JP5609489B2 - Quantum photodetector - Google Patents

Description

  The present invention relates to a quantum photodetector.

2. Description of the Related Art Conventionally, as a photodetector that detects light by a current that flows when incident light is absorbed, there is a quantum photodetector that includes an active layer and a contact layer that sandwiches the active layer.
As a quantum photodetector, for example, as shown in FIG. 13, an active layer 101 composed of quantum dots 104 and an intermediate layer 105 on a substrate 100, and upper and lower contact layers 102 and 103 sandwiching the active layer 101 are provided. There is a quantum dot type photodetector.

  In this quantum dot photodetector, an upper electrode 106 is attached to the upper contact layer 102, and a lower electrode 107 is attached to the lower contact layer 103. A power source 108 and a current detector 109 are connected to the upper electrode 106 and the lower electrode 107. Thus, a potential difference is given between the upper electrode 106 and the lower electrode 107 by the bias voltage supplied from the power supply 108, and the photocurrent flowing between these electrodes can be detected by the current detector 109. It has become.

Zhengmao Ye et al., “InAs quantum dot infrared features with In0.15Ga0.85As strain-relief cap layers”, JOURNAL OF APPLIED PHYSICS, VOLUME 92, NUMBER 12, 15 DECEMBER 2002, PP. 7462-7468

However, in the above-described quantum photodetector, the voltage that can be applied and the current that can be detected with high accuracy are limited by the performance of the power supply 108 and the current detector 109. For this reason, it is necessary to control the resistance of the active layer 101 to a desired value so as to match the performance of the power supply 108 and the current detector 109.
In general, the resistance of the active layer is controlled by adjusting the impurity doping concentration of the active layer.

However, in this method, the impurity doping concentration must be adjusted during device crystal growth. For example, the resistance of the active layer cannot be controlled after the device crystal is processed and the photodetector is configured. For this reason, when the resistance of the active layer deviates from a desired value, it becomes a defective product and the yield is not good.
For example, in order to realize a photodetector with a high signal-to-noise ratio, it is conceivable to increase the thickness of the active layer so that the amount of light absorption increases. However, when the thickness of the active layer is increased, it becomes difficult to control the resistance of the active layer due to the influence of unintentionally mixed background impurities and variations in impurity doping concentration during device crystal growth, and the yield is reduced.

  Therefore, it is desirable to improve the yield by ensuring that the resistance of the active layer of the quantum photodetector can be controlled.

Therefore, the quantum photodetector includes an active layer, a contact layer sandwiching the active layer, an electrode provided on the contact layer, a first insulating film provided on at least one side surface of the active layer, 1 When the active layer has a high resistance provided on the side surface of the active layer through an insulating film, a positive voltage is applied when electrons are used as carriers in order to reduce the resistance of the active layer. When a negative voltage is applied, and when the resistance of the active layer is low, in order to increase the resistance of the active layer, a negative voltage is applied when electrons are used as carriers, and a positive voltage when holes are used as carriers. And a first resistance control electrode to which is applied .

  Therefore, according to the present quantum photodetector, there is an advantage that the resistance of the active layer can be reliably controlled and the yield can be improved.

