A broadband antenna array coupler applicable to broadband quantum well detectors

Abstract

The present invention relates to a broadband antenna array coupler applicable to a broadband quantum well detector, which includes an upper electrode layer, a GaAs active region, and a lower electrode layer from top to bottom; several microcavity array units are distributed in the GaAs active region; the top layer of the microcavity array unit is an upper metal electrode (5), and the upper metal electrodes (5) are connected to each other by microstrip lines to form an upper electrode layer; the upper metal electrode (5) includes 4 independent microcavities with different sizes. The THz QWP optical coupling structure realized by the present invention using a two-dimensional micro-nano structure and the SPPs mechanism enables the THz QWP to achieve both voltage tunability and arrayed broadband detection, and has better market application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor optoelectronic devices, and particularly relates to a broadband antenna array coupler suitable for a broadband quantum well detector. Background Art

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

[0003] The terahertz quantum well photodetector (THz QWPs) based on intersubband transitions is a natural extension of the infrared quantum well photodetector (QWIP) in the THz band. It uses the intersubband transition absorption in a semiconductor quantum well superlattice (usually n-type doped GaAs / AlGaAs) to generate photocurrent, has high detection sensitivity and fast response ability, and has advantages such as a wide linear response range, simple design, mature material growth and device fabrication processes, and can be used to fabricate large-scale imaging arrays. It is an ideal device for space heterodyne detection, high-speed communication, and large-scale focal plane imaging. As Figure 1 shown, the commonly used THz QWPs 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 sequentially arranged on the upper surface of the GaAs substrate 1 from bottom to top, lower electrodes 11 arranged on the upper surface of the GaAs substrate 1 and 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. Among them, the active region 4 is composed of GaAs / Al x Ga 1-xIt is composed of a multi - quantum - well periodic structure. The bound electrons in the quantum well absorb THz photons and then transition to the continuous state. Under an applied bias voltage, a photocurrent is formed, and the detection of THz waves is completed by measuring and analyzing the change in the photocurrent. The operating 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 - tunable broadband THz QWP has been realized. In 2018, H.X. Wang et al. achieved a 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. achieved a voltage - tunable broadband QWP in the range of 2.5 - 4.1 THz.

[0004] It can be seen that the low photon absorption efficiency is the key factor restricting the performance of THz QWPs, and the improvement of the optical coupling method is a way to obtain better performance of THz QWPs. Currently, the two common coupling methods for THz QWPs are: 45° bevel - polished substrate coupling and metal scattering grating coupling. Among them, the 45° bevel - polished substrate coupling mechanism cannot achieve normal incidence of light (as Figure 1 shown, the GaAs substrate 1 needs to be polished at a 45° bevel, and the incident light needs to enter from this 45° bevel), and it is not conducive to device integration. Although grating coupling can achieve normal incidence coupling of light, there is not much improvement in device performance. In 2014, the Todorov group at the University of Paris VII developed a mid - infrared quantum - well detector (Quantum - Well Infrared Fhotodetectors, QWIP) with a working wavelength of 9μm in a micro - cavity antenna array. Compared with the previous QWIP, its background - limited operating temperature increased by 10K. In 2015, Palaferri et al. developed a patch - antenna micro - cavity array QWP with a detection peak frequency of 5 THz. Compared with the traditional 45° polished mesa structure, its responsivity increased several times.

[0005] With the development of integrated photonics, micro-nano structure devices with sub-wavelength characteristic dimensions have emerged in large numbers, and the same is true in the THz band. It has been found that surface plasmon polaritons (SPPs) exist at the interface between various negative dielectric constant media and positive dielectric constant media, such as the most common metal-air interface. In 2006, Chen et al. first realized the amplitude modulation of electromagnetic waves in the THz band using artificial micro-nano structures and doped semiconductors. In 2011, Professor Capasso of Harvard University and his team proposed the generalized Snell's law. They distributed the self-designed V-shaped structure on the plane in a phase-gradual manner to achieve functions such as extraordinary refraction, reflection, and focusing of incident electromagnetic waves. In 2015, Lee et al. used a nano-slit antenna array in the THz band to achieve high-sensitivity identification of low-concentration carbohydrate molecules.

