Nano-air channel photomixer integrated with surface plasmon nanocavity

Abstract

The present invention discloses a surface plasmon nanocavity integrated nano air channel optical mixer, belonging to the technical field of millimeter wave / terahertz devices and photodetectors. The device includes an insulating substrate, a lower electrode, a semiconductor absorption layer, and a nano insulating layer arranged thereon in sequence; an upper electrode is arranged above the nano insulating layer, the upper electrode extends downward from the right side to the insulating substrate, and a lateral isolation layer is arranged between the upper electrode and the lower electrode, the semiconductor absorption layer, and the nano insulating layer; a nano air channel is formed between the upper electrode and the semiconductor absorption layer; and a surface plasmon nanocavity is formed between the upper electrode and the lower electrode. The present invention locally compresses the incident light in an ultra-thin semiconductor absorption layer, so that it can achieve a large bandwidth while maintaining sufficient light absorption and high responsiveness; at the same time, the semiconductor absorption layer is sandwiched between electrodes with high thermal conductivity to improve heat dissipation, thereby achieving high responsiveness, large bandwidth and high output power performance at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of millimeter wave / terahertz devices and photoelectric detectors, and in particular relates to a surface plasmon nanocavity integrated nanometer air channel optical mixer. Background Art

[0002] Optical mixing technology can generate wide-range tunable continuous, coherent millimeter-wave and terahertz signals, and break through the limitations of traditional electronic frequency-multiplied millimeter-wave and terahertz sources in bandwidth, phase noise, etc., to achieve higher communication rates and radar resolution. Optical mixers are the core optoelectronic conversion devices in optical mixing technology. They can not only be used to generate millimeter-wave and terahertz signals, but can also be used as room-temperature heterodyne coherent detectors to down-convert and receive millimeter-wave and terahertz signals. They have become an indispensable core device at both the transmitting and receiving ends of optoelectronic fusion millimeter-wave and terahertz information systems.

[0003] At present, traditional semiconductor-based optical mixers such as photoconductive antennas and photodiodes are limited by the influence of lattice scattering, and the carrier transport speed is difficult to further improve, resulting in technical bottlenecks in bandwidth, responsiveness, energy conversion efficiency and output power. Nano-air channel optical mixers use the external photoelectric effect to realize field-assisted light emission of electrons in the cathode, and enter the nano-air channel that is smaller than the average scattering free path of electrons in the atmosphere for scattering-free ballistic transport. It naturally has more ideal single carrier ballistic transport characteristics than single-carrier photodiodes (UTC-PDs). For air channels of tens of nanometers, the transit time for electrons to reach the anode from the cathode surface is only tens of femtoseconds, and there is no scattering heat during the process, which has a higher breakdown voltage than semiconductors. Therefore, nano-air channel optical mixers have great potential in improving bandwidth, power and other performance.

[0004] However, for nano-air channel optical mixers that use semiconductor thin films as absorption layers, in addition to the transit time in the nano-air channel, there is also the transport time of carriers in the semiconductor thin film. For vertically incident devices, if the semiconductor absorption layer is too thick, the carrier transit time will increase and the bandwidth will be reduced; but if the semiconductor absorption layer is too thin, the light absorption will be insufficient, which will reduce the responsivity and energy conversion efficiency. Some traditional semiconductor detector studies use back-incident device structures, using the reflection of the upper electrode to achieve secondary absorption of the semiconductor layer or using the resonance cavity formed between the upper electrode and the substrate medium to enhance absorption and improve responsivity, but the reflection secondary absorption and the resonance cavity have weak constraints on the light field, and the thin semiconductor absorption layer for large bandwidth devices cannot fully absorb the incident light. The incident direction of light in waveguide-coupled devices is perpendicular to the carrier transport direction. Although this alleviates the constraints between bandwidth and responsivity to a certain extent, on the one hand, the light density in the waveguide is very high and is unevenly distributed in the semiconductor absorption layer with the propagation distance, which leads to the device easily reaching saturation at low incident light power, making it difficult to further increase the mixing output power; on the other hand, for devices with ultra-large bandwidths of hundreds of GHz, the thickness of the semiconductor absorption layer needs to be within one or two hundred nanometers, which is much smaller than the wavelength. At this time, the waveguide-coupled structure also has weak constraints on the light field, making it difficult to fully absorb the incident light, resulting in difficulty in further improving the responsivity and energy conversion efficiency. In addition, ordinary semiconductor substrates have low thermal conductivity and poor heat dissipation performance, and are prone to thermal breakdown at high incident light power, so high-power millimeter-wave terahertz output cannot be achieved. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a surface plasmon nanocavity integrated nano-air channel optical mixer, aiming to provide a technical solution that can locally compress the incident light within an ultra-thin semiconductor absorption layer of several nanometers to hundreds of nanometers, so that it can achieve a large bandwidth while maintaining sufficient light absorption and high responsiveness, and improve heat dissipation to increase the millimeter-wave terahertz output power.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] A surface plasmon nanocavity integrated nano-air channel optical mixer, characterized in that: the nano-air channel optical mixer comprises an insulating substrate, a lower electrode, a semiconductor absorption layer, a nano-insulating layer, an upper electrode, and a lateral isolation layer;

