Infrared detection element

Abstract

To provide a quantum type infrared detection element with high S / N characteristic in a wavelength of 9.5 μm.SOLUTION: An infrared detection element (1) is an infrared detection element having sensibility in a wavelength of 9.5 μm, and comprises: a mesa type compound semiconductor lamination portion (20) in which at least a part of a first conductive semiconductor layer (21), a light reception layer (22), and a second conductive semiconductor layer (23) are laminated in this order; and a first protection film (31) arranged in direct contact with a side surface of the mesa type compound semiconductor lamination portion. The light reception layer is InAsxSb1-x(0.05≤x≤0.2), the first protection film is an oxide silicon, and a film thickness in a vertical direction to the side surface of the mesa type compound semiconductor lamination portion is 5 nm or more and 70 nm or less. The mesa type compound semiconductor lamination portion is arranged on one main surface of a substrate, and includes a concave portion in which a part of the substrate and a part of a region not included in the mesa type compound semiconductor lamination portion of the first conductive semiconductor layer form the side surface of the concave portion. The side surface and a bottom surface of the concave portion are coated with the first protection film.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a quantum infrared detection element having sensitivity at a wavelength of 9.5 μm.

Background Art

[0002] Generally, infrared rays in the long wavelength band with a wavelength of 2 μm or more are used in human sensors for detecting the human body, non-contact temperature sensors, gas sensors, etc. due to their thermal effects and the effect of infrared absorption by gases. For example, gas sensors can be used for monitoring and protecting the atmospheric environment, and further for early detection of fires, and have attracted attention in recent years. In particular, in the region from a wavelength of 2.5 μm to a wavelength of 10.0 μm, there are many absorption bands specific to various gases, which is a wavelength band suitable for use in gas sensors. For example, an absorption band of alcohol exists at a wavelength of 9.5 μm. An alcohol interlock device that links the alcohol concentration in exhaled breath measured by an alcohol detector with the engine of an automobile is expected to be widely used as a system that can prevent accidents caused by drunk driving.

[0003] The principle of a gas sensor using infrared rays is as follows. For example, when a gas is injected into the space between an infrared light source and an infrared detection element, since a specific gas absorbs infrared rays of a specific wavelength, the type and concentration of the gas can be measured by analyzing the wavelength spectra before and after the injection of the gas. Here, as the infrared detection element, there are, for example, thermal infrared detection elements such as pyroelectric sensors and thermopiles, and quantum infrared detection elements using semiconductor light receiving elements. Compared with thermal infrared detection elements, quantum infrared detection elements have the advantage of a fast response.

[0004] Here, according to Patent Document 1, when InAsSb is used as the material of the light absorption layer, the peak wavelength of infrared detection can be controlled from 7.3 μm to 10 μm by changing the mixed crystal composition. For example, a quantum infrared detection element having high sensitivity in the 9.5 μm band is expected as an alcohol sensor.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Here, for a quantum type infrared detection element having sensitivity at a wavelength of 9.5 μm using InAsSb as a material for the light absorption layer, further improvement in S / N characteristics is desired.

[0007] An object of the present disclosure made in view of the above is to provide a quantum type infrared detection element having high S / N characteristics at a wavelength of 9.5 μm.

Means for Solving the Problems

[0008] An infrared detection element according to an embodiment of the present disclosure is an infrared detection element having sensitivity at a wavelength of 9.5 μm, a mesa type compound semiconductor laminated portion in which at least a part of a first conductivity type semiconductor layer, a light receiving layer, and a second conductivity type semiconductor layer are laminated in this order, a first protective film provided so as to be in direct contact with a side surface of the mesa type compound semiconductor laminated portion, the light receiving layer is InAs x Sb 1-x (0.05 ≦ x ≦ 0.2), the first protective film is silicon oxide, and the film thickness in a direction perpendicular to the side surface of the mesa type compound semiconductor laminated portion is 5 nm or more and 70 nm or less, the mesa type compound semiconductor laminated portion is disposed on one main surface of a substrate, a part of the substrate and a part of a region not included in the mesa type compound semiconductor laminated portion of the first conductivity type semiconductor layer form a concave portion having a side surface, the side surface and the bottom surface of the concave portion are covered with the first protective film.