It is typical sectional drawing which shows the structure of the quantum type photodetector concerning this embodiment. It is a typical sectional view showing the composition of the photo detecting element contained in the quantum type photo detector concerning this embodiment. (A)-(C) are the schematic which shows the potential of the MIS structure cross section from the resistance control electrode to the active layer in the quantum type photo detector concerning this embodiment, (A) is a resistance control electrode. (B) shows the potential state when a positive voltage _Vb is applied to the resistance control electrode, and (C) shows the potential state when no voltage is applied to the resistance control electrode. A potential state when a negative voltage _Vb is applied to the resistance control electrode is shown. (A), (B) is the schematic which shows the potential of the active layer cross section between the contact layers in the quantum type photodetector concerning this embodiment, (A) is the voltage applied to the electrode for resistance control. The potential state when the potential of the active layer is high without being present is shown, and (B) shows the potential state when the positive voltage _Vb is applied to the resistance control electrode in that case. (A)-(D) are the schematic which shows the potential of the active layer cross section between the contact layers in the quantum type photodetector concerning this embodiment, (A) uses an electron as a carrier and makes it a resistance control electrode. Indicates the potential state when the resistance of the active layer is high when no voltage is applied, or when the resistance of the active layer is low when no voltage is applied to the resistance control electrode using holes as carriers. (B) shows the potential state when a positive voltage is applied to the resistance control electrode in order to control the resistance of the active layer in these cases, and (C) shows electrons as carriers. When the resistance of the active layer is low when no voltage is applied to the resistance control electrode, or when the resistance of the active layer is high when no voltage is applied to the resistance control electrode using holes as carriers. The potentiala It shows a state, (D) shows the potential state in the case of applying a negative voltage to the resistance control electrode to control the resistance of the active layer in these cases. (A), (B) is a schematic diagram which shows the specific structural example of the quantum type photodetector concerning this embodiment, (A) is a top view, (B) is A of (A). It is sectional drawing which follows the -A 'line. (A)-(F) is a schematic diagram for demonstrating the manufacturing method of the specific structural example of the quantum type photodetector concerning this embodiment, (A)-(C) is a top view. , (D) to (F) are sectional views, and (A) and (D), (B) and (E), and (C) and (F) show the same process. (A)-(F) is a schematic diagram for demonstrating the manufacturing method of the specific structural example of the quantum type photodetector concerning this embodiment, (A)-(C) is a top view. , (D) to (F) are sectional views, and (A) and (D), (B) and (E), and (C) and (F) show the same process. (A)-(F) is a schematic diagram for demonstrating the manufacturing method of the specific structural example of the quantum type photodetector concerning this embodiment, (A)-(C) is a top view. , (D) to (F) are sectional views, and (A) and (D), (B) and (E), and (C) and (F) show the same process. (A)-(F) is a schematic diagram for demonstrating the manufacturing method of the specific structural example of the quantum type photodetector concerning this embodiment, (A)-(C) is a top view. , (D) to (F) are sectional views, and (A) and (D), (B) and (E), and (C) and (F) show the same process. (A)-(F) is a schematic diagram for demonstrating the manufacturing method of the specific structural example of the quantum type photodetector concerning this embodiment, (A)-(C) is a top view. , (D) to (F) are sectional views, and (A) and (D), (B) and (E), and (C) and (F) show the same process. (A), (B) is a schematic diagram for demonstrating the manufacturing method of the specific structural example of the quantum type photodetector concerning this embodiment, (A) is a top view, (B) Is a cross-sectional view, and (A) and (B) show the same process. It is typical sectional drawing which shows the structure of the conventional quantum dot type | mold photodetector.

DESCRIPTION OF EMBODIMENTS Hereinafter, a quantum type photodetector according to an embodiment of the present invention will be described with reference to FIGS.
In this embodiment, the quantum photodetector is, for example, an infrared detector that generates a photocurrent according to the amount of incident infrared rays, and uses a quantum dot infrared detector (Quantum Dot Infrared) Photodetector (QDIP) will be described as an example. Note that the quantum dot infrared detector is also referred to as a quantum dot photodetector.

As shown in FIG. 1, the quantum dot infrared detector according to the present embodiment has an active layer 2 made of a semiconductor material active against light on a substrate 1 and upper and lower contacts sandwiching the active layer 2. An infrared detection element 5 including layers 3 and 4 and an external circuit 16 connected to the infrared detection element 5 are provided. Here, the substrate 1 is a semi-insulating semiconductor substrate.
The active layer 2 is also referred to as an active region. Moreover, since the active layer 2 is a layer that absorbs light, it is also referred to as a light absorption layer. Moreover, since the active layer 2 is a layer in which photoelectric conversion is performed, it is also referred to as a photoelectric conversion layer. The contact layers 3 and 4 are also referred to as electrode layers or contact regions. The infrared detecting element 5 is also referred to as a light detecting element, a detector element, a light receiving element, an optical semiconductor element, or a sensing unit. Further, since the infrared detecting element 5 can be regarded as a resistor whose resistance value changes in accordance with incident light (infrared rays here), it is also referred to as a photoconductor-type element.