[0006] The successful development of the THz QWP array and the continuous improvement of its performance are of great significance for the research and application of developing high-performance THz chip-level detection arrays and THz high-resolution real-time imaging technology. In recent years, voltage-tunable broadband QWP active regions and microcavity-coupled QWPs have been developed, which is one of the important progress in THz QWP research. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a broadband antenna array coupler suitable for a broadband quantum well detector, which overcomes the problem that the current array-type quantum cascade detector, although realizing array detection, can only work in a single-mode state and cannot achieve broadband detection.

[0008] The present invention provides a broadband antenna array coupler suitable for a broadband quantum well detector, which includes an upper electrode layer, a GaAs active region, and a lower electrode layer from top to bottom; several microcavity array units are distributed in the GaAs active region; the top layer of the microcavity array unit is an upper metal electrode, and every two of the upper metal electrodes in each row are connected by a microstrip line to form an upper electrode layer; the upper metal electrode includes 4 independent microcavities with different sizes. The microcavities are squares with the same outer perimeter, and then two mutually perpendicular "I"-shaped defects are respectively introduced into the upper electrode; the main difference between the four microcavities lies in the different geometric sizes of the "I"-shaped defects.

[0009] The microcavity array unit sequentially includes a substrate, a lower metal electrode plate, an epitaxial layer, and an upper metal electrode from bottom to top.

[0010] The epitaxial layer sequentially includes an upper contact layer, an active region, and a lower contact layer from top to bottom, and the geometric size of the epitaxial layer is the same as that of the upper metal electrode.

[0011] The active region includes a semiconductor superlattice structure with alternating growth of GaAs and AlGaAs.

[0012] The lower metal electrode plate and the upper metal electrode are made of a metal capable of forming an ohmic contact with the semiconductor.

[0013] The surface of the lower metal electrode plate is also provided with a passivation layer; the passivation layer fills around the epitaxial layer and has the same thickness as the epitaxial layer.

[0014] The material of the passivation layer is benzocyclobutene BCB, polyimide, SiO2 or Si3N4.

[0015] A back gold layer is also provided on the back of the substrate.

[0016] The lower electrode layer is a metal plate.

[0017] Due to the natural compatibility between the microcavity structure and two-dimensional micro-nano structure devices, for example, the sub-wavelength characteristics of two-dimensional micro-nano structure devices make their device structures compact. Then, the coupling structure based on two-dimensional micro-nano structures can achieve a wider detection bandwidth, more array units, and a stronger local field strength on a smaller area. On the one hand, it makes the array device more compact and has a higher integration degree. On the other hand, due to the reduction of the active region area, at the same temperature, its dark current naturally decreases, indirectly improving the detection sensitivity of the THz QWP.

[0018] Beneficial effects

[0019] The THz QWP optical coupling structure realized by the present invention using two-dimensional micro-nano structures and the SPPs mechanism enables the THz QWP to achieve both voltage tunability and arrayed broadband detection; the arrayed QWP can achieve a larger detection area on the premise of keeping the effective area of the active region unchanged, and the voltage-tunable active region can also achieve detection at any frequency point within the tunable frequency range. Therefore, it simultaneously realizes the detection of terahertz signals with a wide spectrum and a large area, and has better market application prospects. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of common mid-infrared and THz QWPs in the prior art.

[0021] Figure 2 It is a schematic structural diagram of the broadband antenna array coupler provided by the embodiment.

[0022] Figure 3 It is a specific dimension structure diagram of the upper electrode of a group of microcavity array units in the embodiment.

[0023] Figure 4 It is a longitudinal sectional view of the microcavity array unit provided by the embodiment.

[0024] Figure 5 The reflection coefficient of the broadband quantum well detector is calculated when the active region of the broadband quantum well detector provided for the embodiment is used as a bulk material.

[0025] Figure 6 Schematic diagram of preparation step S1 of the broadband antenna array coupler provided for the embodiment.

[0026] Figure 7 Schematic diagram of preparation step S2 of the broadband antenna array coupler provided for the embodiment.

[0027] Figure 8 Schematic diagram of preparation step S3 of the broadband antenna array coupler provided for the embodiment.

[0028] Figure 9 Schematic diagram of preparation step S4 of the broadband antenna array coupler provided for the embodiment.

[0029] Description of component labels:

[0030] 1 Substrate

[0031] 2 Lower metal electrode plate

[0032] 3 Passivation layer

[0033] 4 Active region

[0034] 5 Upper metal electrode

[0035] 6 Microstrip line

[0036] 7 Upper contact layer

[0037] 8 Lower contact layer

[0038] 9 Back gold layer

[0039] 10 Epitaxial layer

[0040] 11 Lower electrode

[0041] 12 Upper electrode Detailed implementation manners

[0042] 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.

