JP2018060919A - Infrared sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared sensor in which both detection characteristics and mass productivity are improved.SOLUTION: An infrared sensor of the present invention includes: a substrate 1; an n-type contact layer 2 formed on the substrate 1; an n-type barrier layer 3 which comprises a compound semiconductor layer mainly composed of AlInAsSb and is formed on the n-type contact layer 2; an active layer 4 which comprises a compound semiconductor layer mainly composed of InAsSb(0≤x≤1) and is formed on the n-type barrier layer 3; and a p-type barrier layer 5 which comprises a compound semiconductor layer mainly composed of AlGaSb and is formed on the active layer 4.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an infrared sensor.

An infrared sensor is an element that converts infrared light into an electrical signal by utilizing a photoconductive effect, a photovoltaic effect, etc., and is generally cooled and used, but a quantum infrared sensor that can operate at room temperature has also been proposed. .
For example, a quantum infrared sensor described in Patent Document 1 includes a compound semiconductor sensor unit that detects infrared rays by a compound semiconductor layer provided on a substrate and outputs an electrical signal, and an electrical signal from the compound semiconductor sensor unit. The compound semiconductor sensor unit and the integrated circuit unit are housed in the same package. InSb, InAsSb, InAsN, or the like is used as a material of the light absorption layer (active layer) of the compound semiconductor sensor unit.
When InAsSb is used as the material of the light absorption layer of the infrared sensor, the peak wavelength of infrared detection can be controlled in the range of 3 μm to 10 μm by changing the As composition ratio of InAsSb.

  In Patent Document 2, an infrared sensor made of a compound semiconductor having a structure of InAsSb (buffer layer) / InAs (intermediate layer) / InAsSb (light absorption layer) is made of InAsSb by making the thickness of InAs larger than the critical thickness. It is described that the crystallinity of the light absorption layer is improved and the detection characteristics are improved. In the infrared sensor of Patent Document 2, a p-type barrier layer made of AlInAsSb is provided on a light absorption layer.

International Publication No. 2005/027228 Pamphlet Japanese Patent Laying-Open No. 2015-90901

The infrared sensor is required to improve both detection characteristics and mass productivity. However, the infrared sensors described in Patent Documents 1 and 2 have room for improvement in this respect.
An object of the present invention is to provide an infrared sensor in which both detection characteristics and mass productivity are improved.

In order to solve the above problems, an infrared sensor according to the first aspect of the present invention includes a substrate, an n-type contact layer formed on the substrate, and a compound semiconductor layer mainly composed of AlInAsSb. An active layer formed on the n-type barrier layer comprising a compound semiconductor layer mainly composed of InAs _x Sb _(1-x) (0 ≦ x ≦ 1), and AlGaSb. A p-type barrier layer made of a compound semiconductor layer as a main component and formed on the active layer.
In order to solve the above problems, an infrared sensor according to a second aspect of the present invention includes a substrate, a p-type contact layer formed on the substrate, and a compound semiconductor layer mainly composed of AlGaSb. A p-type barrier layer formed on the p-type barrier layer, a compound semiconductor layer mainly composed of InAs _x Sb _(1-x) (0 ≦ x ≦ 1), and AlInAsSb. An n-type barrier layer made of a compound semiconductor layer as a main component and formed on the active layer.

  The “compound semiconductor layer mainly composed of OO” means “a compound semiconductor layer substantially composed of OO other than dopant and impurities inevitably mixed during film formation”.

  According to the first and second aspects of the present invention, an infrared sensor with improved detection characteristics and mass productivity can be obtained.

It is sectional drawing which shows the structure of the infrared sensor of a 1st aspect. It is sectional drawing which shows the structure of the infrared sensor of a 2nd aspect. It is sectional drawing which shows the structure of the infrared sensor of 1st embodiment. It is sectional drawing which shows the structure of the infrared sensor of 2nd embodiment.

[First aspect]
<Configuration>
As shown in FIG. 1, the infrared sensor of the first aspect is opposite to the substrate 1, the n-type contact layer 2 formed on one surface (on the substrate) of the substrate 1, and the substrate of the n-type contact layer 2. The n-type barrier layer 3 formed on the side surface (on the n-type contact layer) and the active surface formed on the surface of the n-type barrier layer 3 opposite to the n-type contact layer 2 (on the n-type barrier layer) A layer 4 and a p-type barrier layer 5 formed on the surface of the active layer 4 opposite to the n-type barrier layer 3 (on the active layer). The n-type barrier layer 3 is composed of a compound semiconductor layer containing AlInAsSb as a main component. The active layer 4 is composed of a compound semiconductor layer containing InAs _x Sb _(1-x) (0 ≦ x ≦ 1) as a main component. The p-type barrier layer 5 is composed of a compound semiconductor layer containing AlGaSb as a main component.

<Action, effect>
According to the infrared sensor of the first aspect, the p-type barrier layer composed of the compound semiconductor layer mainly composed of AlGaSb and the n-type barrier layer composed of the compound semiconductor layer mainly composed of AlInAsSb are provided, thereby being active. The band offset of the conductor between the layer and the p-type barrier layer and the band offset of the valence band between the active layer and the n-type barrier layer can be sufficiently increased.
Furthermore, by using a compound semiconductor mainly composed of AlGaSb as a material of the p-type barrier layer and a compound semiconductor mainly composed of AlInAsSb as a material of the n-type barrier layer, Si as both an n-type dopant and a p-type dopant is used. Can be used. Si is a group IV element that is easy to control because of its low vapor pressure and has no toxicity.
Thereby, the infrared sensor of the first aspect has an improved barrier function by the barrier layer and is excellent in dopant controllability when forming each layer. That is, according to the first aspect of the present invention, an infrared sensor with improved detection characteristics and mass productivity can be obtained.

<Preferred form>
In the infrared sensor of the first aspect, the n-type dopant included in the n-type contact layer, the n-type dopant included in the n-type barrier layer, and the p-type dopant included in the p-type barrier layer are preferably Si.
In the infrared sensor of the first aspect, it is preferable that the substrate is a GaAs substrate, and further includes a buffer layer formed of a compound semiconductor layer mainly composed of AlGaSb and formed between the substrate and the n-type contact layer.
The infrared sensor of the first aspect preferably further includes a p-type contact layer made of a compound semiconductor layer mainly composed of GaSb or GaInSb and formed on the p-type barrier layer. The p-type dopant included in the p-type contact layer is preferably Si.

