JP2012195333A - Quantum dot type infrared detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a response wavelength longer without lowering characteristics such as sensitivity and S/N in a quantum dot type infrared detector.SOLUTION: The quantum dot type infrared detector includes: the quantum dot 1; intermediate layers 2 which sandwich the quantum dot 1 and have an energy gap wider than that of the quantum dot 1; a base well layer 5 having the energy gap narrower than that of the intermediate layers 2; a first buried barrier layer 6 having the energy gap wider than that of the intermediate layers 2; and a second buried barrier layer 7 provided on the first buried barrier layer 6 and having the energy gap wider than that of the first buried barrier layer 6.

Description

  The present invention relates to a quantum dot infrared detector.

2. Description of the Related Art In recent years, quantum dot photodetectors have attracted attention as photodetectors that detect light using a current that flows when incident light is absorbed. In contrast to conventional quantum well photodetectors that cannot absorb normal incident light, quantum dot photodetectors can confine carriers in three dimensions and absorb normal incident light.
A typical example is a quantum dot infrared detector.

Here, FIG. 5 shows the structure of a standard quantum dot infrared detector.
As shown in FIG. 5, the quantum dot infrared detector includes an active layer (photoelectric conversion layer) 103 in which an InAs quantum dot 100 is embedded in an i-GaAs intermediate layer 101 and is repeatedly stacked. The contact layer 104 is sandwiched between the contact layers. This structure is referred to as a first structure. Here, the active layer 103 is formed by laminating the quantum dots 100, but may include one layer of quantum dots.

  In the quantum dot infrared detector configured as described above, when light is incident on the active layer 103, the electrons bound to the transition source level of the quantum dot 100 are excited by the light, and the subband is transferred to the transition destination level. The transition is made and the quantum dot 100 is released from the binding by thermal excitation or tunnel effect. Then, the electrons released from the binding of the quantum dots 100 are collected in one n-GaAs electrode layer 104 by a voltage applied through the n-GaAs electrode layers 104 on both sides, and a photocurrent is generated. An optical signal can be detected by a change in the photocurrent flowing through the detector.

There is also a quantum dot infrared detector having a structure in which an InAs quantum dot is surrounded by an AlGaAs barrier layer having a wider energy gap (energy difference between the bottom of the conduction band and the top of the valence band) than the GaAs intermediate layer. This structure is referred to as a second structure.
Further, there is a quantum dot infrared detector having a structure (dot-in-a-well: DWELL structure) in which an InAs quantum dot is sandwiched between InGaAs well layers (and GaAs well layers) and further sandwiched between AlGaAs barrier layers. . This structure is referred to as a third structure.

  In addition, an InGaAs layer is formed on the GaAs layer, an InAs quantum dot is formed on the InGaAs layer, the InAs quantum dot is covered with an AlGaAs layer, and a GaAs layer is formed thereon. There is also a bowl. This structure is referred to as a fourth structure.

JP 2007-242766 A

RV Shenoi et al., “Low-strain InAs / InGaAs / GaAs quantum dots-in-a-well infrared based”, J. Vac. Sci. Technol. B 26 (3), May / Jun 2008, pp. 1136- 1139

By the way, as characteristics of the infrared detector, it is important that the signal (S) is large and the ratio of signal to noise (S / N) is large at a specific response wavelength.
However, in the first structure described above, sufficient photocurrent cannot be generated, and sensitivity (corresponding to a signal) is low. That is, the signal is small and the S / N is small at a specific response wavelength.
Further, in the above-described second structure, the height of the energy barrier around the quantum dot increases, so that the quantum confinement effect in the quantum dot becomes strong, and the electrons excited by light easily transition, and as a result, The sensitivity of the quantum dot infrared detector is improved.

However, when the height of the energy barrier around the quantum dots is increased as in the second structure described above, the energy difference from the transition source level to the transition destination level also increases, and the response wavelength is shortened. End up.
Furthermore, in the above-described third structure, the response wavelength can be increased, but the structure is vertically symmetrical with the quantum dot interposed therebetween, and a well layer is provided around the quantum dot. The barrier height is lowered and the quantum confinement effect is weakened. For this reason, it becomes difficult for the electrons excited by light to make a transition, and as a result, the sensitivity decreases.