[0008] The lower electrode, the semiconductor absorption layer, and the nano-insulation layer are sequentially arranged on the insulating substrate, and a lateral isolation layer is arranged on the right side of the three;

[0009] The upper electrode is arranged on the upper surface of the nano insulating layer and the lateral isolation layer; the upper electrode is isolated from the semiconductor absorption layer and the lower electrode by the lateral isolation layer, and the lateral isolation layer also serves as a passivation layer of the semiconductor absorption layer and a support layer of the upper electrode.

[0010] A nanometer air channel is formed between the upper electrode and the semiconductor absorption layer;

[0011] A surface plasmon nanocavity is formed between the upper electrode and the lower electrode.

[0012] Furthermore, when the nano-air channel optical mixer is a vertical normal incidence device, the upper electrode is a light-transmitting structure with micro-nano through holes; the lower electrode is a flat film structure or a light-impermeable structure with micro-nano gratings;

[0013] When the nanometer air channel optical mixer is a vertical back-incident device, the upper electrode is a flat film structure or an opaque structure with a micro-nano grating; the lower electrode is a light-transmitting structure with a micro-nano through hole;

[0014] When the nano-air channel optical mixer is a transverse waveguide injection type device, the upper electrode is a flat film structure or a light-proof structure with a micro-nano grating; the lower electrode is a flat film structure or a light-proof structure with a micro-nano grating.

[0015] Furthermore, the nano air channel is an out-of-plane nano air channel formed between the semiconductor absorption layer and the upper electrode whose left end faces are aligned, or an in-plane nano air channel formed between the semiconductor absorption layer and the upper electrode after removing part or all of the nano insulating layer on the left side.

[0016] Furthermore, the material of the semiconductor absorption layer is a single crystal semiconductor, a polycrystalline semiconductor or an amorphous semiconductor.

[0017] Furthermore, the insulating substrate is a rigid substrate or a flexible substrate; the insulating substrate is made of insulating material, or is composed of a lower layer of conductive material and an upper layer of insulating material.

[0018] Furthermore, the insulating substrate is made of a material with a thermal conductivity greater than 0.5 W / cm·K.

[0019] Furthermore, the thickness of the nano insulating layer is between a single atomic layer and 1000 nm.

[0020] Furthermore, the thickness of the semiconductor absorption layer is between a single atomic layer and 1000 nm.

[0021] Furthermore, the lateral isolation layer is made of insulating material.

[0022] The advantages of the present invention are as follows:

[0023] 1. The surface plasmon nanocavity integrated nano-air channel optical mixer proposed in the present invention can locally compress incident light of micrometer wavelength into a semiconductor absorption layer hundreds of nanometers thick through the surface plasmon effect, so that it can achieve a large bandwidth while maintaining sufficient light absorption and high responsiveness.

[0024] 2. The material of the semiconductor absorption layer in the device of the present invention can be a variety of semiconductor materials including single crystal semiconductors, polycrystalline semiconductors, and amorphous semiconductors, and there is no need to perform complex PN junction doping on the semiconductor absorption layer, and the dependence on material growth equipment is low.

[0025] 3. The device structure proposed in the present invention sandwiches the semiconductor absorption layer between metal or metal-like electrodes with high thermal conductivity, which can achieve better heat dissipation than traditional semiconductor optical mixers / detectors, thereby withstanding greater incident light power and outputting higher millimeter-wave and terahertz powers.

[0026] 4. The surface plasmon nanocavity integrated nano-air channel optical mixer proposed in the present invention is universally applicable to devices with vertical normal incidence, back incidence, and waveguide-coupled lateral incidence. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of a single crystal InGaAs nano-air channel optical mixer integrated with a normal-incidence surface plasmon nanocavity proposed in Example 1. 11 is a metal aluminum substrate, 12 is a BN insulating layer, 13 is a TiAu thin film lower electrode, 14 is a single crystal n-type InGaAs thin film semiconductor absorption layer, 15 is a SiO2 nano-insulating layer, 16 is an in-plane nano-air channel, 17 is a BN isolation layer, and 18 is a metal Hf thin film upper electrode with a circular through-hole array.