[Second embodiment]
<Configuration>
As shown in FIG. 2, the infrared sensor of the first aspect is opposite to the substrate 1, the p-type contact layer 6 formed on one surface (on the substrate) of the substrate 1, and the substrate of the p-type contact layer 6. The p-type barrier layer 5 formed on the side surface (on the p-type contact layer) and the active surface formed on the surface of the p-type barrier layer 5 opposite to the p-type contact layer 6 (on the p-type barrier layer) The layer 4 and the n-type barrier layer 3 formed on the surface of the active layer 4 opposite to the p-type barrier layer 5 (on the active layer) are provided. The n-type barrier layer 3 is composed of a compound semiconductor layer containing AlInAsSb as a main component. The active layer 4 is composed of a compound semiconductor layer containing InAs _x Sb _(1-x) (0 ≦ x ≦ 1) as a main component. The p-type barrier layer 5 is composed of a compound semiconductor layer containing AlGaSb as a main component.

<Action, effect>
According to the infrared sensor of the second aspect, the p-type barrier layer made of a compound semiconductor layer containing AlGaSb as a main component and the n-type barrier layer made of a compound semiconductor layer containing AlInAsSb as a main component are active. The band offset of the conductor between the layer and the p-type barrier layer and the band offset of the valence band between the active layer and the n-type barrier layer can be sufficiently increased.
Furthermore, by using a compound semiconductor mainly composed of AlGaSb as a material of the p-type barrier layer and a compound semiconductor mainly composed of AlInAsSb as a material of the n-type barrier layer, Si as both an n-type dopant and a p-type dopant is used. Can be used. Si is a group IV element that is easy to control because of its low vapor pressure and has no toxicity.
Thereby, the infrared sensor of a 2nd aspect is excellent in the dopant controllability at the time of forming each layer while the barrier function by a barrier layer is improving. That is, according to the second aspect of the present invention, an infrared sensor with improved detection characteristics and mass productivity can be obtained.

<Preferred form>
In the infrared sensor of the second aspect, the p-type dopant included in the p-type contact layer, the p-type dopant included in the p-type barrier layer, and the n-type dopant included in the n-type barrier layer are preferably Si.
In the infrared sensor of the second aspect, the substrate is preferably a GaAs substrate, and the p-type contact layer is preferably composed of a compound semiconductor layer containing GaSb as a main component.
The infrared sensor of the second aspect preferably further includes an n-type contact layer made of a compound semiconductor layer containing InAsSb as a main component and formed on the n-type barrier layer. The n-type dopant of the n-type contact layer is preferably Si.

[Common to the first and second embodiments]
<Background to knowledge>
In order to realize an infrared sensor having good characteristics, the barrier layer plays an important role. The barrier layer is a layer formed in contact with the active layer and has a function of preventing diffusion current. The p-type barrier layer preferably has a sufficiently large band offset in the conduction band with the active layer. The n-type barrier layer preferably has a sufficiently large band offset in the valence band with the active layer. Since electrons have a longer diffusion length than holes, it is preferable that the barrier layer is sufficiently thick, particularly in the p-type barrier layer.

As a material of the barrier layer, it is conceivable to select a material having a larger band gap than the active layer, but by adding a certain amount of Al or Ga to the material of the active layer and increasing the mixed crystal composition, the band gap, In many cases, the band offset of the conduction band and the band offset of the valence band are largely earned.
However, as the mixed crystal composition of Al or Ga in the barrier layer increases, the lattice mismatch with the active layer tends to increase, and as a result, the critical film thickness of the barrier layer decreases, so that a sufficient film thickness can be obtained. There arises a problem that the barrier layer cannot be formed. That is, particularly in the p-type barrier layer, it is important to select a material having a lattice constant close to that of the active layer and a large band offset of the conduction band. And the infrared sensor of patent document 2 which uses AlInAsSb as a p-type barrier layer has the problem that a sufficient thickness barrier layer cannot be formed.

  On the other hand, in the infrared sensors of the first and second embodiments, the band offset of the conduction band with the active layer can be increased by using AlGaSb as the material for the p-type barrier layer. Moreover, since AlGaSb has a lattice constant close to that of InAsSb, which is the material of the active layer, the thickness of the p-type barrier layer can be increased. Further, by using AlInAsSb as the material of the n-type barrier layer, the band offset of the valence band with the active layer can be increased. Thereby, the function to prevent the diffusion current can be enhanced and the characteristics of the infrared sensor can be improved.

As the p-type dopant used when forming the p-type barrier layer, Be, Zn, Cd, C, Mg, Ge and the like are generally used. In particular, Zn is preferably used because of its high activation rate and low toxicity. However, there is a concern that Zn has a high vapor pressure and is difficult to control and remains in the chamber. In addition, if the n-type dopant and the p-type dopant can be made the same, the productivity can be improved.
In the infrared sensor of the first aspect and the second aspect, AlInAsSb is used as the material of the n-type barrier layer, and AlGaSb is used as the material of the p-type barrier layer, so that both the n-type barrier layer and the p-type barrier layer are used. Si can be used as a dopant. Since Si is a dopant with good controllability, it becomes easy to form each compound semiconductor layer with a desired doping concentration. Further, since both the n-type barrier layer and the p-type barrier layer can be doped with a single dopant, the mass productivity is excellent.

<Production method>
The infrared sensor of the first embodiment and the second embodiment is manufactured through a process of forming each layer on a substrate. This process is performed by, for example, a molecular beam epitaxy (MBE) method or a metal organic vapor phase epitaxy (MOVPE) method. And so on.

<Additional configuration>
The infrared sensor of the first aspect and the second aspect can further include an electrode formed on the n-type barrier layer and the p-type contact layer, and a passivation film.
A plurality of infrared sensors according to the first and second aspects may be formed on a substrate and electrically connected in series. With such a structure, it becomes possible to add the outputs of a single infrared sensor, and the output can be dramatically improved.
Moreover, you may form the infrared sensor of a 1st aspect or a 2nd aspect, and the integrated circuit part which processes the electric signal output from this infrared sensor in a hybrid in the same package. The electrical connection method between the infrared sensor and the integrated circuit portion is not particularly limited. The package is not particularly limited as long as it has a high infrared transmittance, and a hollow package or the like may be used.