In general, in a quantum dot infrared detector, when the response wavelength is increased, the energy difference between the transition source level and the transition destination level is reduced, and noise is relatively increased, and sensitivity, S / N, and the like are increased. The characteristics will deteriorate.
As described above, in the quantum dot infrared detector, the response wavelength is shortened when the characteristics are improved, and the characteristics are deteriorated when the response wavelength is lengthened. That is, it is difficult to achieve both improvement in characteristics and a longer response wavelength.

In the fourth structure described above, a dark current (current other than photocurrent: utilizing a difference in energy gap between the InGaAs layer below the InAs quantum dot and the AlGaAs layer covering the top of the InAs quantum dot is utilized. Noise equivalent) and characteristics can be improved.
However, in the above-described fourth structure, the height of the energy barrier and the response wavelength are determined by the energy gap between the InGaAs layer and the AlGaAs layer provided around the InAs quantum dots, that is, the energy level at the bottom of the conduction band. In this case, if an attempt is made to improve the characteristics by increasing the height of the energy barrier, the energy difference from the transition source level to the transition destination level also increases, and the response wavelength is shortened. On the other hand, if an attempt is made to increase the response wavelength, the height of the energy barrier is lowered and the characteristics are degraded. As described above, it is difficult to improve both the characteristics and to increase the response wavelength.

  Therefore, it is desired to increase the response wavelength without degrading characteristics such as sensitivity and S / N.

  For this reason, this quantum dot type infrared detector has a quantum dot, an intermediate layer with a wider energy gap than the quantum dot, an underlayer with a narrow energy gap than the intermediate layer, and an intermediate layer. It is a requirement to include a first buried barrier layer having a wide energy gap and a second buried barrier layer provided on the first buried barrier layer and having a wider energy gap than the first buried barrier layer.

  Therefore, according to the present quantum dot infrared detector, there is an advantage that the response wavelength can be increased without degrading characteristics such as sensitivity and S / N.

It is a typical sectional view showing the composition of the quantum dot type infrared detector concerning a 1st embodiment. It is a typical sectional view showing the composition of the quantum dot type infrared detector concerning a 2nd embodiment. It is a typical sectional view showing the composition of the quantum dot type infrared detector concerning a 3rd embodiment. It is a typical sectional view showing the composition of the quantum dot type infrared detector concerning a 4th embodiment. It is a typical sectional view showing the composition of a standard quantum dot type infrared detector.

Hereinafter, a quantum dot infrared detector according to an embodiment of the present invention will be described with reference to the drawings.
[First Embodiment]
First, the quantum dot infrared detector according to the first embodiment will be described with reference to FIG.

The quantum dot infrared detector according to the present embodiment is an infrared detector having a quantum dot structure as an infrared absorber.
In the present embodiment, as shown in FIG. 1, the quantum dot infrared detector includes a photoelectric conversion layer (including a quantum dot 1 and an intermediate layer 2 sandwiching the quantum dot 1 and having a wider energy gap than the quantum dot 1 ( Active layer) 3 and an electrode layer (contact layer) 4 sandwiching the photoelectric conversion layer 3.

Here, the quantum dot 1 is an InAs quantum dot and is a self-assembled quantum dot. The intermediate layer 2 is an i-AlGaAs intermediate layer. For example, the i-Al _0.15 Ga _0.85 As intermediate layer 2 has a thickness of about 50 nm. Furthermore, the electrode layer 4 is an n-GaAs electrode layer.
In particular, in the present embodiment, the underlying well layer 5 having a narrow energy gap than the intermediate layer 2, the first buried barrier layer 6 having a wider energy gap than the intermediate layer 2, and the wider energy gap than the first buried barrier layer 6. The second buried barrier layer 7 is provided.

  Here, the base well layer 5 is a base layer of the quantum dots 1. The thickness of the underlying well layer 5 is preferably about 1 ML or more and about 10 ML or less. Thus, the characteristic improvement effect is reliably acquired by making the thickness of the foundation | substrate well layer 5 into about 10 ML or less. That is, by reducing the thickness of the underlying well layer 5, the quantum confinement effect by the intermediate layer 2 can be obtained, the sensitivity can be improved, and the characteristic improvement effect can be surely obtained. Here, the base well layer 5 is a GaAs base well layer, and has a thickness of about 3 ML, for example. Here, the underlying well layer 5 is a GaAs layer. However, the present invention is not limited to this, and the underlying well layer 5 may have a narrow energy gap as compared with the intermediate layer 2. For example, an AlGaAs layer having a narrower energy gap than the intermediate layer 2 may be used as the base well layer 5.

