A long-wave infrared detector type ii superlattice material with a graded hole barrier band

Abstract

The application discloses a long-wave infrared detector second-type superlattice material with gradually changed hole barrier energy band, which comprises a GaSb substrate, a GaSb buffer layer, a p-type electrode contact layer, an electron barrier layer, a second-type superlattice absorption layer, a first hole barrier layer, a second hole barrier layer, a third hole barrier layer, an n-type electrode contact layer and an n-type InAs cover layer; the first hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice; the second hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice; the third hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice; and the n-type electrode contact layer is an InAs / AlSb superlattice. According to the application, the band gap gradually increases from the absorption layer to the n-type electrode contact layer through the transition of the three-layer band gap gradually changed barrier layer, the conduction band is basically flat, the first hole barrier layer and the second hole barrier are weakly doped with p-type, the third hole barrier layer is doped with n-type, and the pn junction interface is moved into the barrier layer with a wider band gap.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic device technology and relates to a type II superlattice material for long-wave infrared detectors, particularly a type II superlattice material for long-wave infrared detectors with a gradually changing hole barrier band that can achieve dark current suppression. Background Technology

[0002] Type II superlattice infrared detectors are a new type of infrared detector with features such as good uniformity, tunable absorption wavelength, easily adjustable band structure, high quantum efficiency, and easy dual-color integration. They have excellent application prospects in high-temperature mid-wave, long-wave, dual-multicolor, and large-area infrared focal plane array devices.

[0003] Because of the short minority carrier lifetime of type II superlattice materials, the dark current of infrared detectors made from them has always been higher than that of mercury cadmium telluride detectors. To suppress dark current and improve device performance, researchers of type II superlattice infrared detectors have proposed different types of dual-barrier infrared detection structures, such as the P-π-MN structure proposed by Northwestern University (BMNguyen, D. Hoffman, D. Delaunay, et al., Dark current suppresion in type IIInAs / GaSb superlattice long wavelength infrared photodiodes with M-structure barrier[J], Appl. Phys. Lett., 2007, 91: 163511), and the complementary barrier infrared detector (CBIRD) structure proposed by Jet Propulsion Laboratory (JPL) (SD Gunapala, DZTing, CJHill, et al., Demonstration of a 1024×1024Pixel InAs / GaSb Superlattice Focal Plane Array, IEEE photon. Technol. Lett., 2010, 22: 1856). The key feature of this type of barrier detector structure is the presence of an electron barrier layer and a hole barrier layer on either side of the absorption layer. Since the valence band of the electron barrier layer is aligned with the valence band of the absorption layer, and the conduction band of the hole barrier layer is aligned with the conduction band of the absorption layer, this design ensures the smooth passage of photogenerated carriers without obstructing their flow, while suppressing the detector's dark current. Because the absorption layer of a type-II superlattice long-wavelength infrared detector is typically weakly p-type doped, while the hole barrier layer is n-type doped, a pn junction exists between the absorption layer and the hole barrier layer. Therefore, the band structure and doping design of the hole barrier layer are crucial for suppressing the dark current in type-II superlattice long-wavelength detectors.

[0004] The short recombination lifetime of SRH in type-II superlattice materials, approximately 30-100 ns, leads to a high recombination current in type-II superlattice infrared detectors. To suppress the SRH recombination current, the n-type doping concentration of the hole barrier layer is typically designed to be an order of magnitude lower than the p-type doping concentration of the absorption layer (the n-type doping concentration of the hole barrier layer is approximately (1-2) × 10¹⁵ cm⁻¹). -3 The absorber layer is doped with approximately (1-2)×10⁻⁶. 16 cm -3This design ensures that most of the space charge region falls within the hole barrier layer; simultaneously, the band gap of the hole barrier layer is more than twice that of the absorption layer, thereby reducing the recombination current generated by the SRH (Short-Range Hierarchy) in superlattice infrared detectors. For the choice of hole barrier layer, Northwestern University chose an M-type superlattice (InAs / GaSb / AlSb / GaSb superlattice) with a band gap of approximately 0.2 meV, while the Jet Propulsion Laboratory chose an InAs / AlSb superlattice with a band gap of approximately 0.4 meV. While this design does suppress recombination current, the high doping concentration in the absorption layer results in a short depletion region on one side, leading to severe band bending and a relatively high tunneling current.