  In order to completely avoid the influence of specific light, a filter may be attached to the light receiving surface of the infrared sensor (for example, the back side of the substrate). Furthermore, a Fresnel lens may be provided on the light receiving surface of the infrared sensor (for example, the back side of the substrate) in order to determine the distance and directionality to be detected and to further improve the light collecting property.

<Details about each configuration>
(substrate)
The substrate is not particularly limited as long as a compound semiconductor layer can be grown thereon, and a single crystal substrate such as a GaAs substrate or a Si substrate is preferable. Further, these single crystal substrates may be doped n-type or p-type with donor impurities or acceptor impurities.
The plane orientation of the single crystal substrate is not particularly limited, but (100), (111), (110) and the like are preferable. Further, it is possible to use a plane orientation inclined by 1 ° to 5 ° with respect to these plane orientations.

When a plurality of infrared sensors formed on the surface of the substrate are used by being connected in series with electrodes, it is preferable that each infrared sensor is insulated and separated at portions other than the electrodes. Therefore, as the substrate, it is preferable to use a semi-insulating substrate or a substrate capable of insulating and separating the stacked body of each layer formed on the substrate and the substrate.
Furthermore, by using a material that transmits infrared rays as the substrate, infrared rays can be incident from the back side of the substrate. In this case, the infrared light is not blocked by the electrode, which is preferable in that the light receiving area of the element can be increased. As a material for such a substrate, semi-insulating Si, GaAs or the like is preferable.
As is usually done, for the purpose of flattening and cleaning the surface of the substrate, a substrate formed with a semiconductor layer made of the same material as the substrate may be used as the substrate. The most representative example of this is that a GaAs layer formed on a GaAs substrate is used as the substrate.

(Buffer layer)
The infrared sensor of the first aspect preferably further includes a buffer layer between the substrate and the n-type contact layer. The buffer layer is formed on the surface of the substrate. The buffer layer functions as a layer for improving all crystallinity formed thereon. Thereby, an active layer with good crystallinity (with few defects) can be obtained.
In the infrared sensor of the second aspect, a buffer layer may be further provided between the substrate and the p-type contact layer.

Examples of the material for the buffer layer include InSb, InAs, InAsSb, AlInSb, GaInSb, AlGaInSb, AlInAsSb, GaInAsSb, AlGaInAsSb, AlSb, GaSb, AlGaSb, AlAsSb, GaAsSb, and AlGaAsSb. The buffer layer may be a single layer made of one of these materials or a multilayer in which a plurality of layers are stacked. In addition, a graded buffer layer formed so that the lattice constant is close to the composition of the layer (n-type contact layer or p-type contact layer) formed thereon while changing the composition of the material continuously or stepwise. May be used.
The GaSb single layer film and the AlGaSb single layer film can be (a) easy to form a film with good crystallinity, (b) the lattice mismatch with the active layer containing InAsSb can be brought close to zero, (c) A single layer film is preferable as a material for the buffer layer from the viewpoint that a film thickness may be smaller than that of a graded layer or the like, and a formation time may be shortened.

In the case where the buffer layer is an AlGaSb single layer film, when the Al composition ratio y of Al _y Ga _(1-y) Sb (0 ≦ y ≦ 1) increases, the electrical resistance increases, but the crystallinity tends to deteriorate. Therefore, the Al composition ratio y is appropriately selected according to the desired resistance and crystallinity. If the Al composition ratio y of Al _y Ga _(1-y) Sb (0 ≦ y ≦ 1) is too large, oxidation corrosion tends to occur. Therefore, from the viewpoint of easy oxidation and corrosion, the Al composition ratio y is set to 0. It is preferable that it is 0.8 or more.
Moreover, since the GaSb single layer film can be formed into a film having better crystallinity than the AlGaSb single layer film, it is more preferable to use the GaSb single layer film from the viewpoint of obtaining good crystallinity.

In a preferred embodiment of the infrared sensor of the first aspect, “a substrate is a GaAs substrate, and a buffer layer made of a compound semiconductor layer mainly composed of AlGaSb is further provided between the substrate and the n-type contact layer”, the AlGaSb Is used as a material for the buffer layer, and as described above, the Al composition ratio is increased to increase the electric resistance of the buffer layer, so that the buffer layer functions as an insulating layer without doping. This is preferable because the buffer layer can be a layer that does not contribute to the PIN structure.
If the thickness of the buffer layer is too thin, the effect of improving the crystallinity of the active layer is lost, and if it is too thick, it takes time to form and the mesa etching process for element isolation becomes difficult, so 0.3 μm to 2 μm Is preferred.

When a GaSb single layer film and an AlGaSb single layer film are used as a buffer layer, they may be non-doped, or may be doped n-type or p-type.
When an n-type contact layer is formed on the buffer layer, an n-type contact layer may be formed on a non-doped GaSb or AlGaSb single-layer film, or an n-type doped GaSb or AlGaSb single-layer film may be used as it is. It may also be used as an n-type contact layer.
However, in order to make a GaSb or AlGaSb single layer film n-type, group IV elements such as Si and Sn having a low vapor pressure cannot be used because they act as p-type dopants, have a high vapor pressure, and are toxic. There is also a certain group VI element such as Te. When Te or the like is used, there is a concern that the control is difficult because the vapor pressure is high, or the chamber of the film forming apparatus is contaminated.

That is, when an n-type contact layer is formed on the buffer layer, it is preferable to use a non-doped GaSb or AlGaSb single layer film as the buffer layer.
On the other hand, when a p-type contact layer is formed on the buffer layer, a p-type doped GaSb or AlGaSb single layer film may be used as a p-type contact layer as it is. Regarding the p-type conversion of GaSb and AlGaSb single layer films, the vapor pressure is low, and Si, which is the most commonly used group IV element, can be used as a dopant.

(N-type contact layer)
The n-type contact layer functions as a contact layer with the electrode for taking out a photocurrent generated when the active layer absorbs infrared rays. Examples of the material of the n-type contact layer include InSb, InAs, InAsSb, AlInSb, GaInSb, AlGaInSb, AlInAsSb, GaInAsSb, AlGaInAsSb, AlSb, GaSb, AlGaSb, AlAsSb, GaAsSb, and AlGaAsSb.
Since the sheet resistance of the n-type contact layer causes Johnson noise that is thermal noise, the sheet resistance is preferably as small as possible. The n-type contact layer needs to be sufficiently doped to reduce contact resistance. Therefore, the doping concentration is preferably 1 × 10 ¹⁸ / cm ³ or more. Examples of the n-type dopant include Si, Sn, S, Se, Te, and Ge.