  In the present embodiment, as shown in FIG. 2, the infrared detection element 5 includes a plurality of quantum dot layers 8 including quantum dots 6 and intermediate layers 7 sandwiching the quantum dots 6 as the active layer 2. That is, the infrared detection element 5 includes an active layer 2 including quantum dots 6 and an intermediate layer 7 made of a semiconductor material having a band gap larger than that of the quantum dots 6 with the quantum dots 6 interposed therebetween. Here, ten quantum dot layers 8 are provided.

The active layer 2 is also referred to as a quantum dot active layer. The intermediate layer 7 is also referred to as a barrier layer.
Specifically, the infrared detection element 5 includes a plurality of quantum dot layers 8 formed by sandwiching a lower n-type GaAs contact layer 4 and upper and lower InAs quantum dots 6 between AlGaAs intermediate layers 7 on a semi-insulating GaAs substrate 1. The upper n-type GaAs contact layer 3 is laminated. That is, each quantum dot layer 8 is formed by embedding InAs quantum dots 6 formed on the lower AlGaAs intermediate layer 7 with the upper AlGaAs intermediate layer 7, and n on both sides so as to sandwich these quantum dot layers 8. Type GaAs contact layers 3 and 4 are provided. Note that an infrared detection element array may be configured by arranging a plurality of infrared detection elements 5 in a two-dimensional array.

Here, since the InAs quantum dots 6 are formed by the self-organization forming method, they are distributed in a plane perpendicular to the growth direction. Here, in order to increase the infrared detection efficiency, a plurality of quantum dot layers 8 including a plurality of InAs quantum dots 6 distributed in the plane are stacked.
The AlGaAs intermediate layer 7 is, for example, an Al _0.2 Ga _0.8 As intermediate layer.
As shown in FIG. 1, an upper electrode 9 and a lower electrode 10 made of, for example, Ti / Pt / Au are attached to the upper n-type GaAs contact layer 3 and the lower n-type GaAs contact layer 4, respectively.

The upper electrode 9 and the lower electrode 10 are also referred to as current extraction electrodes. In addition, the upper electrode 9 and the lower electrode 10 are used to drive the infrared detection element 5 and read the photocurrent generated in response to the incidence of infrared rays on the active layer 2. Alternatively, it is also called a drive / read electrode.
The upper electrode 9 and the lower electrode 10 are connected to an external circuit 16 having a function of driving the infrared detection element 5 and a function of reading a photocurrent flowing through the infrared detection element 5.

Here, the external circuit 16 applies a bias voltage between the upper electrode 9 and the lower electrode 10 to drive the infrared detection element 5 and a current detector that detects the photocurrent flowing through the infrared detection element 5. 12. Here, the power supply 11 is a constant voltage source.
The current detector 12 only needs to detect a photocurrent. For example, the current detector 12 may detect a photocurrent using a voltage. The power supply 11 is also referred to as a drive power supply or a power supply circuit. The current detector 12 is also referred to as a current detection circuit.

A potential difference is given between the upper electrode 9 and the lower electrode 10 by a bias voltage supplied from the power supply 11, and the photocurrent flowing between these electrodes can be detected by the current detector 12. ing.
Thereby, the infrared ray can be detected by detecting the current change when the infrared ray is incident, that is, the current change caused by the incidence of the infrared ray on the active layer 2 and the generation of the photocurrent.

When the infrared detection element array is configured by arranging a plurality of infrared detection elements 5 in a two-dimensional array, the signal processing circuit array connected to the infrared detection element array via bumps includes the external circuit 16. become.
In the quantum dot infrared detector configured as described above, when light enters the active layer 2, the bound electrons existing in the quantum dot 6 are excited by absorbing the incident light, and are released from the binding of the quantum dot 6. The electrons released from the binding of the quantum dots 6 are collected on one electrode by the potential difference between the upper electrode 9 and the lower electrode 10, and a photocurrent is generated. An optical signal can be detected by reading a change in current flowing through the infrared detection element 5.

  By the way, in the present embodiment, in addition to the upper electrode 9 and the lower electrode 10 described above, resistance control is used for controlling the resistance of the active layer 2 on the side surface of the active layer 2 via the insulating film 13. An electrode 14 is attached. The resistance control electrode 14, the insulating film 13, and the active layer 2 form a MIS (Metal Insulator Semiconductor) structure. For this reason, the insulating film 13 preferably has a high dielectric constant.

