A nanometer air channel photodiode array

Abstract

The application provides a nano-air channel photodiode array, which comprises a three-layer structure, a first layer is a transparent substrate and a plurality of nano-air channel photodiodes located thereon, a second layer is a vertical interconnection metal column, and a third layer is a dielectric substrate and a circuit located thereon; the plurality of nano-air channel photodiodes in the first layer are photoelectric conversion elements, and the circuit in the third layer comprises a radio frequency circuit, an antenna array and a signal readout circuit; the nano-air channel photodiodes in the first layer and the circuit in the third layer are electrically interconnected through the vertical interconnection metal column in the second layer. The nano-air channel photodiode array provided by the application can overcome the limitation that the output power of a single device is small, better play the advantages of the nano-air channel photodiode, and can be used for heterodyne detection imaging of millimeter wave terahertz, and can also be used for optical focal plane imaging.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor optoelectronic devices and millimeter wave / terahertz devices, and particularly relates to a nano air channel photodiode array. BACKGROUND

[0002] At present, millimeter wave and terahertz technology based on optical mixing is considered as a promising scheme for realizing terahertz communication and high-resolution terahertz radar. The optical mixer is a core device in optical mixing technology, and is an ultra-high-speed photodetector in terms of working principle. It converts two laser electromagnetic waves with a difference frequency into a modulated high-frequency photocurrent, and then converts it into a radio frequency electromagnetic wave through a load.

[0003] The nano air channel photodiode is a new type of optical mixing device, which combines the advantages of traditional semiconductor solid-state optoelectronic devices and vacuum optoelectronic devices. It utilizes the characteristic that the length of the air channel is less than the average free path of electron scattering in air, and there is no lattice scattering in the nano air channel, so that the electron can do near-light-speed ballistic transport, and the transit time of the electron reaches the ps level. Therefore, the mixing bandwidth of the nano air channel can reach THz or more, and it has the characteristics of ultra-wide bandwidth.

[0004] Since Siwapon Srisonphan, Myungji Kim and others reported the Si / SiO2 / graphene nano vacuum photodetector, the nano air channel photodiode has realized response in the 325nm-1064nm waveband, and the two-dimensional electron gas (2DEG) ionization collision ionization phenomenon under a large electric field has been found, thereby generating carrier multiplication and greatly improving the responsivity. The nano air channel has an ultra-high intrinsic breakdown voltage close to vacuum and lower heating, so that the semiconductor nano air channel optical mixer has the advantage of realizing large output power. This is due to the characteristic that the electron transport process in the nano air channel diode is not affected by the solid lattice scattering. The nano air channel device also has the advantages of radiation resistance and high and low temperature resistance, and can work in harsh environments.

[0005] In addition to being used to generate millimeter wave and terahertz terahertz sources, the nano air channel photodiode can also be used for room-temperature heterodyne coherent detection of millimeter wave / terahertz signals, down-conversion reception, and photodetection of weak terahertz signals close to the quantum limit at room temperature. The nano air channel photodiode has the advantages of miniaturization and compatibility with semiconductor processes, and is one of the most promising solutions for realizing optical mixers. However, there are still some problems with the single nano air channel photodiode, such as low output power of the single device, which can only be used as a single-point detector and cannot be used for millimeter wave terahertz and optical imaging, which greatly limits the application of the nano air channel photodiode in the fields of terahertz sources, imaging and terahertz communication. SUMMARY

[0006] In view of the deficiencies in the prior art, the present application provides a nano-air channel photodiode array, which can output larger power terahertz electromagnetic waves and is applied to millimeter wave terahertz generation, detection imaging communication and optical imaging fields.

[0007] The nano-air channel photodiode array provided by the present application comprises a three-layer structure, the first layer is a transparent substrate and a plurality of nano-air channel photodiodes located thereon, the nano-air channel photodiode is a photoelectric conversion element for processing input signals, the second layer is a plurality of vertical interconnection metal columns for electrical interconnection, and the third layer is a dielectric substrate and a circuit located thereon, the circuit comprising a direct-current alternating-current isolation circuit, a radio frequency circuit, an antenna array, a signal readout circuit.

