity, and the electrons in the quantum dot are excited by light irradiation to leave the quantum level, thereby reducing the channel Fermi energy, and the channel with a light amount equal to or greater than the threshold value. Current is flowing. In addition, the current flowing through the channel is made extremely small with the light quantity below the threshold. As a result, the dynamic range can be occupied only by the response current with respect to the light reception of the detection target that emits light exceeding a certain amount of light, and a device with high detection efficiency can be realized.

FIG. 1 is a cross-sectional view illustrating an example of a compound semiconductor layer stacking process in the manufacturing process of the photodetection semiconductor device according to the embodiment. FIG. 2 is a cross-sectional view illustrating an example of a patterning process of the compound semiconductor layer in the manufacturing process of the photodetection semiconductor device according to the embodiment. FIG. 3 is a cross-sectional view illustrating an example of the photodetection semiconductor device according to the embodiment. 4A and 4B are diagrams illustrating an example of a change in the energy band structure in the photodetection semiconductor device according to the embodiment. FIG. 5 is a characteristic diagram illustrating an example of the relationship between the light amount and the response current of the light detection semiconductor device according to the embodiment. FIG. 6 is a cross-sectional view showing a photodetection semiconductor device according to a comparative example. FIG. 7 is a diagram illustrating an energy band structure in the photodetection semiconductor device according to the comparative example. FIG. 8 is a characteristic diagram illustrating an example of the relationship between the light amount and the response current of the light detection semiconductor device according to the comparative example.

  Embodiments will be described below with reference to the drawings. In the drawings, similar components are given the same reference numerals.

  FIG. 1 is a cross-sectional view illustrating an example of a stacking process of compound semiconductor layers that form the photodetection semiconductor device according to the embodiment. The molecular beam epitaxy (MBE) method is employed as a method for forming the compound semiconductor layer, but an MOCVD method or other formation methods may be employed.

  First, a first i-type GaAs layer 2 is formed on a gallium arsenide (GaAs) substrate 1 at a substrate temperature of, eg, 600 ° C. to a thickness of, eg, about 1000 nm. i-type indicates a non-doped layer.

Subsequently, an n-type aluminum gallium arsenide (Al _x Ga _1-x As) layer 3 is formed on the first i-type GaAs layer 2 at a substrate temperature of, eg, about 600 ° C. to a thickness of, eg, about 50 nm. In this case, the composition ratio x is set to 0.2, for example. For example, silicon (Si) is used as the n-type impurity, and the impurity concentration is, for example, about 5 × 10 ¹⁶ / cm ³ .

The energy band gap of the n-type Al _x Ga _1-x As layer 3 is wider than the energy band gap of the first i-type GaAs layer 2 and serves as a barrier layer. And a two-dimensional electron gas 2DEG is generated in the channel. Thus, the second i-type GaAs layer 2 becomes a channel layer.

Further, a second i-type GaAs layer 4 having an energy band gap narrower than that of the n-type Al _x Ga _1-x As layer 3 is formed on the n-type Al _x Ga _1-x As layer 3 to a thickness of about 50 nm, for example. To form. In the process from the start of formation of the second i-type GaAs layer 4 to the end of formation, the substrate temperature is lowered from 600 ° C. The target temperature for the substrate temperature drop is set to a temperature at which self-composition of quantum dots can occur on the second i-type GaAs layer 4, for example, about 500 ° C.

  Next, while maintaining the substrate temperature at about 500 ° C., indium arsenide (InAs) is deposited on the second i-type GaAs layer 4 by 0.1 atomic layer / second (ML / second) by the self-organization forming method. Supply 2.5 mL at a growth rate of s). During the supply process of InAs, the compressive strain applied to InAs increases, and InAs grows three-dimensionally to form quantum dots 5. The quantum dots 5 are formed of a material having a narrow energy band gap as compared with the first i-type GaAs layer 2 having a channel region. When supplying InAs, for example, silicon (Si) is supplied to InAs as an n-type impurity. The amount of Si supplied is about 1 atom per quantum dot 5 and is controlled so that approximately one electron can be supplied to one quantum dot 5.

  Subsequently, a third i-type GaAs layer 6 is formed on the second i-type GaAs layer 4 and the InAs quantum dots 5 to a thickness of about 50 nm, for example. In the process from the start of formation of the third i-type GaAs layer 6 to the end of formation, the substrate temperature is raised from 500 ° C. to, for example, about 600 ° C.