  Here, a first insulating film 13A provided on one side surface of the active layer 2 and a first resistance control electrode 14A connected to the active layer 2 through the first insulating film 13A are provided. The second insulating film 13B provided on the other side opposite to the one side of the active layer 2 and the second resistance control electrode connected to the active layer 2 via the second insulating film 13B 14B. That is, the second resistance control electrode 14B is provided on the opposite side of the first resistance control electrode 14A with the active layer 2 interposed therebetween. Thus, in the present embodiment, a plurality of resistance control electrodes 14A and 14B are provided on the side surface of the active layer 2.

  Here, the resistance control electrodes 14A and 14B are not provided in the vicinity of the contact layers 3 and 4, but are provided only on the side of the active layer 2. Here, each of the resistance control electrodes 14 </ b> A and 14 </ b> B is provided only in the central portion in the thickness direction of the active layer 2. Thus, the resistance control electrodes 14A and 14B are not provided on the entire side surface of the active layer 2, but are provided at positions away from the electrodes 9 and 10, respectively. This is to prevent dielectric breakdown from occurring due to the voltage applied between the electrodes 9 and 10 and the resistance control electrodes 14A and 14B.

Further, the first resistance control electrode 14A and the second resistance control electrode 14B have a power source 15 (first power source) different from the power source 11 (first power source) to which the upper electrode 9 and the lower electrode 10 are connected. 2 power supplies). Here, the power supply 15 is a variable voltage source.
Since the power supply 15 supplies a control bias voltage for controlling the resistance of the active layer 2, it is also referred to as a resistance control power supply, a control power supply, or a control bias power supply. In addition, the power sources 15 connected to the resistance control electrodes 14A and 14B may be the same power source or different power sources.

A control bias voltage for controlling the resistance of the active layer 2 is supplied from the power supply 15 to each of the resistance control electrodes 14A and 14B.
Thereby, the resistance of the active layer 2 can be controlled by applying a control bias voltage to each of the resistance control electrodes 14A and 14B. As a result, the resistance of the active layer 2 can be controlled even after the optical crystal is configured after the device crystal is grown, and the yield at the time of manufacturing the optical detector is improved.

For this reason, in this embodiment, the external circuit 16 connected to the above-described infrared detection element 5 has a function of controlling the resistance of the active layer 2 of the infrared detection element 5 in addition to the above-described function. That is, the external circuit 16 includes a resistance control power supply 15 in addition to the driving power supply 11 and the current detector 12 described above.
Here, FIG. 3A to FIG. 3C are schematic views showing the potential of the MIS structure cross section from the resistance control electrode 14 to the active layer 2.

The potential state (energy band diagram) when no voltage is applied to the resistance control electrode 14 is as shown in FIG. When a voltage is applied to the resistance control electrode 14, the potential of the active layer 2 is modulated in accordance with the applied voltage, as shown in FIGS. 3 (B) and 3 (C). This change in potential induces carriers in the active layer 2 and changes the conductivity of the active layer 2. For example, when a positive voltage _Vb is applied to the resistance control electrode 14, as shown in FIG. 3B, the potential of the active layer 2 is lowered to induce electrons, and the n-type conductivity of the active layer 2 is increased. . On the other hand, when a negative voltage _Vb is applied to the resistance control electrode 14, the potential of the active layer 2 rises to induce holes, and the p-type conductivity of the active layer 2 increases. Since the resistance of the active layer 2 changes according to the carrier density of the active layer 2, the resistance of the active layer 2 can be controlled by adjusting the voltage applied to the resistance control electrode 14.

FIGS. 4A and 4B are schematic diagrams showing the potential of the cross section of the active layer 2 between the contact layers 3 and 4.
For example, as shown in FIG. 4A, the active layer 2 is not applied with a voltage due to unintentional p-type impurity contamination during crystal growth or the presence of crystal defects. The potential may increase. In this case, since the electron density of the active layer 2 is lowered, the active layer 2 has a high resistance. In such a case, when a positive voltage is applied to the resistance control electrode 14, as shown in FIG. 4B, the potential of the active layer 2 is lowered, electrons are induced, and the resistance of the active layer 2 is lowered. .

