JP2003179249A - Sub-band transition type quantum well photo sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To absorb and remove lights in an undesired wavelength range by a simple constitution of a sub-band transition quantum well type photo sensor. <P>SOLUTION: The photo sensor comprises a photo sensing mechanism having one or more absorption wavelengths and a quantum well-structured light absorption layer 3 added for absorbing lights in a specified wavelength range as a band-cut filter. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intersubband transition quantum well type photodetector, and more particularly to a crosstalk in an infrared sensor utilizing optical absorption due to transition between subbands generated in multiple quantum wells. The present invention relates to an intersubband transition quantum well type photodetector characterized by a structure for removing infrared light in an undesired wavelength region for reducing the noise.

[0002]

2. Description of the Related Art Conventionally, an infrared detector for detecting infrared rays in the vicinity of 10 μm band has a Cd composition ratio of about 0.2,
For example, a pn junction diode formed in the HgCdTe layer having a Cd composition ratio of 0.22 is used as a photodiode, and the photodiode is arranged in a one-dimensional array form or a two-dimensional array form, and the An infrared detection device is known in which an infrared photodiode array substrate and a Si signal processing circuit substrate are bonded to each other by bumps made of a metal such as In to make a specific contact.

However, in the case of such an HgCdTe-based infrared detecting device, it is difficult to obtain a large-area substrate having good crystallinity, so that it is difficult to construct a large infrared detecting array composed of multiple sensor elements. There is a problem that
In recent years, as a solution to such a problem, a quantum well infrared detecting element (Quantum Well) capable of detecting infrared rays in the vicinity of the 10 μm band by utilizing optical absorption due to transition between subbands in a multiple quantum well
Infrared Photodetector: Q
WIP) has come into use.

In particular, Q using a GaAs compound semiconductor
In WIP, it is used as an imaging device due to its mature material processing technology and its ability to increase the area. In recent years, dual-wavelength quantum sensitizers with two wavelengths have been developed to enhance the functionality of captured images. Well type infrared detector (dual wavelength Q
WIP) has come into use.

Here, the basic structure and principle of a conventional two-wavelength quantum well type infrared detector used as an image pickup device will be described with reference to FIGS. 7 and 8. Reference is made to FIG. 7A. FIG. 7A is a schematic partial cross-sectional view of a conventional two-wavelength quantum well infrared detector, which shows an n-type GaAs contact layer 72, an n-type MQW on a semi-insulating GaAs substrate. First light absorption layer 73, n-type GaAs contact layer 74, n-type MQ
After the W second light absorption layer 75 and the n-type GaAs contact layer 76 are sequentially stacked, the reflective diffraction grating 77 is formed on the surface of the n-type GaAs contact layer 76.

Next, after a pixel separation groove 78 reaching the semi-insulating GaAs substrate is formed to separate each pixel 79, a protective film such as a SiON film is formed, though not shown.
Then, an Au film is formed to serve as a reflective film.

Next, an n-type GaAs contact layer 72,
After forming three contact holes respectively reaching the n-type GaAs contact layer 74 and the n-type GaAs contact layer 76 and covering the side surfaces of the contact holes with an insulating film, the inside of the contact holes is made of Au.Ge/Ni. A contact electrode for the n-type MQW first light absorption layer 73 and the n-type MQW second light absorption layer 75 is formed by embedding with a conductive member, and finally the back surface of the semi-insulating GaAs substrate is wet-etched to be a thin layer. As a result, the i-type GaAs base layer 71 is formed.

In such an image pickup device, infrared rays 8
0 is incident in the stacking direction of each layer, that is, in the z-axis direction,
Due to the selection rule of light absorption, infrared rays parallel to the z-axis are not absorbed in the n-type MQW first light-absorbing layer 73 and the n-type MQW second light-absorbing layer 75.
The surface of the type GaAs contact layer 76 is reached.

Then, the reflection type diffraction grating 77 causes infrared rays 8
0 is reflected and diffracted, and the n-type MQW first light absorption layer 73
And is absorbed when the n-type MQW second light absorption layer 75 is obliquely crossed. Since the infrared absorption rate when crossing the MQW light absorption layer once is about several percent, the infrared rays 80 are reflected several times in the pixel 79, and then the n-type MQW first light absorption layer 73 or the n-type MQW first layer. 2 The light is absorbed by the light absorption layer 75.

FIG. 7B is a band diagram along the z-axis direction of the dual wavelength quantum well type infrared detector shown in FIG. 7A, which shows the bottom of the Γ conduction band ( E _c ) energy is shown. Here, for example, the band gap of the barrier layer forming the n-type MQW first light absorption layer 73 is set to the n-type MQW second
It is smaller than the band gap of the barrier layer that constitutes the light absorption layer 75. The energy at the bottom of the Γ conduction band seen from the Fermi level of the i-type GaAs layer 71 is higher than the energy at the bottom of the Γ conduction band of the n ⁻ -type AlGaAs layer forming the barrier layer. There is.

FIG. 8A is a view showing a band diagram on the conduction band side of the n-type MQW first light absorption layer 73 of the one-dimensional quantum well structure. The n-type GaAs well layer 82 is shown in FIG. , A quantum level depending on the layer thickness of the n-type GaAs well layer 82 and the barrier height of the n ⁻ -type Al _x Ga _1-x As barrier layer 81 is formed.
Here, the case where only the first quantum level 83 that is the ground level and the second quantum level 84 that is the first excitation level are formed is illustrated.

