Superlattice infrared detector and preparation method thereof

Abstract

The invention relates to the technical field of semiconductor materials and devices, and provides a superlattice infrared detector which comprises a substrate and an epitaxial structure growing on the substrate, the epitaxial structure comprises a superlattice absorption layer, the superlattice absorption layer is provided with multiple stages of A / B superlattice material layers which are sequentially grown in a laminated mode, and the A / B superlattice material layers are arranged on the substrate. Each stage of A / B superlattice material layer is provided with a plurality of layers of A materials and a plurality of layers of B materials which are periodically and alternately grown in a laminated mode, and in the multiple stages of A / B superlattice material layers, the number of atomic layers of the single layer of A material in each stage of A / B superlattice material layer is increased in a stepped mode compared with the number of atomic layers of the single layer of A material in the previous stage of A / B superlattice material layer. The conduction band of each stage of A / B superlattice material layer descends in a stepped manner, and the valence band of each stage of A / B superlattice material layer is kept unchanged. The limitation of short diffusion length can be reduced, the thickness of the absorption region can be effectively increased, the quantum efficiency of the device is improved, and the detection performance of the device is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor materials and devices, and in particular to a superlattice infrared detector and a preparation method thereof. Background Art

[0002] Infrared detectors have important applications in military fields such as satellite reconnaissance, guidance, and night vision, as well as in civilian fields such as industrial detection, remote sensing, and medical detection. InAs / GaSb type II superlattice has the advantages of flexible band regulation, good uniformity over a large area, and low preparation cost. It has great development potential and application prospects in infrared detection and is a rapidly developing III-V infrared detection technology in recent years.

[0003] The structure of superlattice long-wave infrared detection materials generally includes a buffer layer, a barrier layer, an absorption layer and an ohmic contact layer, among which the thickness, composition, ratio, doping concentration and distribution of the absorption layer have an important influence on the optoelectronic performance of the detector. In recent years, although the performance of long-wave superlattice materials prepared by InAs / GaSb type II superlattice materials epitaxially grown on GaSb substrates has been comparable to that of mercury cadmium telluride, it is limited by technical difficulties such as short minority carrier lifetime, high defect density, low mobility, and difficulty in growing thick absorption regions, so that the optoelectronic performance of its devices, especially the quantum efficiency in the long-wave band, has not yet reached its theoretical expectations.

[0004] Quantum efficiency is a key indicator that determines whether a photodetector can image with high quality, and it can reflect the photoelectric conversion efficiency of the detector. At present, the quantum efficiency of superlattice infrared detectors is mainly improved by combining the following four aspects: First, the absorption coefficient is increased by designing the band structure of the absorption layer material to increase light absorption, but the design and epitaxy are both difficult; second, a thicker absorption layer is used to increase light absorption, but the crystal quality will deteriorate with the increase of epitaxial thickness, and currently, due to the short carrier diffusion length of InAs / GaSb type II superlattice materials, the photogenerated carriers have been recombined and annihilated before reaching the depletion region, so that after the absorption region thickness increases to a critical value, the photogenerated carriers far away from the depletion region cannot be effectively transported and extracted. Therefore, after the absorption region thickness increases to a critical value, the effect of continuing to increase the absorption layer thickness on improving quantum efficiency is no longer obvious; third, a P-type doped absorption layer is used to increase the minority carrier diffusion length, but it is still not enough to obtain a higher quantum efficiency; fourth, the spatial distribution of the incident light is controlled by using the micro-nano structure processing on the device surface to increase light absorption, but its process is relatively complex. Summary of the invention

[0005] The object of the present invention is to provide a superlattice infrared detector and a method for preparing the same, which can at least solve some of the defects in the prior art.

[0006] To achieve the above-mentioned purpose, an embodiment of the present invention provides the following technical solution: a superlattice infrared detector, comprising a substrate and an epitaxial structure grown on the substrate, the epitaxial structure comprising a superlattice absorption layer, the superlattice absorption layer having a plurality of A / B superlattice material layers grown in sequence, each of the A / B superlattice material layers comprising a plurality of layers of A material and a plurality of layers of B material grown in a periodic alternating manner, and in the plurality of the A / B superlattice material layers, the number of atomic layers of a single layer of the A material in each of the A / B superlattice material layers increases in a step-by-step manner compared with the number of atomic layers of a single layer of the A material in the A / B superlattice material layer of the previous level, so that the conduction band of each level of the A / B superlattice material layer decreases in a step-by-step manner, and the valence band of each level of the A / B superlattice material layer remains unchanged.