The first buried barrier layer 6 is a buried layer that embeds the quantum dots 1 and is a barrier layer that forms an energy barrier against electrons bound to the quantum dots 1. The thickness of the first buried barrier layer 6 is preferably smaller than the thickness of the second buried barrier layer 7, and is preferably about 1 ML or more and about 3 ML or less. Here, the first buried barrier layer 6 is an AlGaAs first buried barrier layer. For example, the Al _0.17 Ga _0.83 As first buried barrier layer 6 has a thickness of about 3 ML.

The second embedded barrier layer 7 is provided on the first embedded barrier layer 6. The second embedded barrier layer 7 is an embedded layer that embeds the quantum dots 1 and is a barrier layer that forms an energy barrier against electrons bound to the quantum dots 1. Furthermore, as described above, since the second buried barrier layer 7 has a wider energy gap than the first buried barrier layer 6, the height of the energy barrier of the second buried barrier layer 7 is the same as that of the first buried barrier layer 6. It is higher than the height of the energy barrier. Here, the second buried barrier layer 7 is an AlGaAs second buried barrier layer. For example, the Al _0.3 Ga _0.7 As second buried barrier layer 7 has a thickness of about 6 ML. Here, although the second buried barrier layer 7 is an AlGaAs layer, the present invention is not limited to this, and any second buried barrier layer 7 having a wider energy gap than the first buried barrier layer 6 may be used. For example, an AlAs layer having a wider energy gap than the first buried barrier layer 6 may be used as the second buried barrier layer 7.

In the present embodiment, the same constituent material of Al _x Ga _1-x As (0 ≦ x ≦ 1) is used as the material for the intermediate layer 2, the first buried barrier layer 6, the second buried barrier layer 7, and the underlying well layer 5. The energy gap relationship of the intermediate layer 2, the first buried barrier layer 6, the second buried barrier layer 7, and the underlying well layer 5 is realized by changing the composition of the semiconductor material containing the material.
As described above, in this embodiment, the quantum dot 1 is provided on the underlying well layer 5 and is buried by the two buried barrier layers of the first buried barrier layer 6 and the second buried barrier layer 7. That is, the underlying well layer 5 is in contact with the lower surface (lower part) of the quantum dot 1, and the first embedded barrier layer 6 and the second embedded barrier layer 7 are in contact with the upper surface (upper part) of the quantum dot 1. The first buried barrier layer 6 has a lower energy barrier than the second buried barrier layer 7.

  In this case, the response wavelength is determined by the energy gap between the underlying well layer 5 and the first buried barrier layer 6, that is, the energy level at the bottom of the conduction band. On the other hand, the energy gap of the second buried barrier layer 7, that is, the energy level at the bottom of the conduction band, determines the height of the energy barrier against electrons bound to the quantum dots 1. For this reason, the response wavelength and the height of the energy barrier can be set independently. That is, the response wavelength can be increased by setting the energy gap between the underlying well layer 5 and the first buried barrier layer 6. On the other hand, by setting the energy gap of the second buried barrier layer 7, the height of the energy barrier is increased, the quantum confinement effect is strengthened, and the electrons excited by light are easily transferred, thereby improving the sensitivity. Can do. That is, it is possible to achieve both a longer response wavelength and improved characteristics such as sensitivity and S / N.

  In this embodiment, the quantum dot 1 provided on the underlying well layer 5 and covered with the first buried barrier layer 6 and the second buried barrier layer 7, that is, the underlying well layer 5, the quantum dot 1, the first The intermediate layer 2 is provided so as to sandwich the quantum dot layer 8 including the embedded barrier layer 6 and the second embedded barrier layer 7. In the present embodiment, a plurality of quantum dot layers 8 are repeatedly stacked via the intermediate layer 2. That is, the photoelectric conversion layer 3 has a structure in which a plurality of quantum dot layers 8 are stacked via the intermediate layer 2. Here, the photoelectric conversion layer 3 includes a plurality of quantum dot layers 8, but may include a single quantum dot layer.