[0043] Embodiment 1

[0044] This embodiment is illustrated by taking a THz QWP with a broadband antenna array coupler having a peak detection frequency of 4 - 6 THz as an example. The overall structure is as Figure 2 shown. It is divided into three layers from top to bottom. The top layer is the upper electrode layer, the middle is the GaAs active region, and the bottom layer is the lower electrode layer composed of a single piece of metal. The side lengths of both the upper electrode layer and the GaAs active region are a = 22 μm, and then they form a square array with a spacing of d = 5 μm. The GaAs active region is distributed with several microcavity array units; the top layer of the microcavity array unit is the upper metal electrode 5, and every two of the upper metal electrodes 5 in each row are connected by a microstrip line with a width of 2 μm to form the upper electrode layer; the upper metal electrode 5 includes 4 independent microcavities with different sizes. The microcavities are squares with the same outer perimeter, and then two mutually perpendicular "I"-shaped defects are introduced into the upper electrode respectively, as Figure 2 shown by ABCD in Figure 3 The 4 independent microcavities only have differences in the micro-nano structures in the upper electrode layer, as

[0045]

[0046]

[0047] The longitudinal sectional view of the microcavity array unit is as Figure 4 shown. Each microcavity unit includes the upper metal electrode 5, and an epitaxial layer 10 of a quantum well detector disposed on the lower surface of the upper metal electrode 5. It also includes a shared lower metal electrode plate 2 on which the epitaxial layer 10 of the quantum well detector is disposed, and the lower metal electrode plate 2 is disposed on the upper surface of 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 sequence from top to bottom, and the geometric dimensions of the epitaxial layer 10 are the same as those of the upper metal electrode 5. Among them, the active region 4 includes a semiconductor superlattice structure formed by alternating growth of GaAs and AlGaAs. The upper metal electrode 5 in the microcavity unit is a sub-wavelength patch antenna. The upper metal electrode 5 and the lower metal electrode plate 2 are made of metals that can form ohmic contacts with the semiconductor, and the metal material can be selected according to the conductivity polarity of the semiconductor material. After the device is fabricated, high-temperature rapid annealing is required to form good ohmic contact electrodes.

[0048] As Figure 4As shown, a passivation layer 3 is further provided on the surface of the lower metal electrode plate 2 of the microcavity unit to prevent leakage current in the active region 4. The thickness of the passivation layer 3 is equal to that of the epitaxial layer 10, and its material can be BCB, SiO2 or Si3N4. A back gold layer 9 is further provided on the back surface of the substrate 1 to enable the coupling structure to be more firmly adhered to the heat sink material 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.

[0049] Figure 5 For the active region being GaAs bulk material, the reflection coefficient of this broadband quantum well detector is calculated, and it can be seen that there is obvious absorption of THz waves in the frequency range of 4 - 6 THz.

[0050] This embodiment also provides a preparation method for a broadband antenna array coupler, including the following steps:

[0051] S1: Provide a sample material layer, which sequentially includes a first substrate and an epitaxial layer from bottom to top;

[0052] As Figure 6 shown, provide a first substrate 110 made of semi-insulating GaAs, and sequentially grow a GaAs buffer layer (not shown in the figure), an etching stop layer 111 and the epitaxial layer 10 of the quantum well detector on the upper surface of the first substrate 110. Among them, 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.

[0053] S2: Provide a second substrate, form a first metal material layer on the surface of the epitaxial layer of the sample material layer, and form a second metal material layer on the surface of the second substrate;

[0054] As Figure 7 shown, provide a second substrate 210 made of N+-type GaAs as the substrate 1 in the coupling structure, and the planar geometric size of the second substrate 210 is larger than that of the first substrate 110.

[0055] Then, referring to Figure 6 and Figure 7 shown, a first metal material layer 112 and a second metal material layer 211 are respectively formed on the upper surface of the epitaxial layer 10 in step S1 and the second substrate 210 by electron beam evaporation (or magnetron sputtering). As an example, both 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.

[0056] S3: Perform tablet bonding on the first metal material layer and the second metal material layer to form a lower metal electrode plate;

[0057] As Figure 8 shown, at a temperature of 320 °C and a pressure of 8 MPa, perform tablet bonding on the first metal material layer 112 and the second metal material layer 211 for no less than 20 minutes to form the lower metal electrode plate in the coupling structure.