Here, the second quantum level 84 and the first quantum level 8
Infrared 80 with an energy difference of 3 (λ _{1 in} terms of wavelength)
Is incident, electrons 85 in the first quantum level 83
The infrared ray 80 transits to the quantum level 84, and the infrared ray 80 is absorbed instead, and the wavelength λ ₁ corresponding to this energy difference changes to n-type MQ.
It becomes the absorption wavelength of the W first light absorption layer 73.

FIG. 8B is a view showing a band diagram on the conduction band side of the n-type MQW second light absorption layer 75 of the one-dimensional quantum well structure, and n ⁻ -type Al _y Ga. _{By making} the Al composition y of the _1-y As barrier layer 86 larger than the Al composition x of the n ⁻ -type Al _x Ga _1-x As barrier layer 81, the absorption wavelength λ _{2 of the} n-type MQW second light absorption layer 75. The n-type MQW first light absorption layer 7
The absorption wavelength λ ₁ is shorter than the absorption wavelength λ ₁ , and the absorption wavelengths λ ₁ and λ ₂ are different from each other.

See FIG. 8C. FIG. 8C is an explanatory view of the light absorption characteristics of the two-wavelength quantum well type infrared detector shown in FIG. 7A, in which the infrared ray having the wavelength λ ₁ is n. The infrared rays having the wavelength λ ₂ are absorbed only in the first type MQW light absorbing layer 73 and only in the n-type second MQW light absorbing layer 75. The wavelengths λ ₁ and λ ₂ may be of any size, and therefore, the n-type MQW first light absorption layer 73 and the n-type MQW second light absorption layer 75 may be stacked in any order.

As described above, the carriers, that is, the electrons excited by the absorption of the infrared rays are independently biased at both ends of each MQW light absorption layer through the n-type GaAs contact layers to go out of the well. The emitted light can be taken out as a current to the outside, whereby the MQW light absorption layer can independently detect infrared rays having absorption wavelengths of two specific wavelengths.

[0016]

[Problems to be Solved by the Invention] However, such MQ
In the W light absorption layer, since the multiple quantum wells are one-dimensional quantum wells, carrier confinement is insufficient, and since the bias is applied during infrared detection, the shape of each quantum well is the same. Then, the quantum levels and the absorption wavelengths are deviated, and the absorption wavelength spectrum is broadened as shown in FIG. 8B.

Therefore, when the central absorption wavelengths of the two MQW light absorption layers are close to each other, there is a problem that a wavelength range absorbed by both MQW light absorption layers is generated and a crosstalk phenomenon occurs. This hinders enhancement of the functionality of the imaging device.

Therefore, an object of the present invention is to absorb and remove infrared rays in an undesired wavelength range with a simple structure.

[0019]

FIG. 1 is an explanatory view of the principle configuration of the present invention, and means for solving the problems in the present invention will be described with reference to FIG. In order to achieve the above object, the present invention provides an intersubband transition quantum well structure photodetection device having a photodetection mechanism having one or more absorption wavelengths, and at the same time, as a band cut filter, a photodetector having a predetermined wavelength range. It is characterized in that a quantum well structure light absorption layer 3 for absorbing is added.

As described above, by providing the band cut filter, it is possible to efficiently detect only the light having the wavelength to be detected by the light detecting mechanism. Reference numeral 8 in the drawing is a reflection type diffraction grating for changing the incident angle in order to efficiently absorb incident light, usually infrared rays 9.

In this case, the light detection mechanism is composed of one quantum well structure light absorption layer, and the region on the short wavelength side of the absorption wavelength of the quantum well structure light absorption layer which constitutes this light detection mechanism is the absorption wavelength. A band-cut filter may be constituted by a quantum well structure light absorption layer and a quantum well structure light absorption layer having an absorption wavelength in the long wavelength side, whereby only light in an extremely narrow wavelength region is selectively selected. Can be detected.

The photodetection mechanism may be composed of n quantum well structure light absorption layers 1 and 2 having different absorption wavelengths. In that case, the band cut filter is (n-1).
It suffices that the light absorption layer 3 has a number of quantum well structure layers 3, and thereby crosstalk between the n number of quantum well structure light absorption layers 1 and 2 can be reduced. In order to operate the plurality of quantum well structure light absorption layers 1 and 2 independently of each other, it is desirable to provide contact layers 4 to 6 on both sides of each quantum well structure light absorption layers 1 and 2.

Further, the band cut filter in such a case may be provided on the back surface side of the base layer 7 or may be provided adjacent to the quantum well structure light absorption layers 1 and 2 constituting the light detection mechanism. When it is provided adjacently, it is desirable to provide a non-doped layer on both sides of the quantum well structure light absorption layer 3 functioning as a band cut filter in order to prevent diffusion of impurities.

Further, in order that the absorption wavelength range of the quantum well structure light absorption layer 3 functioning as a band cut filter does not adversely affect the absorption wavelength range of the quantum well structure light absorption layers 1 and 2 constituting the light detection mechanism. If the band-cut filter is used in a non-biased state and the impurity concentration is made higher than that of the quantum well structure light absorption layers 1 and 2 forming the photodetection mechanism, the light absorption rate in a narrow wavelength region can be dramatically increased. good.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A dual wavelength quantum well type infrared detector according to a first embodiment of the present invention will be described with reference to FIGS. 2 and 3. See FIG. 2A. First, on a semi-insulating GaAs substrate (not shown), MO
By the VPE method (metal organic chemical vapor deposition method), dummy MQ
The W light absorption layer 11, the i-type GaAs base layer 12 having a thickness of 0.5 to 2.0 μm, for example, 1.0 μm, and the thickness is
0.5 to 2.0 μm, for example, 1.0 μm, and carrier concentration is 1 × 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ , for example, 1 × 1.
0 ¹⁸ cm ^-3 n-type GaAs contact layer 13, n-type MQ
The W first light absorption layer 14 has a thickness of 0.5 to 2.0 μm, for example, 1.0 μm, and a carrier concentration of 1 × 10 ^{17 to} 5 ×.
10 ¹⁸ cm ⁻³ , for example, 1 × 10 ¹⁸ cm ⁻³ n-type GaA
s contact layer 15, n-type MQW second light absorption layer 16, thickness is 0.5 to 2.0 μm, for example, 1.0 μm, carrier concentration is 1 × 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ , For example,
The 1 × 10 ¹⁸ cm ⁻³ n-type GaAs contact layer 17 is sequentially epitaxially grown.

