Metal-graphene patch antenna microcavity array coupled terahertz quantum well detector and manufacturing method thereof

Abstract

The invention relates to a metal-graphene patch antenna coupled terahertz quantum well detector and a manufacturing method thereof. The metal-graphene patch antenna coupled terahertz quantum well detector comprises a substrate and microcavity units which are periodically arranged on the substrate, the micro-cavity units are split rings which are made of metal and have different front and rear opening widths, the openings are connected through single-layer graphene, the single-layer graphene and the upper metal electrodes on the upper surfaces of the micro-cavity units form metal-graphene patch antennas, and metal wires are introduced into the two sides of the split rings to connect the adjacent micro-cavity units. The light absorption efficiency of the quantum well can be effectively improved, and the dark current of the device is reduced, so that the working temperature of the device is improved. The normal incidence metal-graphene patch antenna microcavity array coupling structure of the invention is of great significance to the high-speed detection and modulation of the terahertz wave band.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor infrared and terahertz detectors, and particularly relates to a terahertz quantum well detector coupled with a metal-graphene patch antenna microcavity array and a manufacturing method thereof. Background Art

[0002] Terahertz (THz) waves generally refer to the electromagnetic spectrum region between millimeter waves and infrared light, with frequencies ranging from 100 GHz to 10 THz and corresponding wavelengths in the range of 3 mm to 30 μm. The THz band is in the transition region from electronics to photonics, has unique physical properties, and has very broad application potential in fields such as high-speed wireless communication, super-resolution medical imaging, and space exploration.

[0003] Terahertz quantum well photodetectors (THz QWPs) based on intersubband transitions have high detection sensitivity and fast response capabilities, and also have advantages such as a wide linear response range, simple design, mature material growth and device fabrication processes, and the ability to fabricate large-scale imaging arrays. They are ideal devices for space heterodyne detection, high-speed communication, and large-scale focal plane imaging.

[0004] Bound states in the continuum (BIC) is a surface system effect of strong light-matter interaction that can capture electromagnetic wave energy with wavelengths much larger than the diffraction limit. It has the characteristics of approaching zero bandwidth and much higher electromagnetic energy spatial concentration ability than surface plasmons. By breaking the structural topological protection to a certain extent, BIC can be converted into a quasi-BIC mode with a finite bandwidth.

[0005] The active region of THz QWPs consists of GaAs / Al x Ga 1-xIt is composed of an As multiple quantum well periodic structure and upper and lower contact layers. When the bound electrons in the ground state in the quantum well absorb THz photons, they transition to the quasi-continuous state at the barrier edge, and the generated photoexcited carriers form a photocurrent under an applied bias voltage, thereby realizing the detection of THz waves. Since the light absorption of QWPs originates from intersubband transitions, the selection rule determines that THz QWPs require an electric field component perpendicular to the quantum well growth direction to couple the incident THz wave into the device. Common coupling methods for THz QWPs include: 45° bevel polished substrate coupling and metal scattering grating coupling. The 45° bevel polished substrate coupling mechanism has a low coupling efficiency for the incident THz light and is not conducive to device integration; although metal grating coupling can achieve normal incidence coupling of light, the large exposed area of the active region brings a large dark current, and once the complete metal structure is fabricated, the frequency selection region and absorption rate of the device cannot be changed. In summary, it is of great significance to find a better light coupling method to improve the performance of THz QWPs. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a terahertz quantum well detector coupled with a metal-graphene patch antenna microcavity array and its manufacturing method to achieve strong normal incidence coupling of light, achieve the effect of enhancing the electric field in the cavity, improve the light coupling efficiency of the device; at the same time reduce the dark current and improve the detectivity of the device; and realize dynamic electrical tunability of the absorption amplitude, thereby laying a foundation for the THz communication system.

[0007] The present invention provides a terahertz quantum well detector coupled with a metal-graphene patch antenna microcavity array, including a substrate and microcavity units arranged periodically on the substrate; the microcavity units are open rings with different front and rear opening widths constructed by metal, connected with a single layer of graphene at the opening, forming a metal-graphene patch antenna with the upper metal electrode on the upper surface of the microcavity unit, and metal wires are introduced on both sides of the open ring to connect adjacent microcavity units.