[0007] Furthermore, in each level of the A / B superlattice material layer, the number of atomic layers of the single layer of the A material and the number of atomic layers of the single layer of the B material remain unchanged.

[0008] Furthermore, in each level of the A / B superlattice material layer, the number of atomic layers of the single layer of the A material gradually increases, and the number of atomic layers of the single layer of the B material remains unchanged.

[0009] Furthermore, the superlattice absorption layer is an InAs / GaSb superlattice absorption layer, the A material is InAs, and the B material is GaSb.

[0010] Furthermore, the epitaxial structure also includes a buffer layer, a lower contact layer, an electron barrier layer, a hole barrier layer, an upper contact layer and a cap layer, and the buffer layer, the lower contact layer, the electron barrier layer, the superlattice absorption layer, the hole barrier layer, the upper contact layer and the cap layer are grown on the substrate in sequence.

[0011] Furthermore, the buffer layer is a GaSb buffer layer, the lower contact layer is a P-type heavily doped GaSb lower contact layer, the superlattice absorption layer is a P-type weakly doped InAs / GaSb superlattice absorption layer, the upper contact layer is an N-type heavily doped InAs / AlSb upper contact layer, and the cap layer is an N-type heavily doped InAs cap layer.

[0012] Furthermore, the electron barrier layer is an InAs / GaSb superlattice electron barrier layer, and the hole barrier layer is an InAs / AlSb superlattice hole barrier layer.

[0013] The embodiment of the present invention provides another technical solution: a method for preparing a superlattice infrared detector, comprising the following steps:

[0014] growing an epitaxial structure on a substrate, the epitaxial structure comprising a superlattice absorption layer;

[0015] When the superlattice absorption layer is grown, multiple levels of A / B superlattice material layers are grown, and the A material and the B material in each level of the A / B superlattice material layer are grown in a periodic alternating stacking manner;

[0016] During the growth process, the number of atomic layers of the single layer of the A material in each level of the A / B superlattice material layer increases in a step-by-step manner compared to the number of atomic layers of the single layer of the A material in the previous level of the A / B superlattice material layer, so that the conduction band of each level of the A / B superlattice material layer decreases in a step-by-step manner, and the valence band of each level of the A / B superlattice material layer remains unchanged.

[0017] Furthermore, the superlattice absorption layer adopts an InAs / GaSb superlattice absorption layer. When growing each level of the InAs / GaSb superlattice absorption layer, the InAs material and the GaSb material are grown in a periodic alternating stacking manner; the number of atomic layers of a single layer of the InAs material and the number of atomic layers of a single layer of the GaSb material remain unchanged; or the number of atomic layers of a single layer of the InAs material gradually increases, and the number of atomic layers of a single layer of the GaSb material remains unchanged.

[0018] Furthermore, the thickness of the InSb atomic layer of the superlattice absorption layer is adjusted to achieve zero mismatch between the superlattice absorption layer and the substrate.

[0019] Compared with the prior art, the beneficial effects of the present invention are: the conduction band of the A / B superlattice material layer at each level decreases in a step-like manner, and the valence band of the A / B superlattice material layer at each level remains unchanged, thereby forming a graded bandgap width, and generating a built-in quasi-electric field in the absorption layer, which is beneficial to the transport of carriers through drift, strengthens the directional transport of photogenerated carriers in the absorption layer, alleviates the limitation of the short diffusion length, can effectively increase the thickness of the absorption region, improve the quantum efficiency of the device, and improve the detection performance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of a superlattice infrared detector provided by an embodiment of the present invention;

[0021] Figure 2 A diagram showing the relationship between energy and position of each layer in the structure of a superlattice infrared detector provided by an embodiment of the present invention;