  That is, as shown in FIG. 5A, when the resistance of the active layer 2 is high when electrons are carriers and no voltage is applied to the resistance control electrode 14, a positive voltage is applied to the resistance control electrode 14. Is applied, the resistance of the active layer 2 can be lowered as shown in FIG. Similarly, when a positive voltage is applied to the resistance control electrode 14 even when holes are carriers and the resistance of the active layer 2 is low when no voltage is applied to the resistance control electrode 14, The resistance of 2 can be increased.

  On the other hand, as shown in FIG. 5C, when the resistance of the active layer 2 is low when electrons are used as carriers and no voltage is applied to the resistance control electrode 14, a negative voltage is applied to the resistance control electrode 14. Is applied, the resistance of the active layer 2 can be increased as shown in FIG. Similarly, when the resistance of the active layer 2 is high in a state where holes are carriers and no voltage is applied to the resistance control electrode 14, a negative voltage is applied to the resistance control electrode 14. 2 can be lowered.

Thus, when the resistance of the active layer 2 is not a desired value, the resistance of the active layer 2 can be controlled by applying a voltage of an appropriate polarity to the resistance control electrode 14.
As described above, the resistance of the active layer 2 is controlled by applying a voltage to the resistance control electrode 14 and modulating the potential of the active layer 2. Since this occurs in a region close to the control electrode 14, it is preferable to make the width of the active layer 2 sufficiently thin. That is, the width of the active layer 2 is sufficiently set so that the potential can be modulated over the entire width direction of the active layer 2 by the voltage applied to the resistance control electrode 14 provided on the side surface of the active layer 2. It is preferable to make it thin.

Next, a method for manufacturing the quantum photodetector according to the present embodiment will be described with reference to FIGS.
Here, a manufacturing method of a specific configuration example of the quantum dot infrared detector as shown in FIGS. 6A and 6B, that is, a plurality of infrared detection elements 5 separated by the separation groove 20 is provided. A method of manufacturing the quantum dot infrared detector provided will be described as an example. In FIGS. 6A and 6B, reference numerals 21 to 23 denote metal wirings, and reference numeral 24 denotes an SiO ₂ film (insulating film).

First, as shown in FIGS. 7A and 7D, for example, a molecular beam epitaxy (MBE) method is performed on the semi-insulating GaAs substrate 1 at a substrate temperature of about 600 ° C. An n-type GaAs contact layer 4 to be a contact layer is formed. Here, the thickness of the n-type GaAs contact layer 4 is about 1000 nm, for example, Si is used as the n-type dopant, and the concentration is about 2 × 10 ¹⁸ / cm ³ , for example.

Next, the quantum dot active layer 2 is formed on the n-type GaAs contact layer 4.
That is, firstly, on the n-type GaAs contact layer _4, to form the _{i-Al x Ga 1-x} As intermediate layer 7 (see FIG. 2). _{Here, i-Al x Ga 1-} x As intermediate layer 7, and the Al composition x for example about 0.2, and the thickness of, for example, about 50nm.
Next, while the i-Al _x Ga _1-x As intermediate layer 7 is grown, the substrate temperature is lowered from about 600 ° C. to about 485 ° C., for example.

Then, for example, the growth rate is about 0.2 molecular layer / second (ML / s), and InAs is supplied for about 2.3 molecular layers. By supplying a certain amount, the compressive strain applied to InAs increases, and InAs grows three-dimensionally to form InAs quantum dots 6 (self-organization forming method) (see FIG. 2).
Next, an i-Al _x Ga _1-x As intermediate layer 7 is formed so as to cover the InAs quantum dots 6 (see FIG. 2). _{Here, i-Al x Ga 1-} x As intermediate layer 7, and the Al composition x for example about 0.2, and the thickness of, for example, about 50nm.

Thereafter, the process of forming the InAs quantum dots 6 and the process of forming the i-Al _x Ga _1-x As intermediate layer 7 are repeated, for example, nine times alternately (see FIG. 2).
Then, while the final i-Al _x Ga _1-x As intermediate layer 7 is grown, the substrate temperature is raised from about 485 ° C. to about 600 ° C., for example.
In this manner, the quantum dot active layer 2 including the InAs quantum dots 6 and the i-Al _x Ga _1-x As intermediate layer 7 is formed on the n-type GaAs contact layer 4.