[0005] To reduce the tunneling current in type-II superlattice long-wave infrared detectors, researchers have p-doped the hole barrier layer to form a pn junction with the n-type electrode contact layer, thus shifting the depletion region into a wide bandgap material and suppressing the tunneling current. However, p-type doping of the hole barrier raises the conduction band of the hole barrier, forming a conduction band barrier that blocks photogenerated electrons from the absorption layer from flowing to the n-type electrode contact layer, reducing the quantum efficiency of the long-wave infrared detector or increasing the turn-on voltage. To obtain a type-II superlattice long-wave infrared detector with low dark current and the ability to operate at a relatively low bias voltage, there is an urgent need to develop new type-II superlattice materials for long-wave infrared detectors.

[0006] Current superlattice long-wavelength detector structures suffer from high tunneling current. To suppress this current, researchers have p-doped the hole barrier layer and formed a pn junction with the n-type electrode contact layer, shifting the depletion region into a wide bandgap material, thereby suppressing the tunneling current. However, p-type doping of the hole barrier raises the conduction band of the hole barrier, forming a conduction band barrier that blocks photogenerated electrons from the absorption layer from flowing to the n-type electrode contact layer, reducing the quantum efficiency of the long-wavelength detector or increasing the turn-on voltage. Summary of the Invention

[0007] The purpose of this invention is to provide a type II superlattice material for long-wave infrared detectors with low dark current and a gradually changing hole barrier band under a relatively small bias voltage.

[0008] The type II superlattice material of the long-wave infrared detector with gradually changing hole barrier band in this invention consists of the following layers from bottom to top: GaSb substrate, buffer layer, p-type electrode contact layer, electron barrier layer, type II superlattice absorption layer, first hole barrier layer, second hole barrier layer, third hole barrier layer, n-type electrode contact layer, and n-type InAs capping layer.

[0009] The GaSb substrate is a (001)GaSb substrate.

[0010] The buffer layer is a GaSb buffer layer, grown on a GaSb substrate, and doped with Be at a concentration of 5 × 10⁻⁶. 17 ~2×10 18 cm-3 The thickness is 300-500 nm.

[0011] The p-type electrode contact layer is an InAs / GaSb superlattice with 60-80 periods, doped with Be at a concentration of 5 × 10⁻⁶. 17 ~2×10 18 cm -3 Its periodic thickness is 8ML (monolayer, ML) of InAs and 8-12ML of GaSb.

[0012] The described electron barrier layer, an InAs / GaSb superlattice, has 50–60 periods and is Be-doped at a concentration of 5 × 10⁻⁶. 15 ~2×10 16 cm -3 Its periodic thickness is 8 mL of InAs and 8–12 mL of GaSb.

[0013] The aforementioned type-II superlattice absorption layer is an InAs / GaSb superlattice with 300–500 periods, doped with Be at a concentration of 2 × 10⁻⁶. 15 ~2×10 16 cm -3 The period thickness needs to be adjusted according to the specific cutoff wavelength. If the cutoff wavelength is 9μm, the period thickness is 12ML of InAs and 7ML of GaSb; if the cutoff wavelength is 10μm, the period thickness is 13ML of InAs and 7ML of GaSb; if the cutoff wavelength is 11μm, the period thickness is 14ML of InAs and 7ML of GaSb.

[0014] The first hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice with 20-25 periods, doped with Be at a concentration of 2×10⁻⁶. 15 ~5×10 15 cm -3 Its periodic thickness is 14-16 mL of InAs, 3 mL of GaSb, 1 mL of AlSb and 3 mL of GaSb.

[0015] The second hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice with 20-25 periods, doped with Be at a concentration of 2×10⁻⁶. 15 ~5×10 15 cm -3 Its periodic thickness is 14-16 mL of InAs, 2 mL of GaSb, 2 mL of AlSb and 2 mL of GaSb.

[0016] The third hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice with 20-25 periods, doped with Si at a concentration of 2×10⁻⁶. 15 ~1×10 16 cm -3 Its periodic thickness is 14-16 mL of InAs, 1 mL of GaSb, 3 mL of AlSb and 1 mL of GaSb.

[0017] The n-type electrode contact layer is an InAs / AlSb superlattice with 50-60 periods, doped with Si at a concentration of 5 × 10⁻⁶. 17 ~2×10 18 cm -3 Its periodic thickness is 14-16 mL of InAs and 4 mL of AlSb.

[0018] The n-type InAs capping layer, with a thickness of 10–20 nm, is Si-doped with a doping concentration of 1 × 10⁻⁶. 18 ~2×10 18 cm -3 .

[0019] This enables the development of a type II superlattice long-wave infrared detector material with a gradually changing hole barrier band.