  In the quantum dot infrared detector configured as described above, when light is incident on the photoelectric conversion layer 3, the electrons bound to the transition source level of the quantum dot 1 are excited by the light, and the electrons are sublimated to the transition destination level. Transition between bands causes the quantum dot 1 to be released from the binding by thermal excitation or tunnel effect. Then, the electrons released from the binding of the quantum dots 1 are collected in one n-GaAs electrode layer 4 by a voltage applied via the n-GaAs electrode layers 4 on both sides, and a photocurrent is generated. An optical signal is detected by a change in the photocurrent flowing through the detector.

Next, the manufacturing method of the quantum dot type infrared detector concerning this embodiment is demonstrated.
First, an n-type GaAs electrode layer 4 to be a lower electrode layer is formed on a semi-insulating GaAs substrate (not shown), for example, at a substrate temperature of about 600 ° C. by, for example, molecular beam epitaxy (MBE). To do. Here, the thickness of the n-type GaAs electrode 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 i-AlGaAs intermediate layer 2 is formed on the n-type GaAs electrode layer 4. Here, the i-Al _0.15 Ga _0.85 As intermediate layer 2 having a thickness of about 50 nm is grown.
Next, for example, after the substrate temperature is lowered from about 600 ° C. to about 500 ° C., about 3 ML of GaAs is grown on the i-AlGaAs intermediate layer 2 to form a GaAs underlayer 5 having a thickness of about 3 ML. To do.

Next, InAs quantum dots 1 are formed on the GaAs underlayer 5. For example, the InAs supply rate is about 0.1 ML / s, and InAs is supplied for about 2.3 ML. Thereby, InAs exceeding the critical film thickness becomes the self-assembled quantum dot 1.
Next, the AlGaAs first buried barrier layer 6 is formed on the GaAs underlayer 5 so that the InAs quantum dots 1 are buried with the AlGaAs first buried barrier layer 6. For example, Al _0.17 Ga _0.83 As is grown by about 3 ML to form an Al _0.17 Ga _0.83 As first buried barrier layer 6 having a thickness of about 3 ML.

Next, the AlGaAs second buried barrier layer 7 is formed on the AlGaAs first buried barrier layer 6 so that the InAs quantum dots 1 are buried with the AlGaAs second buried barrier layer 7. For example, Al _0.3 Ga _0.7 As is grown by about 6 ML to form the Al _0.3 Ga _0.7 As second buried barrier layer 7 having a thickness of about 6 ML.
Then, for example, after raising the substrate temperature from about 500 ° C. to about 600 ° C., the i-AlGaAs intermediate layer 2 is formed on the AlGaAs second buried barrier layer 7. Here, the i-Al _0.15 Ga _0.85 As intermediate layer 2 having a thickness of about 50 nm is grown. Thereby, a quantum dot layer 8 including the GaAs underlayer 5, InAs quantum dots 1, AlGaAs first buried barrier layer 6 and AlGaAs second buried barrier layer 7 is formed between the i-AlGaAs intermediate layer 2.

  Thereafter, the above-described steps, that is, the steps from the step of forming the GaAs underlayer 5 to the step of forming the i-AlGaAs intermediate layer 2 are repeated, for example, 29 times. Thereby, the photoelectric conversion layer 3 including, for example, 30 quantum dot layers 8, that is, the photoelectric conversion layer 3 having a structure in which, for example, 30 quantum dot layers 8 are stacked via the intermediate layer 2 is formed. That is, the InAs quantum dot 1 and the photoelectric conversion layer 3 including the InAs quantum dot 1 and the i-AlGaAs intermediate layer 2 having a wider energy gap than the InAs quantum dot 1 are formed. In FIG. 1, only two quantum dot layers 8 are shown for convenience of explanation.

Next, an n-type GaAs electrode layer 4 serving as an upper electrode layer is formed on the photoelectric conversion layer 3, that is, on the uppermost i-AlGaAs intermediate layer 2 at a substrate temperature of 600 ° C., for example. Here, the thickness of the n-type GaAs electrode 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. Thereby, the n-type GaAs electrode layer 4 is formed so as to sandwich the photoelectric conversion layer 3.

The wafer on which each semiconductor layer has been grown in this manner is patterned by, for example, lithography, and etched to the n-type GaAs electrode layer 4 that becomes the lower electrode layer, and pixel separation is performed at a pitch of 30 μm, for example. Here, the pixel size is 25 μm square.
Next, the reflective film is coated. For example, a film made of a highly reflective material such as a metal film such as gold, silver, or aluminum, or a composite film such as AuGe / Au is formed as the reflective film by sputtering or vacuum deposition. Here, the reflective film is made of a conductive material and is used as a part of the electrode. For this reason, the upper electrode and the lower electrode are simultaneously formed on the upper and lower n-type GaAs electrode layers.