[0008] Preferably, the microcavity unit includes a lower metal electrode plate, an epitaxial layer and an upper metal electrode from bottom to top; the geometric size of the epitaxial layer is the same as that of the metal-graphene patch antenna.

[0009] More preferably, all microcavity units share a common lower metal electrode plate.

[0010] Preferably, the epitaxial layer includes a lower contact layer, a QWPs active region and an upper contact layer from bottom to top.

[0011] Preferably, the QWPs active region can adopt any active region structure in the prior art.

[0012] More preferably, the QWPs active region includes, but is not limited to, a semiconductor superlattice structure with alternating growth of GaAs / AlGaAs.

[0013] Preferably, a passivation layer is provided on the surface of the lower metal electrode plate and filled between the microcavity units; the material of the passivation layer includes but is not limited to Si 3 N 4 .

[0014] Preferably, the material of the upper electrode metal includes any one of non-alloyed Ti / Au or continuously grown Pd / Ge / Ti / Au, wherein Pd / Ge / Ti / Au is more conducive to forming a good ohmic contact between the metal and the GaAs materials doped in the upper and lower contact layers of the device; the material of the metal wire is the same as that of the upper metal electrode.

[0015] Preferably, a back metal layer is grown on the back surface of the substrate.

[0016] The present invention also provides a method for manufacturing a terahertz quantum well detector with a metal-graphene patch antenna microcavity array coupling structure, including the following steps:

[0017] (1) A GaAs buffer layer, an etching stop layer and an epitaxial layer are sequentially grown on a first substrate; the epitaxial layer includes an n-type doped lower contact layer, a QWPs active region, and an n-type doped upper contact layer from bottom to top; a first metal material layer is deposited on the upper surface of the epitaxial layer;

[0018] (2) A second substrate is provided, and a second metal material layer is deposited on the second substrate;

[0019] (3) The first metal material layer and the second metal material layer are bonded by a gold-gold bond to form a lower metal electrode plate;

[0020] (4) After thinning the first substrate, the first substrate and the etching stop layer are removed by wet etching to expose the n-type doped lower contact layer of the epitaxial layer as the upper contact layer of the microcavity unit, and the n-type doped upper contact layer of the epitaxial layer serves as the lower contact layer of the microcavity unit;

[0021] (5) A graphene layer is transferred onto the upper contact layer surface of the microcavity unit;

[0022] (6) A graphene pattern is etched out by reactive ion beam etching;

[0023] (7) A third metal material layer is deposited on the upper contact layer surface of the microcavity unit as the upper metal electrode;

[0024] (8) A patch antenna array pattern is lithographed on the upper metal electrode surface, and a photoresist is used as a mask to etch out the microcavity unit array structure;

[0025] (9) A passivation layer is grown in the area outside the microcavity unit;

[0026] (10) Deposit a metal wire to connect all microcavity units to the upper metal electrode;

[0027] (11) After thinning the second substrate, grow a fourth metal material layer on the back of the substrate as the back metal layer;

[0028] (12) Perform rapid thermal annealing at high temperature in a nitrogen atmosphere;

[0029] (13) Bond with gold wire, encapsulate, and complete the device fabrication.

[0030] Preferably, the material of the first substrate in the step (1) includes semi-insulating GaAs, the material of the second substrate in the step (2) includes N + -type GaAs, and the size of the second substrate is larger than that of the first substrate.

[0031] Preferably, the deposition method in the steps (1), (2) and (7) includes any one of electron beam evaporation method or magnetron sputtering method.

[0032] Preferably, the Au-Au bonding in the step (3) is carried out at 320 °C, 8 Mpa, and the pressing time is not less than 20 min.

[0033] Preferably, in order to suppress the dark current of the detector, after the device process is completed, high temperature annealing needs to be carried out in a nitrogen atmosphere at not less than 350 °C for not less than 30 s to form a good ohmic contact.

