CN114203837B - Photon screening type terahertz phototransistor and multi-photon detection method thereof - Google Patents

Abstract

The invention relates to a photon screening terahertz phototransistor and a multiphoton detection method thereof, comprising a coupling grating layer, a photosensitive floating gate layer and a channel layer which are arranged oppositely from top to bottom in sequence, wherein the coupling grating layer comprises a plurality of sub gratings for coupling and enhancing terahertz photons of different targets, the photosensitive floating gate layer is used for correspondingly absorbing photons which are coupled and enhanced by a sub grating structure so as to change electrochemical potential and further change conductivity of the channel layer, one end of the channel layer is connected to a source electrode, and the other end of the channel layer is connected to a drain electrode. The coupling grating layer screens and distinguishes different terahertz photons in space in the super cell period of the coupling grating layer, and then the coupling grating layer is coupled to the corresponding terahertz photosensitive floating gate region, and optical signals corresponding to different photons are read out according to the source leakage current of the phototransistor. Compared with the prior art, the invention can break through the limit that the detection efficiency of each single photon is less than 1/n, and realize the purpose of multi-photon synchronous high-sensitivity detection.

Description

A photon screening terahertz optical transistor and multi-photon detection method thereof

Technical Field

The present invention relates to the technical field of terahertz multi-photon detection, and in particular to a photon screening type terahertz optical transistor and a multi-photon detection method thereof.

Background technique

Research on high-sensitivity multi-photon detectors for terahertz is of great significance to the expansion of the application of terahertz detectors. Quantum well terahertz detectors have the advantages of good stability, fast response speed, and easy production of large planar arrays. They have become a research hotspot in the field of terahertz detectors in recent years. However, traditional semiconductor quantum well terahertz detectors do not have optical gain function, so the light response rate is poor, and their application is greatly limited. Not only that, with the continuous development of semiconductor technology, narrow-band detectors for single terahertz photons can no longer meet the needs of more functions. How to synchronously and highly sensitively detect multiple different terahertz photons in the incident light beam has always been a frontier problem that has been pursued for a long time in this field but faces severe challenges.

Traditionally, in order to detect multiple photons in an incident light beam, the incident light beam must be spatially split, that is, different photons are split into different spatial regions through technologies such as diffraction gratings, and then a special detector unit is designed to detect each single photon. However, such a dispersion splitting scheme must be carried out with the cooperation of multiple spatial optical elements and cannot be implemented on a monolithic integrated detector. This not only seriously affects the convenience of application, but also makes it more difficult to achieve synchronous and precise calibration of multiple light paths for different photons in applications such as confocal microscopy that require strict optical path calibration accuracy. Therefore, monolithic integrated multi-photon detection is an inevitable trend in the development of this field.

The current monolithic integrated multi-photon detection technology mainly adopts a method based on filtering and spectroscopy, that is, the incident light beam is irradiated onto a monolithic integrated array detector containing multiple pixels, and different filter materials or grating structures are used at different pixels, so that different pixels only detect one of the target photons. However, this method loses incident photons of other wavelengths except the target photons at each detection pixel, which makes the overall multi-photon detection efficiency performance of the monolithic integrated array detection device poor. For example: for the detection of n different photons, assuming that the detection pixel area of each photon is a, the total detection area is na, and the incident light beam should be no less than na. At this time, the theoretical maximum detection efficiency limit for each photon is 1/n. In addition, since the photosensitive detection areas for different photons are spatially dispersed, it is also difficult to accurately optimize the spatial optical path of different photons in applications that require precise optical paths. To achieve multi-photon detection in a single area, the prior art has implemented a method that uses the same broadband response grating to switch between two wavelength photon detection by switching the semiconductor band structure. However, this method must distinguish the detection of the two photons in terms of timing, that is, only λ ₁ photons can be detected in the t ₁ period (or λ ₂ photons can be detected in the t ₂ period). Therefore, the λ ₂ photons that are simultaneously incident in the t ₁ period will inevitably be lost (or the λ ₁ photons that are simultaneously incident in the t ₂ period will be lost), indicating that this method is also limited to the effective detection efficiency upper limit of 1/n for each detected photon.

Summary of the invention

The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a photon screening terahertz optical transistor and a multi-photon detection method thereof, so as to break through the limit of less than 1/n detection efficiency for each single photon and achieve the purpose of multi-photon synchronous high-sensitivity detection.