  Next, a fourth i-type GaAs layer 7 is formed on the third i-type GaAs layer 6 at a temperature of about 600 ° C. to a thickness of about 500 nm, for example.

  Next, as shown in FIG. 2, after the silicon oxide film 21 is formed on the fourth i-type GaAs layer 7 by the CVD method, the silicon oxide film 21 is patterned by using a photolithography technique and etching. Thereby, two openings 21a and 21b are formed in the source region and the drain region at an interval of, for example, 10 μm.

  Thereafter, using the silicon oxide film 21 as a mask, for example, etching is performed from the fourth i-type GaAs layer 7 to the second i-type GaAs layer 4 through the openings 21a and 21b by dry etching using a chlorine-based gas. To do. As a result, the first i-type GaAs layer 2 is exposed from the openings 21a and 21b. A channel region is formed between the two regions of the exposed first i-type GaAs layer 2. Thereafter, the silicon oxide film 21 is removed by etching using, for example, hydrofluoric acid.

  Next, as illustrated in FIG. 3, the source electrode 8 and the drain electrode 9 are formed on the first i-type GaAs layer 2 in the two exposed regions, and the remaining portions in the region between them are formed. A gate electrode 10 is formed on the four i-type GaAs layers 7. As the source electrode 8, the drain electrode 9, and the gate electrode 10, a stacked metal of a gold germanium (AuGe) film and a gold (Au) film or other metal is formed by, for example, a sputtering method or a vapor deposition method.

  Then, it heats at the temperature of 400-450 degreeC, for example. As a result, the junction between each of the source electrode 8 and the drain electrode 9 and the second GaAs layer 2 is alloyed. Similarly, the junction between the gate electrode 10 and the fourth i-type GaAs layer 7 is also alloyed.

  Since the length of the gap between the source electrode 8 and the drain electrode 9, that is, the channel length is set to be as large as about 10 μm, for example, the number of quantum dots 5 on the channel region is much larger than 1, for example, about 1000 to It is formed into 10,000 pieces.

  Thus, the basic structure of the light detection semiconductor device is formed. As illustrated in FIG. 3, the photodetection semiconductor device has a DC power supply 11 connected to the source electrode 8 and the drain electrode 9, and between the DC power supply 11 and the source electrode 8, or between the DC power supply 11 and the drain electrode 9. A current detector 12 is connected in series therebetween. Further, a gate voltage supply power source 13 is connected to the gate electrode 10 via a switch circuit 14. Note that the DC power supply 11, the gate voltage supply power supply 13, and the switch circuit 14 are connected to a circuit (not shown) including a CMOS to control on / off and voltage. The current detector 12 has a current amplification circuit (not shown).

  The structure shown in FIGS. 1 to 3 is an explanation of one pixel portion of the light detection semiconductor device, and the light detection semiconductor device includes a plurality of gate electrodes 10 and the like, and has a plurality of pixels. Yes.

  In the above-described photodetector, the conduction band Ec side of the energy band structure in the longitudinal section of the layers from the first i-type GaAs layer 2 to the fourth GaAs layer 7 with a voltage applied to the gate electrode 10 For example, the profile is as shown in FIG. Since the n-type impurity is added to the quantum dots 5 as described above, approximately one electron e is supplied to each quantum dot 5 in the initial state.

Thereby, the Fermi energy E _f is located at substantially the same level as the quantum level E _b of the quantum dot 5. In addition, the energy band gap of the first i-type GaAs layer 2 that generates the channel of the two-dimensional electron gas 2DEG and the n-type Al _x Ga _1-x As layer 3 is larger than the energy band gap of the quantum dots 5. Yes. For this reason, the quantum level of the channel is positioned in a state that is substantially higher than the Fermi energy E _f in the initial state.

Further, when applying a positive voltage to the gate electrode 10, the conduction band E _c energy potential is lowered in the fourth i-type GaAs layer 7 is also pushed down. If infrared rays are not incident in this state, electrons e exist in the quantum dots 5 and the channel energy is higher than the Fermi energy E _f , so that almost no current flows in the channel.

  Further, when infrared rays are incident on the quantum dots 5 through the GaAs substrate 1, the electrons e restrained by the quantum dots 5 are excited by absorbing the infrared energy. Thereby, the electron e photoexcited in the quantum dot 5 causes an intersubband transition, or moves toward the gate electrode 10 and moves away from the quantum dot 5 in position.

