A quantum well array detector operable in single mode and double mode

Abstract

The application relates to a quantum well array detector capable of single-mode and double-mode operation, which comprises an upper electrode layer, a GaAs active region and a lower electrode layer from top to bottom; the GaAs active region is distributed with a plurality of microcavity array units; the top layer of the microcavity array units is an upper metal electrode (5), two upper metal electrodes (5) in each row are connected through two-stage stepped microstrip lines, thereby forming the upper electrode layer; the upper metal electrode (5) has a plurality of angle-adjustable defects. The quantum well array detector can realize single-mode and double-mode detection modes through the regulation and control of the coupling mechanism, and has a better market application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of semiconductor optoelectronic devices, and particularly relates to a quantum well array detector capable of single-mode and dual-mode operation. BACKGROUND

[0002] Terahertz (THz) waves generally refer to electromagnetic waves with a frequency from 100 GHz to 10 THz and a corresponding wavelength in the range of 3 mm to 30 μm, between millimeter waves and infrared light. THz waves occupy a special position in the electromagnetic spectrum, in the transition region from electronics to photonics, with the long-wave end coinciding with sub-millimeter waves and the short-wave end coinciding with far-infrared waves. THz wave technology has very wide application potential in the fields of information communication technology, biomedicine, space exploration and global environmental detection.

[0003] THz quantum well photodetectors (THz QWPs) based on inter-subband transition are a natural extension of infrared quantum well photodetectors (QWIPs) in the THz band, which use inter-subband transition absorption in semiconductor quantum well superlattices (generally n-doped GaAs / AlGaAs) to generate photocurrent. THz QWPs have high detection sensitivity and fast response capability, and have the advantages of wide linear response range, simple design, mature material growth and device preparation process, and can be prepared into large-scale imaging arrays, and are ideal devices for space heterodyne detection, high-speed communication and large-scale focal plane imaging. Figure 1 As shown in the figure, the commonly used THz QWP structure in the prior art includes a GaAs substrate 1, a lower contact layer 8, an active region 4 and an upper contact layer 7 arranged in order from bottom to top on the upper surface of the GaAs substrate 1, a lower electrode 11 arranged on the upper surface of the GaAs substrate 1 and located on both sides of the lower contact layer 8, and an upper electrode 12 arranged on the upper surface of the upper contact layer 7, wherein the active region 4 is composed of GaAs / AlGaAs quantum well superlattices, and the lower contact layer 8 and the upper contact layer 7 are composed of n-doped GaAs. x Ga 1-xAs multiple quantum well periodic structure, the bound electrons in the quantum well absorb THz photons and transition to the continuous state, and form a photocurrent under an applied bias, and the changes of the photocurrent are measured and analyzed to complete the detection of THz waves. The working frequency of the THz QWP can be adjusted by changing the barrier height, well width and doping concentration. Through the special design of the barrier and well, a voltage-adjustable broadband THz QWP can be realized. In 2018, H.X. Wang et al. realized the voltage-tunable broadband QWP in the frequency band of 4.0-6.5 THz by designing a stepped quantum well structure. In 2022, M. Almassri et al. realized the voltage-tunable broadband QWP in the range of 2.5-4.1 THz.

[0004] Therefore, the lower photon absorption efficiency is the key factor restricting the performance of the THz QWP, and the improvement of the light coupling mode is a method to obtain better performance of the THz QWP. At present, the two commonly used coupling modes of the THz QWP are: 45° inclined polished substrate coupling and metal scattering grating coupling. Among them, the 45° inclined polished substrate coupling mechanism cannot realize the normal incidence of light (as shown in Figure 1 , the GaAs substrate 1 needs to be polished at 45°, and the incident light needs to be incident from the 45° inclined surface), and is not conducive to device integration. Although the grating coupling can realize the normal incidence coupling of light, there is no great improvement in device performance. In 2015, D. Palaferri et al. published a microcavity THz QWP based on a patch antenna array, which pushed the research of QWP to the array level. This research can detect a single frequency point of THz, but cannot realize the detection of multiple frequency points. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a quantum well array detector capable of single-mode and dual-mode operation, which overcomes the problem that the current array-type quantum cascade detector can only work in a single-mode state although it realizes array detection.

[0006] The present application provides a top-down structure including an upper electrode layer, a GaAs active region and a lower electrode layer; the GaAs active region is distributed with a plurality of microcavity array units; the top layer of the microcavity array unit is an upper metal electrode 5, and each pair of upper metal electrodes 5 in each row is connected by a two-stage stepped microcavity connection line to form an upper electrode layer; the upper metal electrode (5) has a plurality of adjustable angle defects.