[0008] The nano-air channel photodiode array adopts a vertical structure as a whole, the first layer comprises a transparent substrate and a plurality of nano-air channel photodiodes, a photocathode is arranged on the substrate, a nano dielectric layer is arranged on the photocathode, an anode is arranged on the nano dielectric layer, a nano air channel is arranged outside the edge of the nano dielectric layer between the photocathode and the anode, and the length of the nano air channel is determined by the nano dielectric layer; the second layer is provided with a plurality of vertical interconnection metal columns, the vertical interconnection metal columns are connected together with the anode and the photocathode and serve as the support of the dielectric substrate; and the third layer is provided with a dielectric substrate, a direct-current bias line, a radiation / receiving antenna, an intermediate frequency output circuit, a signal readout circuit and a processing circuit, which are used to meet the needs of millimeter wave terahertz output and detection imaging.

[0009] Further, the plurality of nano-air channel photodiodes are used to realize photoelectric conversion, the nano-air channel photodiode array can be used as an optical mixer to mix and generate millimeter wave terahertz signals, can be used as a photodetector to detect terahertz signals, and can be used as an infrared focal plane imager to realize focal plane imaging.

[0010] Further, the photocathode material is a semiconductor material or a metalloid, and the anode is composed of a high-conductivity material.

[0011] Further, the length of the nano air channel is less than the average free path of electron scattering in air.

[0012] Further, the plurality of vertical interconnection metal columns are respectively arranged on the photocathode and the anode.

[0013] Further, when the array is used as a light mixer to generate a millimeter wave terahertz source, the photocathode realizes mixing under the excitation of two incident lights, emits photoelectrons, the photoelectrons enter the nanometer air channel and are received by the anode after high-speed ballistic transport under the electric field without scattering, thereby generating a high-frequency photocurrent, and the frequency of the photocurrent is regulated by the two incident lights, the high-frequency photocurrent is transmitted to the direct-current-alternating-current separation circuit and the radiation antenna on the vertical structure through the vertical interconnection metal column, and then millimeter wave terahertz waves are radiated.

[0014] Further, when the array is used as a light mixer to generate a millimeter wave terahertz source, the photocathode realizes mixing under the excitation of two incident lights, emits photoelectrons, the photoelectrons enter the nanometer air channel and are received by the anode after high-speed ballistic transport under the electric field without scattering, thereby generating a high-frequency photocurrent, and the frequency of the photocurrent is regulated by the two incident lights, the high-frequency photocurrent is transmitted to the direct-current-alternating-current separation circuit and the radiation antenna on the vertical structure through the vertical interconnection metal column, and then millimeter wave terahertz waves are radiated.

[0015] Further, when the array is used as a light mixer to generate a millimeter wave terahertz source, the photocathode realizes mixing under the excitation of two incident lights, emits photoelectrons, the photoelectrons enter the nanometer air channel and are received by the anode after high-speed ballistic transport under the electric field without scattering, thereby generating a high-frequency photocurrent, and the frequency of the photocurrent is regulated by the two incident lights, the high-frequency photocurrent is transmitted to the direct-current-alternating-current separation circuit and the radiation antenna on the vertical structure through the vertical interconnection metal column, and then millimeter wave terahertz waves are radiated.

[0016] Further, when the array is used as a light mixer to generate a millimeter wave terahertz source, the photocathode realizes mixing under the excitation of two incident lights, emits photoelectrons, the photoelectrons enter the nanometer air channel and are received by the anode after high-speed ballistic transport under the electric field without scattering, thereby generating a high-frequency photocurrent, and the frequency of the photocurrent is regulated by the two incident lights, the high-frequency photocurrent is transmitted to the direct-current-alternating-current separation circuit and the radiation antenna on the vertical structure through the vertical interconnection metal column, and then millimeter wave terahertz waves are radiated.