Next, the element surface (region other than the electrode) is covered with a protective film made of, for example, SiN or SiON.
Then, bumps made of, for example, indium (In) are formed on the reflective films as upper and lower electrodes of all the pixels, and a semiconductor integrated circuit (readout circuit: for example) formed on the silicon substrate through the bumps. CMOS circuit). Thereby, the quantum dot infrared detector is completed.

Such a quantum dot infrared detector gives a potential difference of, for example, 1 V between the n-type GaAs electrode layers 4 (for example, the lower electrode is a cathode and the upper electrode is an anode), and the current flowing between them is measured, so that infrared rays are incident. Since the photocurrent flowing as a response of the quantum dot 1 to can be observed, it functions as an infrared detector.
Therefore, according to the quantum dot infrared detector according to the present embodiment, there is an advantage that the response wavelength can be increased without degrading characteristics such as sensitivity and S / N.
[Second Embodiment]
Next, a quantum dot infrared detector according to the second embodiment will be described with reference to FIG.

  The quantum dot infrared detector according to the present embodiment is different from that of the first embodiment described above in that the first between the first embedded barrier layer 6 and the second embedded barrier layer 7, as shown in FIG. The difference is that a buried well layer (first buried well layer) 9 having a narrow energy gap is provided rather than the one buried barrier layer 6. In FIG. 2, the same components as those in the first embodiment (see FIG. 1) are denoted by the same reference numerals.

  Here, the buried well layer 9 is provided on the first buried barrier layer 6. A second buried barrier layer 7 is provided on the buried well layer 9. That is, the buried well layer 9 is in contact with the upper surface of the first buried barrier layer 6 and in contact with the lower surface of the second buried barrier layer 7. The buried well layer 9 is, for example, a GaAs buried well layer, and has a thickness of about 6 ML. Here, although the buried well layer 9 is a GaAs layer, the present invention is not limited to this, and any buried well layer 9 having a narrow energy gap as compared with the first buried barrier layer 6 may be used. For example, an AlGaAs layer having a narrower energy gap than the first buried barrier layer 6 may be used as the buried well layer 9.

In the present embodiment, Al _x Ga _1-x As (0 ≦ x ≦ 1) is used as the material for the intermediate layer 2, the first buried barrier layer 6, the second buried barrier layer 7, the underlying well layer 5, and the buried well layer 9. The semiconductor material containing the same constituent material is used and the composition is changed to change the energy gap of the intermediate layer 2, the first buried barrier layer 6, the second buried barrier layer 7, the underlying well layer 5, and the buried well layer 9. Realizing the relationship.

Next, the manufacturing method of the quantum dot type infrared detector concerning this embodiment is demonstrated.
The manufacturing method of the quantum dot infrared detector according to the present embodiment includes the step of forming the first embedded barrier layer 6 and the second embedded barrier layer in the method of manufacturing the quantum dot infrared detector of the first embodiment described above. What is necessary is just to add the process of forming the buried well layer 9 between the processes of forming 7.

Specifically, first, as in the case of the first embodiment described above, a step of forming an n-type GaAs electrode layer 4 serving as a lower electrode layer, a step of forming an i-AlGaAs intermediate layer 2, a GaAs underlayer 5, a process for forming InAs quantum dots 1, and a process for forming the AlGaAs first buried barrier layer 6.
Next, the GaAs buried well layer 9 is formed on the AlGaAs first buried barrier layer 6 so that the InAs quantum dots 1 are buried in the GaAs buried well layer 9. For example, GaAs is grown by about 6 ML to form a GaAs buried well layer 9 having a thickness of about 6 ML.

Next, the AlGaAs second buried barrier layer 7 is formed on the GaAs buried well layer 9 so that the InAs quantum dots 1 are buried with the AlGaAs second buried barrier layer 7. For example, Al _0.3 Ga _0.7 As is grown by about 4 ML to form the Al _0.3 Ga _0.7 As second buried barrier layer 7 having a thickness of about 4 ML.
Thereafter, the quantum dot infrared detector is completed through the same process as in the first embodiment.