Next, a photoresist is applied to the entire surface, and then a primary diffraction grating 18 is formed on the surface of the n-type GaAs contact layer 17 by using the interference exposure method, and then a SiON film (not shown) is formed on the entire surface. And a SiON mask (not shown) having an opening for forming the pixel isolation groove 19 is formed by a normal photolithography process, and wet etching is performed using this SiON mask as a mask to perform i-type GaAs. An element isolation trench 19 reaching the base layer 12 is formed.

Then, after removing the SiON mask,
An SiON film (not shown) is newly provided on the entire surface, and the n-type Ga of each pixel 20 is formed by using a normal photolithography process.
As contact layer 13, n-type GaAs contact layer 1
5, a contact hole for the n-type GaAs contact layer 17 is formed, and then the sidewall of the contact hole is covered with a SiON film, and then an ohmic electrode made of Au.Ge/Ni is provided. The reflection type diffraction grating 1
A reflective electrode (not shown) made of, for example, Au is provided on the surface of 8.

Finally, a semi-insulating GaAs substrate is used as a dummy M.
The basic configuration of the dual wavelength quantum well type infrared detector according to the first embodiment of the present invention is completed by performing wet etching until the QW light absorption layer 11 is removed.

See FIG. 2B. FIG. 2B is a band diagram along the z direction, that is, the stacking direction, and shows the energy at the bottom (E _c ) of the Γ conduction band. Dummy MQW light absorption layer 11 in this case
Has a thickness of 50 nm and a carrier concentration of 1 × 10 5.
An n ⁻ -type Al _0.30 Ga _0.70 As barrier layer having a thickness of ¹⁶ cm ^{−3 and} an n having a thickness of 5.5 nm and a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ .
And the n-type GaAs well layer is 20
It is formed by alternately depositing layers.
In this case, the n ⁻ -type Al _0.30 Ga _0.70 As barrier layer is formed sufficiently thick so that electrons do not tunnel between adjacent n-type GaAs well layers.

On the other hand, the n-type MQW first light absorption layer 14 has, for example, a thickness of 50 nm and a carrier concentration of 1 × 10 ¹⁶ cm.
^-3 n ^- type Al _0.25 Ga _0.75 As barrier layer and n-type G having a thickness of 5.5 nm and a carrier concentration of 1 × 10 ¹⁸ cm ^-3.
In this case, the n ^- type Al _0.25 Ga _0.75 As barrier layer is formed by alternately depositing the aAs well layer and the n-type GaAs well layer so as to have 20 layers. It is formed sufficiently thick so that electrons do not tunnel between layers.

The n-type MQW second light absorption layer 16 has, for example, a thickness of 50 nm and a carrier concentration of 1 × 10 ¹⁶ cm.
^-3 n ⁻ -type Al _0.35 Ga _0.65 As barrier layer and n-type G having a thickness of 5.5 nm and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³
In this case, the n ^- type Al _0.35 Ga _0.65 As barrier layer is formed by alternately depositing the aAs well layer and the n-type GaAs well layer so as to have 20 layers. It is formed sufficiently thick so that electrons do not tunnel between layers.

See FIG. 3A. FIG. 3A is a diagram showing a light absorption characteristic in the light detecting portion. The n-type MQW first light absorption layer 14 has a light absorption spectrum having a center wavelength of λ _1. On the other hand, the n-type MQW second light absorption layer 16 shows a light absorption spectrum having a center wavelength of λ ₂ .

In use, a bias is applied to the n-type MQW first light absorption layer 14 and the n-type MQW first light absorption layer 16, so that a bend in the shape of E _C is seen in these layers, that is, , The shape of the quantum well can be bent.

In this case, since the shape of each quantum well is not the same, the quantum levels and the absorption wavelengths are deviated, and the quantum well is one-dimensional, so that the absorption spectrum is broadened. The width is widening.

See FIG. 3 (b) FIG. 3B shows the light absorption characteristics of the dummy MQW light absorption layer 11.
FIG. 2 is a diagram showing the absorption center wavelength of the multiple quantum well structure.
Due to the forbidden band width of the barrier layer that makes up the structure, λ ₁And λ₂
Λ in the middle of₃And the n-type MQW first optical absorption
Infrared absorption of the condensing layer 14 and the n-type MQW second light absorbing layer 16
Are set so that the areas overlap.

Since the MQW light absorption layer 11 is not biased at the time of use, the shape of each quantum well can be made uniform, and the n-type MQW first light absorption layer 14 and the n-type MW absorption layer 14 can be formed.
The spread of the absorption wavelength is smaller than that of the QW second light absorption layer 16, and the dummy MQW light absorption layer 11
Is more highly doped than the n-type MQW first light-absorbing layer 14 and the n-type MQW second light-absorbing layer 16, the absorption sensitivity is also higher than that of the n-type MQW first light-absorbing layer 14 and the n-type MQW first light-absorbing layer 14. 2 It is higher than the light absorption layer 16.