As a material of the n-type contact layer, (d) InAsSb forming the active layer is close to the lattice constant, (e) the vapor pressure is low, and Si, which is the most commonly used group IV element, can be used as a dopant. (F) InAs or InAsSb is particularly preferable from the viewpoint that sheet resistance can be reduced. The use of InAsSb, which is the same material as the active layer, is more preferable because the lattice constant can be made to coincide completely.
The thickness of the n-type contact layer is preferably as thick as possible in order to reduce the sheet resistance. However, if it is too thick, it takes time to form and a mesa etching process for element isolation becomes difficult. For this reason, as a film thickness of an n-type contact layer, 0.1 to 1 micrometer is mentioned as a preferable range.

(N-type barrier layer)
1st aspect and 2nd aspect The n-type barrier layer of an infrared sensor consists of a compound semiconductor layer which has AlInAsSb as a main component, and has a function which prevents the diffused current from an active layer. By using AlInAsSb having a large band gap as an n-type barrier layer with respect to the active layer made of InAsSb, a large band offset of the valence band can be obtained.
When the lattice constants of the active layer and the n-type barrier layer are different, if the thickness of the n-type barrier layer exceeds the critical thickness, the crystallinity of the n-type barrier layer deteriorates. Alternatively, it is necessary to consider both the band offset of the valence band and the deterioration of crystallinity. From the viewpoint of increasing the thickness of the n-type barrier layer, the difference in lattice constant between the active layer and the n-type barrier layer is preferably as small as possible.

The n-type barrier layer not only has a function of preventing a diffusion current, but also has a function of allowing electrons and holes generated in the active layer to flow as a photocurrent. Therefore, the n-type barrier layer needs to be sufficiently doped, and the doping concentration is preferably 1 × 10 ¹⁸ / cm ³ or more. Examples of the n-type dopant include Si, Sn, S, Se, Te, and Ge.
By using AlInAsSb as the material of the n-type barrier layer, the lattice constant between the active layer made of InAsSb and the n-type barrier layer is close, the vapor pressure is low, and Si, which is the most commonly used group IV element, is changed. It can be used as an n-type dopant.

In this case, if the Al composition ratio of AlInAsSb is too small, a sufficient valence band offset cannot be secured, and if the Al composition ratio of AlInAsSb is too large, the difference in lattice constant from the active layer containing InAsSb increases. Since the critical film thickness of the n-type barrier layer becomes small, a sufficient film thickness as the n-type barrier layer cannot be secured. Therefore, the Al composition ratio of AlInAsSb is preferably 0.1 or more and 0.5 or less.
The thickness of the n-type barrier layer is preferably as thin as possible in order to reduce the resistance of the infrared sensor. However, a thickness that does not cause tunnel leakage between the electrode and the active layer is required. For this reason, the film thickness of the n-type barrier layer is preferably 0.01 μm or more, more preferably 0.02 μm or more. Note that the upper limit of the thickness of the n-type barrier layer is limited by the critical thickness determined by the difference between the lattice constants of the active layer and the n-type barrier layer.

(Active layer)
The active layer of the first and second embodiments of the infrared sensor is made of InAs _x Sb _(1-x) (0 ≦ x ≦ 1). The As composition ratio x of the active layer is not particularly limited, but the peak wavelength of infrared detection can be controlled over a wide range of 3 μm to 10 μm by setting the As composition ratio x to a desired value. When AlGaSb or GaSb is used as the buffer layer, a better crystal is obtained when the lattice constant of InAsSb in the active layer is closer to the lattice constant of the buffer layer, so that the As composition ratio x is 0.7 or more and 1 or less. preferable.
The thickness of the active layer is preferably thick in order to increase the amount of light absorption, but if it is too thick, it takes time to form and the mesa etching process for element isolation becomes difficult, so 0.5 μm or more and 3 μm or less Is preferred.

The active layer may be non-doped or may be doped n-type or p-type. Since InAsSb has a very small band gap, the intrinsic carrier density is very large. This leads to an increase in diffusion current and acceleration of the Auger recombination process. These effects can be reduced by doping the active layer p-type. The doping amount is set as appropriate.
In general, Be, Zn, Cd, C, Mg, Ge, etc. are preferably used as the p-type dopant of the active layer made of InAs _x Sb _(1-x) (0 ≦ x ≦ 1). Since activation rate is high and toxicity is low, it is more preferably used.

(P-type barrier layer)
The p-type barrier layer of the infrared sensor of the first aspect and the second aspect is composed of a compound semiconductor layer containing AlGaSb as a main component and has a function of preventing a diffusion current from the active layer. By using AlGaSb having a large band gap as a material of the p-type barrier layer with respect to the active layer made of InAsSb, a large band offset of the conduction band can be obtained.
The p-type barrier layer not only has a function of preventing a diffusion current but also has a function of allowing electrons and holes generated in the active layer to flow as a photocurrent. Therefore, the p-type barrier layer needs to be sufficiently doped, and the doping concentration is preferably 1 × 10 ¹⁸ / cm ³ or more.

Examples of the p-type dopant include Be, Zn, Cd, C, Mg, and Ge. Si is generally known as an n-type dopant, but can be used as a p-type dopant for AlGaSb.
By using AlGaSb as the material of the p-type barrier layer, the lattice constant between the active layer made of InAsSb and the p-type barrier layer is close, the vapor pressure is low, and Si, which is the most commonly used group IV element, is changed. It can be used as a p-type dopant, and the band offset of the conduction band can be increased.

Since the difference in lattice constant from InAsSb forming the active layer is sufficiently small, the Al composition ratio of AlGaSb in the p-type barrier layer is not limited by the critical film thickness, but if the Al composition ratio is too large, there are concerns about oxidation, corrosion, and the like. Therefore, the Al composition ratio is preferably 0 or more and 0.8 or less.
The thickness of the p-type barrier layer is preferably as thin as possible in order to reduce the element resistance of the sensor. However, the thickness of the p-type barrier layer is required so as not to cause a tunnel leak between the electrode and the active layer. For this reason, the film thickness of the p-type barrier layer is preferably 0.01 μm or more, more preferably 0.02 μm or more. Note that the upper limit of the thickness of the p-type barrier layer is limited by the critical thickness determined by the difference between the lattice constants of the active layer and the n-type barrier layer.