Since other details are the same as those of the first embodiment described above, the description thereof is omitted here.
Therefore, according to the quantum dot infrared detector according to the present embodiment, the response wavelength can be increased without degrading characteristics such as sensitivity and S / N, as in the case of the first embodiment described above. There is an advantage.

In particular, according to the structure of the present embodiment described above, electrons that have passed over the first buried barrier layer 6 can stay in the buried well layer 9, and the probability of overcoming the second buried barrier layer 7 can be increased. For this reason, the photocurrent increases and the sensitivity can be improved.
[Third Embodiment]
Next, a quantum dot infrared detector according to a third embodiment will be described with reference to FIG.

  The quantum dot infrared detector according to this embodiment is different from that of the first embodiment described above in that a buried well layer (second buried well layer) 10 is formed on the second buried barrier layer 7 as shown in FIG. And the third buried barrier layer 11 is provided on the buried well layer 10. In FIG. 3, the same components as those in the first embodiment described above (see FIG. 1) are denoted by the same reference numerals.

  That is, the present quantum dot infrared detector includes the buried well layer 10 having a narrower energy gap than the second buried barrier layer 7 on the second buried barrier layer 7, and further the second buried barrier 10 on the buried well layer 10. A third buried barrier layer 11 having the same energy gap as the layer 7 is provided. That is, the buried well layer 10 is provided between the second buried barrier layer 7 and the third buried barrier layer 11, is in contact with the upper surface of the second buried barrier layer 7, and is formed on the third buried barrier layer 11. It touches the bottom surface.

  Here, the buried well layer 10 is, for example, a GaAs buried well layer and has a thickness of about 6 ML. Here, although the buried well layer 10 is a GaAs layer, the present invention is not limited to this, and any buried well layer 10 having a narrow energy gap as compared with the second buried barrier layer 7 may be used. For example, an AlGaAs layer having a narrower energy gap than the second buried barrier layer 7 may be used as the buried well layer 10.

The third buried barrier layer 11 is the same buried barrier layer as the second buried barrier layer 7. That is, the third embedded barrier layer 11 is an embedded layer that embeds the quantum dots 1 and is a barrier layer that forms an energy barrier against electrons bound to the quantum dots 1. Further, since the third buried barrier layer 11 has a wider energy gap than the first buried barrier layer 6, the height of the energy barrier of the third buried barrier layer 11 is higher than the height of the energy barrier of the first buried barrier layer 6. Is also expensive. Here, the third buried barrier layer 11 is an AlGaAs third buried barrier layer. For example, the Al _0.3 Ga _0.7 As third buried barrier layer 11 has a thickness of 4 ML. Here, although the third buried barrier layer 11 is an AlGaAs layer, the present invention is not limited to this, and any third buried barrier layer 11 having a wider energy gap than the first buried barrier layer 6 may be used. For example, an AlAs layer having a wider energy gap than the first buried barrier layer 6 may be used as the third buried barrier layer 11. Further, since the second buried barrier layer 7 and the third buried barrier layer 11 are the same buried barrier layer, it can be considered that the buried well layer 10 is provided in the buried barrier layer.

In the present embodiment, Al _x Ga _1-x As is used as the material for the intermediate layer 2, the first buried barrier layer 6, the second buried barrier layer 7, the third buried barrier layer 11, the underlying well layer 5, and the buried well layer 10. By using a semiconductor material containing the same constituent material (0 ≦ x ≦ 1) and changing its composition, the intermediate layer 2, the first embedded barrier layer 6, the second embedded barrier layer 7, the third embedded barrier layer 11, The above energy gap relationship between the underlying well layer 5 and the buried well layer 10 is realized.

Next, the manufacturing method of the quantum dot type infrared detector concerning this embodiment is demonstrated.
The method of manufacturing the quantum dot infrared detector according to the present embodiment is the same as the method of manufacturing the quantum dot infrared detector of the first embodiment described above, and the step of forming the second buried barrier layer 7 and the intermediate layer 2 are formed. A step of forming the buried well layer 10 and a step of forming the third buried barrier layer 11 may be added between the steps of performing the step.

Specifically, first, as in the case of the first embodiment described above, a step of forming an n-type GaAs electrode layer 4 serving as a lower electrode layer, a step of forming an i-AlGaAs intermediate layer 2, a GaAs underlayer 5, a process for forming InAs quantum dots 1, and a process for forming the AlGaAs first buried barrier layer 6.
Next, the AlGaAs second buried barrier layer 7 is formed on the AlGaAs first buried barrier layer 6 so that the InAs quantum dots 1 are buried with the AlGaAs second buried barrier layer 7. For example, Al _0.3 Ga _0.7 As is grown by about 4 ML to form the Al _0.3 Ga _0.7 As second buried barrier layer 7 having a thickness of about 4 ML.