[0028] Figure 2 This is a schematic diagram of the structure of a back-incident surface plasmon nanocavity integrated polycrystalline GaSb nano-air channel optical mixer proposed in Example 2. Among them, 21 is an aluminum nitride ceramic substrate, 22 is a TiN film lower electrode with a disordered square through-hole array, 23 is a polycrystalline p-type GaSb thin film semiconductor absorption layer, 24 is a Si3N4 thin film nano-insulating layer, 25 is an out-of-plane nano-air channel, 26 is a HfO2 thin film isolation layer, and 27 is an Au thin film upper electrode.

[0029] Figure 3This is a schematic diagram of the structure of a single crystal GeSn nano-air channel optical mixer integrated with a waveguide-injection type surface plasmon nanocavity proposed in Example 3. Among them, 31 is a metal copper substrate, 32 is an AlN insulating layer, 33 is a ZrN thin film lower electrode, 34 is a single crystal n-type GeSn thin film semiconductor absorption layer, 35 is an Al2O3 thin film nano-insulating layer, 36 is an in-plane nano-air channel, 37 is an AlN isolation layer, and 38 is a Pt thin film upper electrode.

[0030] Figure 4 This is a schematic diagram of the structure of an amorphous Ge nano-air channel optical mixer integrated with a waveguide-injection type surface plasmon nanocavity proposed in Example 4. 41 is a diamond substrate, 42 is an opaque CrAu thin film lower electrode with a grating, 43 is an amorphous p-type Ge thin film semiconductor absorption layer, 44 is an in-plane nano-air channel, 45 is a Si3N4 isolation layer, and 46 is a Ti thin film upper electrode. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0032] Example 1

[0033] A single crystal InGaAs nano-air channel optical mixer integrated with a normal-incidence surface plasmon nanocavity, such as Figure 1 As shown, the substrate in this embodiment is composed of a lower metal aluminum layer and an upper BN insulating layer; above the substrate are a TiAu thin film lower electrode, a peeled and transferred single crystal n-type InGaAs thin film semiconductor absorption layer, and a SiO2 thin film nano-insulating layer, and a lateral BN isolation layer is arranged on the right side of the three; a metal Hf thin film light-transmitting upper electrode with a circular through-hole array is arranged on the upper surface of the SiO2 thin film nano-insulating layer and the lateral BN isolation layer, and the Hf thin film is provided with a light-transmitting metal Hf thin film upper electrode having a circular through-hole array.

[0034] The electrode extends downward from the left side of the lateral isolation layer to the upper surface of the substrate; after selectively etching away part of the SiO2 thin film nano-insulation layer, an in-plane nano-air channel is formed between the InGaAs thin film semiconductor absorption layer and the metal Hf thin film upper electrode.

[0035] The working principle of the device is as follows: two laser beams of different wavelengths are combined and irradiated onto the transparent upper electrode with a circular through-hole array. Under the action of the surface plasmon anomalous transmission effect, the laser beam enters the surface plasmon nanocavity formed by the upper and lower electrodes. Then the light field is compressed in the InGaAs thin film semiconductor absorption layer for full absorption. The single crystal n-type InGaAs thin film semiconductor absorption layer generates photogenerated carriers after absorbing light. When a positive bias is applied to the lower electrode, the photogenerated electrons generated in the InGaAs thin film semiconductor absorption layer drift toward the lower electrode and are collected, while the photogenerated holes drift upward and form a two-dimensional hole gas at the interface of the InGaAs thin film semiconductor absorption layer close to the SiO2 thin film nano-insulating layer. Under the action of Coulomb force, the two-dimensional hole gas on the surface of the InGaAs thin film semiconductor absorption layer induces a high concentration of electrons on the lower surface of the upper electrode. Under the action of the electric field, the electrons overcome the surface potential barrier and are emitted into the nano-air channel and are collected by the InGaAs thin film semiconductor absorption layer to form a high-frequency photocurrent; the high-frequency photocurrent oscillates in the upper and lower electrodes to generate millimeter wave and terahertz signals, and the frequency of the signal is equal to the wavelength difference between the two lasers.