[0017] The nanometer air channel photodiode array provided by the application has the advantages that when the transport distance of electrons between the cathode and the anode (i.e., the length of the nanometer air channel) is in the nanometer level, the transport time of the electrons can be as short as tens of femtoseconds, and the corresponding cutoff frequency can be as high as hundreds of THz; when the electric field strength generated by an external voltage between the cathode and the anode in the semiconductor 2EDG serving as the cathode or the anode is greater than the ionization threshold electric field strength, the carrier multiplication effect occurs in the semiconductor. The discrete nanometer air channel photodiodes are interconnected by the vertical interconnection metal column of the vertical structure, so that the photocurrent, responsivity, terahertz output power and light-to-terahertz conversion efficiency generated by the discrete devices are significantly increased. The nanometer air channel photodiode array combines the advantages of the ballistic transport of electrons at near light speed in the nanometer air channel photodiode and the high integration and batch processing of semiconductor solid-state devices, and is a new scheme for breaking through the technical bottlenecks of traditional semiconductor light mixers and vacuum light mixers. The application has the following beneficial technical effects:

[0018] 1. The nanometer air channel photodiode array of the present invention can superimpose the photocurrents generated by discrete devices through vertically interconnected metal pillars, thereby improving the shortcoming of insufficient optical power output of a single nanometer air channel photodiode and significantly improving the output terahertz photocurrent and output power;

[0019] 2. Due to the larger area of ​​the monolithic integrated nano-air channel photodiode array, it can be used for stronger incident light power and intensity, enhancing terahertz detection sensitivity. It can also improve the defect that a single nano-air channel photodiode can only perform single-point detection and cannot perform terahertz imaging, thus meeting the growing demand for terahertz imaging.

[0020] 3. After changing the photocathode semiconductor absorption layer material, the nano air channel photodiode array can be applied to optical imaging in multiple frequency bands such as infrared and near infrared;

[0021] 4. The nanometer air channel photodiode array of the present invention can be mass-produced on large-area wafers using semiconductor micro-nano technology. Compared with traditional vacuum optoelectronic devices, it has the advantages of miniaturization, high integration, large-scale batch production, and reduced single-chip production costs.

[0022] 5. The nanometer air channel photodiode array of the present invention can be integrated with ADC / DAC, optical modulator and other modules for on-chip photonics, thereby enhancing the device's signal processing capability for millimeter-wave terahertz and its application in optical communications and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 Schematic diagram of a millimeter-wave terahertz source based on a nanometer air channel photodiode array provided by an embodiment of the present invention; wherein: 11, transparent substrate; 12, photocathode; 13, nanometer air channel; 14, nanometer dielectric layer; 15, anode; 16, vertical conductive copper pillar; 17, dielectric substrate; 18, radiating antenna; 19, DC bias line; 10, incident light;

[0025] Figure 2A schematic diagram of a millimeter wave terahertz detector based on a nano-air channel photodiode array is provided for the embodiment of the present application; wherein: 20, two light sources for generating optical local oscillation; 21, a transparent substrate; 22, a photocathode; 23, a nano-air channel; 24, a nano dielectric layer; 25, an anode; 26, a vertical conductive indium column; 27, a dielectric substrate; 28, a receiving antenna; 29, a to-be-detected terahertz signal; 210, a medium frequency signal; 211, a medium frequency output circuit;

[0026] Figure 3 A schematic diagram of an infrared focal plane imager based on a nano-air channel photodiode array is provided for the embodiment of the present application; wherein: 31, a transparent substrate; 32, a photocathode; 33, a nano-air channel; 34, a nano dielectric layer; 35, an anode; 36, a vertical conductive indium column; 37, a dielectric substrate; 38, a signal readout circuit; 39, a processing circuit. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0028] The nano-air channel photodiode array provided by the present application comprises a three-layer structure, the first layer is a transparent substrate and a plurality of nano-air channel photodiodes located thereon, the nano-air channel photodiode is a photoelectric conversion element for processing input signals, the second layer is a plurality of vertical interconnection metal columns for electrical interconnection, and the third layer is a dielectric substrate and a circuit located thereon, the circuit comprising a direct-current alternating-current isolation circuit, a radio frequency circuit, an antenna array, a signal readout circuit;