See FIG. 3C. FIG. 3C is a diagram showing the light absorption characteristics of the two-wavelength quantum well infrared detector as a whole. The n-type MQW first light absorption layer 14 and the n-type MQW second Light in the region where the infrared absorption of the light absorption layer 16 overlaps is absorbed by the dummy MQW light absorption layer 11, so that the light is absorbed between the n-type MQW first light absorption layer 14 and the n-type MQW second light absorption layer 16. No crosstalk will occur. That is, since the dummy MQW light absorption layer 11 can be considered as a filter that passes light other than light in the wavelength region λ ₃ , it can be called a band cut filter.

Although the dummy MQW light absorption layer 11 is doped with a high concentration to increase the current component due to thermal excitation at the same time, the dummy MQW light absorption layer 11 absorbs infrared rays, Since there is no need to detect it, it is not necessary to consider the increase or decrease of the current component due to thermal excitation, and the quantum well layer of the dummy MQW light absorption layer 11 has a limit, for example, the solid solubility limit of an impurity of a semiconductor material such as GaAs. It is possible to dope up to the point where the infrared absorption rate can be dramatically increased.

Further, since the i-type GaAs base layer 12 serves as a barrier against electrons and plays a role of preventing the electrons in the dummy MQW light absorption layer 11 from leaking to the pixel 19 side, noise is not generated. There is no need to make any further efforts.

As described above, in the first embodiment of the present invention, the simple structure of providing the dummy MQW light absorption layer 11 having a high impurity concentration allows the entire structure of the device to be realized without reducing the pixel density. The n-type MQW first light absorption layer 14 and the n-type MQW second light absorption layer 16 are not enlarged.
It is possible to effectively reduce the crosstalk between and.

Next, with reference to FIG. 4, a dual wavelength quantum well type infrared detector according to a second embodiment of the present invention will be described. See FIG. 4A. First, the thickness is 0.5 to 2.0 μm, for example, 1.0 μm on the semi-insulating GaAs substrate by MOVPE method.
And the n-type GaAs contact layer 2 has a carrier concentration of 1 × 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ , for example, 1 × 10 ¹⁸ cm ^−3.
2, n-type MQW first light absorption layer 23, the thickness is 0.5 ~
2.0 μm, for example 1.0 μm, carrier concentration is 1
× 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ , for example, 1 × 10 ¹⁸ cm
^-3 n-type GaAs contact layer 24 having a thickness of 0.2 to
1.0 μm, for example, 0.5 μm i-type GaAs separation layer 25, dummy MQW light absorption layer 26, thickness of 0.2 to
The i-type GaAs separation layer 27 has a thickness of 1.0 μm, for example, 0.5 μm, and has a thickness of 0.5 to 2.0 μm, for example, 1.0 μm.
m, the carrier concentration is 1 × 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ ,
For example, the n-type GaAs contact layer 28 of 1 × 10 ¹⁸ cm ⁻³ , the n-type MQW second light absorption layer 29, and the thickness of 0.5 to
2.0 μm, for example 1.0 μm, carrier concentration is 1
× 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ , for example, 1 × 10 ¹⁸ cm
^-3 n-type GaAs contact layer 30 is sequentially epitaxially grown.

Next, a photoresist is applied on the entire surface, and then a primary diffraction grating 31 is formed on the surface of the n-type GaAs contact layer 30 by using the interference exposure method, and then a SiON film (not shown) is formed on the entire surface. And an SiON mask (not shown) having an opening for forming the pixel isolation trench 32 is formed by a normal photolithography process, and wet etching is performed using this SiON mask as a mask to obtain semi-insulating property. An element isolation groove 32 reaching the GaAs substrate is formed.

Then, after removing the SiON mask,
An SiON film (not shown) is newly provided on the entire surface, and the n-type Ga of each pixel 33 is formed by using a normal photolithography process.
As contact layer 30, n-type GaAs contact layer 2
8, n-type GaAs contact layer 24, and n-type GaA
After forming a contact hole for the s contact layer 22 and then covering the side wall of the contact hole with a SiON film, an ohmic electrode made of Au.Ge/Ni is provided. A reflective electrode (not shown) made of Au, for example, is provided on the surface of the reflective diffraction grating 31.

Finally, the semi-insulating GaAs substrate is wet-etched to a thickness of 0.5 to 2.0 μm, for example,
By forming the i-type GaAs base layer 21 having a thickness of 1.0 μm, the basic configuration of the dual wavelength quantum well type infrared detector according to the second embodiment of the present invention is completed.

See FIG. 4B. FIG. 4B is a band diagram along the z direction, that is, the stacking direction, and shows the energy at the bottom (E _c ) of the Γ conduction band. N-type MQW first light absorption layer 2 in this case
3 is the first n-type MQW in the first embodiment.
Similar to the light absorption layer 14, for example, n ⁻ -type Al _0.25 Ga _0.75 having a thickness of 50 nm and a carrier concentration of 1 × 10 ¹⁶ cm ^−3.
As barrier layer with a thickness of 5.5 nm and a carrier concentration of 1
X10 ¹⁸ cm ⁻³ n-type GaAs well layer and n-type Ga
It is formed by alternately depositing 20 As well layers.