[0007] The defects of the upper metal electrode 5 include adjustable rotation angle rectangular defects and / or adjustable opening angle check mark-shaped defects.

[0008] The microcavity array sequentially includes a substrate, a lower metal electrode plate, an epitaxial layer and an upper metal electrode from bottom to top.

[0009] The epitaxial layer comprises, from top to bottom, an upper contact layer, an active region and a lower contact layer, and the geometric size of the epitaxial layer is the same as that of the upper metal electrode.

[0010] The active region comprises a semiconductor superlattice structure alternately grown by GaAs and AlGaAs.

[0011] The lower metal electrode plate and the upper metal electrode are made of a metal capable of forming an ohmic contact with a semiconductor.

[0012] The surface of the lower metal electrode plate is further provided with a passivation layer; the passivation layer is filled around the epitaxial layer, and the thickness is the same as that of the epitaxial layer.

[0013] The material of the passivation layer is benzocyclobutene (BCB), polyimide, SiO2 or Si3N4.

[0014] The back surface of the substrate is further provided with a back gold layer.

[0015] The lower electrode layer is a metal plate.

[0016] Beneficial effects

[0017] The present application can realize single-mode and double-mode detection modes of the quantum well array detector by regulating the coupling mechanism. Currently, the array type quantum well detector on the market can only realize single-frequency detection, but the present application realizes double-frequency detection of the device under the condition that other parameters remain unchanged, i.e., the background noise and dark current of the device remain unchanged, and has better market application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of a common mid-infrared and THz QWP in the prior art.

[0019] Figure 2 It is a structural schematic diagram of the quantum well array detector capable of single-mode and double-mode work provided in the embodiment.

[0020] Figure 3 It is a longitudinal sectional view of the microcavity array unit provided in the embodiment.

[0021] Figure 4 a-b are schematic diagrams of adjusting single-frequency and double-frequency working modes of the microcavity array unit in the embodiment.

[0022] Figure 5 a-b are schematic diagrams of fine-tuning working frequencies of the microcavity array unit in the embodiment.

[0023] Figure 6 It is a schematic diagram of the preparation step S1 of the quantum well array detector provided in the embodiment.

[0024] Figure 7 Schematic diagram of preparation step S2 of quantum well array detector provided for the embodiment.

[0025] Figure 8 Schematic diagram of preparation step S3 of quantum well array detector provided for the embodiment.

[0026] Figure 9 Schematic diagram of preparation step S4 of quantum well array detector provided for the embodiment.

[0027] Element number explanation:

[0028] 1 substrate

[0029] 2 lower metal electrode plate

[0030] 3 passivation layer

[0031] 4 active region

[0032] 5 upper metal electrode

[0033] 6 microcavity connecting line

[0034] 7 upper contact layer

[0035] 8 lower contact layer

[0036] 9 back metal layer

[0037] 10 epitaxial layer

[0038] 11 lower electrode

[0039] 12 upper electrode DETAILED DESCRIPTION

[0040] The application will be further described below in connection with specific embodiments. It should be understood that these embodiments are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that after reading the content of the application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope of the appended claims.

[0041] Embodiment 1

[0042] This embodiment takes a dual-frequency microcavity array THz QWP working at 4.2 THz and 4.7 THz as an example to illustrate the application. The overall structure is as follows: Figure 2As shown, from top to bottom, the uppermost layer is the upper electrode layer, the middle is the GaAs active region, and the lower layer is the lower electrode layer composed of a whole piece of metal. The side length of the upper electrode layer and the GaAs active region is a = 10 μm, and then a square matrix with a spacing of d = 15 μm is formed. The GaAs active region is distributed with a plurality of microcavity array units; the top layer of the microcavity array unit is the upper metal electrode 5, and each row of the upper metal electrode 5 is connected by a two-step microcavity connecting line (reducing the mutual influence between microcavities) between every two upper metal electrodes 5, forming an upper electrode layer; the upper metal electrode 5 has a plurality of adjustable angle defects.