[0034] The present invention combines graphene with metal. By adjusting the bias voltage, without changing the structure, the surface structure can be switched between the BIC mode without radiation leakage and the quasi-BIC mode with limited radiation leakage, realizing amplitude modulation of the signal. The strong electromagnetic energy spatial aggregation of the quasi-BIC can concentrate the incident THz wave energy directly below the coupling structure, reduce the exposed area of the active region, achieve higher optical coupling efficiency and detection rate, and greatly improve the device performance.

[0035] Beneficial effects

[0036] (1) The subwavelength metasurface structure in the present invention can increase the effective absorption area of the photosensitive surface of the detector and improve the absorption efficiency of the device for incident THz light; the double-sided metal microcavity can enhance the resonance of the THz light field in the cavity and improve the responsivity of the device; the multipole effect of the quasi-BIC can change the electric field direction of the normally incident THz light in the active region to satisfy the transition selection rule, so that it can be absorbed by the active region of the device;

[0037] (2) By changing the microcavity structure size, the resonance position of the structure can be adjusted. The active region can change the operating frequency through voltage regulation. The combination of the two can achieve voltage-tunable broadband THz QWPs. The design of separating the independent active regions and connecting them to the structure wires can also achieve amplitude modulation of the absorption resonance peaks that are independent of each other in different columns.

[0038] (3) The present invention has a high degree of design freedom. The designer can design the geometric size of the microcavity according to the intrinsic frequency of the detector, so that the microcavity supports electromagnetic waves of a single or multiple specific oscillation frequencies, and independently modulates different resonance peaks. Description of the Drawings

[0039] Figure 1 It is a three-dimensional structure schematic diagram of the THz QWPs coupled by the metal-graphene patch antenna microcavity array of the present invention.

[0040] Figure 2 It is a three-dimensional structure schematic diagram of the QWPs active region of the microcavity unit of the present invention.

[0041] Figure 3 It is a three-dimensional structure schematic diagram of the metal-graphene patch antenna of the microcavity unit of the present invention.

[0042] Figure 4 It is a cross-sectional view taken along the A-A' direction of the structure unit of the THz QWPs coupled by the metal-graphene patch antenna microcavity array of the present invention.

[0043] Figure 5 It is a structure schematic diagram of the common mid-infrared and THz QWPs in the prior art.

[0044] Figure 6 It is a flowchart of the manufacturing method of the THz QWPs coupled by the metal-graphene patch antenna microcavity array of the present invention.

[0045] Reference Numerals: 1 - Substrate, 2 - Lower Metal Electrode Plate, 3 - Passivation Layer, 4 - Epitaxial Layer, 41 - Lower Contact Layer, 42 - QWPs Active Region, 43 - Upper Contact Layer, 5 - Upper Metal Electrode, 6 - Metal Wire, 110 - First Substrate, 111 - First Metal Material Layer, 112 - Etching Stop Layer, 210 - Second Substrate, 211 - Second Metal Material Layer, 311 - Third Metal Material Layer, 411 - Fourth Metal Material Layer. Detailed Embodiments

[0046] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0047] The illustrations provided in this embodiment only schematically illustrate the basic concept of the present invention. The illustrations only show the components related to the present invention, rather than being drawn according to the number, shape, and size of the components in actual implementation. The actual morphology, quantity, and ratio of each component during actual implementation can be arbitrarily changed, and the component layout pattern may also be more complex.

[0048] Embodiment

[0049] This embodiment provides a broadband terahertz quantum well coupled by a metal-graphene patch antenna microcavity array. The three-dimensional structure schematic diagram is as Figure 1 shown, and the cross-sectional view along the A-A' direction is as Figure 4 shown, including a substrate 1 and microcavity units ( Figure 1 C in) arranged periodically on the substrate 1; the microcavity units are split rings with different front and rear opening widths constructed of metal, connected by a single layer of graphene at the opening, forming a metal-graphene patch antenna with the upper metal electrode 5 on the upper surface of the microcavity unit, and metal wires 6 are introduced on both sides of the split ring to connect adjacent microcavity units; the microcavity unit includes a lower metal electrode plate 2, an epitaxial layer 4, and an upper metal electrode 5 from bottom to top; the epitaxial layer 4 includes a lower contact layer 41, a QWPs active region 42, and an upper contact layer 43 from bottom to top; the geometric dimensions of the QWPs active region 42 are the same as those of the upper metal electrode 5; a passivation layer 3 is provided on the surface of the lower metal electrode plate 2 and filled between the microcavity units; a back metal layer is grown on the back of the substrate 1.