On the other hand, the dummy MQW light absorption layer 26 is also the dummy MQW light absorption layer 11 in the first embodiment.
Similarly, for example, the thickness is 50 nm and the carrier concentration is 1
An n ⁻ -type Al _0.30 Ga _0.70 As barrier layer of × 10 ¹⁶ cm ^-3 and a carrier concentration of 1 × 10 ¹⁹ cm with a thickness of 5.5 nm.
^-3 n-type GaAs well layers are alternately deposited to form 20 n-type GaAs well layers.

The n-type MQW second light absorption layer 29 has, for example, a thickness of 50 nm and a carrier concentration of 1 ×, similarly to the n-type MQW second light absorption layer 16 in the first embodiment. An n ⁻ -type Al _0.35 Ga _0.65 As barrier layer of 10 ¹⁶ cm ⁻³ and a carrier concentration of 1 × 10 ¹⁸ with a thickness of 5.5 nm.
It is formed by alternately depositing cm ⁻³ n-type GaAs well layers so as to have 20 n-type GaAs well layers. The AlGaAs barrier layer of each MQW light absorption layer is formed sufficiently thick so that electrons do not tunnel between adjacent n-type GaAs well layers.

Since the light absorption characteristics of the respective light absorption layers in the second embodiment are the same as those in the first embodiment, the light absorption characteristics of the two-wavelength quantum well type infrared detecting device as a whole are also the same. The same characteristics as those of the above-described first embodiment can be obtained.

In the second embodiment,
Since the dummy MQW light absorption layer 26 is provided between the n-type MQW first light absorption layer 23 and the n-type MQW second light absorption layer 29, the dummy MQW light absorption layer 26 is generated due to light absorption in the dummy MQW light absorption layer 26. Electrons to be generated are n-type MQW first light absorption layer 23 and n
In order not to leak to the MQW second light absorption layer 29 and affect the infrared detection, the i-type GaAs separation layer 2
5, 27 are provided.

Next, referring to FIG. 5, a third embodiment of the present invention will be described.
The three-wavelength quantum well infrared detector of the embodiment will be described.
It See Figure 5 (a) First, on a semi-insulating GaAs substrate (not shown), MO
By the VPE method, the first dummy MQW light absorption layer 41,
2 dummy MQW light absorption layer 42, thickness is 0.5 to 2.0
μm, for example, 1.0 μm i-type GaAs base layer 4
3, thickness is 0.5 to 2.0 μm, for example, 1.0 μm
And carrier concentration is 1 × 10¹⁷~ 5 x 10 ¹⁸cm^-3, Example
For example, 1x10¹⁸cm^-3N-type GaAs contact layer 4
4, n-type MQW first light absorption layer 45, the thickness is 0.5 ~
2.0 μm, for example 1.0 μm, carrier concentration is 1
× 10¹⁷~ 5 x 10¹⁸cm^-3, For example, 1 × 10¹⁸cm
^-3N-type GaAs contact layer 46, n-type MQW second light
The absorption layer 47 has a thickness of 0.5 to 2.0 μm, for example,
1.0 μm, carrier concentration 1 × 10¹⁷~ 5 x 10¹⁸
cm^-3, For example, 1 × 10¹⁸cm^-3N-type GaAs controller
Tact layer 48, n-type MQW third light absorption layer 49, and thickness
Is 0.5 to 2.0 μm, for example 1.0 μm,
Carrier concentration is 1 × 10¹⁷~ 5 x 10¹⁸cm^-3, For example,
1 x 10¹⁸cm^-3N-type GaAs contact layer 50 in order
Next, epitaxial growth is performed.

Next, a photoresist is applied on the entire surface, and then a primary diffraction grating 51 is formed on the surface of the n-type GaAs contact layer 50 by using an interference exposure method, and then a SiON film (not shown) is formed on the entire surface. And a SiON mask (not shown) having an opening for forming the pixel isolation groove 19 is formed by a normal photolithography process, and wet etching is performed using this SiON mask as a mask to perform i-type GaAs. An element isolation trench 52 reaching the base layer 43 is formed.

Then, after removing the SiON mask,
An SiON film (not shown) is newly provided on the entire surface, and the n-type Ga of each pixel 53 is formed by using a normal photolithography process.
As contact layer 44, n-type GaAs contact layer 4
6, n-type GaAs contact layer 48, and n-type GaA
After forming a contact hole for the s contact layer 50 and then covering the sidewall of the contact hole with a SiON film, an ohmic electrode made of Au.Ge/Ni is provided. A reflective electrode (not shown) made of Au, for example, is provided on the surface of the reflective diffraction grating 51.

Finally, the semi-insulating GaAs substrate is removed by wet etching until it reaches the first dummy MQW light absorption layer 41, whereby the three-wavelength quantum well type infrared detector according to the third embodiment of the present invention. The basic configuration of is completed.

In this case, the n-type MQW first light absorption layer 45
Has a thickness of 50 nm and a carrier concentration of 1 × 10 5.
An n ⁻ -type Al _0.25 Ga _0.75 As barrier layer having a thickness of ¹⁶ cm ^{−3 and} an n having a thickness of 5.5 nm and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ .
And the n-type GaAs well layer is 20
It is formed by alternately depositing layers.

The n-type MQW second light absorption layer 47 has, for example, a thickness of 50 nm and a carrier concentration of 1 × 10 ¹⁶ cm.
^-3 n ^- type Al _0.30 Ga _0.70 As barrier layer and n-type G having a thickness of 5.5 nm and a carrier concentration of 1 × 10 ¹⁸ cm ^-3.
The aAs well layer and the n-type GaAs well layer are alternately deposited so as to have 20 layers.