The objective of the present invention can be achieved through the following technical scheme: a photon screening terahertz optical transistor, comprising a coupling grating layer, a photosensitive floating gate layer and a channel layer arranged in sequence from top to bottom, wherein the coupling grating layer comprises a plurality of sub-gratings for coupling and enhancing different target terahertz photons, the photosensitive floating gate layer is used to correspondingly absorb photons enhanced by coupling of the sub-grating structure to change the electrochemical potential and thereby change the conductivity of the channel layer, one end of the channel layer is connected to the source, and the other end of the channel layer is connected to the drain.

Furthermore, the coupling grating layer specifically adopts a periodic metamaterial structure with multi-periodic characteristics.

Furthermore, reset electrical pulse signals with different timings are applied to different sub-gratings in the coupled grating layer respectively.

Furthermore, the photosensitive floating gate layer is located in the near field range directly below the coupling grating layer so as to be able to directly absorb photons corresponding to the sub-grating coupling enhancement.

Furthermore, the photosensitive floating gate layer includes a plurality of phototransistor floating gates corresponding to different sub-photogratings, and the plurality of phototransistor floating gates are electrically isolated from each other.

Furthermore, the source and drain are both composite metal electrodes.

Furthermore, a capacitive coupling relationship is formed between the photosensitive floating gate layer and the channel layer.

A multi-photon detection method of a photon screening terahertz optical transistor comprises the following steps:

S1. According to the detection requirements of multi-target photons, a supercellular grating structure with multiple sub-gratings is designed and constructed to obtain a coupled grating layer;

S2, designing and constructing a plurality of phototransistor floating gates that match the plurality of sub-gratings and have corresponding terahertz band response capabilities to obtain a photosensitive floating gate layer;

S3, arranging the coupling grating layer and the photosensitive floating gate layer corresponding to each other up and down, and arranging a channel layer below the photosensitive floating gate layer, connecting the two ends of the channel layer to the source and the drain respectively, to manufacture a monolithic integrated photon screening type terahertz optical transistor structure;

S4, connect the source and drain to an external ammeter, connect the source to a potential and detect the path current at the same time;

Applying reset electrical pulse signals with different timings to the multiple sub-gratings respectively;

According to the synchronous changes of the current on the source and the drain, the signal intensities of multiple different photons are obtained.

Furthermore, the step S1 specifically adopts an electromagnetic field numerical calculation simulation method to design a supercellular grating structure with multiple sub-gratings, wherein the electromagnetic field numerical calculation simulation method includes a finite time-domain difference method and a finite element method.

Furthermore, the step S2 specifically adopts a semiconductor energy band engineering design method to design a plurality of phototransistor floating gates.

Compared with the prior art, the present invention adopts a multi-photon screening method. By setting a coupling grating layer with a photon screening function, it can simultaneously couple the incident multi-photons and compress them to different sub-grating near-field ranges respectively, and then directly couple with the photosensitive floating grating layer and be efficiently absorbed by the photosensitive floating grating layer. After the photosensitive floating grating layer absorbs each photon, the potential changes, and the intensity of the light signal is further reflected in the current signal of the channel layer through the transconductance effect. Therefore, the present invention comprehensively utilizes the efficient multi-photon coupling and screening efficiency of the grating structure and the transconductance photoelectric gain function of the phototransistor to achieve efficient and high-sensitivity synchronous detection of multi-photons in a single pixel area. The present invention breaks through the limit of less than 1/n detection efficiency for each single photon, and has the advantage of not requiring light splitting. Multi-photon detection devices can be performed simultaneously in the same photosensitive detection area, and there is no need to perform separate optical path calibration for multiple photons in the application.