(P-type contact layer)
The p-type contact layer functions as a contact layer with the electrode for taking out a photocurrent generated when the active layer absorbs infrared rays. Examples of the material of the p-type contact layer include InSb, InAs, InAsSb, AlInSb, GaInSb, AlGaInSb, AlInAsSb, GaInAsSb, AlGaInAsSb, AlSb, GaSb, AlGaSb, AlAsSb, GaAsSb, and AlGaAsSb.
Since the sheet resistance of the p-type contact layer causes Johnson noise, which is thermal noise, the sheet resistance should be as small as possible. The p-type contact layer needs to be sufficiently doped to reduce the contact resistance. Therefore, the doping concentration is preferably 1 × 10 ¹⁸ / cm ³ or more. Examples of the p-type dopant include Be, Zn, Cd, C, Mg, and Ge.

As a material of the p-type contact layer, (d) the lattice constant is close to that of InAsSb forming the active layer, (e) Si, which is the most commonly used group IV element, can be used as a dopant. (F) AlGaSb and GaSb are preferable from the viewpoint that sheet resistance can be reduced. It is preferable that the material of the p-type contact layer is GaSb because the sheet resistance can be made smaller than that in the case of AlGaSb.
In addition, since lattice matching with InAsSb is possible by controlling the In composition, it is also preferable to use GaInSb as the material of the p-type contact layer.
The p-type contact layer is preferably as thick as possible in order to reduce the sheet resistance. However, if it is too thick, it takes time to form and a mesa etching process for element isolation becomes difficult. For this reason, the preferable thickness of the p-type contact layer is 0.1 μm or more and 1 μm or less.

(Passivation film)
The passivation film is not particularly limited as long as it is an insulating film. Examples of the material for the passivation film include a silicon nitride film (Si ₃ N ₄ ), a silicon oxide film (SiO ₂ ), and a silicon oxynitride film (SiON).
(electrode)
The electrodes include a p-type electrode that is electrically connected to the p-type contact layer and an n-type electrode that is electrically connected to the n-type contact layer. The electrode is not particularly limited as long as it is composed of a conductive film, and examples thereof include a laminated film (upper layer / lower layer) such as Au / Ti and Au / Cr.

Embodiment
Hereinafter, although embodiment of this invention is described, this invention is not limited to embodiment shown below. In the embodiment described below, a technically preferable limitation is made for carrying out the present invention, but this limitation is not an essential requirement of the present invention.
Note that in the drawings used in the following description, the dimensional relationships of the respective parts illustrated may be different from the actual dimensional relationships.

<First embodiment>
(Constitution)
As shown in FIG. 3, the infrared sensor according to the first embodiment includes a substrate 1, a buffer layer 7, an n-type contact layer 2, an n-type barrier layer 3, an active layer 4, and a p-type barrier layer 5. , A p-type contact layer 6, an n-type electrode 8, a p-type electrode 9, and a passivation film 10.
On the substrate 1, a buffer layer 7, an n-type contact layer 2, an n-type barrier layer 3, an active layer 4, a p-type barrier layer 5, and a p-type contact layer 6 are formed in this order. That is, a compound semiconductor stacked body including the buffer layer 7, the n-type contact layer 2, the n-type barrier layer 3, the active layer 4, the p-type barrier layer 5, and the p-type contact layer 6 is formed on the substrate 1. .
The widths of the buffer layer 7 and the n-type contact layer 2 are larger than the widths of the n-type barrier layer 3, the active layer 4, the p-type barrier layer 5, and the p-type contact layer 6. That is, there is a step between the n-type contact layer 2 and the n-type barrier layer 3. An n-type electrode 8 is formed on the upper surface of the n-type contact layer 2 generated by this step, and a p-type electrode 9 is formed on the upper surface of the p-type contact layer 6.

The passivation film 10 covers the upper surface of the substrate 1, the side surfaces and the upper surface of the compound semiconductor stacked body. Upper portions of the n-type electrode 8 and the p-type electrode 9 are exposed from the passivation film 10.
The substrate 1 is made of GaAs. The buffer layer 7 is made of AlGaSb. The n-type contact layer 2 is made of InAsSb containing Si (n-type dopant). The n-type barrier layer 3 is made of AlInAsSb containing Si (n-type dopant). The active layer 4 is made of InAs _x Sb _(1-x) (0 ≦ x ≦ 1). The p-type barrier layer 5 is made of AlGaSb containing Si (p-type dopant). The p-type contact layer 6 is made of GaSb or GaInSb containing Si (p-type dopant). The n-type electrode 8 is made of Au / Ti. The p-type electrode 9 is made of Au / Ti. The passivation film 10 is made of silicon nitride.

(Function, effect)
According to the infrared sensor of the first embodiment, the band offset of the conductor between the active layer 4 and the p-type barrier layer 5 can be sufficiently increased by including the p-type barrier layer 5 made of AlGaSb containing Si. . Further, by including the buffer layer 7 made of AlGaSb, the crystallinity of the active layer 4 made of InAs _x Sb _(1-x) (0 ≦ x ≦ 1) is improved. Further, since the n-type contact layer 2 is made of the same InAsSb as the active layer 4, the lattice constants of the n-type contact layer 2 and the active layer 4 are the same.

Further, since the n-type barrier layer 3 is made of AlInAsSb having a large band gap energy with respect to InAs _x Sb _(1-x) (0 ≦ x ≦ 1) forming the active layer 4, a large band offset of the valence band can be obtained. The p-type contact layer 6 is made of GaSb or GaInSb having a lattice constant close to that of InAs _x Sb _(1-x) (0 ≦ x ≦ 1) forming the active layer 4.
From the above, according to the infrared sensor of the first embodiment, good detection characteristics can be obtained.
Moreover, since the infrared sensor of 1st embodiment uses controllable Si as both an n-type dopant and a p-type dopant, it is excellent also in mass-productivity.

(Production method)
First, the buffer layer 7, the n-type contact layer 2, the n-type barrier layer 3, the active layer 4, the p-type barrier layer 5 are formed on the upper surface of the GaAs wafer (substrate 1) using MBE (molecular beam epitaxy). A p-type contact layer 6 is formed. Next, the n-type barrier layer 3, the active layer 4, the p-type barrier layer 5, and the p-type contact layer 6 are partially removed for each element by wet etching using an acid or an ion milling method. A step for forming contact between the n-type contact layer 2 and the n-type electrode 8 is formed. As a result, a plurality of compound semiconductor stacks having steps are formed on the GaAs wafer.