[0022] Figure 3 This is a diagram showing the relationship between the energy and position of each layer in the structure of a traditional superlattice infrared detector. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] See also Figure 1 and Figure 2 An embodiment of the present invention provides a superlattice infrared detector, comprising a substrate and an epitaxial structure grown on the substrate, characterized in that: the epitaxial structure comprises a superlattice absorption layer, the superlattice absorption layer has a plurality of A / B superlattice material layers grown in sequence, each of the A / B superlattice material layers has a plurality of layers of A material and a plurality of layers of B material grown in a periodic alternating manner, and in the plurality of A / B superlattice material layers, the number of atomic layers of a single layer of the A material in each of the A / B superlattice material layers increases in a step-by-step manner compared with the number of atomic layers of a single layer of the A material in the A / B superlattice material layer of the previous level, so that the conduction band of each level of the A / B superlattice material layer decreases in a step-by-step manner, and the valence band of each level of the A / B superlattice material layer remains unchanged. In this embodiment, the conduction band of each level of the A / B superlattice material layer decreases in a step-like manner, and the valence band of each level of the A / B superlattice material layer remains unchanged, which can form a graded bandgap width, and can generate a built-in quasi-electric field in the absorption layer, which is conducive to the transport of carriers through drift, strengthens the directional transport of photogenerated carriers in the absorption layer, and alleviates the limitation of the short diffusion length, which can effectively increase the thickness of the absorption region, improve the quantum efficiency of the device, and improve the detection performance of the device. Specifically, the bandgap width is the energy difference between the lowest point of the conduction band and the highest point of the valence band, such as Figure 2 As shown in FIG. 1 , Eg(n), Eg(2), and Eg(1), where Eg is the bandgap width. By increasing the number of atomic layers of the A material in each A / B superlattice material layer in a stepwise manner compared to the number of atomic layers of the A material in the previous A / B superlattice material layer, a built-in quasi-electric field can be generated in the absorption layer, thereby improving the quantum efficiency of the device. Figure 3 The absorption layer shown in FIG. 1 does not have a graded bandgap width. After experiments, the present application is compared with Figure 3 Compared with the traditional form, the quantum efficiency can be significantly improved. Preferably, in each level of the A / B superlattice material layer, the number of atomic layers of the single layer of the A material and the number of atomic layers of the single layer of the B material remain unchanged. In another embodiment, in each level of the A / B superlattice material layer, the number of atomic layers of the single layer of the A material gradually increases, and the number of atomic layers of the single layer of the B material remains unchanged, which is more conducive to the formation of the quasi-electric field, further increases the thickness of the absorption zone, improves the quantum efficiency of the device, and improves the detection performance of the device.

[0025] See also Figure 1 and Figure 2 , the superlattice absorption layer is an InAs / GaSb superlattice absorption layer, the A material is InAs, and the B material is GaSb. Of course, in addition to these two materials, other existing materials are also acceptable, and this embodiment does not limit this. Specifically, the absorption layer can adopt a P-type weakly doped 14InAs / 7GaSb superlattice absorption layer, such as Figure 2 As shown, due to the spatial separation of electron and hole microbands in the InAs / GaSb type II superlattice, the transport of electrons and holes can be regulated separately; and the change in the number of InAs atomic layers in a single period of the absorption region mainly causes the movement of the electron microband (conduction band), but has no effect on the movement of the hole microband (valence band), so that the bandgap width is gradually reduced from Eg(n) near the electron barrier layer to Eg(1) near the hole barrier layer, where n is the number of levels of graded changes, which can be designed to be more than 2 levels as needed. Preferably, the thickness of the InSb atomic layer of the absorption layer is adjusted to make the absorption layer zero mismatch with the substrate, that is, while regulating the valence band and conduction band, the thickness of InSb in each level of the absorption region can be regulated to achieve zero mismatch between the overall absorption layer and the GaSb substrate, and it is easy to grow an epitaxial layer with strain balance. The absorption layer has a gradient absorption region, the upper contact layer has an upper contact region, and the lower contact layer has a lower contact region.