Advantages of the Invention

[0009] According to the present disclosure, a quantum infrared detection element with high S / N characteristics at a wavelength of 9.5 μm can be provided.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0011] [Infrared Detection Element] An infrared detection element according to an embodiment of the present disclosure is an infrared detection element having sensitivity at a wavelength of 9.5 μm, and includes a mesa-type compound semiconductor stacked portion in which at least a part of a first conductivity type semiconductor layer, a light receiving layer, and a second conductivity type semiconductor layer are stacked in this order, and a first protective film provided so as to be in direct contact with the side surface of the mesa-type compound semiconductor stacked portion. The first protective film is silicon oxide and satisfies a film thickness of 5 nm or more and 70 nm or less.

[0012] Here, the infrared detection element having sensitivity at a wavelength of 9.5 μm means a D * (specific detection sensitivity) of 5×10 6 [cm·√Hz / W] or more. D * indicates how much the AC S / N of the detection element is when there is a light input of 1 W, and is a parameter that can compare the characteristics of the material itself regardless of the detection element area. An infrared detection element with high S / N characteristics can be said to be an infrared detection element with high D * .

[0013] (Measurement method of D of infrared detection element) * The measurement of D of the infrared detection element * can be performed as follows, for example. In the measurement, a point light source blackbody furnace, a bandpass filter having a center transmission wavelength of 9.5 μm, and a calibrated thermopile with known light reception sensitivity are used. The bandpass filter and the thermopile are arranged so that the infrared rays emitted from the opening of the point light source blackbody furnace pass through the bandpass filter and enter the thermopile. The thermopile is arranged at a position 10 cm from the opening of the point light source blackbody furnace. From the output value of the thermopile at this time, the irradiance at a position 10 cm away from the opening of the point light source blackbody furnace is calculated. Next, the thermopile is replaced with the infrared detection element to be measured, and the output current value of the infrared detection element is measured. Also, the noise current and the detection element area of the infrared detection element are measured.

[0014] D *It is obtained from the following formula (1). S is the output current (signal) of the infrared detection element. N is the noise current. P is the incident energy [W / cm 2 . A is the detection element area [cm 2 . Also, Δf represents the noise bandwidth [Hz].

[0015] [Equation]

[0016] In this embodiment, the driving conditions of the point light source blackbody furnace are a temperature of 500 °C, a light chopping frequency of 10 Hz, an aperture of 22.2 mm, and D at room temperature with a noise bandwidth of 1 Hz * was measured.

[0017] [Compound semiconductor layer section] The compound semiconductor layer section in the infrared detection element of this embodiment has a mesa structure. The compound semiconductor layer section is not particularly limited as long as it includes a photodiode structure by a PN junction or a PIN junction. The first conductivity type semiconductor layer and the second conductivity type semiconductor layer have opposite conductivity types. For example, if the first conductivity type semiconductor layer is p-type, the second conductivity type semiconductor layer is n-type. For example, if the first conductivity type semiconductor layer is n-type, the second conductivity type semiconductor layer is p-type. As materials for the first conductivity type semiconductor layer and the second conductivity type semiconductor layer, there are InSb, InAsSb, AlInSb, etc., but it is not limited to these, and a laminated structure of a plurality of materials may be used.

[0018] The light receiving layer preferably uses InAs x Sb 1-x (0.05 ≦ x ≦ 0.2) having a bandgap capable of receiving infrared rays with a wavelength of 9.5 μm. More preferably, InAs x Sb 1-x (0.08 ≦ x ≦ 0.16) is used.

[0019] The compound semiconductor laminate may further include a first wide bandgap layer having a larger bandgap than the first conductivity type semiconductor layer between the first conductivity type semiconductor layer and the light receiving layer. Further, the compound semiconductor laminate may further include a second wide bandgap layer having a larger bandgap than the second conductivity type semiconductor layer between the second conductivity type semiconductor layer and the light receiving layer. The wide bandgap layer functions as a layer that prevents diffusion current from the light receiving layer. In this case, the wide bandgap layer only needs to have a sufficient band offset with respect to the light receiving layer, and it is preferable to select a material with a wide bandgap. The material of the wide bandgap layer is not particularly limited, and examples thereof include AlInAsSb and AlInSb.

[0020] (Method for Measuring As Composition of Light Receiving Layer) The As composition of the light receiving layer is determined by inverse photon space mapping by X-ray diffraction (XRD) using an X-ray diffractometer X´Pert MPD manufactured by Spectris Co., Ltd. to measure the lattice constant of the light receiving layer. Specifically, after fixing 2θ to a certain value and performing rocking curve measurement, 2θ is slightly changed and rocking curve measurement is performed again repeatedly. From the peak position of the light receiving layer in the obtained inverse lattice space mapping image, the lattice constant a in the in-plane direction of the substrate surface of the light receiving layer and the lattice constant c in the normal direction to the substrate surface are obtained. Using the Poisson's ratio ν of the crystal of the light receiving layer, the relationship between the lattice constant a0 when there is no strain, the measured lattice constants a and c, and Δa = a - a0 is expressed by the following formula (2).

