Vertical nanometer air channel photoelectric device with built-in electric field for regulating and controlling photocathode and preparation method of vertical nanometer air channel photoelectric device

Abstract

The invention discloses a vertical nanometer air channel photoelectric device with a built-in electric field regulation and control photocathode and a preparation method thereof, and belongs to the technical field of photoelectric devices and high-speed photoelectric conversion. The device comprises a substrate, a lower electrode located on the substrate, an insulating isolation layer, a photocathode layer located on the lower electrode, and an upper electrode located above the photocathode layer; the nano air channel is positioned between the photocathode layer and the upper electrode; the preparation method comprises the steps of forming the lower electrode; forming a photocathode layer and constructing a built-in electric field; forming an insulating isolation layer; forming a spacer / sacrificial structure and preparing an upper electrode; and removing the sacrificial structure to form a nano air channel. The photoelectric device provided by the invention is suitable for high-speed photoelectric detection and millimeter wave / terahertz light mixing and coherent receiving.

Description

Technical Field

[0001] This application belongs to the field of optoelectronic devices and high-speed photoelectric conversion technology, and particularly relates to a vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode and its fabrication method. Background Technology

[0002] Nanoscale air-channel optoelectronic devices typically employ a vertical structure of "photocathode—nanoscale air channel (air / vacuum gap)—upper electrode (anode)." During operation, incident light generates photogenerated carriers in the photocathode. Electrons, aided by an applied bias voltage, are emitted from the cathode surface into the nanoscale gap and transported to the upper electrode under the influence of the gap's electric field, forming a photocurrent. Since the gap medium is air or vacuum, there is no solid lattice or related phonon scattering mechanisms within the gap; the movement of electrons within the nanoscale gap is primarily controlled by electric field acceleration. When the gap thickness is on the nanometer scale, the electron flight distance is short, the collision probability is reduced, and the gap-side transport can be approximated as a drift or even ballistic transit process, resulting in a shorter gap-side transit time. Therefore, this type of device has the potential to achieve high-speed photoelectric responses and for use in optical mixing, millimeter-wave / terahertz signal generation and reception.

[0003] However, in existing structures, the main voltage drop of the applied voltage is often concentrated in the nano-air channel and the region near the cathode surface, resulting in insufficient electric field within the photocathode. The transport of photogenerated carriers from the generation site to the emitting surface is easily dominated by diffusion or weak field drift, and the bulk transport time may become a bottleneck in the device bandwidth, making the output more sensitive to bias voltage changes. Common improvement paths to address this problem mainly include: electric field enhancement (increasing the applied bias voltage and reducing the gap to enhance the electric field near the surface), geometric shortening (thinning the photocathode layer to shorten the bulk transport distance), and surface engineering (surface treatment, NEA activation, etc. to improve emission conditions). Each of these methods has limitations: electric field enhancement still struggles to establish a sufficient driving electric field within the photocathode, and the bulk transport bottleneck may not be eliminated; geometric shortening may reduce light absorption and carrier generation and introduce process consistency issues; surface engineering mainly improves the surface emission stage and is sensitive to process / environment, making it difficult to solve the problem of insufficient directional transport within the bulk. Summary of the Invention

[0004] The purpose of this application is to overcome the defects of the prior art by providing a vertical nano-air channel optoelectronic device with built-in electric field-controlled photocathode and its fabrication method. While maintaining the short transit advantage of nano-air channels, it can provide a stable directional transport driving force inside the photocathode to reduce the bandwidth limitation of the bulk transport time and reduce the bias voltage dependence.

[0005] The objective of this application is achieved through the following technical solution: A vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode, comprising a substrate, the device further comprising: An electrode, comprising an upper electrode and a lower electrode, wherein the upper electrode and the lower electrode are disposed above the substrate; A photocathode layer is disposed above the lower electrode and below the upper electrode. An internal electric field is provided along the thickness direction to drive photogenerated carriers to be directionally transported to the emitting surface within the photocathode layer. Electrons are emitted from the emitting surface into the nano air channel and transported to the upper electrode under the assistance of an external bias voltage to form a photocurrent. An insulating isolation layer is disposed on both sides or the outer periphery of the photocathode layer to support the upper electrode; A nano-air channel is disposed between the photocathode layer and the upper electrode.

[0006] Furthermore, the built-in electric field is achieved by gradient doping formed by ion implantation and / or gradient doping formed by in-situ doping growth.