Thereby, the space charge in the quantum dot 5 is positive, as illustrated in FIG. 4 (b), the conduction band E _c end quantum dots 5 vicinity is depressed, the channel energy depressed for affected by this The soil in which the electrons e of the two-dimensional electron gas 2DEG in the channel flow is formed.

  However, in a state where one photon enters the photodetecting semiconductor device, such an action is performed only in the vicinity of one quantum dot 5, and the current is generated over the entire channel by the electric field generated by the source electrode 8 and the drain electrode 9. Does not flow.

Therefore, when the light intensity is gradually increased to increase the amount of light and photoexcitation as shown in FIG. 4B occurs with a certain number of quantum dots, the entire region between the source electrode 8 and the drain electrode 9 is a channel. As shown in FIG. 5, a current starts to flow as a response to light incidence. After the detection of the image once, the switch circuit 14 controls the voltage applied from the gate voltage supply power source 13 to the gate electrode 10 to increase the energy potential of the fourth i-type GaAs layer 7. to push up the conduction band E _c, supplying electrons e in the quantum dots 5.

Therefore, when detecting the presence position of the human body using the photodetection semiconductor device of this embodiment, between the source electrode 8 and the drain electrode 9 for the infrared light with a small amount of light emitted from the environment around the human body. The flowing current is extremely small. In contrast, it is possible for the light amount threshold L _th or more large infrared emitted from the human body to increase in response to a current which flows between a source electrode 8 and drain electrode 9 to the light amount. Therefore, there is no need to obtain the difference between the current generated by the infrared rays emitted from the human body and the current generated by the infrared rays emitted from the surrounding environment, the dynamic range for specifying the human body can be increased, and the detection sensitivity is increased. Can do.

  Next, the structure of the light detection device according to the comparative example will be described. FIG. 6 shows a photodetection semiconductor device according to a comparative example.

  The photodetection semiconductor device according to the comparative example has a structure in which a substrate-side barrier layer 32, a quantum well layer 33, a barrier semiconductor layer 34, and a gate electrode 36 are sequentially formed on a semiconductor substrate 31. Quantum dots 35 are formed in the barrier semiconductor layer 34. Further, on both sides of the gate electrode 36, first and second ohmic electrodes 38 and 39 are formed via ohmic contact alloys 37 a and 37 b formed from the barrier semiconductor layer 34 to the depth of the substrate-side barrier layer 32. ing.

  In the photodetection semiconductor device having such a structure, a DC power supply 40 is connected in series to the first ohmic electrode 38 and the second ohmic electrode 39, and a current is connected between the DC power supply 40 and the first ohmic electrode 38. The detector 41 is connected in series. A gate voltage supply power source 42 is connected to the gate electrode 36.

  When a positive voltage is applied to the gate electrode 36 from the gate voltage supply power source 42, the surface potential of the substrate side barrier layer 32 is pushed downward. Therefore, as illustrated in FIG. 7, when the Fermi level of the quantum well layer 33 and the quantum level of the quantum dot 35 are aligned, the electrons in the quantum well layer 33 that is the channel are quantum mechanically barrier semiconductor layers. It passes through 34 and is confined in the quantum dot 35.

  Thereby, the electrons in the quantum well layer 33 are moved away by the repulsive force of the Coulomb potential of the electrons e captured by the quantum dots 35, and the amount of current in the quantum well layer 33 between the first and second ohmic electrodes 38 is reduced. Decrease. That is, the amount of current flowing in the initial state is reduced by applying a voltage to the gate electrode 36.

  After that, when the gate electrode 36 becomes lower than the threshold voltage, the potential of the substrate-side barrier layer 32 increases. Therefore, when light is irradiated from the outside, the trapped electrons e of the quantum dots 35 are energized to be excited and jumped to the outside. The current in the quantum well layer 33, which is a channel, easily flows and the amount of current increases.

  When a voltage equal to or higher than the threshold value is applied to the gate electrode 36, the electrons e in the quantum dots 35 jump out to the outside due to light irradiation, and at the same time, the electrons e are supplied from the quantum well layers 33 to the quantum dots 35. The amount of current in 33 remains reduced.