Next, the GaAs buried well layer 10 is formed on the AlGaAs second buried barrier layer 7 so that the InAs quantum dots 1 are buried in the GaAs buried well layer 10. For example, GaAs is grown by about 6 ML to form a GaAs buried well layer 10 having a thickness of about 6 ML.
Next, the AlGaAs third buried barrier layer 11 is formed on the GaAs buried well layer 10 so that the InAs quantum dots 1 are buried with the AlGaAs third buried barrier layer 11. For example, Al _0.3 Ga _0.7 As is grown by about 4 ML to form the Al _0.3 Ga _0.7 As third buried barrier layer 11 having a thickness of about 4 ML.

Thereafter, the quantum dot infrared detector is completed through the same process as in the first embodiment.
Since other details are the same as those of the first embodiment described above, the description thereof is omitted here.
Therefore, according to the quantum dot infrared detector according to the present embodiment, the response wavelength can be increased without degrading characteristics such as sensitivity and S / N, as in the case of the first embodiment described above. There is an advantage.

In particular, according to the structure of the present embodiment described above, electrons that have passed over the second buried barrier layer 7 can stay in the buried well layer 10, and the probability of overcoming the third buried barrier layer 11 can be increased. For this reason, the photocurrent increases and the sensitivity can be improved.
In addition, although this embodiment is demonstrated as a modification of the above-mentioned 1st Embodiment, it is not restricted to this, The structure of this embodiment and the structure of the above-mentioned 2nd Embodiment are combined. Also good.
[Fourth Embodiment]
Next, a quantum dot infrared detector according to a fourth embodiment will be described with reference to FIG.

The quantum dot infrared detector according to the present embodiment includes a base barrier layer 12 having a wider energy gap than the intermediate layer 2 as shown in FIG. The difference is that a base well layer 5 is provided on 12. In FIG. 4, the same components as those in the first embodiment described above (see FIG. 1) are denoted by the same reference numerals.
Here, the base barrier layer 12 is a base layer of the quantum dots 1. The underlying barrier layer 12 is provided between the intermediate layer 2 and the underlying well layer 5. That is, the underlying barrier layer 12 is in contact with the upper surface of the intermediate layer 2 and is in contact with the lower surface of the underlying well layer 5. The under barrier layer 12 is, for example, an AlAs under barrier layer, and has a thickness of about 1 ML. Here, the base barrier layer 12 is an AlAs layer, but the present invention is not limited to this, and any base barrier layer 12 having a wider energy gap than the intermediate layer 2 may be used. For example, an AlGaAs layer having a wider energy gap than the intermediate layer 2 may be used as the base barrier layer 12.

In the present embodiment, Al _x Ga _1-x As (0 ≦ x ≦ 1) is used as the material for the intermediate layer 2, the first buried barrier layer 6, the second buried barrier layer 7, the foundation well layer 5, and the foundation barrier layer 12. The semiconductor material including the same constituent material is used and the composition is changed to change the energy gap of the intermediate layer 2, the first embedded barrier layer 6, the second embedded barrier layer 7, the underlying well layer 5, and the underlying barrier layer 12. Realizing the relationship.

Next, the manufacturing method of the quantum dot type infrared detector concerning this embodiment is demonstrated.
The manufacturing method of the quantum dot type infrared detector according to the present embodiment is the step of forming the intermediate layer 2 and the step of forming the base well layer 5 in the manufacturing method of the quantum dot type infrared detector of the first embodiment described above. A step for forming the base barrier layer 12 may be added between the two.
Specifically, first, as in the case of the first embodiment described above, the step of forming the n-type GaAs electrode layer 4 serving as the lower electrode layer and the step of forming the i-AlGaAs intermediate layer 2 are performed.

Next, for example, after the substrate temperature is lowered from about 600 ° C. to about 500 ° C., AlAs is grown by about 1 ML on the i-AlGaAs intermediate layer 2 to form an AlAs base barrier layer 12 having a thickness of about 1 ML. .
Next, about 3 ML of GaAs is grown on the AlAs base barrier layer 12 to form a GaAs base well layer 5 having a thickness of about 3 ML.