[0050] Designed using a multi-physics field simulation software, as shown in 2 and Figure 3 shown, the geometric parameters of the patch antenna on the upper surface of the microcavity unit include the period P of the structure, the outer side length L1 and the inner side length L2 of the split ring, as well as the two openings d1, d2, and the width d0 of the metal wire between two adjacent microcavity units. After determining the intrinsic detection frequency of the THz QWPs material, the geometric dimensions of the patch antenna microcavity unit can be designed so that the microcavity supports an electromagnetic wave mode equal to the intrinsic detection frequency of the THz QWPs.

[0051] In this embodiment, in order to compare with the THz QWPs of the conventional 45° inclined plane polished substrate coupling structure as Figure 5 shown, the total lateral area of the QWPs active region in the array is equal to the photosensitive area of the THz QWPs of the 45° inclined plane polished substrate coupling structure.

[0052] In this embodiment, the fabrication process of the terahertz quantum well detector coupled with the metal-graphene patch antenna microcavity array is as Figure 6 shown, and includes the following steps:

[0053] (1) A GaAs buffer layer (not shown in the figure), an AlGaAs etching stop layer 112, and an epitaxial layer 4 are sequentially grown on a first substrate 110 made of semi-insulating GaAs material; the epitaxial layer 4 includes an n-type doped lower contact layer, a QWPs active region 42, and an n-type doped upper contact layer from bottom to top; a first metal material layer 111 is deposited on the upper surface of the epitaxial layer 4 by electron beam evaporation or magnetron sputtering;

[0054] (2) Provide a second substrate 210 made of N + -type GaAs material, whose size is slightly larger than that of the first substrate 110, and a second metal material layer 211 is deposited on the second substrate 210 by electron beam evaporation or magnetron sputtering;

[0055] (3) The first metal material layer 111 and the second metal material layer 211 are bonded by gold-gold bonding at 320 °C, 8 MPa for not less than 20 minutes to form a lower metal electrode plate 2;

[0056] (4) After thinning the first substrate 110 with a grinding and polishing machine, the remaining first substrate 110 and the etching stop layer 112 are removed by wet etching, and the n-type doped lower contact layer of the epitaxial layer 4 is exposed as the upper contact layer 43 of the microcavity unit, and the n-type doped upper contact layer of the epitaxial layer is used as the lower contact layer 41 of the microcavity unit;

[0057] (5) Transfer a layer of graphene on the upper contact layer 43 of the microcavity unit;

[0058] (6) Use reactive ion beam etching to etch out the graphene pattern;

[0059] (7) Deposit a third metal material layer 311 on the upper contact layer 43 of the microcavity unit by electron beam evaporation or magnetron sputtering as the upper metal electrode 5;

[0060] (8) Lithographically pattern the patch antenna array as shown on the upper metal electrode 5, and use photoresist as a mask to etch out the microcavity unit array structure; Figure 3 shown, and use photoresist as a mask to etch out the microcavity unit array structure;

[0061] (9) To prevent leakage current in the QWPs active region 42, a passivation layer 3 is grown in the area outside the microcavity unit, and the material can be selected as Si 3 N 4 ;

[0062] (10) To power each microcavity unit, it is necessary to deposit metal wires 6 to connect all microcavity units to the upper metal electrode 5;

[0063] (11) To paste more firmly with the heat sink and achieve good heat dissipation, the second substrate 210 is thinned and a fourth metal material layer 411 (gold) is grown on the back of the substrate as the back metal layer;

[0064] (12) Based on the materials of the upper metal electrode 5 and the lower metal electrode plate 2, appropriate temperature and time conditions are set, and rapid high-temperature annealing is carried out in a nitrogen atmosphere to form an ohmic contact between the upper metal electrode 5 and the lower metal electrode plate 2 without damaging the graphene structure;

[0065] (13) Gold wire bonding and encapsulation are performed to complete the device fabrication.