[0020] Working principle and beneficial effects of the present invention:

[0021] When long-wave infrared radiation enters the material of a type-II superlattice long-wave infrared detector, it excites the absorption layer material to generate photogenerated electron-hole pairs. These pairs are then separated by a built-in electric field or an applied electric field. Electrons are accelerated by the built-in electric field and transported to the n-type electrode contact layer, while holes are accelerated by the built-in electric field and transported to the p-type electrode contact layer, where they are collected to generate a signal, thus enabling the detection of long-wave infrared radiation.

[0022] This invention employs a three-layer barrier layer with gradually increasing bandgap, transitioning from the absorption layer to the n-type electrode contact layer. The conduction bands are essentially flush, while the bandgap gradually increases. Furthermore, the first and second hole barrier layers are weakly p-type doped, and the third hole barrier layer is n-type doped, shifting the pn junction interface into the wider bandgap barrier layer. This reduces recombination and tunneling currents without hindering the transport and collection of photogenerated electrons. Consequently, it enables the fabrication of a type-II superlattice long-wavelength infrared detector material with low dark current and the ability to operate at relatively low bias voltages. Attached Figure Description

[0023] Figure 1 Material band structure diagram. Detailed Implementation

[0024] Example

[0025] Referring to Table 1, the type II superlattice materials of the long-wave infrared detector with gradually changing hole barrier bands of the present invention are, from bottom to top: GaSb substrate, buffer layer, p-type electrode contact layer, electron barrier layer, type II superlattice absorption layer, first hole barrier layer, second hole barrier layer, third hole barrier layer, n-type electrode contact layer, and n-type InAs capping layer.

[0026] The GaSb substrate is a (001)GaSb substrate.

[0027] The GaSb buffer layer is grown on GaSb substrate 1 and is Be-doped with a doping concentration of 5 × 10⁻⁶. 17 ~2×10 18 cm -3 The thickness is 300-500 nm.

[0028] The p-type electrode contact layer is an InAs / GaSb superlattice with 60-80 periods, doped with Be at a concentration of 5 × 10⁻⁶. 17 ~2×10 18 cm -3 Its periodic thickness is 8 monolayers (ML) of InAs and 8–12 ML of GaSb.

[0029] The electron barrier layer is an InAs / GaSb superlattice with 50-60 periods, doped with Be at a concentration of 5 × 10⁻⁶. 15 ~2×10 16 cm -3 Its periodic thickness is 8 mL of InAs and 8–12 mL of GaSb.

[0030] The aforementioned type-II superlattice absorption layer is an InAs / GaSb superlattice with 300–500 periods, doped with Be at a concentration of 2 × 10⁻⁶. 15 ~2×10 16 cm -3 The period thickness needs to be adjusted according to the specific cutoff wavelength. If the cutoff wavelength is 9μm, the period thickness is 12ML of InAs and 7ML of GaSb; if the cutoff wavelength is 10μm, the period thickness is 13ML of InAs and 7ML of GaSb; if the cutoff wavelength is 11μm, the period thickness is 14ML of InAs and 7ML of GaSb.

[0031] The first hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice with 20-25 periods, doped with Be at a concentration of 2×10⁻⁶. 15 ~5×10 15 cm -3Its periodic thickness is 14-16 mL of InAs, 3 mL of GaSb, 1 mL of AlSb and 3 mL of GaSb.

[0032] The second hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice with 20-25 periods, doped with Be at a concentration of 2×10⁻⁶. 15 ~5×10 15 cm -3 Its periodic thickness is 14-16 mL of InAs, 2 mL of GaSb, 2 mL of AlSb and 2 mL of GaSb.

[0033] The third hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice with 20-25 periods, doped with Si at a concentration of 2×10⁻⁶. 15 ~1×10 16 cm -3 Its periodic thickness is 14-16 mL of InAs, 1 mL of GaSb, 3 mL of AlSb and 1 mL of GaSb.

[0034] The n-type electrode contact layer is an InAs / AlSb superlattice with 50-60 periods, doped with Si at a concentration of 5 × 10⁻⁶. 17 ~2×10 18 cm -3 Its periodic thickness is 14-16 mL of InAs and 4 mL of AlSb.

[0035] The n-type InAs capping layer has a thickness of 10–20 nm and is doped with Si at a concentration of 1 × 10⁻⁶. 18 ~2×10 18 cm -3 .

[0036] Table 1

[0037]

[0038]

[0039] The band arrangement of the type-II superlattice material for the hole barrier band-gradient long-wave infrared detector of this invention is described in the following section. Figure 1 This invention transitions from the absorption layer to the n-type electrode contact layer through three barrier layers with gradually increasing band gaps, resulting in a nearly flush conduction band and a gradually increasing band gap. Furthermore, the first and second hole barrier layers are weakly p-type doped, while the third hole barrier layer is n-type doped, causing the pn junction interface to shift into the barrier layer with a wider band gap.