Thereafter, the quantum dot infrared detector is completed through the same process as in the first embodiment.
Since other details are the same as those of the first embodiment described above, the description thereof is omitted here.
Therefore, according to the quantum dot infrared detector according to the present embodiment, the response wavelength can be increased without degrading characteristics such as sensitivity and S / N, as in the case of the first embodiment described above. There is an advantage.

In particular, according to the structure of the above-described embodiment, since the underlying barrier layer 12 is provided below the underlying well layer 5, the quantum confinement effect is reduced when the thickness of the underlying well layer 5 is increased. Can be prevented and sensitivity can be increased.
Although this embodiment has been described as a modification of the first embodiment described above, the present embodiment is not limited to this, and the structure of the present embodiment and the structure of the second embodiment described above may be combined. The structure of the present embodiment may be combined with the structure of the third embodiment described above, or the structure of the present embodiment may be combined with the structures of the second and third embodiments described above.
[Others]
In addition, this invention is not limited to the structure described in each 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 each of the above-described embodiments, InAs is used as the material of the quantum dot 1 and AlGaAs or AlAs is used as the material of the first buried barrier layer 6, the second buried barrier layer 7, the third buried barrier layer 11, and the base barrier layer 12. , AlGaAs or GaAs is used as the material for the underlying well layer 5, the first buried well layer 9, and the second buried well layer 10, AlGaAs is used as the material for the intermediate layer 2, and GaAs is used as the material for the electrode layer 4. Although the case where Si is used as the dopant material has been described as an example, the present invention is not limited to this, and the quantum dot infrared detector can be formed using other materials.

For example, the materials constituting the quantum dot 1, the barrier layers 6, 7, 11, 12, the well layers 5, 9, 10, the intermediate layer 2, and the electrode layer 4 include InAs, GaAs, AlAs, InP, GaP, It is effective to use AlP, InSb, GaSb, AlSb, InN, GaN, AlN and mixed crystals thereof.
In each of the above-described embodiments, the conductivity type of the upper and lower electrode layers 4 is n-type. However, the present invention is not limited to this, and the polarity of the conductivity type (p / n type) is reversed to obtain the p-type. Also good. That is, the upper and lower electrode layers 4 may be doped with a p-type impurity (for example, Be) instead of the doped n-type impurity. The quantum dot 1, the intermediate layer 2, the barrier layers 6, 7, 11, 12 and the well layers 5, 9, 10 may be doped with n-type impurities or p-type impurities.

  In each of the above-described embodiments, the MBE method is used as the growth method. However, the growth method is not limited to this. For example, a MOCVD (Metal Organic Chemical Vapor Deposition) method may be used. That is, a growth method that can form self-assembled quantum dots may be used.

1,100 Quantum dots 2,101 Intermediate layer 3,103 Photoelectric conversion layer (active layer)
4,104 Electrode layer (contact layer)
5 Underlying well layer 6 First embedded barrier layer 7 Second embedded barrier layer 8 Quantum dot layer 9 Embedded well layer (first embedded well layer)
10 buried well layer (second buried well layer)
11 Third buried barrier layer 12 Underlying barrier layer

Claims (5)

Quantum dots,
Sandwiching the quantum dots, an intermediate layer with a wider energy gap than the quantum dots,
An underlying well layer with a narrower energy gap than the intermediate layer;
A first buried barrier layer having a wider energy gap than the intermediate layer;
A quantum dot infrared detector, comprising: a second buried barrier layer provided on the first buried barrier layer and having a wider energy gap than the first buried barrier layer.   2. The quantum dot according to claim 1, further comprising a first buried well layer having a narrower energy gap than the first buried barrier layer between the first buried barrier layer and the second buried barrier layer. Type infrared detector. A second buried well layer provided on the second buried barrier layer and having a narrower energy gap than the second buried barrier layer;
3. The quantum dot infrared ray according to claim 1, further comprising a third buried barrier layer provided on the second buried well layer and having the same energy gap as the second buried barrier layer. 4. Detector. A base barrier layer having a wider energy gap than the intermediate layer;
The quantum dot infrared detector according to any one of claims 1 to 3, wherein the base well layer is provided on the base barrier layer.   The quantum dot infrared detector according to any one of claims 1 to 4, wherein the thickness of the foundation well layer is 1 ML or more and 10 ML or less.

Images