[0029] The nano-air channel photodiode array adopts a vertical structure as a whole, the first layer comprises a transparent substrate and a plurality of nano-air channel photodiodes, a photocathode is arranged on the substrate, a nano dielectric layer is arranged on the photocathode, an anode is arranged on the nano dielectric layer, and a nano-air channel is arranged outside the edge of the nano dielectric layer between the photocathode and the anode, the length of the nano-air channel is determined by the nano dielectric layer; a plurality of vertical interconnection metal columns are arranged on the second layer, the vertical interconnection metal columns are connected together with the anode and the photocathode, and serve as the support of the dielectric substrate; the third layer is provided with a dielectric substrate, a direct-current bias line, a radiation / receiving antenna, a medium frequency output circuit, a signal readout circuit, and a processing circuit, for meeting the needs of millimeter wave terahertz output and detection imaging.

[0030] The following is a detailed description of the technical solutions of using nano-air channel photodiode arrays as optical mixers, photodetectors, and focal plane imaging.

[0031] Example 1

[0032] This embodiment provides a nanometer air channel photodiode array millimeter wave terahertz source, such as Figure 1 As shown, the substrate in this embodiment is a SOI (Silicon-On-Insulator) substrate with a thickness of 200μm, and the photocathode material on the substrate is a p-type Ge semiconductor film with a thickness of 200nm; a SiO2 nano-dielectric layer with a thickness of 60nm is provided on the photocathode, and a Ti / Au anode is provided on the SiO2 nano-dielectric layer; a nano-air channel with a length of 60nm is provided between the outer edge of the SiO2 nano-dielectric layer, the p-type Ge semiconductor film and the Ti / Au anode, which is equivalent to the thickness of the nano-dielectric layer; a copper pillar is provided on the Ge semiconductor film and the anode; Al2O3 with a thickness of 50nm is provided on the copper pillar as a substrate for the radiation antenna; the radiation antenna adopts a planar bow tie structure, whose material is Ni / Au alloy, connected to the copper pillar and provided with a DC bias by a DC bias line.

[0033] The working process of the nano-air channel photodiode array millimeter wave terahertz source is as follows: the DC bias line sets the potential. Since the bias line and the photocathode are connected through a conductive copper column, the photocathode on the p-type Ge film is negatively biased. The p-type Ge film produces a depletion region under reverse bias, and an inversion layer is generated near its surface to form 2DEG; under the irradiation of two beams of near-infrared light near the 1550nm band and the wavelength difference in the terahertz band, the photogenerated electrons in the depletion region drift to the 2DEG layer under the action of a large electric field to increase its concentration, and ionization collisions and multiplication occur in the process. In addition, the Coulomb repulsion between electrons also increases accordingly; the electrons at the edge of the 2DEG are repelled by the Coulomb repulsion of the internal electrons. Under the action of the large electric field between the anode and the cathode, the electrons on the upper surface of the semiconductor film are pulled by the large electric field, and field emission occurs and is also emitted into the nano-air channel. They are absorbed by the anode within ps of time to form a photocurrent, which is fed back into the radiation antenna. The photocurrent is modulated by two beams of near-infrared light, and its frequency is the difference between the frequencies of the two incident near-infrared light beams. The changes in amplitude and phase are also synchronized with the amplitude and phase of the superposition of the two near-infrared light beams. The high-frequency photocurrent is transmitted to the planar bowtie radiation antenna through the conductive copper column. Finally, the terahertz wave generated by the discrete device is superimposed by the radiation antenna array to radiate the terahertz wave, thereby generating a high-power terahertz signal.