[0007] Furthermore, the built-in electric field is achieved by a band gradient formed by a gradual change in material composition along the thickness direction.

[0008] Furthermore, the built-in electric field is formed by a heterojunction or a space charge region.

[0009] Furthermore, the thickness of the nano-air channel does not exceed 1000 nm.

[0010] On the other hand, the present invention also provides a method for fabricating a vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode, the method being used to fabricate any of the aforementioned optoelectronic devices, the method comprising: The lower electrode is formed and patterned on the substrate; A photocathode layer is formed on the lower electrode, and a built-in electric field is prepared; An insulating layer was fabricated to serve as a structure that isolates and supports the upper and lower electrodes, while simultaneously defining a nano-air channel region. Prepare spacer or sacrificial structures to define nano-air channels and form an upper electrode on top of them; Remove the sacrificial structure or release the spacer structure to form the nano-air channel, thereby forming a nano-air channel between the photocathode layer and the upper electrode.

[0011] Furthermore, the sacrificial structure includes an inorganic sacrificial layer and / or an organic sacrificial layer, and the removal method includes one or more of wet etching, dry etching, thermal decomposition, or solvent stripping.

[0012] Furthermore, the insulating layer is a ring-shaped, columnar, or stepped support structure, formed through deposition and patterning.

[0013] Furthermore, the method also includes: forming an upper electrode by sputtering, evaporation, electroplating or transfer for connecting a radio frequency lead-out structure or an antenna structure.

[0014] Furthermore, the preparation of the built-in electric field includes: A built-in electric field can be obtained by forming a doping gradient through ion implantation and annealing activation or in-situ doping growth, or by controlling the material composition along the thickness direction through epitaxy / deposition to obtain a built-in electric field with a band gradient, or by forming a heterojunction in the photocathode layer to obtain a built-in electric field in the space charge region.

[0015] The beneficial effects of this application are as follows: (1) Improve speed / bandwidth: The built-in electric field accelerates the internal transport of the photocathode and reduces the bandwidth limitation of the transit time on the photocathode side; (2) Reduce bias dependence: Even when the applied voltage is mainly concentrated in the air channel, it can still ensure directional transport inside the photocathode and reduce the strong dependence of photocurrent on the magnitude of bias. (3) Scalable and easy to integrate: The material system and electrode materials have a wide range of choices and can be integrated with millimeter wave / terahertz antennas and radio frequency lead-out structures.

[0016] (4) Improved high light intensity / high current working capability: The built-in electric field can accelerate the transport of charge carriers in the photocathode, shorten the residence time of charge carriers, and reduce the probability of uneven spatial distribution of charge carriers and charge accumulation inside the photocathode. Thus, under high light intensity or high current conditions, it is beneficial to reduce the limitation of space charge effect on the emission and collection process, and increase the upper limit of saturated photocurrent and output power. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a vertical nano-air channel optoelectronic device structure with a built-in electric field-controlled photocathode according to the present invention. Figure 2 This is a schematic diagram illustrating the implementation of the built-in electric field-controlled photocathode in this invention; Figure 3 This is a schematic diagram illustrating the working principle of the vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode in this invention.

[0018] Figure reference numerals: 11-upper electrode, 12-nanometer air channel, 13-built-in electric field-controlled photocathode, 14-lower electrode, 15-substrate, 16-insulating isolation layer. Detailed Implementation

[0019] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.

[0020] Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] In existing structures, the main voltage drop of the applied voltage is often concentrated in the area near the nano air channel and the cathode surface, resulting in insufficient electric field in the photocathode. The process of transporting photogenerated carriers from the generation location to the emitting surface is easily dominated by diffusion or weak field drift. The bulk transport time may become the device bandwidth bottleneck and make the output more sensitive to changes in bias voltage.

[0022] To address the aforementioned technical problems, the present application presents various embodiments of a vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode and its fabrication method.

[0023] This embodiment provides a vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode, referring to... Figure 1 ,like Figure 1 The diagram shows a schematic of a vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode. The device includes a substrate 15, a lower electrode 14, an insulating layer 16, a photocathode layer 13, an upper electrode 11, and a nano-air channel 12 located between the semiconductor photocathode layer and the upper electrode. The insulating layer 16 is disposed in the lateral or circumferential region between the upper and lower electrodes to achieve electrical isolation between the upper and lower electrodes and provide structural support. The thickness of the nano-air channel 12 is greater than 0 and does not exceed 1000 nm. The lower electrode 14 forms an electrical connection with the photocathode layer 13 and provides external leads. It can be a metal electrode layer or a composite electrode structure including a highly doped semiconductor contact layer (ohmic contact layer) and a metal conduction / lead-out layer; the metal conduction / lead-out layer constitutes the external electrical connection portion of the lower electrode.