[0043] The longitudinal sectional view of the microcavity array unit is as shown in Figure 3 . Each microcavity unit includes an upper metal electrode 5, an epitaxial layer 10 of a quantum well detector disposed on the lower surface of the upper metal electrode 5, and a shared lower metal electrode 2 disposed below the quantum well detector epitaxial layer 10 and above the substrate 1. As an example, the epitaxial layer 10 of the quantum well detector includes an upper contact layer 7, an active region 4, and a lower contact layer 8 connected in turn from top to bottom, and the geometric size of the epitaxial layer 10 is the same as that of the upper metal electrode 5, wherein the active region 4 includes a semiconductor quantum well structure alternately grown by GaAs and AlGaAs. The upper metal electrode 5 in the microcavity unit is a subwavelength fractal patch antenna, and the upper metal electrode 5 and the lower metal electrode plate 2 are made of a metal that can form an ohmic contact with a semiconductor. The metal material can be selected according to the conductive polarity of the semiconductor material, and high-temperature rapid annealing needs to be performed after the device is prepared to form a good ohmic contact electrode.

[0044] As shown in Figure 3 , the surface of the lower metal electrode plate 2 of the microcavity unit is also provided with a passivation layer 3 to prevent leakage current of the active region 4. The thickness of the passivation layer 3 is equal to the thickness of the epitaxial layer 10, and the material thereof can adopt BCB, SiO2 or Si3N4. The back surface of the substrate 1 is also provided with a back gold layer 9 to enable the coupling structure to be more firmly pasted with a heat sink and to have better heat dissipation. As an example, the material of the back gold layer 9 is the same as that of the upper metal electrode 5, for example, it can be made of non-alloyed Ti and Au or continuous growth Pd, Ge, Ti and Au.

[0045] The specific working condition of the upper metal electrode 5 is analyzed by Figure 4 , Figure 5 . As shown in Figure 4 (a), the upper metal electrode 5 introduces a rectangular defect of c*s = 1*7 μm. When other conditions remain unchanged, by changing the rotation angle of the defect, different working modes of the microcavity array coupled QWP can be obtained, as shown in Figure 4 (b). It can be seen that as the rotation angle The device presents two working modes of single frequency and double frequency. Meanwhile, the working frequency of the device also changes greatly.

[0046] On the basis of Figure 4 , another defect of the shape of a cross is further introduced, as shown in Figure 5 (a). With the change of the opening angle of the defect, as shown in Figure 5 (b), the working frequency of the device in the double frequency mode changes slightly. Therefore, the cross-shaped defect can fine-tune the coupling frequency of the device and make up for the functional blank of the first defect.

[0047] The embodiment also provides a preparation method of a quantum well array detector, including the following steps:

[0048] S1: providing a sample material layer, which includes a first substrate and an epitaxial layer from bottom to top;

[0049] As shown in Figure 6 , a first substrate 110 made of semi-insulating GaAs is provided, and a GaAs buffer layer (not shown in the figure), an etching stop layer 111 and an epitaxial layer 10 of a quantum well detector are sequentially grown from bottom to top on the upper surface of the first substrate 110, wherein the epitaxial layer 10 includes an N-type doped lower contact layer, an active region and an N-type doped upper contact layer (not shown in the figure). As an example, the material of the etching stop layer 111 can be selected as AlGaAs.

[0050] S2: providing a second substrate, forming a first metal material layer on the epitaxial layer surface of the sample material layer, and forming a second metal material layer on the surface of the second substrate;

[0051] As shown in Figure 7 , a second substrate 210 made of N+ type GaAs is provided as a substrate 1 in the coupling structure, and the planar geometric size of the second substrate 210 is greater than the planar geometric size of the first substrate 110.

[0052] Then, referring to Figure 6 and Figure 7 , the upper surfaces of the epitaxial layer 10 in step S1 and the second substrate 210 are respectively formed with a first metal material layer 112 and a second metal material layer 211 by electron beam evaporation (or magnetron sputtering). As an example, the first metal material layer 112 and the second metal material layer 211 can be made of non-alloyed Ti and Au or made of continuously grown Pd, Ge, Ti and Au, and preferably made of continuously grown Pd, Ge, Ti and Au.

[0053] S3: tabletting and bonding the first metal material layer and the second metal material layer to form a lower metal electrode plate;

[0054] like Figure 8 As shown, the first metal material layer 112 and the second metal material layer 211 are pressed and bonded for no less than 20 minutes at a temperature of 320°C and a pressure of 8 MPa to form the lower metal electrode plate in the coupling structure.

[0055] S4: Remove the first substrate to expose the epitaxial layer;

[0056] like Figure 9 As shown, after the first substrate 110 is thinned by a grinding and polishing machine, the remaining first substrate 110 and the etch barrier layer 111 are etched away by a wet etching solution to expose the N-type doped lower contact layer in the epitaxial layer 10 in step S1, which serves as the upper contact layer of the epitaxial layer 10. At this time, the N-type doped upper contact layer in the epitaxial layer 10 in step S1 serves as the lower contact layer of the epitaxial layer 10.