[0034] Example 2

[0035] This embodiment provides a nanometer air channel photodiode array millimeter wave terahertz detector, such asFigure 2 As shown, the substrate in this embodiment is a SOI substrate with a thickness of 200μm, and the photocathode material on the substrate is a TiN film with a thickness of 50nm; a SiO2 nano-dielectric layer with a thickness of 50nm is provided on the photocathode, and a Ti / Au anode is provided on the SiO2 nano-dielectric layer; a nano-air channel is provided between the outer edge of the SiO2 nano-dielectric layer, the TiN film and the Ti / Au anode, and its length is 50nm, which is equivalent to the thickness of the nano-dielectric layer; an indium column is provided on the TiN film and the anode; and a 50nm thick Al2O3 is provided on the indium column as a substrate for the intermediate frequency output circuit and the receiving antenna.

[0036] The working process of the nano-air channel photodiode array millimeter wave terahertz detector is as follows: by setting the electrode polarity, the photoelectrode on the TiN film is negatively biased. Under the reverse bias, the potential barrier between the surface of the TiN film and the air is compressed to form a thin triangular potential; when irradiated by two beams of light near the 1550nm band and with a wavelength difference in the terahertz frequency band, the photoexcited electrons are emitted from the TiN surface to generate a photocurrent modulated by the two incident beams. The frequency of the photocurrent is the frequency difference of the two incident near-infrared beams, and the changes in amplitude and phase are also synchronized with the amplitude and phase of the superposition of the two near-infrared beams; after the terahertz signal to be measured is received by the receiving antenna, it is transmitted through the conductive indium column and down-mixed with the local oscillator to output an intermediate frequency signal F if ; Finally, the intermediate frequency signal is output through the intermediate frequency output circuit, thereby achieving millimeter wave terahertz detection.

[0037] Example 3

[0038] This embodiment provides a nanometer air channel photodiode array infrared focal plane imager, such as Figure 3 As shown, the substrate in this embodiment is a GaSb substrate with a thickness of 200μm, and the photocathode material on the substrate is gallium antimonide with a thickness of 500nm; a Si3N4 nano-dielectric layer with a thickness of 50nm is provided on the photocathode, and a Hf / Au anode is provided on the Si3N4 nano-dielectric layer; a nano-air channel is provided between the outer edge of the Si3N4 nano-dielectric layer and the gallium antimonide and the Ti / Au anode, and its length is determined by the thickness of the nano-dielectric layer; vertically interconnected indium pillars are provided on the gallium antimonide and the Hf / Au anode; BeO with a thickness of 100μm is provided on the indium pillars as a dielectric substrate; a driving circuit is provided on the dielectric substrate to drive the processing circuit and the mixing down conversion of the nano-air channel diode; the signal processing circuit is composed of a field programmable gate array (FPGA), a DAC and an ADC.

[0039] The working process of the infrared focal plane imager of the nano-air-channel photodiode array is as follows: the working state of the nano-air-channel photodiode is set by the driving circuit, under the irradiation of two beams of near-infrared light near the 850 nm wave band and with a wavelength difference in the terahertz frequency band, a 2DEG is generated near the surface of the photoelectrode on the gallium antimonide due to the negative bias, and in this process, ionization collision and multiplication occur due to the high electric field in the 2EDG, and in addition, the Coulomb repulsion between electrons also increases; the electrons at the edge of the 2DEG overcome the surface potential barrier and are emitted into the nano-air-channel under the action of the internal electron Coulomb repulsion and the large electric field between the cathode and the anode, the electrons at the surface of the gallium antimonide are pulled by the large electric field and are field emitted into the nano-air-channel, and are absorbed by the anode within ps, thereby generating a local oscillator terahertz signal with frequency, amplitude and phase controlled by the two beams of infrared light; when detecting a terahertz wave signal, the local oscillator generated by the two beams of infrared light is mixed down to generate a radio frequency signal, which is then transmitted to a processing circuit for data processing, thereby realizing high-resolution and high-power infrared imaging.