The n-type MQW third light absorption layer 49 has, for example, a thickness of 50 nm and a carrier concentration of 1 × 10 ¹⁶ cm.
^-3 n ⁻ -type Al _0.35 Ga _0.65 As barrier layer and n-type G having a thickness of 5.5 nm and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³
The aAs well layer and the n-type GaAs well layer are alternately deposited so as to have 20 layers.

On the other hand, the first dummy MQW light absorption layer 41 is
For example, the thickness is 50 nm and the carrier concentration is 1 × 10 ¹⁶ c
m ⁻³ n ⁻ type Al _0.27 Ga _0.73 As barrier layer and n type G having a thickness of 5.5 nm and a carrier concentration of 1 × 10 ¹⁹ cm ^−3.
The aAs well layer and the n-type GaAs well layer are alternately deposited so as to have 20 layers.

Further, the second dummy MQW light absorption layer 42 is
For example, the thickness is 50 nm and the carrier concentration is 1 × 10 ¹⁶ c
m ⁻³ n ⁻ type Al _0.32 Ga _0.68 As barrier layer and n type G having a thickness of 5.5 nm and a carrier concentration of 1 × 10 ¹⁹ cm ^−3.
The aAs well layer and the n-type GaAs well layer are alternately deposited so as to have 20 layers. The AlGaAs barrier layer of each MQW light absorption layer is formed sufficiently thick so that electrons do not tunnel between adjacent n-type GaAs well layers.

FIG. 5 (b) is a diagram showing the light absorption characteristics of the three-wavelength quantum well type infrared detector of the third embodiment of the present invention. As shown in FIG. n-type MQW first light absorption layer 45 and n-type MQ
Since the light in the region where the infrared absorption of the W second light absorption layer 47 overlaps is absorbed by the first dummy MQW light absorption layer 41, the n-type MQW first light absorption layer 45 and the n-type MQW second
Crosstalk does not occur with the light absorption layer 47.

The light in the region where the infrared absorptions of the n-type MQW second light absorption layer 47 and the n-type MQW third light absorption layer 49 overlap is absorbed by the second dummy MQW light absorption layer 42, so that n Type MQW second light absorbing layer 47 and n-type MQW
Crosstalk does not occur with the third light absorption layer 49.

Next, referring to FIG. 6, a fourth embodiment of the present invention will be described.
The one-wavelength quantum well infrared detector of the embodiment will be described.
It See Figure 6 (a) First, on a semi-insulating GaAs substrate (not shown), MO
By the VPE method, the first dummy MQW light absorption layer 61,
2 dummy MQW light absorption layer 62 having a thickness of 0.5 to 2.0
μm, for example, 1.0 μm i-type GaAs base layer 6
3, thickness is 0.5 to 2.0 μm, for example, 1.0 μm
And carrier concentration is 1 × 10¹⁷~ 5 x 10 ¹⁸cm^-3, Example
For example, 1x10¹⁸cm^-3N-type GaAs contact layer 6
4, the n-type MQW light absorption layer 65, and the thickness is 0.5 to
2.0 μm, for example 1.0 μm, carrier concentration is 1
× 10¹⁷~ 5 x 10¹⁸cm^-3, For example, 1 × 10¹⁸cm
^-3Of the n-type GaAs contact layer 66 of FIG.
Grow.

Next, a photoresist is coated on the entire surface, and then a first-order diffraction grating 67 is formed on the surface of the n-type GaAs contact layer 66 by using an interference exposure method, and then a SiON film (not shown) is formed on the entire surface. And a SiON mask (not shown) having an opening for forming the pixel separation groove 68 is formed by a normal photolithography process, and wet etching is performed using the SiON mask as a mask to perform i-type GaAs. An element isolation groove 68 reaching the base layer 63 is formed.

Then, after removing the SiON mask,
An SiON film (not shown) is newly provided on the entire surface, and the n-type Ga of each pixel 69 is formed by using a normal photolithography process.
As contact layer 64 and n-type GaAs contact layer 6
After forming a contact hole for No. 6 and then covering the side wall of the contact hole with a SiON film, Au.
An ohmic electrode made of Ge / Ni is provided. A reflective electrode (not shown) made of Au, for example, is provided on the surface of the reflective diffraction grating 67.

Finally, the semi-insulating GaAs substrate is removed by wet etching until it reaches the first dummy MQW light absorption layer 61, thereby removing the single wavelength quantum well infrared detector of the fourth embodiment of the present invention. The basic configuration of is completed.

In this case, the first dummy MQW light absorption layer 61
Has a thickness of 50 nm and a carrier concentration of 1 × 10 5.
An n ⁻ -type Al _0.25 Ga _0.75 As barrier layer of ¹⁶ cm ^{−3 and} an n ^- type Al _0.25 Ga _0.75 As barrier layer having a thickness of 5.5 nm and a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ .
And the n-type GaAs well layer is 20
It is formed by alternately depositing layers.
Thereby, the central absorption wavelength becomes λ _a .

Further, the second dummy MQW light absorption layer 62 is
For example, the thickness is 50 nm and the carrier concentration is 1 × 10 ¹⁶ c
m ⁻³ n ⁻ type Al _0.35 Ga _0.65 As barrier layer and n type G having a thickness of 5.5 nm and a carrier concentration of 1 × 10 ¹⁹ cm ^−3.
The aAs well layer and the a-type GaAs well layer are alternately deposited so that the number of the n-type GaAs well layers becomes 20 layers, whereby the central absorption wavelength becomes λ _b .