Next, mesa etching for element isolation is performed on the plurality of compound semiconductor stacks having steps. Here, the n-type contact layer and the buffer layer appearing at the bottom of the step are partially removed sequentially. Thereby, the upper surface of the substrate 1 is exposed in the element isolation region.
Next, a passivation film 10 made of silicon nitride covers the upper surface of the substrate 1 and the upper surface and side surfaces of the compound semiconductor stacked body from which elements have been separated.
Next, a portion of the passivation film 10 where the n-type electrode 8 and the p-type electrode 9 are formed is etched to form a through hole. Next, an Au / Ti electrode is formed so as to fill the through hole by a lift-off method or the like.

<Second embodiment>
(Constitution)
As shown in FIG. 4, the infrared sensor according to the second embodiment includes a substrate 1, a p-type contact layer 6, a p-type barrier layer 5, an active layer 4, an n-type barrier layer 3, and an n-type contact layer. 2, an n-type electrode 8, a p-type electrode 9, and a passivation film 10.
A p-type contact layer 6, a p-type barrier layer 5, an active layer 4, an n-type barrier layer 3, and an n-type contact layer 2 are formed on the substrate 1 in this order. That is, a compound semiconductor stacked body including the p-type contact layer 6, the p-type barrier layer 5, the active layer 4, the n-type barrier layer 3, and the n-type contact layer 2 is formed on the substrate 1. .

The width of the p-type contact layer 6 is larger than the widths of the p-type barrier layer 5, the active layer 4, the n-type barrier layer 3, and the n-type contact layer 2. That is, there is a step between the p-type contact layer 6 and the p-type barrier layer 5. A p-type electrode 9 is formed on the upper surface of the p-type contact layer 6 generated by this step, and an n-type electrode 8 is formed on the upper surface of the n-type contact layer 2.
The passivation film 10 covers the upper surface of the substrate 1, the side surfaces and the upper surface of the compound semiconductor stacked body. Upper portions of the n-type electrode 8 and the p-type electrode 9 are exposed from the passivation film 10.

The substrate 1 is made of GaAs. The n-type contact layer 2 is made of InAsSb containing Si (n-type dopant). The n-type barrier layer 3 is made of AlInAsSb containing Si (n-type dopant). The active layer 4 is made of InAs _x Sb _(1-x) (0 ≦ x ≦ 1). The p-type barrier layer 5 is made of AlGaSb containing Si (p-type dopant). The p-type contact layer 6 is made of GaSb containing Si (p-type dopant). The n-type electrode 8 is made of Au / Ti. The p-type electrode 9 is made of Au / Ti. The passivation film 10 is made of silicon nitride.

(Function, effect)
According to the infrared sensor of the second embodiment, the band offset of the conductor between the active layer 4 and the p-type barrier layer 5 can be sufficiently increased by including the p-type barrier layer 5 made of AlGaSb containing Si. .
Further, since the n-type contact layer 2 is made of the same InAsSb as the active layer 4, the lattice constants of the n-type contact layer 2 and the active layer 4 are the same. Further, since the n-type barrier layer 3 is made of AlInAsSb having a large band gap energy with respect to InAs _x Sb _(1-x) (0 ≦ x ≦ 1) forming the active layer 4, a large band offset of the valence band can be obtained. The p-type contact layer 6 is made of GaSb having a lattice constant close to that of InAs _x Sb _(1-x) (0 ≦ x ≦ 1) forming the active layer 4, so that InAs _x Sb _{(1 -x)} The crystallinity of (0 ≦ x ≦ 1) can be improved.
From the above, according to the infrared sensor of the second embodiment, good detection characteristics can be obtained.
Moreover, since the infrared sensor of the second embodiment uses controllable Si as both the n-type dopant and the p-type dopant, it is excellent in mass productivity.

(Production method)
Since the infrared sensor of the second embodiment is different from the infrared sensor of the first embodiment in the configuration of the compound semiconductor laminate, the formation order of each layer is different, but can basically be manufactured by the method described in the first embodiment. .

Examples of the present invention will be described below.
[Example 1]
An infrared sensor having the structure shown in FIG. 3 was produced as follows.
On the substrate 1 made of semi-insulating GaAs single crystal, the buffer layer 7, the n-type contact layer 2, the n-type barrier layer 3, the active layer 4, the p-type barrier layer 5, and the p-type barrier layer are formed by the MBE method. By sequentially laminating the type contact layer 6, a compound semiconductor laminated body having a PIN structure was formed.
In this lamination process, a non-doped Al _0.55 Ga _0.45 Sb layer was formed as a buffer layer 7 by 0.5 μm. As the n-type contact layer 2, an n-type InAs _0.91 Sb _0.09 layer doped with Si of 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.7 μm. As the n-type barrier layer 3, an n-type Al _0.3 In _0.7 As _0.91 Sb _0.09 layer doped with Si at 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.02 μm. As the active layer 4, a non-doped InAs _0.91 Sb _0.09 layer having a thickness of 2 μm was formed. As the p-type barrier layer 5, a p-type Al _0.4 Ga _0.6 Sb layer doped with 3 × 10 ¹⁸ / cm ^{3 of} Si was formed to a thickness of 0.02 μm. As the p-type contact layer 6, a 0.5 μm p-type GaSb layer doped with Si at 3 × 10 ¹⁸ / cm ³ was formed.

In this lamination process, since the vapor pressure is low, the control is simple, and only Si that is generally used without toxicity is used as a dopant. That is, this method is a method with excellent mass productivity as a method for manufacturing a compound semiconductor stacked body having a PIN structure.
The half width (FWHM value) of the rocking curve of the X-ray diffraction peak of the active layer 4 made of InAs _0.91 Sb _{0.09 of the} obtained compound semiconductor stack was evaluated to be 304 arcsec.
The infrared sensor of Example 1 was produced by performing the following processes with respect to this compound semiconductor laminated body.

First, a step for making contact with the n-type contact layer 2 was formed by wet etching using an acid or ion milling. Next, mesa etching for element isolation was performed on the compound semiconductor stacked body on which the step was formed. Thereafter, the passivation film 10 made of SiN covered the upper surface of the substrate 1 and the upper surface and side surfaces of the compound semiconductor stacked body from which the elements were separated. Next, a through hole was formed in the electrode formation portion of the passivation film 10. Next, Au / Ti is deposited by EB (electron beam) evaporation on the stepped portion of the n-type contact layer 2 and on the p-type contact layer 6, and the n-type electrode 8 and the p-type electrode are formed in each through hole by a lift-off method. 9 were formed respectively.
In this way, an infrared sensor having the structure shown in FIG. 3 was obtained.