[0026] See also Figure 1 and Figure 2 , the epitaxial structure further includes a buffer layer, a lower contact layer, an upper contact layer and a cap layer, and the buffer layer, the lower contact layer, the electron barrier layer, the superlattice absorption layer, the hole barrier layer, the upper contact layer and the cap layer are sequentially grown on the substrate. In this embodiment, the above-mentioned epitaxial structure includes the buffer layer, the lower contact layer, the electron barrier layer, the superlattice absorption layer, the hole barrier layer, the upper contact layer and the cap layer, which are sequentially grown on the substrate. Among them, the superlattice absorption layer is a P-type weakly doped InAs / GaSb superlattice absorption layer, the buffer layer is a GaSb buffer layer, the lower contact layer is a P-type heavily doped GaSb lower contact layer, the upper contact layer is an N-type heavily doped 15InAs / 4AlSb upper contact layer, the cap layer is an N-type heavily doped InAs cap layer, the electron barrier layer is a 7InAs / 7GaSb superlattice electron barrier layer, and the hole barrier layer is a 15InAs / 4AlSb hole barrier layer.

[0027] An embodiment of the present invention provides a method for preparing a superlattice infrared detector, comprising the following steps: growing an epitaxial structure on a substrate, the epitaxial structure comprising a superlattice absorption layer; when the superlattice absorption layer is grown, growing multiple levels of A / B superlattice material layers, and making the A material and the B material in each level of the A / B superlattice material layer grow in a periodic alternating stacking manner; during the growth process, the number of atomic layers of the single layer of the A material in each level of the A / B superlattice material layer increases in a step-by-step manner compared to the number of atomic layers of the single layer of the A material in the previous level of the A / B superlattice material layer, so that the conduction band of each level of the A / B superlattice material layer decreases in a step-by-step manner, and the valence band of each level of the A / B superlattice material layer remains unchanged. In this embodiment, the focus of this method is to control the bandgap width. By forming a graded bandgap width, a built-in quasi-electric field can be generated in the absorption layer, which is conducive to the transport of carriers through drift, strengthens the directional transport of photogenerated carriers in the absorption layer, and alleviates the limitation of short diffusion length. It can effectively increase the thickness of the absorption region, improve the quantum efficiency of the device, and improve the detection performance of the device. Specifically, at the atomic level, by increasing the number of atomic layers of the single layer of the A material in each level of the A / B superlattice material layer in a step-by-step manner compared to the number of atomic layers of the single layer of the A material in the previous level of the A / B superlattice material layer, a built-in quasi-electric field can be generated in the absorption layer. In addition, the thickness of InSb is adjusted to make the absorption layer zero mismatch with the substrate, so that it is easy to grow an epitaxial layer with strain balance. While keeping the number of GaSb atomic layers the same, only the number of single-period InAs atomic layers in the InAs / GaSb type II superlattice absorption layer is adjusted (i.e., only the InAs thickness is adjusted), which changes the position of the electron microband in the absorption layer but has no effect on the position of the hole microband. This eliminates the need for complex band structure design and makes it easy to control growth process parameters and prepare thin films epitaxially.

[0028] The following is a specific implementation method:

[0029] Two rounds of continuously grown InAs / GaSb type II superlattice long-wavelength superlattice materials, where the structure of material 1 is as follows Figure 2 As shown, the absorption layer adopts a graded gradient bandgap width, which consists of 3 levels in total. The number of InAs atomic layers in a single period increases successively, namely 12.5ML, 12.75ML, and 13ML, respectively. At the same time, the number of GaSb atomic layers in a single period is guaranteed to be 7ML. The InSb layer is adjusted to make it close to zero mismatch with the GaSb substrate, resulting in the corresponding bandgap width decreasing successively, namely Eg(3)=135meV, Eg(2)=130meV, and Eg(1)=125meV; the structure of material 2 is as shown in Figure 3As shown, the number of InAs atomic layers in a single period of the absorption region is 13ML, and that of GaSb is 7ML. The electron microband and the hole microband are located at the same position, ensuring the same bandgap width of the entire absorption layer, and its Eg = Eg(1) = 125meV, and the rest of the structure is the same as that of material 1. The two samples were prepared using the same device processing technology for unit device preparation, and then the same test method was used for photocurrent testing. Under the same pixel size, the photocurrent of material 1 was measured to be 310nA, and the photocurrent of material 2 was 280nA. Compared with material 2, the photoresponse of material 1 was improved by 10.7%, which improved the quantum efficiency of the device.