[0021] [Number]

[0022] In the case of many semiconductor crystals, ν is close to 1 / 3, so approximately Δa = (c - a) / 2, and the lattice constant a0 of the light receiving layer when there is no strain is determined.

[0023] Then, the As composition x is determined from the obtained lattice constant a0 of the light receiving layer using Vegard's law. Specifically, Vegard's law is expressed by the following formula (3).

[0024]

Number

[0025] Here, a InAs is the lattice constant of InAs. a InSb is the lattice constant of InSb. a InAsSb is the lattice constant a0 of InAs x Sb 1-x obtained by the above X-ray diffraction. a InAs uses 6.058 Å. Also, a InSb uses 6.4794 Å.

[0026] [Protective film] The first protective film in the infrared detection element of the present embodiment is silicon oxide provided so as to be in direct contact with the side surface of the mesa-type compound semiconductor laminated portion, and the film thickness in the direction perpendicular to the side surface of the mesa-type compound semiconductor laminated portion is 5 nm or more and 70 nm or less. The film thickness is more preferably 5 nm or more and 50 nm or less. Even more preferably, it is 5 nm or more and 40 nm or less.

[0027] The upper surface of the first protective film may further be provided with a second protective film made of silicon nitride. Silicon nitride is known to be excellent in moisture resistance and is suitable for protecting the infrared detection element.

[0028] Dangling bonds are formed at the interface between the side surface of the mesa-type compound semiconductor laminated portion and the first protective film provided so as to be in direct contact with this side surface. The above interface becomes a current leakage path and is a factor that reduces the light reception sensitivity of the infrared detection element. Therefore, from the viewpoint of reducing the contact area between the side surface of the mesa-type compound semiconductor laminated portion and the first protective film, the mesa angle of the mesa-type compound semiconductor laminated portion is preferably 50 degrees or more.

[0029] Also, not only the light-receiving layer but also constituent materials other than the light-receiving layer such as the protective film absorb infrared rays and reduce the light reception sensitivity of the infrared detection element. InAs used as the light-receiving layer x Sb 1-xSince the refractive index at a wavelength of 9.5 μm in the range of (0.05 ≤ x ≤ 0.2) is approximately 4, and the refractive index of silicon oxide used as the first protective film at a wavelength of 9.5 μm is approximately 2.7, the total reflection angle of infrared light with a wavelength of 9.5 μm incident from the light-receiving layer to the first protective film is approximately 42 degrees. Therefore, from the perspective of avoiding infrared light incident from the light-receiving layer to the first protective film in contact with the side surface of the mesa-type compound semiconductor laminated portion and causing absorption loss, the mesa angle of the mesa-type compound semiconductor laminated portion is preferably 50 degrees or more.

[0030] Here, if the mesa angle is large, problems such as deterioration of the coverage of the first protective film may occur. Therefore, the mesa angle is preferably 80 degrees or less.

[0031] Here, the mesa angle refers to the angle formed by the side surface of the mesa-type compound semiconductor laminated portion and the lamination surface of the compound semiconductor. The side surface of the mesa-type compound semiconductor laminated portion may have an angle of two or more steps. When it has an angle of two or more steps, the angle formed by the lowermost first-step side surface and the lamination surface is the mesa angle.

[0032] Although details will be described later, since the sensitivity change of the infrared detection element at a wavelength of 9.5 μm with respect to the film thickness change of the first protective film is large, a uniform film thickness is desirable. To avoid peeling of the first protective film due to stress concentration, the film thickness t1 of the first protective film in the direction perpendicular to the side surface of the mesa-type compound semiconductor laminated portion and the film thickness t2 of the first protective film in the direction perpendicular to the uppermost surface are preferably as close as possible.

[0033] Specifically, it is preferable that the film thickness t1 and the film thickness t2 satisfy 0.75 < t1 / t2 ≤ 1. For example, after performing etching for electrically separating a plurality of infrared detection elements described later, by using PCVD or the like, the first protective film (silicon oxide) can be formed on the entire surface of the infrared detection element. At this time, generally, the film formed on the inclined surface is thinner than the film formed on the flat surface.