[0058] S4: Remove the first substrate to expose the epitaxial layer;

[0059] As Figure 9 shown, after thinning the first substrate 110 with a grinding and polishing machine, use a wet etching solution to etch away the remaining first substrate 110 and the etching stop layer 111 to expose the N-type doped lower contact layer in the epitaxial layer 10 in step S1 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.

[0060] S5: Etch the epitaxial layer to form multiple microcavity units in the coupling structure, and the microcavity units are the microcavity units described in Embodiment 1;

[0061] Next, etch a square active region array on the epitaxial layer 10, using a photoresist as a mask, to etch and form multiple square active region microcavity units in the coupling structure.

[0062] S6: Fill and form a passivation layer between the multiple microcavity units and in the grooves of the microcavity units, and deposit and form an upper electrode and microcavity connection lines on the surface of the passivation layer to connect the multiple microcavity units to an external power supply.

[0063] Refer to Figure 4 shown, fill and form a passivation layer 3 between the 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.

[0064] Next, deposit and form an upper electrode 5 and microcavity connection lines 6 on the upper surface of the passivation layer 3 and the active region to connect the multiple microcavity units to an external power supply. As an example, the material of the microcavity connection lines 6 is selected from materials that can conduct electricity, for example, it can be the same as the material of the upper metal electrode 5, such as made of non-alloyed Ti and Au or made of continuously grown Pd, Ge, Ti and Au.

[0065] Next, the second substrate 210 is thinned, and a back gold layer 9 is formed on a side thereof away from the lower metal electrode plate 2, so that the coupling structure can be more firmly adhered to the heat sink and has better heat dissipation. As an example, the material of the back gold layer 9 can be made of non-alloyed Ti and Au or continuously grown Pd, Ge, Ti, and Au.

[0066] Next, high-temperature rapid annealing is performed at a temperature not lower than 350 °C for not less than 30 seconds, so that a good ohmic contact is formed between the upper metal electrode 5 and the lower metal electrode plate 2 in the coupling structure, effectively suppressing the dark current of the quantum well detector.

[0067] Finally, the device is cleaved, wire-bonded, and packaged, thus completing the fabrication of the coupling structure.

[0068] The above is only an example. Any change in geometric parameters that causes changes in the working frequency band, dispersion curve, and other results falls within the protection scope of this patent.

Claims

1. A broadband antenna array coupler applicable to a broadband quantum well detector, which includes an upper electrode layer, a GaAs active region, and a lower electrode layer from top to bottom; 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 every two of the upper metal electrodes (5) in each row are connected by a microstrip line to form an upper electrode layer; the microcavity array unit includes 4 independent microcavities with different sizes, the microcavities are squares with the same outer side length, and then two mutually perpendicular "I"-shaped defects are respectively introduced into the upper metal electrode (5); the microcavity array unit successively includes a substrate (1), a lower metal electrode plate (2), an epitaxial layer (10) and an upper metal electrode (5) from bottom to top, and the outer geometric dimensions of the epitaxial layer (10) are the same as the outer geometric dimensions of the upper metal electrode (5).

2. The broadband antenna array coupler according to claim 1, wherein: The epitaxial layer (10) successively includes an upper contact layer (7), an active region (4) and a lower contact layer (8) from top to bottom.

3. The broadband antenna array coupler according to claim 2, wherein: The active region (4) includes a semiconductor superlattice structure formed by alternating growth of GaAs and AlGaAs.

4. The broadband antenna array coupler according to claim 1, wherein: The lower metal electrode plate (2) and the upper metal electrode (5) are made of a metal capable of forming an ohmic contact with the semiconductor.

5. The broadband antenna array coupler according to claim 1, wherein: A passivation layer (3) is further provided on the surface of the lower metal electrode plate (2); the passivation layer (3) fills around the epitaxial layer (10), and the thickness is the same as the thickness of the epitaxial layer (10).

6. The broadband antenna array coupler according to claim 5, wherein: The material of the passivation layer (3) is benzocyclobutene BCB, polyimide, SiO2 or Si3N4.

7. The broadband antenna array coupler according to claim 1, wherein: A back gold layer (9) is further provided on the back of the substrate (1).

8. The broadband antenna array coupler according to claim 1, wherein: The lower electrode layer is a metal plate.

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