On the other hand, the n-type MQW light absorption layer 65 has, for example, a thickness of 50 nm and a carrier concentration of 1 × 10 ¹⁶ cm ^−3.
N ^- type Al _0.30 Ga _0.70 As barrier layer with a thickness of 5.
N-type GaA with a carrier concentration of 1 × 10 ¹⁸ cm ^-3 at 5 nm
The s-well layer and the n-type GaAs well layer are alternately deposited so as to have 20 layers, and the central absorption wavelength λ is λ _a >λ> λ _b .

Reference is made to FIG. 6 (b). FIG. 6 (b) is a diagram showing the light absorption characteristics of the single-wavelength quantum well infrared detector of the fourth embodiment of the present invention. N-type MQW light absorption layer 65 indicated by a chain line
Of the absorption wavelength spectrum is absorbed by the absorption wavelength spectrum portions of the first dummy MQW light absorption layer 61 and the second dummy MQW light absorption layer 62 indicated by broken lines, and the steep absorption wavelengths shown by the solid line Will show a spectrum.

As described above, in the fourth embodiment of the present invention, even if the doping is performed at a relatively high concentration in order to enhance the light absorption sensitivity, the broadening of the absorption wavelength spectrum due to the high concentration doping is caused in the device. Since it can be cut and only specific wavelengths can be selectively detected, it is possible to configure an infrared detection device having sharp wavelength sensitivity.

Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations and conditions described in the embodiments, and various modifications can be made. For example, in each of the above embodiments, the absorption wavelength in each MQW light absorption layer is controlled by the Al composition ratio of the barrier layer forming the multiple quantum well, but it may be controlled by the layer thickness of the well layer. It is a thing.

Alternatively, the well layer forming the multiple quantum well may be an AlGaAs layer and controlled by the Al composition ratio of the well layer.
The absorption wavelength in each MQW light absorption layer may be controlled by compositely controlling the composition ratio, the Al composition ratio of the well layer, and the layer thickness of the well layer.

Further, in each of the above-mentioned embodiments, in order to increase the light absorption efficiency in the dummy MQW light absorption layer, the dummy MQW light absorption layer is doped at a higher concentration than the MQW light absorption layer constituting the light detection section, but it is not essential. Instead, the doping amount may be approximately the same as that of the MQW light absorption layer that constitutes the light detection unit.

Further, in the third and fourth embodiments described above, the dummy MQW light absorption layer is provided on the back surface side of the i-type GaAs base layer, but similar to the second embodiment described above. It may be provided on the pixel side.

Further, in the second embodiment, the dummy MQW light absorption layer is provided between the two MQW light absorption layers forming the photo detector, but it is not always necessary to use two MW light absorption layers.
It does not have to be between the QW light absorption layers, and may be provided so as to be in contact with the i-type GaAs base layer.

In addition, in the first to third embodiments, the plurality of MQW light absorption layers forming the light detection section are
The layers are stacked from the side closer to the i-type GaAs base layer so that the wavelength becomes longer to shorter. However, the order of stacking the wavelengths is arbitrary, and when three or more MQW light absorption layers are provided, The arrangement of absorption wavelengths is arbitrary.

Further, in the above description of each embodiment, the Al composition of the barrier layer and the layer thickness of the well layer in each MQW light absorption layer are specified, but the Al composition and the layer thickness described are This is merely an example, and the thickness of the barrier layer, the composition ratio, and the thickness of the n-type GaAs well layer may be appropriately selected so that a quantum level and a subband depending on the wavelength to be detected are formed. Further, the number of n-type GaAs well layers may be appropriately selected according to the required sensor sensitivity.

Further, in the above description of the respective embodiments, each MQW light absorption layer is constituted by the AlGaAs multiple quantum well structure.
It is also possible to use a multiple quantum well structure of other III-V group compound semiconductor such as a system, and any material system that is lattice-matched to the large-area substrate used.

Further, in the above description of each embodiment, the quantum well type infrared detector is shown as one pixel, but in reality, such a pixel is formed as a two-dimensional array or a one-dimensional array. Although it is arranged, on the contrary,
It may be used as a single infrared detection element.

Here, the detailed configuration of the present invention will be described again with reference to FIG. See FIG. 1 (Appendix 1), which has a photodetection mechanism having one or more absorption wavelengths, and a quantum well structure light absorption layer 3 that absorbs light in a predetermined wavelength range is added as a band-cut filter. Band-to-band transition quantum well photodetector. (Supplementary Note 2) The photodetection mechanism is composed of one quantum well structure light absorption layer, and the band cut filter is on the short wavelength side of the absorption wavelength of the quantum well structure light absorption layer constituting the light detection mechanism. A quantum well structure light absorption layer having an absorption wavelength in a region, and a quantum well structure light absorption layer having an absorption wavelength in a region on the long wavelength side of the absorption wavelength of the quantum well structure light absorption layer constituting the light detection mechanism. An intersubband transition quantum well type photodetector according to appendix 1. (Supplementary Note 3) The photodetection mechanism is composed of n quantum well structure light absorption layers 1 and 2 having different absorption wavelengths, and the band cut filter is (n-1) quantum well structure light absorption layers. 3. The intersubband transition quantum well type photodetector according to appendix 1, characterized in that (Supplementary Note 4) The quantum well structure light absorption layer 3 that functions as the band cut filter is provided on the back surface side of the base layer 7 that supports the quantum well structure light absorption layers 1 and 2 that form the light detection mechanism. 4. The intersubband transition quantum well type photodetector according to any one of appendices 1 to 3. (Supplementary Note 5) The quantum well structure light-absorbing layer 3 functioning as the band cut filter is provided adjacent to the quantum well structure light-absorbing layers 1 and 2 forming the photodetection mechanism. 4. The intersubband transition quantum well type photodetector according to any one of 1 to 3. (Supplementary Note 6) The intersubband transition quantum well type photodetector according to Supplementary Note 5, wherein non-doped layers are provided on both sides of the quantum well structure light absorption layer 3 functioning as the band cut filter. (Additional remark 7) The impurity concentration of the quantum well structure light absorption layer 3 functioning as the band-cut filter is higher than the impurity concentration of the quantum well structure light absorption layers 1 and 2 constituting the photodetection mechanism. Any one of 1 to 6
An intersubband transition quantum well type photodetector according to the item 1. (Supplementary Note 8) The subband according to any one of Supplementary Notes 1 to 7, wherein the absorption wavelength region of the quantum well structure light absorption layers 1 and 2 constituting the photodetection mechanism is an infrared region. Transition quantum well photodetector.