Next, the n-type GaAs contact layer 3 serving as the upper contact layer is formed on the uppermost i-Al _x Ga _1-x As intermediate layer 7 at a substrate temperature of 600 ° C., for example. Here, the thickness of the n-type GaAs contact layer 3 is about 1000 nm, for example, Si is used as the n-type dopant, and the concentration is about 2 × 10 ¹⁸ / cm ³ , for example.
In this manner, a wafer having a laminated structure in which a plurality of quantum dot layers 8 constituting the active layer 2 are sandwiched between the n-type GaAs contact layers 3 and 4 on the semi-insulating GaAs substrate 1 (after the MBE film formation). Substrate) is formed.

Next, as shown in FIGS. 7B and 7E, separation grooves 20 are formed so that a plurality of infrared detection elements 5 (pixels) are formed by lithography and dry etching, for example. Here, the separation groove 20 reaching from the surface side to the n-type GaAs contact layer 4 located on the substrate side is formed.
In forming the separation groove 20, the active layer 2 of each infrared detection element 5 is controlled so that the resistance of the active layer 2 can be controlled by the voltage applied to the resistance control electrodes 14 provided on both side surfaces of the active layer 2. Determine the width.

  Here, when a voltage is applied to the resistance control electrode 14, the depth of the region where the applied electric field reaches in the active layer 2 is the impurity doping concentration of the active layer 2, the thickness of the insulating film 13, the thickness of the active layer 2. It can be estimated from parameters such as the dielectric constant of the material and the material of the insulating film 13. See, for example, S.M.Sze et al., “Physics of Semiconductor Devices third edition”, Wiley-Interscience, pp. 198-207.

Here, it is assumed that an unintended background impurity is mixed in the i-Al _x Ga _1-x As intermediate layer 7 at a concentration of about 10 ¹⁵ / cm ^{3 and functions} as a donor impurity or an acceptor impurity. Is about 10 nm, and the relative dielectric constant of the active layer material and the insulating film material is about 10. When the voltage is applied to each of the resistance control electrodes 14 provided on both sides of the active layer 2 in the range of about 1 to about 4 V, the total depth of the region where the electric field applied from both sides of the active layer 2 reaches Is estimated to be about 2 to about 4 μm. Therefore, when the resistance control electrodes 14 are provided on both sides of the active layer 2, the potential can be modulated over the entire width of the active layer 2 if the width of the active layer 2 is about 2 to about 4 μm. become. Based on this, here, the separation groove 20 is formed so that the width of the active layer 2 of each infrared detection element 5 is about 3 μm.

Next, as shown in FIGS. 7C and 7F, for example, a SiO ₂ film 24 is embedded and grown by a CVD (Chemical Vapor Deposition) method using, for example, tetraethoxysilane (TEOS). Let See, for example, IAShareef et al., “Subatmaspheric chemical vapor deposition ozone / TEOS process for SiO ₂ trench filling”, J. Vac. Sci. Technol. B 13 (4), Jul / Aug 1995, pp. 1888-1892.

Then, as shown in FIGS. 8A and 8D, planarization is performed by, for example, a CMP (Chemical Mechanical Polishing) process. For example, by using an abrasive such as CeO ₂ , the polishing can be automatically stopped due to the difference in the polishing rate between GaAs and SiO ₂ when the surface of the upper GaAs contact layer 3 is exposed. .
Next, as shown in FIGS. 8B and 8E, a contact hole 25 reaching the lower GaAs contact layer 4 is formed by lithography and dry etching, for example.

  Next, after removing the resist, as shown in FIGS. 8C and 8F, the lower electrode 10 is formed on the lower GaAs contact layer 4 by, for example, lithography, electron beam evaporation, sputtering, and lift-off. An upper electrode 9 is formed on the GaAs contact layer 3. That is, first, a resist having a window in the electrode formation region is formed by lithography, an electrode material such as Ti / Pt / Au is formed by electron beam evaporation or sputtering, and lift-off is performed together with the resist to form the upper electrode 9. Then, the lower electrode 10 is patterned. Thereafter, heat treatment is performed to form an alloy. In this way, the upper electrode 9 and the lower electrode 10 are formed.