  Therefore, according to the light detection semiconductor device of the comparative example, the number of trapped electrons e of the quantum dots decreases as the amount of light increases. Therefore, as illustrated in FIG. 8, the amount of current is approximately the same according to the amount of light. Will increase.

  For this reason, in order to detect and detect an image of a human body by receiving infrared rays emitted from both the human body and its surrounding environment by a photodetection semiconductor device having a plurality of quantum dots 35, the human body and its A difference in the amount of current by each infrared detection in the surrounding environment is obtained, and a portion where the difference exists is displayed as an image of a human body. According to this, the dynamic range for the human body is reduced by the amount of current in the surrounding environment, and in addition, a circuit for calculating the difference in the amount of current is required to make the human body a clear image, which hinders simplification of the structure. Come on.

On the other hand, according to the photodetection semiconductor device of this embodiment, electrons e exist in the quantum level of the quantum dots 5 in the initial state, and the infrared ray is not irradiated between the source electrode 8 and the drain electrode 9. The material of the compound semiconductor layer is adjusted so that almost no current flows.
Therefore, the threshold value L _th is infrared radiation in the following quantity response current is reduced between the source electrode 8 and drain electrode 9 also, a large current flows for amount of light from the surrounding environment. Further, a structure in which the response current increases steeply for a large increase in light intensity than the threshold L _th.

Thereby, the calculation of the difference in current for extracting the human body required in the comparative example becomes unnecessary, and a large dynamic range for the human body image can be ensured, and a clear image display can be performed. In the optical sensing semiconductor device of the present embodiment, adjustment of the threshold L _th, shown in relation of the amount of light and the response current of FIG. 5, it is done by adjusting parameters such as the number of quantum dots 5, the channel length Can do.

By the way, in the above-described embodiment, the periphery of the quantum dot 5 is formed of a GaAs layer, and further, a GaAs layer is formed as an electron transit layer of the two-dimensional electron gas 2DEG. However, other materials may be used. . For example, an Al _y Ga _1-y As layer may be formed in place of the GaAs layer, and a value that maintains the above-described relationship between the magnitudes of the energy band gaps, for example, 0.1 or less is selected as the composition ratio y. Further, the n-type Al _y Ga _1-y As layer 3 formed as an electron supply layer bends the conduction band of the GaAs layer 2, but the n _- type impurity concentration contained in the n _- type Al _x Ga _1-x As layer 3 Is too high, the bend effect on the electron loss from the quantum dots 5 becomes weak, so the above concentration is preferable.

  All examples and conditional expressions given here are intended to help the reader understand the inventions and concepts that have contributed to the promotion of technology, such examples and It should be construed without being limited to the conditions, and the organization of such examples in the specification is not related to showing the superiority or inferiority of the present invention. Although embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and variations can be made thereto without departing from the spirit and scope of the present invention.

1 GaAs substrate 2,4, 6,7 i-type GaAs layer 3 n-type _Al x _{Ga 1-x} As layer 5 quantum dots 8 source electrode 9 drain electrode 10 gate electrode

Claims (5)

A first semiconductor layer;
Formed on the first semiconductor layer, has an energy band gap larger than that of the first semiconductor layer, and a channel is formed on the first semiconductor layer side of the interface with the first semiconductor layer. A second semiconductor layer,
A third semiconductor layer formed on the second semiconductor layer and having an energy band gap smaller than that of the second semiconductor layer;
A quantum dot formed by doping impurities on the third semiconductor layer and having a smaller energy band gap than the first semiconductor layer;
A fourth semiconductor layer formed on the third semiconductor layer and the quantum dots and made of the same material as the third semiconductor layer;
A first electrode formed on the fourth semiconductor layer;
Second and third electrodes formed on the first semiconductor layer on both sides of the first electrode,
A photodetection semiconductor device comprising:   The photodetection semiconductor device according to claim 1, wherein the impurity is supplied at a rate of one atom per one quantum dot. A DC power source is connected to the second and third electrodes,
The photodetecting semiconductor device according to claim 1, wherein a voltage source that applies a positive voltage at the time of light detection is connected to the first electrode.   4. The photodetection semiconductor device according to claim 1, wherein a plurality of the quantum dots are formed along a region between the second and third electrodes. 5.   5. The photodetecting semiconductor device according to claim 1, wherein a plurality of the first electrodes are formed on the fourth semiconductor layer. 6.

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