In addition, the present invention adopts a phototransistor structure with a transconductance amplification function to construct a photosensitive floating gate layer, which can simultaneously realize the multi-photon photoelectric gain amplification function and realize multi-photon synchronous high-sensitivity detection of a single pixel; the present invention adopts existing mature materials and device processes to effectively realize a monolithic integrated multi-photon single-pixel detection device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of a photon screening terahertz optical transistor in Example 1;

FIG2 is a typical spectrum response of the photon screening grating in Example 1;

FIG3 is a near-field light field distribution of the photon screening grating in Example 1;

FIG4 is a schematic diagram of a photon screening grating provided with an isolation grating in Embodiment 2;

FIG5 is a schematic diagram of a two-dimensional photon screening grating structure in Embodiment 3;

Explanation of the marks in the figure: 100, λ ₁ photon corresponds to sub-grating, 101, λ ₂ photon corresponds to sub-grating, 200, λ ₁ photon corresponds to phototransistor floating gate, 201, λ ₂ photon corresponds to phototransistor floating gate, 300, phototransistor channel, 301, phototransistor source, 302, phototransistor drain, 400, λ ₁ photon corresponds to sub-grating reset electric pulse, 401, λ ₂ photon corresponds to sub-grating reset electric pulse.

Detailed ways

The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

Embodiment 1

As shown in FIG1 , a photon screening type terahertz optical transistor includes a coupling grating layer (composed of a sub-grating 100 corresponding to a λ ₁ photon and a sub-grating 101 corresponding to a λ ₂ photon) arranged in an upper, middle and lower direction, a photosensitive floating gate layer (composed of a phototransistor floating gate 200 corresponding to a λ ₁ photon and a phototransistor floating gate 201 corresponding to a λ ₂ photon) and a channel layer (composed of an optical crystal channel 300, a phototransistor source ₃₀₁ and a phototransistor drain 302). The upper coupling grating layer includes a photosensitive floating gate 200 and a phototransistor source 301. ₂ photons) to couple and enhance the near-field light fields of different photons respectively; the middle photosensitive floating gate layer (200 and 201) has photosensitive characteristics corresponding to the coupled sub-gratings, and the electrochemical potential changes after absorbing the corresponding photons, thereby changing the conductivity of the lower channel layer through the transconductance effect; one end of the lower channel layer (300) is connected to the source (301), and the other end of the lower channel layer (300) is connected to the drain (302).

In practical applications, the metal coupling grating layer uses a periodic metamaterial structure with multi-period characteristics, which can screen and spatially distinguish different photons, thereby achieving the coupling effect of photons (λ ₁ ) being concentrated in the sub-grating (100) area for near-field enhancement and photons (λ ₂ ) being concentrated in the sub-grating (101) area for near-field enhancement. A metamaterial coupling grating with a supercell structure is used to achieve the light field enhancement effect of different photons in different areas within the supercell period after coupling with the incident photons, so that the effective absorption cross section of the device is significantly increased, overcoming the complexity of traditional off-chip spectroscopy and the loss of detection efficiency caused by filter-type spectroscopy, while achieving ideal detection performance for multiple photons.

The middle photosensitive floating gate layer (200 and 201) is in the near field range directly below the sub-grating (100 and 101), and can directly absorb the photons (λ ₁ and λ ₂ ) coupled and enhanced by the grating (100 and 101). After the absorption, the potential of the photosensitive floating gate layer (200 and 201) will change;

The middle photosensitive floating gate layer (200 and 201) and the lower channel (300) form a transistor device structure and have a good transconductance amplification effect;

The lower channel layer (300) is connected to the source (301) and the drain (302) respectively. The source (301) and the drain (302) are both composite metal electrodes. The current passing through the source (301) and the drain (302) can be directly measured. The potential change of the photosensitive floating gate layer (200 and 201) after absorbing light can change the current passing through the source (301) and the drain (302) through the transconductance effect of the transistor structure.

The photogenerated carriers in the photosensitive floating gate layer (200 and 201) can be reset and initialized by applying electric pulses (400 and 401) to the sub-gratings (100 and 101), and the corresponding light signal intensity can be reflected in the change amplitude of the source (301) and drain (302) current before and after the reset.

This embodiment uses the above-mentioned photon screening terahertz optical transistor to perform multi-photon detection, which mainly includes the following processes:

Firstly, a super-cell grating structure with corresponding multiple sub-grating structures is designed according to the target multi-photon. The design method is specifically electromagnetic field numerical calculation simulation, including finite time-domain difference method and finite element method.

Then, a photosensitive floating gate structure having a corresponding terahertz band response capability matching the above grating is designed, and a monolithically integrated photon screening terahertz optical transistor device structure is manufactured, wherein the design method specifically adopts a semiconductor energy band engineering design method;

Finally, the source and drain are connected to an external ammeter, and the source is connected to an electric potential while the path current is detected; by controlling the output of the electric pulse generator, reset pulses (400 and 401) with different timings are applied to the sub-gratings (100 and 101) respectively, and according to the synchronous changes of the source (301) and drain (302) currents, the signal strength of the corresponding photons (λ ₁ and λ ₂ ) can be read.