Here, since the lower GaAs contact layer 4 and the lower electrode 10 are common to the plurality of infrared detection elements 5, they are also referred to as a common contact layer and a common electrode, respectively. On the other hand, the upper GaAs contact layer 3 and the upper electrode 9 are provided separately for each infrared detection element 5.
Next, as shown in FIGS. 9A and 9D, a resist 26 having a window 26A is formed above the separation groove 20 by lithography, for example, and the time shown in FIG. B) As shown in FIG. 9E, the SiO ₂ film 24 is removed to a desired depth. Here, so as to leave only the thickness of the SiO ₂ film 24, for example, about 200 nm, etching the SiO ₂ film 24. The depth to which the SiO ₂ film 24 is etched is determined by the height position where the resistance control electrode 14 is provided.

Next, after removing the resist, as shown in FIGS. 9C and 9F, an Al ₂ O ₃ film 13X is formed on the entire surface in order to form the insulating film 13. Here, for example, at about 300 ° C., for example, about 10 nm of Al by an atomic layer deposition (ALD) method using alternating supply of trimethylaluminum (TMA) (Al (CH ₃ ) ₃ ) and H ₂ O. _{A 2} O ₃ film 13X is formed. For example, PDYe et al, “GaAs metal-oxide-semiconductor field-effect transistor with nanometer-thin dielectrc grown by atomic layer deposition”, Applied Physics Letters, Vol. 83, No. 1, 7 July 2003, pp. 180-182 reference.

Note that before the film formation by the ALD method, the GaAs-based natural oxide film or the damaged layer may be removed by etching, for example, with NH ₄ solution or the like.
Next, as shown in FIGS. 10A and 10D, in order to form the resistance control electrode 14, for example, a Ti / Au layer 14X is grown on the entire surface.
Thereafter, as shown in FIGS. 10B and 10E, a resist 27 having a window 27A is formed above the separation groove 20 by lithography, for example, and the separation groove 20 is formed by anisotropic ion milling, for example. A part of the Ti / Au layer 14X buried above is removed. Here, the Ti / Au layer 14X having a desired thickness (here, about 150 nm) is left. Thereby, the resistance control electrode 14 made of the Ti / Au layer 14X having a desired thickness is formed. The resistance control electrode 14 is also referred to as a buried electrode because it is buried in the separation groove 20. The resistance control electrode 14 is also referred to as a side electrode.

Next, as shown in FIGS. 10C and 10F, after the resist 27 is removed, a resist 28 is formed again so as to cover the upper part of the separation groove 20 by lithography, for example. Thereafter, the Ti / Au layer 14X formed in the region not covered with the resist 28 is removed by, for example, ion milling, and the Al ₂ O ₃ layer 13X is removed by etching using, for example, dilute HF.

In this manner, the insulating film 13 is formed on the side surface of each infrared detection element 5, that is, one side surface and the other side surface of the active layer 2. In addition, a resistance control electrode 14 connected to the side surface of each infrared detection element 5, that is, one side surface and the other side surface of the active layer 2 via the insulating film 13 is formed.
Next, as shown in FIGS. 11 (A) and 11 (D), after the resist 28 is removed, as shown in FIGS. 11 (B) and 11 (E), for example, by the TEOS-CVD method, SiO 2 is used. _Two films 24 (insulating film) are embedded and grown, and planarized by CMP.

Then, as shown in FIGS. 11C and 11F, the SiO ₂ film 24 above the contact region, that is, the upper electrode 9, the lower electrode 10, and the resistance control electrode 14, for example, by lithography and dry etching. Open the window 24A. Then, as shown in FIGS. 12A and 12B, metal wirings 21 to 23 are formed so as to be connected to the electrodes 9, 10, and 14, respectively.

Next, the wafer is diced to a chip size.
Thereafter, an external circuit 16 is connected to each infrared detection element 5. That is, the drive power supply 11 and the current detector 12 are connected to the upper electrode 9 and the lower electrode 10 provided in each infrared detection element 5, and the resistance provided on the side surface of each infrared detection element 5 via the insulating film 13. A control power supply 15 is connected to the control electrode 14 (see FIG. 1). Thereby, the quantum dot infrared detector is completed.