[0057] S5: Etch the epitaxial layer to form multiple microcavity units in the coupling structure, wherein the microcavity unit is the microcavity unit described in Embodiment 1;

[0058] Next, a square active region array is etched on the epitaxial layer 10, and photoresist is used as a mask to etch and form multiple square active region microcavity units in the coupling structure.

[0059] S6: A passivation layer is formed by filling the spaces between the multiple microcavity units and in the grooves of the microcavity units, and an upper electrode and a microcavity connection line are deposited on the surface of the passivation layer to connect the multiple microcavity units to an external power source.

[0060] Reference Figure 4 As shown, a passivation layer 3 is formed between multiple microcavity units and in the grooves of the microcavity units to prevent leakage current in the active region 4. The thickness of the passivation layer 3 is equal to the thickness of the epitaxial layer 10, and its material can be BCB, polyimide, SiO2 or Si3N4.

[0061] Next, an upper electrode 5 and microcavity interconnects 6 are deposited on the passivation layer 3 and the upper surface of the active region to connect the plurality of microcavity units to an external power source. As an example, the material of the microcavity interconnects 6 is selected to be a conductive material, such as the same material as the upper metal electrode 5, for example, unalloyed Ti and Au or continuously grown Pd, Ge, Ti and Au.

[0062] Next, the second substrate 210 is thinned, and a back gold layer 9 is formed on the side away from the lower metal electrode plate 2 to enable the coupling structure to adhere more firmly to the heat sink and improve its heat dissipation. As an example, the material of the back gold layer 9 can be unalloyed Ti and Au or continuously grown Pd, Ge, Ti and Au.

[0063] Then, high temperature rapid annealing is performed at a temperature not lower than 350℃ for not less than 30 seconds, so that the upper metal electrode 5 and the lower metal electrode plate 2 in the coupling structure form a good ohmic contact, effectively inhibiting the dark current of the quantum well detector.

[0064] Finally, cleaving the device, gold wire welding, packaging, and thus completing the fabrication of the coupling structure.

[0065] The above is only an example, and any change in geometric parameters resulting in changes in the working frequency band, peak detection frequency, dispersion curve and other results is within the scope of protection of the present patent.

Claims

1. A quantum well array detector capable of single-mode and dual-mode operation, comprising, from top to bottom, an upper electrode layer, a GaAs active region, and a lower electrode layer; characterized in that: The GaAs active region is distributed with several microcavity array units; the top layer of the microcavity array unit is an upper metal electrode (5), and each row of upper metal electrodes (5) is connected to each other by a two-stage stepped microcavity connecting line to form an upper electrode layer; the upper metal electrode (5) has several defects with adjustable angles; the defects of the upper metal electrode (5) include rectangular defects with adjustable rotation angles and checkmark-shaped defects with adjustable opening angles.

2. The quantum well array detector according to claim 1, characterized in that: The microcavity array unit comprises, from bottom to top, a substrate (1), a lower metal electrode plate (2), an epitaxial layer (10), and an upper metal electrode (5).

3. The quantum well array detector according to claim 2, characterized in that: The epitaxial layer (10) includes an upper contact layer (7), an active region (4) and a lower contact layer (8) from top to bottom, and the geometric dimensions of the epitaxial layer (10) are the same as those of the upper metal electrode (5).

4. The quantum well array detector according to claim 3, characterized in that: The active region (4) includes a semiconductor superlattice structure with alternating GaAs and AlGaAs growth.

5. The quantum well array detector according to claim 2, characterized in that: The lower metal electrode plate (2) and the upper metal electrode (5) are made of metals that can form ohmic contacts with semiconductors.

6. The quantum well array detector according to claim 2, characterized in that: The surface of the lower metal electrode plate (2) is also provided with a passivation layer (3); the passivation layer (3) fills around the epitaxial layer (10) and has the same thickness as the epitaxial layer (10).

7. The quantum well array detector according to claim 6, characterized in that: The passivation layer (3) is made of benzocyclobutene (BCB), polyimide, SiO2, or Si3N4.

8. The quantum well array detector according to claim 2, characterized in that: The back side of the substrate (1) is also provided with a back gold layer (9).

9. The quantum well array detector according to claim 1, characterized in that: The lower electrode layer is a metal plate.

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