[0036] Example 2

[0037] A back-incident surface plasmon nanocavity integrated polycrystalline GaSb nano-air channel optical mixer, such as Figure 2 As shown, the substrate in this embodiment is aluminum nitride ceramic; above the substrate are a TiN thin film light-transmitting lower electrode with a disordered square through-hole array, an evaporated annealed polycrystalline p-type GaSb thin film semiconductor absorption layer, and a Si3N4 thin film nano-insulating layer, and a lateral HfO2 thin film isolation layer is arranged on the right side of the three; an Au thin film upper electrode is arranged on the upper surface of the Si3N4 thin film nano-insulating layer, and the Au thin film upper electrode extends downward from the left side of the lateral isolation layer to the upper surface of the substrate; an out-of-plane nano air channel is formed between the GaSb thin film semiconductor absorption layer and the Au thin film upper electrode, and outside the end face of the Si3N4 thin film nano-insulating layer.

[0038] The working principle of the device is as follows: after two laser beams of different wavelengths are combined, they are irradiated from the back to the transparent lower electrode with a disordered square through-hole array, and enter the surface plasmon nanocavity composed of the upper and lower electrodes under the action of the surface plasmon anomalous transmission effect; then the light field is compressed in the GaSb thin film semiconductor absorption layer for full absorption; the p-type InGaAs thin film semiconductor absorption layer generates photogenerated carriers after absorbing light, and when a negative bias is applied to the lower electrode, the photogenerated holes generated in the GaSb thin film semiconductor absorption layer drift toward the lower electrode and are collected, while the photogenerated electrons drift upward to form a two-dimensional electron gas at the interface of the GaSb thin film semiconductor absorption layer near the Si3N4 insulating layer. The electrons in the two-dimensional electron gas overcome the surface potential barrier under the action of the mutual Coulomb repulsion and the electric field between the upper and lower electrodes, and are emitted into the nano air channel and collected by the upper electrode to form a high-frequency photocurrent; the high-frequency photocurrent oscillates in the upper and lower electrodes to generate millimeter wave and terahertz signals, and the frequency of the signal is equal to the wavelength difference of the two lasers.

[0039] Example 3

[0040] Single crystal GeSn nano-air channel optical mixer integrated with waveguide-injection surface plasmon nanocavity, such as Figure 3 As shown, the substrate in this embodiment is composed of a lower layer of metallic copper and an upper layer of AlN insulating layer; above the substrate are a ZrN thin film lower electrode, a peeled and transferred single crystal n-type GeSn thin film semiconductor absorption layer, and an Al2O3 thin film nano-insulating layer, and a lateral AlN isolation layer is arranged on the right side of the three; a Pt thin film upper electrode is arranged on the upper surface of the Al2O3 thin film nano-insulating layer and the lateral AlN isolation layer, and the Pt thin film upper electrode extends downward from the left side of the lateral isolation layer to the upper surface of the substrate; after selectively etching away part of the Al2O3 thin film nano-insulating layer, an in-plane nano air channel is formed between the GeSn thin film semiconductor absorption layer and the Pt thin film upper electrode.

[0041] The working principle of the device is as follows: after two laser beams of different wavelengths are combined, they are laterally coupled from the waveguide to the GeSn thin film semiconductor absorption layer, and are compressed in the three-dimensional surface plasmon nanocavity formed by the upper and lower electrodes and fully absorbed in the GeSn thin film semiconductor absorption layer; the n-type GeSn thin film semiconductor absorption layer generates photogenerated carriers after absorbing light, and when a positive bias is applied to the lower electrode, the photogenerated electrons generated in the GeSn thin film semiconductor absorption layer drift toward the lower electrode and are collected, while the photogenerated holes drift upward to form a two-dimensional hole gas at the interface of the GeSn thin film semiconductor absorption layer near the Al2O3 insulating layer, and under the action of Coulomb force, the two-dimensional hole gas on the surface of the GeSn thin film semiconductor absorption layer induces the generation of high-concentration electrons on the lower surface of the upper electrode, and the electrons overcome the surface potential barrier under the action of the electric field and are emitted into the nano air channel and collected by the GeSn thin film semiconductor absorption layer to form a high-frequency photocurrent; the high-frequency photocurrent oscillates in the upper and lower electrodes to generate millimeter wave and terahertz signals, and the frequency of the signal is equal to the wavelength difference of the two lasers.

[0042] Example 4

[0043] A waveguide-injection type surface plasmon nanocavity integrated amorphous Ge nano-air channel optical mixer, such as Figure 4 As shown, the substrate in this embodiment is diamond; above the substrate are an opaque CrAu lower electrode with a micro-nano grating structure and an amorphous p-type Ge thin film semiconductor absorption layer grown by magnetron sputtering, and a lateral Si3N4 isolation layer is arranged on the right side of both; the upper end face of the lateral Si3N4 isolation layer exceeds the Ge thin film semiconductor absorption layer, and a surface Ti thin film upper electrode is arranged above the lateral AlN isolation layer, and the Pt thin film upper electrode extends downward from the left side of the lateral isolation layer to the upper surface of the substrate; an in-plane nano air channel is formed between the Ge thin film semiconductor absorption layer and the Ti thin film upper electrode.