Therefore, according to the quantum photodetector according to the present embodiment, there is an advantage that the resistance of the active layer 2 can be reliably controlled and the yield can be improved.
In addition, this invention is not limited to the structure described in embodiment mentioned above, A various deformation | transformation is possible in the range which does not deviate from the meaning of this invention.
For example, in the above-described embodiment, the width of the active layer 2 is reduced, and the resistance control electrode 14 is provided on each of one side surface and the other side surface of the active layer 2, but this is not limitative. It is not a thing. For example, the resistance control electrode may be provided only on one of the one side surface and the other side surface of the active layer. In addition, for example, without making the width of the active layer thin, for example, the width and depth of the active layer may be the same, and a resistance control electrode may be provided on each of the four side surfaces. Resistance control electrodes may be provided on the two side surfaces of this side surface and the other side surface opposite to the one side surface. In short, a resistance control electrode may be provided on at least one side surface of the active layer. In this case, the insulating film may be provided on at least one side surface of the active layer, that is, one side surface on which the resistance control electrode is provided.

In the above-described embodiment, the active layer 2 is a quantum dot active layer. However, the present invention is not limited to this. For example, the active layer may be a quantum well active layer. That is, the present invention can also be applied to a quantum well type photodetector.
In the above-described embodiment, the active layer 2 is not doped with impurities. However, the present invention is not limited to this. For example, as long as the resistance of the active layer can be controlled by the voltage applied to the resistance control electrode. The active layer may be doped with impurities.

In addition, the materials and forming methods of the semiconductor layers, insulating films, electrodes, and the like that constitute the infrared detection element of the above-described embodiment are not limited to those of the above-described embodiment. For example, in the above-described embodiment, an Al ₂ O ₃ film is used as an insulating film provided between the active layer 2 and the resistance control electrode 14, but the present invention is not limited to this. For example, an HfO ₂ film or SiO _{2 Two} films or the like may be used as the insulating film.

1 substrate (semi-insulating GaAs substrate)
2 Active layer 3 Upper contact layer (upper n-type GaAs contact layer)
4 Lower contact layer (lower n-type GaAs contact layer)
5 Infrared detector 6 Quantum dot (InAs quantum dot)
7 Intermediate layer (AlGaAs intermediate layer)
8 Quantum dot layer 9 Upper electrode 10 Lower electrode 11 Power supply (drive power supply)
12 Current detector 13 Insulating film 13A First insulating film 13B Second insulating film 13X Al ₂ O ₃ film 14 Resistance control electrode 14A First resistance control electrode 14B Second resistance control electrode 14X Ti / Au layer 15 Power supply ( Control power)
16 External circuit 20 Separation groove 21-23 Metal wiring 24 SiO ₂ film 25 Contact hole 26 Resist 26A Window 27 Resist 27A Window 28 Resist

Claims (5)

An active layer,
A contact layer sandwiching the active layer;
An electrode provided in the contact layer;
A first insulating film provided on at least one side surface of the active layer;
Provided on the side surface of the active layer through the first insulating film, and when the resistance of the active layer is high, a positive voltage is applied when electrons are used as carriers in order to reduce the resistance of the active layer, When holes are used as carriers, a negative voltage is applied. When the resistance of the active layer is low, a negative voltage is applied when electrons are used as carriers to increase the resistance of the active layer. A quantum type photodetector comprising a first resistance control electrode to which a positive voltage is applied when a carrier is used. A first power source connected to the electrode;
2. The quantum photodetector according to claim 1, further comprising a second power source connected to the first resistance control electrode and different from the first power source.   3. The quantum photodetector according to claim 1, wherein the first resistance control electrode is provided only in a central portion in a thickness direction of the active layer.   The quantum type according to any one of claims 1 to 3, wherein the active layer includes a quantum dot and an intermediate layer sandwiching the quantum dot and having a band gap larger than that of the quantum dot. Photo detector. A second insulating film provided on the other side opposite to the one side of the active layer;
Provided on the side surface of the active layer through the second insulating film, and when the resistance of the active layer is high, a positive voltage is applied when electrons are used as carriers in order to reduce the resistance of the active layer, When holes are used as carriers, a negative voltage is applied. When the resistance of the active layer is low, a negative voltage is applied when electrons are used as carriers to increase the resistance of the active layer. 5. The quantum photodetector according to claim 1, further comprising a second resistance control electrode to which a positive voltage is applied when the carrier is used.