[Example 2]
As the n-type contact layer 2, an n-type InAs _0.87 Sb _0.13 layer doped with Si at 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.7 μm. Further, as the n-type barrier layer 3, an n-type Al _0.3 In _0.7 As _0.87 Sb _0.13 layer doped with Si at 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.02 μm. Further, as the active layer 4, a non-doped InAs _0.87 Sb _0.13 layer was formed to 2 μm. Further, as the p-type contact layer 6, a 0.5 μm p-type Ga _0.96 In _0.04 Sb layer doped with Si 3 × 10 ¹⁸ / cm ³ was formed. Except this, a compound semiconductor stacked body having a PIN structure was formed in the same manner as in Example 1.

When the half width (FWHM value) of the rocking curve of the X-ray diffraction peak of the active layer 4 made of InAs _0.87 Sb _{0.13 of the} obtained compound semiconductor laminate was evaluated, it was 306 arcsec.
The infrared sensor of Example 2 was produced by performing the same process as Example 1 with respect to this compound semiconductor laminated body.

[Example 3]
An infrared sensor having the structure shown in FIG. 4 was produced as follows.
By the MBE method, a p-type contact layer 6 also serving as a buffer layer, a p-type barrier layer 5, an active layer 4, an n-type barrier layer 3, and an n-type substrate are formed on a substrate 1 made of semi-insulating GaAs single crystal. By sequentially laminating the type contact layer 2, a compound semiconductor multilayer body having a PIN inverse structure was formed.
In this stacking step, a p-type GaSb layer doped with 3 × 10 ¹⁸ / cm ^{3 of} Si was formed as a p-type contact layer 6 also serving as a buffer layer, and a thickness of 1.0 μm was formed. As the p-type barrier layer 5, a p-type Al _0.4 Ga _0.6 Sb layer doped with Si at 3 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.02 μm. Further, as the active layer 4, a non-doped InAs _0.87 Sb _0.13 layer was formed to 2 μm. Further, as the n-type barrier layer 3, an n-type Al _0.3 In _0.7 As _0.87 Sb _0.13 layer doped with Si at 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.02 μm. Further, as the n-type contact layer 2, an n-type InAs _0.87 Sb _0.13 layer doped with Si at 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.5 μm.

In this lamination process, since the vapor pressure is low, the control is simple, and only Si that is generally used without toxicity is used as a dopant. That is, this method is excellent in mass productivity as a method for manufacturing a compound semiconductor stacked body having a PIN inverse structure.
With respect to the active layer 4 made of InAs _0.87 Sb _{0.13 of the} obtained compound semiconductor laminated body, the half-value width (FWHM value) of the rocking curve of the X-ray diffraction peak was evaluated, and it was 184 arcsec. This value is small compared with the value of the compound semiconductor laminated body obtained in Examples 1 and 2. That is, the active layer 4 of the compound semiconductor stack obtained in Example 3 was better in crystallinity than the active layer 4 of the compound semiconductor stack obtained in Examples 1 and 2.
The reason why this effect was obtained was that the buffer layer 7 made of AlGaSb was formed on the substrate 1 with a thickness of 0.5 μm in Examples 1 and 2, whereas the buffer layer was used in Example 3 as well. This is presumably because the p-type contact layer 6 made of GaSb is formed with a thickness of 1.0 μm.

The infrared sensor of Example 4 was produced by performing the following processes with respect to this compound semiconductor laminated body.
First, step formation for making contact with the p-type contact layer 6 was performed by wet etching using an acid or ion milling. Next, mesa etching for element isolation was performed on the compound semiconductor stacked body on which the step was formed. Thereafter, the passivation film 10 made of SiN covered the upper surface of the substrate 1 and the upper surface and side surfaces of the compound semiconductor stacked body from which the elements were separated. Next, a through hole was formed in the electrode formation portion of the passivation film 10. Next, Au / Ti is deposited by EB (electron beam) deposition on the stepped portion of the p-type contact layer 6 and on the n-type contact layer 2, and the p-type electrode 9 and the n-type electrode are placed in each through hole by a lift-off method. 8 were formed respectively.
In this way, an infrared sensor having the structure shown in FIG. 4 was obtained.

[Example 4]
As the active layer 4, a non-doped InAs _0.91 Sb _0.09 layer having a thickness of 2 μm was formed. Further, as the n-type barrier layer 3, an n-type Al _0.3 In _0.7 As _0.91 Sb _0.09 layer doped with Si at 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.02 μm. Further, as the n-type contact layer 2, an InAs _0.91 Sb _0.09 layer doped with Si of 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.5 μm. Except this, a compound semiconductor stacked body having a PIN inverse structure was formed in the same manner as in Example 3.
The half width (FWHM value) of the rocking curve of the X-ray diffraction peak of the active layer 4 made of InAs _0.91 Sb _{0.09 of the} obtained compound semiconductor laminate was evaluated to be 199 arcsec. This value is small compared with the value of the compound semiconductor laminated body obtained in Examples 1 and 2. That is, the active layer 4 of the compound semiconductor stacked body obtained in Example 4 had better crystallinity than the active layer 4 of the compound semiconductor stacked body obtained in Examples 1 and 2.

The reason why this effect was obtained was that the buffer layer 7 made of AlGaSb was formed on the substrate 1 with a thickness of 0.5 μm in Examples 1 and 2, whereas the buffer layer was used in Example 4 as well. This is presumably because the p-type contact layer 6 made of GaSb is formed with a thickness of 1.0 μm.
The infrared sensor of Example 4 was produced by performing the same process as Example 3 with respect to this compound semiconductor laminated body.

[Example 5]
As the active layer 4, a 2 μm thick non-doped InAs _0.96 Sb _0.04 layer was formed. Further, as the n-type barrier layer 3, an Al _0.3 In _0.7 As _0.96 Sb _0.04 layer doped with Si of 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.02 μm. Further, as the n-type contact layer 2, an InAs _0.96 Sb _0.04 layer doped with Si of 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.5 μm. Except this, a compound semiconductor stacked body having a PIN inverse structure was formed in the same manner as in Example 3.
With respect to the active layer 4 made of InAs _0.96 Sb _{0.04 of the} obtained compound semiconductor laminated body, the half width (FWHM value) of the rocking curve of the X-ray diffraction peak was evaluated and found to be 203 arcsec. This value is small compared with the value of the compound semiconductor laminated body obtained in Examples 1 and 2. That is, the active layer 4 of the compound semiconductor stack obtained in Example 5 was better in crystallinity than the active layer 4 of the compound semiconductor stack obtained in Examples 1 and 2.