[0044] The working principle of the device is as follows: after two laser beams of different wavelengths are combined, they are laterally coupled from the waveguide to the Ge thin film semiconductor absorption layer, and are compressed in the plasmon nanocavity formed by the upper and lower electrodes and fully absorbed in the Ge thin film semiconductor absorption layer; the p-type Ge thin film semiconductor absorption layer generates photogenerated carriers after absorbing light, and when a negative bias is applied to the lower electrode, the photogenerated holes generated in the Ge thin film semiconductor absorption layer drift toward the lower electrode and are collected, while the photogenerated electrons drift upward to form a two-dimensional electron gas at the interface of the Ge thin film semiconductor absorption layer close to the air. The electrons in the two-dimensional electron gas overcome the surface potential barrier under the action of the mutual Coulomb repulsion and the electric field between the upper and lower electrodes, and are emitted into the nano air channel and collected by the upper electrode to form a high-frequency photocurrent; the high-frequency photocurrent oscillates in the upper and lower electrodes to generate millimeter wave and terahertz signals, and the frequency of the signal is equal to the wavelength difference between the two lasers.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A surface plasmon nanocavity integrated nano-air channel optical mixer, characterized in that: The nanometer air channel optical mixer comprises an insulating substrate, a lower electrode, a semiconductor absorption layer, a nanometer insulating layer, an upper electrode, and a lateral isolation layer; The lower electrode, the semiconductor absorption layer, and the nano-insulation layer are sequentially arranged on the insulating substrate, and a lateral isolation layer is arranged on the right side of the three; The upper electrode is arranged on the upper surface of the nano insulating layer and the lateral isolation layer; the upper electrode is isolated from the semiconductor absorption layer and the lower electrode by the lateral isolation layer, and the lateral isolation layer also serves as a passivation layer of the semiconductor absorption layer and a support layer of the upper electrode; A nanometer air channel is formed between the upper electrode and the semiconductor absorption layer; A surface plasmon nanocavity is formed between the upper electrode and the lower electrode.

2. The surface plasmon nanocavity integrated nano-air channel optical mixer according to claim 1, characterized in that: When the nanometer air channel optical mixer is a vertical normal incidence type device, the upper electrode is a light-transmitting structure with micro-nano through holes; the lower electrode is a flat film structure or a light-impermeable structure with micro-nano gratings; When the nanometer air channel optical mixer is a vertical back-incident device, the upper electrode is a flat film structure or an opaque structure with a micro-nano grating; the lower electrode is a light-transmitting structure with a micro-nano through hole; When the nano-air channel optical mixer is a transverse waveguide injection type device, the upper electrode is a flat film structure or a light-proof structure with a micro-nano grating; the lower electrode is a flat film structure or a light-proof structure with a micro-nano grating.

3. The surface plasmon nanocavity integrated nano-air channel optical mixer according to claim 2, characterized in that: The nano air channel is an out-of-plane nano air channel formed between the semiconductor absorption layer and the upper electrode whose left end faces are aligned, or an in-plane nano air channel formed between the semiconductor absorption layer and the upper electrode after removing part or all of the nano insulating layer on the left side.

4. A surface plasmon nanocavity integrated nano-air channel optical mixer as claimed in claim 2 or 3, characterized in that: The material of the semiconductor absorption layer is a single crystal semiconductor, a polycrystalline semiconductor or an amorphous semiconductor.

5. A surface plasmon nanocavity integrated nano-air channel optical mixer as claimed in claim 2 or 3, characterized in that: The insulating substrate is a rigid substrate or a flexible substrate; the insulating substrate is made of insulating material, or is composed of a lower layer of conductive material and an upper layer of insulating material.

6. A surface plasmon nanocavity integrated nano-air channel optical mixer as claimed in claim 2 or 3, characterized in that: The transverse isolation layer is made of insulating material.

7. The surface plasmon nanocavity integrated nano-air channel optical mixer according to claim 5, characterized in that: The insulating substrate is made of a material with a thermal conductivity greater than 0.5 W / cm·K.

8. The surface plasmon nanocavity integrated nano-air channel optical mixer according to claim 3, characterized in that: The thickness of the nano insulating layer is between a single atomic layer and 1000 nm.

9. The surface plasmon nanocavity integrated nano-air channel optical mixer according to claim 4, characterized in that: The thickness of the semiconductor absorption layer is between a single atomic layer and 1000 nm.

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