[0034] Conventionally, after forming a silicon oxide hard mask with a thickness of 200 to 500 nm, etching has been performed to electrically isolate a plurality of infrared detection elements. In this case, although the silicon oxide hard mask is also etched away, the remaining silicon oxide is used as the first protective film. Generally, since etching of the sloped portion proceeds faster than that of the flat portion, it has been difficult to maintain the film thickness uniformity of the side surface and the uppermost surface of the mesa-type compound semiconductor laminate of the silicon oxide remaining film. For example, in Comparative Example 2 described later fabricated by the conventional method, the film thickness t1 of silicon oxide was 197 nm and the film thickness t2 was 277 nm. In the infrared detection element according to the present embodiment, silicon oxide with a uniform film thickness is formed by the method described later.

[0035] (Method for measuring the film thickness of the protective film) The film thickness of the protective film can be measured by the cross-sectional TEM (TEM: Transmission Electron Spectroscopy) method. Specifically, a sample with a thickness of approximately 500 nm or less was prepared by the FIB method using a FIB apparatus (FB-2100) manufactured by Hitachi High-Technologies Corporation, and cross-sectional observation was performed in a transmission image at an acceleration voltage of 200 kV using a Hitachi STEM apparatus (HD-2300A) to measure the film thickness of the protective film.

[0036] [Substrate] In the infrared detection element of the present embodiment, it is preferable that the mesa-type compound semiconductor laminate is disposed on one main surface of the substrate, and the other main surface of the substrate is the light incident surface.

[0037] An electrode for extracting current to the outside is provided on the upper surface of the mesa-type compound semiconductor laminate. By using the other main surface without the electrode as the light incident surface, it becomes possible to efficiently irradiate infrared rays onto the mesa-type compound semiconductor laminate. At this time, since light is incident from the substrate side, it is necessary to use a material having a larger bandgap than the light receiving layer as the substrate. As an example, GaAs substrate, Si substrate, InP substrate, InSb substrate can be mentioned, but it is not limited to this. Since it has a larger bandgap than the light receiving layer and crystal growth of the compound semiconductor is easy, a GaAs substrate is preferable.

[0038] The substrate is not restricted by doping with donor impurities or acceptor impurities. However, from the viewpoint of enabling connection of a plurality of independent infrared detection elements formed on the substrate in series or in parallel, it is desirable that the substrate be semi-insulating or that it be insulation-separable from the compound semiconductor laminated portion.

[0039] In order to connect a plurality of infrared detection elements formed on the substrate in series or in parallel, it is necessary to electrically isolate each infrared detection element. To electrically isolate them, the first conductivity type semiconductor layer (especially the lowermost layer portion) of each infrared detection element may be removed by etching or the like so as not to be connected to other infrared detection elements. As a removal method, for example, a dry etching method may be used. At this time, a resist may be provided in a region of the first conductivity type semiconductor layer that is not desired to be etched and used as a mask, or silicon oxide or the like may be provided and used as a hard mask. When silicon oxide is used as a hard mask, it is conceivable to use the remaining silicon oxide after etching as the first protective film. However, considering in-plane variations in the process and apparatus fluctuations in production, it is difficult to control the remaining film of silicon oxide after etching to be 5 nm or more and 70 nm or less. Therefore, the substance used as a mask is removed after etching, and silicon oxide is uniformly formed over the entire surface using PCVD or the like to form the first protective film. Therefore, the infrared detection element of the present embodiment further includes a part of the substrate and a recess whose side surface is a part of a region not included in the mesa-type compound semiconductor laminated portion of the first conductivity type semiconductor layer, and the side surface and the bottom surface of the recess are covered with the first protective film. Here, the film thickness of the first protective film is thinner than the depth of the recess, and the first protective film is embedded in the recess.

[0040] [Band-pass filter] The infrared detection element of this embodiment may further include a band-pass filter that transmits at least 50% of light with a wavelength of 9.5 μm or more. By providing the band-pass filter, the sensitivity wavelength range of the infrared detection element can be restricted, and when used as an alcohol sensor, it is less likely to be affected by interfering gases having absorption bands in other wavelength ranges.

[0041] [Electrode portion] The infrared detection element of this embodiment further includes a first electrode electrically connected to the first conductive semiconductor layer of the mesa-type compound semiconductor laminate portion, and a second electrode electrically connected to the second conductive semiconductor layer of the mesa-type compound semiconductor laminate portion. As the constituent material of the electrode, it is preferable that the contact resistance with the compound semiconductor laminate portion is low and the electrical resistance is low. Specifically, Ti, Ni, Pt, Cr, Al, Cu, etc. can be mentioned. Also, the electrode may be composed of a laminate of a plurality of electrode materials.