The reason why this effect was obtained was that the buffer layer 7 made of AlGaSb was formed on the substrate 1 with a thickness of 0.5 μm in Examples 1 and 2, whereas the buffer layer was also used in Example 5. This is presumably because the p-type contact layer 6 made of GaSb is formed with a thickness of 1.0 μm.
The infrared sensor of Example 5 was obtained by performing the same process as Example 3 with respect to this compound semiconductor laminated body.

[Example 6]
As the active layer 4, a 2 μm thick non-doped InAs _0.98 Sb _0.02 layer was formed. Further, as the n-type barrier layer 3, an Al _0.3 In _0.7 As _0.98 Sb _0.02 layer doped with Si 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.02 μm. As the n-type contact layer 2, an InAs _0.98 Sb _0.02 layer doped with Si at 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.5 μm. Except this, a compound semiconductor stacked body having a PIN inverse structure was formed in the same manner as in Example 3.
The half width (FWHM value) of the rocking curve of the X-ray diffraction peak of the active layer 4 made of InAs _0.98 Sb _{0.02 of the} obtained compound semiconductor stack was evaluated to be 248 arcsec. This value is small compared with the value of the compound semiconductor laminated body obtained in Examples 1 and 2. In other words, the active layer 4 of the compound semiconductor stack obtained in Example 6 had better crystallinity than the active layer 4 of the compound semiconductor stack obtained in Examples 1 and 2.

The reason why this effect was obtained was that the buffer layer 7 made of AlGaSb was formed on the substrate 1 with a thickness of 0.5 μm in the examples 1 and 2, whereas the buffer layer was used in the example 6 as well. This is presumably because the p-type contact layer 6 made of GaSb is formed with a thickness of 1.0 μm.
The infrared sensor of Example 6 was obtained by performing the same process as Example 3 with respect to this compound semiconductor laminated body.

[Example 7]
As the active layer 4, a 2 μm thick non-doped InAs layer was formed. Further, as the n-type barrier layer 3, an Al _0.3 In _0.7 As layer doped with Si of 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.02 μm. Further, as the n-type contact layer 2, an InAs layer doped with Si of 7 × 10 ¹⁸ / cm ³ was formed to a thickness of 0.5 μm. Except this, a compound semiconductor stacked body having a PIN inverse structure was formed in the same manner as in Example 3.

With respect to the active layer 4 made of InAs of the obtained compound semiconductor stack, the half-value width (FWHM value) of the rocking curve of the X-ray diffraction peak was evaluated to be 265 arcsec. This value is small compared with the value of the compound semiconductor laminated body obtained in Examples 1 and 2. That is, the active layer 4 of the compound semiconductor stack obtained in Example 7 had better crystallinity than the active layer 4 of the compound semiconductor stack obtained in Examples 1 and 2.
The reason why this effect was obtained was that the buffer layer 7 made of AlGaSb was formed on the substrate 1 with a thickness of 0.5 μm in Examples 1 and 2, whereas the buffer layer was used in Example 7 as well. This is presumably because the p-type contact layer 6 made of GaSb is formed with a thickness of 1.0 μm.

The infrared sensor of Example 7 was obtained by performing the same process as Example 3 with respect to this compound semiconductor laminated body.
Table 1 shows the configuration of each layer other than the substrate of the infrared sensor of Examples 1 and 2 and the FWHM value of the obtained active layer, and the configuration of each layer other than the substrate of the infrared sensor of Examples 3 to 7 was obtained. Table 2 summarizes the FWHM values of the active layers.

1 Substrate 2 n-type contact layer 3 n-type barrier layer 4 active layer 5 p-type barrier layer 6 p-type contact layer 7 buffer layer 8 n-type electrode 9 p-type electrode 10 passivation film

Claims (10)

A substrate,
An n-type contact layer formed on the substrate;
An n-type barrier layer formed of a compound semiconductor layer containing AlInAsSb as a main component and formed on the n-type contact layer;
An active layer made of a compound semiconductor layer mainly composed of InAs _x Sb _(1-x) (0 ≦ x ≦ 1), and formed on the n-type barrier layer;
A p-type barrier layer formed of a compound semiconductor layer mainly composed of AlGaSb and formed on the active layer;
Infrared sensor comprising.   The infrared sensor according to claim 1, wherein the n-type dopant included in the n-type contact layer, the n-type dopant included in the n-type barrier layer, and the type dopant included in the p-type barrier layer are Si. The substrate is a GaAs substrate;
The infrared sensor according to claim 1, further comprising a buffer layer made of a compound semiconductor layer containing AlGaSb as a main component and formed between the substrate and the n-type contact layer.   The infrared sensor according to any one of claims 1 to 3, further comprising a p-type contact layer made of a compound semiconductor layer containing GaSb or GaInSb as a main component and formed on the p-type barrier layer.   The infrared sensor according to claim 4, wherein the p-type dopant included in the p-type contact layer is Si. A substrate,
A p-type contact layer formed on the substrate;
A p-type barrier layer formed of a compound semiconductor layer mainly composed of AlGaSb and formed on the p-type contact layer;
An active layer formed of a compound semiconductor layer mainly composed of InAs _x Sb _(1-x) (0 ≦ x ≦ 1), and formed on the p-type barrier layer;
An n-type barrier layer comprising a compound semiconductor layer mainly composed of AlInAsSb and formed on the active layer;
Infrared sensor comprising.   The infrared sensor according to claim 6, wherein the p-type dopant included in the p-type contact layer, the p-type dopant included in the p-type barrier layer, and the n-type dopant included in the n-type barrier layer are Si. The substrate is a GaAs substrate;
The infrared sensor according to claim 6, wherein the p-type contact layer is made of a compound semiconductor layer containing GaSb as a main component.   The infrared sensor according to any one of claims 6 to 8, further comprising an n-type contact layer made of a compound semiconductor layer containing InAsSb as a main component and formed on the n-type barrier layer.   The infrared sensor according to claim 9, wherein the n-type dopant included in the n-type contact layer is Si.

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