[0080]

According to the present invention, in an intersubband transition quantum well type photodetector, particularly in a multi-wavelength quantum well type infrared detector, an undesired wavelength range, in particular, an intermediate wavelength of a wavelength to be detected. Since a multi-quantum well type band cut filter that absorbs infrared rays in the region is provided, it is possible to reduce the spread of absorption wavelengths and reduce spectral crosstalk between wavelengths in the case of multiple wavelengths. It greatly contributes to the practical application of high resolution infrared solid-state imaging devices.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a principle configuration of the present invention.

FIG. 2 is a structural explanatory view of a dual wavelength quantum well type infrared detector according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of light absorption characteristics of the two-wavelength quantum well infrared detection device according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of a two-wavelength quantum well type infrared detection device according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram of a three-wavelength quantum well type infrared detection device according to a third embodiment of the present invention.

FIG. 6 is an explanatory diagram of a one-wavelength quantum well infrared detector according to a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram of a conventional two-wavelength quantum well type infrared detection device.

FIG. 8 is an explanatory diagram of light absorption characteristics of a conventional dual wavelength quantum well type infrared detector.

[Explanation of symbols]

1 quantum well structure light absorption layer 2 quantum well structure light absorption layer 3 quantum well structure light absorption layer 4 contact layer 5 contact layer 6 contact layer 7 base layer 8 reflection type diffraction grating 9 infrared ray 11 dummy MQW light absorption layer 12 i-type GaAs Base layer 13 n-type GaAs contact layer 14 n-type MQW first light absorption layer 15 n-type GaAs contact layer 16 n-type MQW second light absorption layer 17 n-type GaAs contact layer 18 reflection-type diffraction grating 19 pixel separation groove 20 pixel 21 i-type GaAs base layer 22 n-type GaAs contact layer 23 n-type MQW first light absorption layer 24 n-type GaAs contact layer 25 i-type GaAs separation layer 26 dummy MQW light absorption layer 27 i-type GaAs separation layer 28 n-type GaAs contact layer 29 n-type MQW second light absorption layer 30 n-type GaAs contact layer 31 reflection-type diffraction grating 32 Element separation groove 33 Pixel 41 First dummy MQW light absorption layer 42 Second dummy MQW light absorption layer 43 i-type GaAs base layer 44 n-type GaAs contact layer 45 n-type MQW first light-absorption layer 46 n-type GaAs contact layer 47 n Type MQW second light absorption layer 48 n-type GaAs contact layer 49 n-type MQW third light absorption layer 50 n-type GaAs contact layer 51 reflective diffraction grating 52 pixel separation groove 53 pixel 61 first dummy MQW light absorption layer 62 second Dummy MQW light absorption layer 63 i-type GaAs base layer 64 n-type GaAs contact layer 65 n-type MQW light absorption layer 66 n-type GaAs contact layer 67 reflective diffraction grating 68 pixel separation groove 69 pixel 71 i-type GaAs base layer 72 n-type GaAs contact layer 73 n-type MQW first light absorption layer 74 n-type GaAs contact layer 75 n-type MQW second Light absorption layer 76 n-type GaAs contact layer 77 reflective diffraction grating 78 pixel separation groove 79 pixel 80 infrared ray 81 n ^- type Al _x Ga _{1 -x} As barrier layer 82 n-type GaAs well layer 83 first quantum level 84 second Quantum level 85 Electron 86 n ^- type Al _y Ga _1-y As barrier layer 87 n-type GaAs well layer 88 First quantum level 89 Second quantum level 90 Electron

Claims (5)

[Claims] 1. An intersubband transition characterized by having a photodetection mechanism having one or more absorption wavelengths and adding a quantum well structure light absorption layer for absorbing light in a predetermined wavelength region as a band cut filter. Quantum well type photo detector. 2. The photodetection mechanism is composed of n quantum well structure light absorption layers having mutually different absorption wavelengths, and the band cut filter is composed of (n-1) quantum well structure light absorption layers. The intersubband transition quantum well type photodetector according to claim 1, wherein: 3. A quantum well structure light absorption layer functioning as the band cut filter is provided on a back surface side of a base layer supporting the quantum well structure light absorption layer constituting the light detection mechanism. The intersubband transition quantum well type photodetector according to claim 1 or 2. 4. The quantum well structure light absorption layer functioning as the band cut filter is provided adjacent to the quantum well structure light absorption layer constituting the light detection mechanism. 2. An intersubband transition quantum well type photodetector according to item 2. 5. The impurity concentration of the quantum well structure light absorption layer functioning as the band cut filter is higher than the impurity concentration of the quantum well structure light absorption layer constituting the light detection mechanism. 4. The intersubband transition quantum well type photodetector according to any one of 4 above.