[0040] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A nanometer air channel photodiode array, characterized in that, The array comprises a three-layer structure, the first layer is a transparent substrate and a plurality of nano-air-channel photodiodes located thereon, the nano-air-channel photodiode is a photoelectric conversion element for processing an input signal, the second layer is a plurality of vertical interconnection metal columns for electrical interconnection, and the third layer is a dielectric substrate and a circuit located thereon, the circuit comprises a direct-current-to-alternating-current isolation circuit, a radio frequency circuit, an antenna array, and a signal readout circuit. The nano-air-channel photodiode array adopts a vertical structure, the first layer comprises a transparent substrate and a plurality of nano-air-channel photodiodes, a photocathode is arranged on the substrate, a nano dielectric layer is arranged on the photocathode, an anode is arranged on the nano dielectric layer, and a nano-air-channel is arranged outside the edge of the nano dielectric layer between the photocathode and the anode, and the length of the nano-air-channel is determined by the nano dielectric layer. The second layer is provided with a plurality of vertical interconnection metal columns, the vertical interconnection metal columns are connected with the anode and the photocathode together and serve as a support of the dielectric substrate, and the third layer is provided with a dielectric substrate, a direct-current bias line, a radiation / receiving antenna, a medium frequency output circuit, a signal readout circuit, and a processing circuit, which are used to meet the needs of millimeter wave terahertz output and detection imaging. When the nano-air-channel photodiode array adopts an array structure, the plurality of vertical interconnection metal columns and the plurality of radiation antennas enable the light response generated by a single nano-air-channel photodiode to be synthesized, so that the photocurrent, responsivity, terahertz output power, and light-to-terahertz conversion efficiency are increased exponentially. When the array is used as a light frequency mixer to generate a millimeter wave terahertz source, the photocathode realizes frequency mixing under the excitation of two incident lights, emits photoelectrons, the photoelectrons enter the nano-air-channel and are received by the anode after high-speed ballistic transport under an electric field without scattering, thereby generating a high-frequency photocurrent, and the frequency of the photocurrent is controlled by the two incident lights, the high-frequency photocurrent is transmitted to the direct-current-to-alternating-current isolation circuit and the radiation antenna on the vertical structure through the vertical interconnection metal column, and then millimeter wave terahertz waves are radiated.

2. The nanometer air channel photodiode array of claim 1, wherein, The plurality of nano-air-channel photodiodes are used to realize photoelectric conversion, the nano-air-channel photodiode array can be used as a light frequency mixer to generate a millimeter wave terahertz signal, can be used as a photoelectric detector to detect a terahertz signal, and can be used as an infrared focal plane imager to realize focal plane imaging.

3. The nanometer air channel photodiode array of claim 1, wherein, The photocathode material is a semiconductor material or a metalloid, and the anode is composed of a high-conductivity material.

4. The nanometer air channel photodiode array of claim 1, wherein, The length of the nano-air-channel is less than the average free path of electron scattering in air.

5. The nanometer air channel photodiode array of claim 1, wherein, The plurality of vertical interconnection metal columns are respectively arranged on the photocathode and the anode.

6. The nanometer air channel photodiode array of claim 1, wherein, When the array is used as a photoelectric detector to realize millimeter wave terahertz heterodyne detection imaging, there are three input signals, including two incident lights for generating a terahertz local oscillator and a terahertz signal to be detected, the terahertz signal is received by the receiving antenna and mixed with the local oscillator signal by the nano-air-channel photodiode, and finally a medium frequency signal is output by difference frequency, and then the medium frequency signal is transmitted to the medium frequency output circuit on the vertical structure through the vertical interconnection metal column for processing, thereby realizing detection of the terahertz signal.

7. The nanometer air channel photodiode array of claim 1, wherein, When the array is used as a focal plane imaging, there are three input beams, including two laser beams for generating a terahertz local oscillator and a terahertz signal to be measured, the input signal is mixed by a nano-air channel photodiode, and finally an intermediate frequency signal is output, which is transmitted to a signal readout circuit on a vertical structure through a vertical interconnection metal column, and the signal is reprocessed through a processing circuit.

Images