[0030] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A superlattice infrared detector, comprising a substrate and an epitaxial structure grown on the substrate, characterized in that: The epitaxial structure includes a superlattice absorption layer, which has multiple levels of A / B superlattice material layers that are grown in sequence, each level of the A / B superlattice material layer has several layers of A material and several layers of B material that are grown in a periodic and alternating manner. In the multiple levels of the A / B superlattice material layers, the number of atomic layers of a single layer of the A material in each level of the A / B superlattice material layer increases in a step-by-step manner compared to the number of atomic layers of a single layer of the A material in the previous level of the A / B superlattice material layer, so that the conduction band of each level of the A / B superlattice material layer decreases in a step-by-step manner, and the valence band of each level of the A / B superlattice material layer remains unchanged.

2. The superlattice infrared detector according to claim 1, characterized in that: In each level of the A / B superlattice material layer, the number of atomic layers of the single layer of the A material and the number of atomic layers of the single layer of the B material remain unchanged.

3. The superlattice infrared detector according to claim 1, characterized in that: In each level of the A / B superlattice material layer, the number of atomic layers of the single layer of the A material gradually increases, and the number of atomic layers of the single layer of the B material remains unchanged.

4. The superlattice infrared detector according to claim 1, characterized in that: The superlattice absorption layer is an InAs / GaSb superlattice absorption layer, the A material is InAs, and the B material is GaSb.

5. The superlattice infrared detector according to claim 1 or 4, characterized in that: The epitaxial structure also includes a buffer layer, a lower contact layer, an electron barrier layer, a hole barrier layer, an upper contact layer and a cap layer. The buffer layer, the lower contact layer, the electron barrier layer, the superlattice absorption layer, the hole barrier layer, the upper contact layer and the cap layer are grown on the substrate in sequence.

6. The superlattice infrared detector according to claim 5, characterized in that: The buffer layer is a GaSb buffer layer, the lower contact layer is a P-type heavily doped GaSb lower contact layer, the superlattice absorption layer is a P-type weakly doped InAs / GaSb superlattice absorption layer, the upper contact layer is an N-type heavily doped InAs / AlSb upper contact layer, and the cap layer is an N-type heavily doped InAs cap layer.

7. The superlattice infrared detector according to claim 5, characterized in that: The electron barrier layer is an InAs / GaSb superlattice electron barrier layer, and the hole barrier layer is an InAs / AlSb superlattice hole barrier layer.

8. A method for preparing a superlattice infrared detector, characterized in that: The steps include: growing an epitaxial structure on a substrate, the epitaxial structure comprising a superlattice absorption layer; When the superlattice absorption layer is grown, multiple levels of A / B superlattice material layers are grown, and the A material and the B material in each level of the A / B superlattice material layer are grown in a periodic alternating stacking manner; During the growth process, the number of atomic layers of the single layer of the A material in each level of the A / B superlattice material layer increases in a step-by-step manner compared to the number of atomic layers of the single layer of the A material in the previous level of the A / B superlattice material layer, so that the conduction band of each level of the A / B superlattice material layer decreases in a step-by-step manner, and the valence band of each level of the A / B superlattice material layer remains unchanged.

9. The method for preparing a superlattice infrared detector according to claim 8, characterized in that: The superlattice absorption layer adopts an InAs / GaSb superlattice absorption layer. When growing each level of the InAs / GaSb superlattice absorption layer, the InAs material and the GaSb material are grown in a periodic alternating stacking manner; the number of atomic layers of a single layer of the InAs material and the number of atomic layers of a single layer of the GaSb material remain unchanged; or the number of atomic layers of a single layer of the InAs material gradually increases, and the number of atomic layers of a single layer of the GaSb material remains unchanged.

10. The method for preparing a superlattice infrared detector according to claim 9, characterized in that: The thickness of the InSb atomic layer of the superlattice absorption layer is adjusted to achieve zero mismatch between the superlattice absorption layer and the substrate.

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