Claims

1. A type-II superlattice material for a long-wavelength infrared detector with a gradually changing hole barrier band, characterized in that: This material is prepared by molecular beam epitaxy on a GaSb substrate from bottom to top, consisting of a GaSb buffer layer, a p-type electrode contact layer, an electron barrier layer, a type II superlattice absorption layer, a first hole barrier layer, a second hole barrier layer, a third hole barrier layer, an n-type electrode contact layer, and an n-type InAs capping layer. The first hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice, doped with Be; The second hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice, doped with Be; The third hole barrier layer is an InAs / GaSb / AlSb / GaSb superlattice, doped with Si. The n-type electrode contact layer is an InAs / AlSb superlattice; From the type II superlattice absorption layer to the n-type electrode contact layer, a transition occurs through three barrier layers with gradually changing band gaps, from the first hole barrier layer to the third hole barrier layer. The conduction bands are aligned, and the band gap gradually increases. The first and second hole barrier layers are weakly p-type doped, and the third hole barrier layer is n-type doped, so that the pn junction interface moves into the barrier layer with a wider band gap. This reduces the generation of recombination current and tunneling current without hindering the transport and collection of photogenerated electrons.

2. The type II superlattice material for long-wave infrared detectors according to claim 1, characterized in that: The GaSb buffer layer is grown on a GaSb substrate and is Be-doped with a doping concentration of 5 × 10⁻⁶. 17 ~2×10 18 cm -3 The thickness is 300~500nm.

3. The type II superlattice material for long-wave infrared detectors according to claim 1, characterized in that: The p-type electrode contact layer is doped with Be, with a doping concentration of 5 × 10⁻⁶. 17 ~2×10 18 cm -3 The number of cycles is 60-80, and the cycle thickness is 8 mL for InAs and 8-12 mL for GaSb.

4. The type-II superlattice material for long-wave infrared detectors according to claim 1, characterized in that: The electron barrier layer is doped with Be, with a doping concentration of 5 × 10⁻⁶. 15 ~2×10 16 cm -3 The number of cycles is 50-60, and the cycle thickness is 8 mL for InAs and 8-12 mL for GaSb.

5. The type II superlattice material for long-wave infrared detectors according to claim 1, characterized in that: The type-II superlattice absorption layer is Be-doped with a doping concentration of 2×10⁻⁶. 15 ~2×10 16 cm -3 The number of cycles is 300 to 500, and the cycle thickness needs to be adjusted according to the specific cutoff wavelength. If the cutoff wavelength is 9 μm, the cycle thickness is 12 mL of InAs and 7 mL of GaSb; if the cutoff wavelength is 10 μm, the cycle thickness is 13 mL of InAs and 7 mL of GaSb; if the cutoff wavelength is 11 μm, the cycle thickness is 14 mL of InAs and 7 mL of GaSb.

6. The type-II superlattice material for long-wave infrared detectors according to claim 1, characterized in that: The first hole barrier layer has a Be doping concentration of 2×10⁻⁶. 15 ~5×10 15 cm -3 The number of cycles is 20-25, and the cycle thickness is 14-16 mL of InAs, 3 mL of GaSb, 1 mL of AlSb and 3 mL of GaSb.

7. The type-II superlattice material for long-wave infrared detectors according to claim 1, characterized in that: The second hole barrier layer has a Be doping concentration of 2×10⁻⁶. 15 ~5×10 15 cm -3 The number of cycles is 20-25, and the cycle thickness is 14-16 mL of InAs, 2 mL of GaSb, 2 mL of AlSb and 2 mL of GaSb.

8. The type II superlattice material for long-wave infrared detectors according to claim 1, characterized in that: The third hole barrier layer has a Si doping concentration of 2×10⁻⁶. 15 ~1×10 16 cm -3 The number of cycles is 20-25, and the cycle thickness is 14-16 mL of InAs, 1 mL of GaSb, 3 mL of AlSb and 1 mL of GaSb.

9. The type-II superlattice material for long-wave infrared detectors according to claim 1, characterized in that: The n-type electrode contact layer is Si-doped with a doping concentration of 5 × 10⁻⁶. 17 ~2×10 18 cm -3 The number of cycles is 50-60, and the cycle thickness is 14-16 mL of InAs and 4 mL of AlSb.

10. The type-II superlattice material for long-wave infrared detectors according to claim 1, characterized in that: The n-type InAs capping layer has a thickness of 10~20 nm and is doped with Si at a concentration of 1×10⁻⁶. 18 ~2×10 18 cm -3 .

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