[0042] Hereinafter, with reference to the drawings, a configuration example of the infrared detection element of this embodiment will be described.

[0043] FIG. 1 is a schematic cross-sectional view of an infrared detection element according to the first embodiment. The infrared detection element 1 includes a substrate 10, a first conductive semiconductor layer 21, a light-receiving layer 22, and a second conductive semiconductor layer 23. The upper part 21a of the first conductive semiconductor layer 21, the light-receiving layer 22, and the second conductive semiconductor layer 23 form a mesa-type compound semiconductor laminate portion 20. The mesa angle of the mesa-type compound semiconductor laminate portion 20 is θ. Further, the infrared detection element according to the first embodiment further includes a first protective film 31 that is in direct contact with the side surface of the mesa-type compound semiconductor laminate portion 20. The first protective film 31 is also in direct contact with the uppermost surface of the mesa-type compound semiconductor laminate portion 20 and the upper surface of the lower part 21b of the first conductive semiconductor layer 21. Also, it has a recess 40 surrounded by a part of the substrate 10 and the side surface of the lower part 21b of the first conductive semiconductor layer 21, and the first protective film 31 is also in direct contact with its surface. Furthermore, the infrared detection element 1 according to the first embodiment further includes a second protective film 32 on the upper surface of the first protective film 31. By covering the side surface and the bottom surface of the recess 40 with the first protective film 31 made of silicon oxide, the influence of leakage from the recess can be suppressed.

[0044] Also, the film thickness (t3 in FIG. 1) of the first protective film 31 is thinner than the depth (d in FIG. 1) of the concave portion 40. In the concave portion, the first protective film 31 is embedded in the concave portion 40, and the upper surface of the first protective film 31 is lower than the upper surface (upper end) of the concave portion 40. Thus, even in the first protective film 31 made of highly hygroscopic silicon oxide, when it absorbs moisture and expands, the space where the first protective film 31 is not provided in the concave portion 40 functions as a buffer region, preventing the film of the first protective film 31 from peeling off and maintaining a good insulating state.

[0045] Furthermore, the combined film thickness of the first protective film 31 and the second protective film 32 is thinner than the depth of the concave portion 40. In the concave portion, the second protective film 32 may also be embedded in the concave portion 40, and the upper surface of the second protective film 32 may be lower than the upper surface (upper end) of the concave portion 40.

[0046] FIG. 2 is a schematic cross-sectional view of an infrared detection element according to a second embodiment. Compared with the infrared detection element of FIG. 1, the side surface of the mesa-type compound semiconductor laminated portion 20 has side surfaces with different inclination angles. In this case, the angle θ formed by the lowermost first-stage side surface (the side surface of the upper portion 21a of the first compound semiconductor layer) and the laminated surface (the upper surface of the lower portion 21b of the first compound semiconductor layer) as described above is defined as the mesa angle.

[0047] FIG. 3 is a schematic cross-sectional view of an infrared detection element according to a third embodiment. Compared with the infrared detection element of FIG. 1, the mesa-type compound semiconductor laminated portion 20 further includes a first wide bandgap layer 24 and a second wide bandgap layer 25. Also, the first protective film 31 and the second protective film 32 are partially removed, and contact holes are formed in a part of the top of the mesa-type compound semiconductor laminated portion 20 and a part of the upper surface of the lower portion 21b of the first compound semiconductor layer, and an electrode portion 50 is provided in contact therewith.

Example

[0048] [Example 1] On a semi-insulating GaAs substrate as the substrate 10, using an MBE apparatus, a first conductivity type semiconductor layer 21, a first wide bandgap layer 24, a light receiving layer 22, a second wide bandgap layer 25, and a second conductivity type semiconductor layer 23 were sequentially laminated. In this lamination process, As the first conductivity type semiconductor layer 21, an n-type InSb layer doped with 7×10 18 [cm -3 of Sn with a thickness of 1 μm, and As the first wide bandgap layer 24, an n-type Al 18 [cm -3 of Sn doped In 0.18 Sb layer with a thickness of 0.02 μm, and 0.82 As the light receiving layer 22, an InAs 17 [cm -3 of Zn doped Sb 0.14 0.86 layer with a thickness of 2.4 μm, and As the second wide bandgap layer 25, a p-type Al 18 [cm -3 of Zn doped In 0.18 Sb layer with a thickness of 0.02 μm, and As the second conductivity type semiconductor layer 23, a p-type InSb layer doped with 3×10 0.82 [cm 18 of Zn with a thickness of 0.5 μm were formed. -3