Claims

1. A terahertz quantum well detector coupled with a metal-graphene patch antenna microcavity array, characterized in that: The terahertz quantum well detector comprises a substrate (1) and microcavity units arranged in a periodic manner on the substrate (1); the microcavity unit is an open ring constructed of metal with front and rear openings of different widths, connected at the opening with a single layer of graphene to form a metal-graphene patch antenna with an upper metal electrode (5) on the upper surface of the microcavity unit, and metal wires (6) are introduced on both sides of the open ring to connect adjacent microcavity units.

2. The terahertz quantum well detector according to claim 1, characterized in that: The microcavity unit comprises, from bottom to top, a lower metal electrode plate (2), an epitaxial layer (4) and an upper metal electrode (5); the epitaxial layer (4) has the same geometric dimensions as the metal-graphene patch antenna.

3. The terahertz quantum well detector according to claim 2, characterized in that: The epitaxial layer (4) comprises, from bottom to top, a lower contact layer (41), a QWPs active region (42) and an upper contact layer (43).

4. The terahertz quantum well detector according to claim 3, characterized in that: The QWPs active region (42) comprises a semiconductor superlattice structure of GaAs / AlGaAs alternately grown.

5. The terahertz quantum well detector according to claim 2, characterized in that: A passivation layer (3) is provided on the surface of the lower metal electrode plate (2) and is filled between the microcavity units; the material of the passivation layer (3) includes Si3N4.

6. The terahertz quantum well detector according to claim 1, characterized in that: The material of the upper metal electrode (5) includes any one of non-alloyed Ti / Au or continuously grown Pd / Ge / Ti / Au; the material of the metal wire (6) is the same as that of the upper metal electrode (5).

7. The terahertz quantum well detector according to claim 1, characterized in that: A back metal layer is grown on the back side of the substrate (1).

8. A method for manufacturing a terahertz quantum well detector coupled with a metal-graphene patch antenna microcavity array, comprising the following steps: (1) A GaAs buffer layer, an etching stop layer (112) and an epitaxial layer (4) are sequentially grown on a first substrate (110); the epitaxial layer (4) comprises, from bottom to top, an n-type doped lower contact layer, a QWPs active region, and an n-type doped upper contact layer; and a first metal material layer (111) is deposited on the upper surface of the epitaxial layer (4); (2) providing a second substrate (210), and depositing a second metal material layer (211) on the second substrate (210); (3) performing gold-gold bonding on the first metal material layer (111) and the second metal material layer (211) to form a lower metal electrode plate (2); (4) after thinning the first substrate (110), wet etching is used to remove the first substrate (110) and the etching stop layer (112), exposing the n-type doped lower contact layer of the epitaxial layer (4) as the upper contact layer (43) of the microcavity unit, and the n-type doped upper contact layer of the epitaxial layer (4) as the lower contact layer (41) of the microcavity unit; (5) transferring a graphene layer onto the surface of the upper contact layer (43) of the microcavity unit; (6) etching a graphene pattern using a reactive ion beam; (7) depositing a third metal material layer (311) on the surface of the upper contact layer (43) of the microcavity unit as an upper metal electrode (5); (8) photolithography a patch antenna array pattern on the surface of the upper metal electrode (5), using photoresist as a mask to etch out a microcavity unit array structure; (9) growing a passivation layer (3) in a region outside the microcavity unit; (10) depositing metal wires (6) to connect all microcavity units to the upper metal electrode (5); (11) thinning the second substrate (210) and growing a fourth metal material layer (411) on the back side of the substrate as a back side metal layer; (12) high temperature rapid annealing in a nitrogen atmosphere; (13) Gold wire welding and packaging to complete device manufacturing.

9. The manufacturing method according to claim 8, characterized in that: In the step (1), the material of the first substrate (110) includes semi-insulating GaAs, and the material of the second substrate (210) in the step (2) includes N + Type GaAs, the second substrate (210) is larger than the first substrate (110).

10. The manufacturing method according to claim 8, characterized in that: The deposition method in step (1), step (2) and step (7) includes any one of electron beam evaporation method and magnetron sputtering method.

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