[0024] The photocathode layer 13 has a built-in electric field along its thickness direction. The built-in electric field is used to drive photogenerated carriers to be transported directionally to the emitting surface within the photocathode layer. This allows electrons to be emitted from the emitting surface into the nano-air channel and transported to the upward electrode under the assistance of an external bias voltage, forming a photocurrent.

[0025] Built-in electric fields can be achieved in at least one of the following ways: (1) Ion implantation or in-situ doping growth to form a doping gradient; (2) The material composition gradually changes along the thickness direction to form an energy band gradient; (3) A strong built-in electric field is formed in the heterojunction / space charge region.

[0026] Reference Figure 2 ,like Figure 2 The diagram shows the working principle of a vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode.

[0027] The photocathode layer 13 is made of materials including but not limited to Si, Ge, and Ge x Si 1-x InAl x As 1-x InGa x As 1-x AlGa x As 1-x One or more of GaAs, InGaAsP; the substrate is an insulating, semi-insulating, or a combination of insulating and semi-insulating materials; the upper electrode and / or lower electrode is a highly doped semiconductor, metal, alloy, half-metal, highly conductive two-dimensional material, or highly conductive transparent oxide material.

[0028] In the structure of this optoelectronic device, an external positive bias voltage forms a strong electric field in the nano-air channel, which is used to assist electrons to be emitted from the emission surface and accelerate through the air channel. At the same time, the built-in electric field pre-constructed inside the photocathode layer provides a stable drift driving force in the cathode body, so that the photogenerated carriers in the cathode are changed from diffusion-dominated to drift-dominated, shortening the transport time from the photogenerated position to the emission surface.

[0029] Therefore, even if the applied voltage is mainly concentrated near the air channel and cathode surface, resulting in a decrease in the internal pressure of the cathode, the photocathode still has directional transport capability, avoiding the internal transport of the photocathode from becoming the overall bandwidth bottleneck, and reducing the sensitivity of the photocurrent to the applied bias voltage.

[0030] Example 1: Photocathode with built-in electric field controlled by doping gradient (homogeneous semiconductor).

[0031] A lower electrode (e.g., Au, AuGe, TiN, highly doped Si) is formed on an insulating or semi-insulating substrate (e.g., SiO2, Al2O3, AlN). A photocathode layer (e.g., Ge or Si) is fabricated on the lower electrode, forming a doping gradient along the thickness direction: a highly doped layer near the lower electrode and a lightly doped layer near the emitter surface, so that the built-in electric field points towards the emitter surface along the thickness direction. The doping gradient can be achieved through multi-energy, multi-dose ion implantation followed by annealing activation, or through in-situ doping growth.

[0032] An upper electrode is formed above the photocathode layer, and a nano-air channel with a thickness greater than 0 and not exceeding 1000 nm is formed between the photocathode and the upper electrode. (Refer to...) Figure 3 ,like Figure 3 The diagram illustrates the working principle of a vertical nano-air channel optoelectronic device with a built-in electric field controlling the photocathode. During operation, the cathode is set to zero, and a positive bias voltage is applied to the anode. The external field is mainly established in the air channel to assist in emission and acceleration. The built-in electric field drives photogenerated carriers to drift directionally within the photocathode to the emission surface, thereby improving the response speed and reducing dependence on the bias voltage.

[0033] Example 2: Gradual-varying built-in electric field modulated photocathode (alloy semiconductor).

[0034] Ge is epitaxially or deposited on the lower electrode. x Si 1-x or InGa x As 1-x The alloy photocathode layer has compositional parameters that change continuously or gradually in segments along the thickness direction, forming an energy band gradient and generating a built-in electric field. The rest of the structure is the same as in Example 1.

[0035] Example 3: Photocathode with built-in electric field in heterojunction / space charge region.