[0049]

[0049] Next, a resist pattern was formed on the compound semiconductor laminate, and by performing etching, a mesa-type compound semiconductor laminate was fabricated. Further, in order for each infrared detection element to be electrically independent, a resist pattern was formed again, and by performing etching for element isolation, a recess 40 was formed. After removing the resist pattern, a 5-nm silicon oxide layer was formed as a first protective film on the entire surface (the GaAs substrate and the mesa-type compound semiconductor laminate formed on the GaAs substrate) using PCVD. Next, a 200-nm silicon nitride layer was formed as a second protective film on this silicon oxide layer using PCVD. A contact hole was formed in a part of these two protective films, and titanium (Ti), platinum (Pt), and gold (Au) were deposited in this order so as to cover the contact hole to form an electrode portion, and 643 serially connected infrared detection elements were obtained. The obtained infrared detection element has a structure as shown in the cross-sectional schematic diagram of FIG. 3. The film thickness t1 of the first protective film in the direction perpendicular to the side surface of the silicon oxide layer of the first protective film was 4 nm. Also, the film thickness t2 of the first protective film in the direction perpendicular to the uppermost surface of the silicon oxide layer of the first protective film was 5 nm.

[0050] [Example 2] An infrared detection element was obtained in the same manner as in Example 1, except that the film thickness t1 of the silicon oxide layer as the first protective film was 14 nm and the film thickness t2 was 17 nm.

[0051] [Example 3] An infrared detection element was obtained in the same manner as in Example 1, except that the film thickness t1 of the silicon oxide layer as the first protective film was 21 nm and the film thickness t2 was 24 nm.

[0052] [Example 4] An infrared detection element was obtained in the same manner as in Example 1, except that the film thickness t1 of the silicon oxide layer as the first protective film was 40 nm and the film thickness t2 was 47 nm.

[0053] [Example 5] An infrared detection element was obtained in the same manner as in Example 1, except that the film thickness t1 of the silicon oxide layer as the first protective film was 51 nm and the film thickness t2 was 60 nm.

[0054] [Example 6] An infrared detection element was obtained in the same manner as in Example 1, except that the film thickness t1 of the silicon oxide layer, which is the first protective film, was 68 nm and the film thickness t2 was 80 nm.

[0055] [Comparative Example 1] On a semi-insulating GaAs substrate, using an MBE apparatus, a first conductivity type semiconductor layer, a first wide bandgap layer, a light receiving layer, a second wide bandgap layer, and a second conductivity type semiconductor layer were sequentially laminated. In this lamination process, an n-type InSb layer doped with Sn at 7×10 18 [cm -3 was 1 μm, and an n-type Al 18 [cm -3 doped with Sn at 7×10 0.18 In 0.82 Sb layer was 0.02 μm, and an InAs 17 [cm -3 doped with Zn at 3×10 0.14 Sb 0.86 layer (light receiving layer) was 2.4 μm, and a p-type Al 18 [cm -3 doped with Zn at 3×10 0.18 In 0.82 Sb layer was 0.02 μm, and a p-type InSb layer doped with Zn at 3×10 18 [cm -3 was 0.5 μm, and were formed.

[0056] Next, a resist pattern was formed on the compound semiconductor layer, and mesa-type compound semiconductor layers were fabricated by etching. Again, a resist pattern was formed so that each infrared detection element would be electrically independent, and etching for element isolation was performed. After removing the resist pattern, a silicon nitride layer was formed as a protective film with a thickness of 200 nm on the entire surface (GaAs substrate and mesa-type compound semiconductor layers formed on the GaAs substrate) using PCVD. Contact holes were formed in a part of this silicon nitride layer, and titanium (Ti), platinum (Pt), and gold (Au) were deposited in this order to cover the contact holes, forming electrode portions, and 643 serially connected infrared detection elements were obtained. The obtained infrared detection elements had a structure as shown in the cross-sectional schematic diagram of FIG. 4.

[0057] [Comparative Example 2] On a semi-insulating GaAs substrate, using an MBE apparatus, a first conductivity type semiconductor layer, a first wide bandgap layer, a light-receiving layer, a second wide bandgap layer, and a second conductivity type semiconductor layer were sequentially laminated. In this lamination process, Sn was doped at 7×10 18 [cm -3 to form an n-type InSb layer with a thickness of 1 μm, and Sn was doped at 7×10 18 [cm -3 to form an n-type Al 0.18 In 0.82 Sb layer with a thickness of 0.02 μm, and Zn was doped at 3×10 17 [cm -3 to form an InAs 0.14 Sb 0.86 layer (light-receiving layer) with a thickness of 2.4 μm, and Zn was doped at 3×10 18 [cm -3 to form a p-type Al 0.18 In 0.82 Sb layer with a thickness of 0.02 μm, and Zn was doped at 3×10 18 [cm -3 to form a p-type InSb layer with a thickness of 0.5 μm.

[0058] Next, a resist pattern was formed on the compound semiconductor laminate, and mesa-type compound semiconductor laminates were fabricated by etching. Further, a hard mask of silicon oxide was formed to a thickness of 350 nm so that each infrared detection element became electrically independent, and etching for element isolation was performed. Thereafter, a silicon nitride layer was formed to a thickness of 200 nm on the entire surface (the GaAs substrate and the silicon oxide layer formed on the mesa-type compound semiconductor laminate) by using PCVD. Contact holes were formed in a part of these two protective films, and titanium (Ti), platinum (Pt), and gold (Au) were deposited in this order so as to cover the contact holes to form electrode portions, and 643 serially connected infrared detection elements were obtained. The obtained infrared detection elements had a structure as shown in the cross-sectional schematic diagram of FIG. 5. The film thickness t1 of the silicon oxide layer after fabricating the infrared detection elements was 197 nm. Also, the film thickness t2 was 277 nm.

[0059] <Evaluation (1)> The sensitivity and D at a wavelength of 9.5 μm of the infrared detection elements obtained in Examples 1 to 6 and Comparative Examples 1 and 2 * were measured. The sensitivity was measured with an FT-IR apparatus. Specifically, an IR light source was used as the light source, and signal amplification and noise removal were performed using an IV conversion amplifier and a lock-in amplifier, and then the output from the infrared detection element was measured. D * was measured by the above measurement method.

[0060] Based on the measurement results of Examples 1 to 6 and Comparative Examples 1 and 2, the relationships shown in FIGS. 6 and 7 were obtained. FIG. 6 shows the relationship between the film thickness t1 of the first protective film and the sensitivity at a wavelength of 9.5 μm. FIG. 7 shows the relationship between the film thickness t1 of the first protective film and D * at a wavelength of 9.5 μm.

[0061] As shown in FIG. 7, when the film thickness t1 of the first protective film (silicon oxide layer) is 5 nm or more and 70 nm or less, D at a wavelength of 9.5 μm *A high infrared detection element, i.e., an element with high S / N characteristics, can be realized. The film thickness t1 is more preferably 5 nm or more and 50 nm or less. The film thickness t1 is even more preferably 5 nm or more and 40 nm or less.

[0062] [Example 7] On a semi-insulating GaAs substrate as the substrate 10, using an MBE apparatus, a first conductivity type semiconductor layer 21, a first wide bandgap layer 24, a light receiving layer 22, a second wide bandgap layer 25, and a second conductivity type semiconductor layer 23 were sequentially laminated. In this lamination process, As the first conductivity type semiconductor layer 21, an n-type InSb layer doped with 7×10 18 [cm -3 was 1 μm, and As the first wide bandgap layer 24, an n-type Al 18 [cm -3 doped In 0.18 Sb layer was 0.02 μm, and 0.82 As the light receiving layer 22, an InAs Sb layer doped with 3×10 17 [cm -3 was 2 μm, and 0.06 As the second wide bandgap layer 25, a p-type Al 0.94 Sb layer doped with 3×10 18 [cm -3 was 0.02 μm, and As the second conductivity type semiconductor layer 23, a p-type InSb layer doped with 3×10 0.18 0.82 18 -3 18 -3 [cm -3 was 0.5 μm, and were formed.

[0063] Next, a resist pattern was formed on the compound semiconductor layer, and mesa-type compound semiconductor layers were fabricated by etching. Further, in order for each infrared detection element to be electrically independent, a resist pattern was formed again, and etching for element isolation was performed. After removing the resist pattern, a 17-nm silicon oxide layer was formed on the entire surface (the GaAs substrate and the mesa-type compound semiconductor layer formed on the GaAs substrate) using PCVD. Next, a 200-nm silicon nitride layer was formed on this silicon oxide layer using PCVD. Contact holes were formed in a part of these two protective films, and titanium (Ti), platinum (Pt), and gold (Au) were deposited in this order so as to cover the contact holes, and electrode portions were formed, and 486 serially connected infrared detection elements were obtained.