[0036] The photocathode with built-in electric field modulation employs a heterostructure, comprising a first semiconductor layer and a second semiconductor layer with different materials and / or doping types, forming a space charge region and a built-in electric field at the interface. By controlling the position of the heterojunction, charge carriers generated by light absorption are rapidly separated under the influence of the built-in electric field in the junction region and transported towards the emitting surface along the direction of the built-in electric field, thereby reducing the bandwidth limitation imposed by the internal transport time of the cathode. The thickness of the nano-air channel is greater than 0 and does not exceed 1000 nm.

[0037] Example 4: Preparation method example.

[0038] S1: Deposit and pattern the lower electrode on the substrate; S2: A photocathode layer is formed on the lower electrode, and a doping gradient is formed by ion implantation / annealing or in-situ doping, or the composition is controlled by the growth process to form a compositional gradient built-in electric field, or a heterojunction is formed to obtain a built-in electric field in the space charge region. S3: Form an insulating isolation layer to achieve electrical isolation between the upper and lower electrodes and structural support, and to define the nano-air channel region; S4: Forming a spacer / sacrificial structure that defines the nano-gap and fabricating the top electrode; S5: Release the gap to obtain a nano-air channel with a thickness greater than 0 and not exceeding 1000 nm. The spacer structure / sacrificial structure is used to provide mechanical support and gap definition when forming the upper electrode. After the upper electrode is completed, the nano-air channel is formed by removing the sacrificial structure or releasing the spacer structure, so that the upper electrode is suspended above the photocathode layer and supported by the insulating isolation layer. S6: Forms leads and packages; the upper and lower electrodes can be further integrated with RF antenna / waveguide structures.

[0039] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode, comprising a substrate, characterized in that, The device also includes: An electrode, comprising an upper electrode and a lower electrode, wherein the upper electrode and the lower electrode are disposed above the substrate; A photocathode layer is disposed above the lower electrode and below the upper electrode. An internal electric field is provided along the thickness direction to drive photogenerated carriers to be directionally transported to the emitting surface within the photocathode layer. Electrons are emitted from the emitting surface into the nano air channel and transported to the upper electrode under the assistance of an external bias voltage to form a photocurrent. An insulating isolation layer is disposed on both sides or the outer periphery of the photocathode layer to support the upper electrode; A nano-air channel is disposed between the photocathode layer and the upper electrode.

2. The vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode as described in claim 1, characterized in that, The built-in electric field is achieved by gradient doping formed by ion implantation and / or gradient doping formed by in-situ doping growth.

3. The vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode as described in claim 1, characterized in that, The built-in electric field is achieved by a band gradient formed by the gradual change of material composition along the thickness direction.

4. The vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode as described in claim 1, characterized in that, The built-in electric field is formed by a heterojunction or a space charge region.

5. The vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode as described in claim 1, characterized in that, The thickness of the nano-air channel does not exceed 1000 nm.

6. A method for fabricating a vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode, the method being used to fabricate the optoelectronic device according to any one of claims 1-5, characterized in that, The method includes: The lower electrode is formed and patterned on the substrate; A photocathode layer is formed on the lower electrode, and a built-in electric field is prepared; An insulating layer was fabricated to serve as a structure that isolates and supports the upper and lower electrodes, while simultaneously defining a nano-air channel region. Prepare spacer or sacrificial structures to define nano-air channels and form an upper electrode on top of them; Remove the sacrificial structure or release the spacer structure to form the nano-air channel, thereby forming a nano-air channel between the photocathode layer and the upper electrode.

7. The method for fabricating a vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode as described in claim 6, characterized in that, The sacrificial structure includes an inorganic sacrificial layer and / or an organic sacrificial layer, and the removal method includes one or more of wet etching, dry etching, thermal decomposition, or solvent stripping.

8. The method for fabricating a vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode as described in claim 6, characterized in that, The insulating layer is a ring-shaped, columnar, or stepped support structure, formed through deposition and patterning.

9. The method for fabricating a vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode as described in claim 6, characterized in that, The method further includes forming an upper electrode by sputtering, vapor deposition, electroplating, or transfer for connecting a radio frequency lead-out structure or an antenna structure.

10. The method for fabricating a vertical nano-air channel optoelectronic device with a built-in electric field-controlled photocathode as described in claim 6, characterized in that, The preparation of the built-in electric field includes: A built-in electric field can be obtained by forming a doping gradient through ion implantation and annealing activation or in-situ doping growth, or by controlling the material composition along the thickness direction through epitaxy / deposition to obtain a built-in electric field with a band gradient, or by forming a heterojunction in the photocathode layer to obtain a built-in electric field in the space charge region.

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