[0064] [Example 8] An infrared detection element was obtained in the same manner as in Example 7, except that the light-receiving layer was InAs 0.094 Sb 0.906

[0065] [Example 9] An infrared detection element was obtained in the same manner as in Example 7, except that the light-receiving layer was InAs 0.133 Sb 0.867

[0066] [Example 10] An infrared detection element was obtained in the same manner as in Example 7, except that the light-receiving layer was InAs 0.188 Sb 0.812

[0067] [Reference Example 1] An infrared detection element was obtained in the same manner as in Example 7, except that the light-receiving layer was InSb.

[0068] <Evaluation (2)> Regarding the infrared detection elements of Examples 7 to 10 and Reference Example 1, in the same manner as in Evaluation (1), the sensitivity and D at a wavelength of 9.5 μm * ​​​was measured. Based on the measurement results of Examples 7 to 10 and Comparative Example 1, the relationships shown in FIGS. 8 and 9 were obtained. FIG. 8 shows the relationship between the As composition x of the light-receiving layer and the sensitivity at a wavelength of 9.5 μm. FIG. 9 shows the relationship between the As composition x of the light-receiving layer and D * at a wavelength of 9.5 μm.

[0069] As shown in FIG. 9, when the light-receiving layer is InAs x Sb 1-x (0.05 ≦ x ≦ 0.2), compared with an infrared detection element using a light-receiving layer with different As compositions, an infrared detection element with a high D * at a wavelength of 9.5 μm, that is, a high S / N characteristic, can be realized. The light-receiving layer is preferably InAs x Sb 1-x (0.08 ≦ x ≦ 0.16).

Description of Reference Numerals

[0070] 1 Infrared detection element 10 Substrate 20 Mesa-type compound semiconductor laminated portion 21 First conductivity type semiconductor layer 22 Light-receiving layer 23 Second conductivity type semiconductor layer 24 First wide bandgap layer 25 Second wide bandgap layer 31 First protective film 32 Second protective film 40 Concave portion 50 Electrode portion

Claims

1. An infrared detection element having sensitivity to a wavelength of 9.5 μm, comprising: a mesa-type compound semiconductor stacked portion in which at least a part of a first conductivity type semiconductor layer, a light receiving layer, and a second conductivity type semiconductor layer are stacked in this order; a first protective film provided so as to be in direct contact with a side surface of the mesa-type compound semiconductor stacked portion; The light-receiving layer is InAs ｘ Sb １－ｘ (0.05 ≦ x ≦ 0.2), and the first protective film is silicon oxide, and the film thickness in the direction perpendicular to the side surface of the mesa-type compound semiconductor stacked portion is 5 nm or more and 70 nm or less; the mesa-type compound semiconductor stacked portion is disposed on one main surface of a substrate; a part of the substrate and a part of a region not included in the mesa-type compound semiconductor stacked portion of the first conductivity type semiconductor layer have a concave portion whose side surface serves as a side surface; the side surface and the bottom surface of the concave portion are covered with the first protective film; the film thickness of the first protective film is thinner than the depth of the concave portion; an infrared detection element.

2. The film thickness of the first protective film is 5 nm or more and 50 nm or less. The infrared detection element according to Claim 1.

3. The film thickness of the first protective film is 5 nm or more and 40 nm or less. The infrared detection element according to Claim 1 or 2.

4. The light-receiving layer is InAs ｘ Sb １－ｘ where (0.08 ≤ x ≤ 0.16), The infrared detection element according to any one of Claims 1 to 3.

5. The first protective film further includes a second protective film made of silicon nitride on its upper surface. The infrared detection element according to any one of Claims 1 to 4.

6. The mesa angle of the mesa-type compound semiconductor stacked portion is 50 degrees or more and 80 degrees or less. The infrared detection element according to any one of Claims 1 to 5.

7. The film thickness t of the first protective film in the direction perpendicular to the side surface of the mesa-type compound semiconductor laminated portion １ and the film thickness t of the first protective film in the direction perpendicular to the uppermost surface of the mesa-type compound semiconductor laminated portion ２ satisfy 0.75 < t １ / t ２ ≦ 1 The infrared detection element according to any one of Claims 1 to 6.

8. The other main surface of the substrate is a light incident surface. The infrared detection element according to any one of Claims 1 to 7.

9. Further comprising a band-pass filter that transmits at least light having a wavelength of 9.5 μm. The infrared detection element according to any one of Claims 1 to 8.

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