In this embodiment, the coupled grating layer (such as 100 and 101 in FIG. 1 ) has a spectral response as shown in FIG. 2 , and can realize the photon screening function of the incident light beam (λ ₁ , λ ₂ ), that is, the λ ₁ photon is screened and compressed to the vicinity of the sub-beam 100, and the λ ₂ photon is screened and compressed to the vicinity of the sub-beam 101. The light field distribution is shown in FIG. 3 . The arrow in the structural schematic diagram of FIG. 3 indicates the area where the light field is enhanced. The field distribution diagram shows the spatial distribution of the electric field E _z component obtained by finite time-domain difference method simulation. It can be seen from the figure that after the λ ₁ photon is screened, it is mainly distributed under the sub-grating 100, and after the λ ₂ photon is screened, it is mainly distributed under the sub-grating 101.

In this embodiment, the metal coupling gratings 100 and 101 are 5nm Ti/100nm Au composite layers, and the grating structure parameters are (as shown in FIG1 ): W ₁ =1.0μm (width of sub-grating 100 ), W ₂ =1.6μm (width of sub-grating 101 ); the period between sub-gratings 101 is D ₁ =4.5μm, and the center spacings between sub-gratings 100 and 101 are D ₂ =3μm and D ₃ =1.5μm respectively;

The metal coupling gratings 100 and 101 are located 100 nm above the floating gate layers 200 and 201. The floating gate layers 200 and 201 are 7 nm gallium arsenide quantum well layers. The electrical isolation between adjacent floating gates can be achieved by wet and dry etching.

The floating gate layers 200 and 201 are located 100 nm above the channel layer 300, forming capacitive coupling with the channel and having a transconductance amplification function;

An aluminum gallium arsenide barrier layer is formed between the coupling grating layer, the floating gate layer and the channel layer.

The present embodiment only detects two photons, namely, the λ ₁ photon and the λ ₂ photon. In practical applications, more different target photons can be detected. It can be seen that the present technical solution includes a coupling grating layer, a photosensitive floating grating layer and a channel layer which are relatively arranged at the upper, middle and lower parts. The coupling grating layer at the upper part includes a sub-grating structure which can couple a variety of target terahertz photons, and can couple and enhance the near-field light fields of different photons respectively. The process can be regarded as that the multi-photons (λ ₁ , λ ₂ , ..., λ _n ) in the incident light beam are automatically screened and compressed into their respective sub-grating regions. Since each sub-grating structure has a sub-wavelength feature (i.e., line width < wavelength), its effective detection cross-sectional area (σ _effective ) for the target photons is no longer limited by the geometric area (σ _geometry ) of the sub-grating itself, but is amplified by the near-field enhancement effect of the sub-grating (assuming the enhancement factor is κ>>1), i.e., σ _effective = κσ _geometry . In the optimally designed coupled grating with a multi-period structure, σ _can be infinitely close to the photosensitive detection area of the detector, that is, the detection efficiency of photons incident on the photosensitive detection area is close to 100%. It is particularly noteworthy that this process and efficiency are valid for each photon in the incident light beam, so the ideal detection of each photon with a detection efficiency close to 100% can be achieved at the same time, and it is no longer limited by the 1/n detection efficiency upper limit of the disclosed technology.

The photosensitive floating gate layer in the middle layer has photosensitivity corresponding to the coupled sub-grating. After absorbing the corresponding photons, the electrochemical potential changes, thereby changing the conductivity of the lower layer through the transconductance amplification effect.

One end of the lower channel layer is connected to the source and the other end is connected to the drain. By measuring the current of the source and the drain, the light intensity information corresponding to the multiple photons (λ ₁ , λ ₂ , …, λ _n ) can be reflected. In order to distinguish and read out the signals of different photons, pulse reset operations can be performed on different sub-grating structures. While the i-th sub-grating is pulse reset, the light signal intensity of the λ _i photon can be read out according to the synchronous change of the source and drain currents.

Embodiment 2

In order to realize electrical isolation between the floating gates of each phototransistor in the photosensitive floating gate layer, for the structure of the first embodiment, a capacitive coupling method is adopted to cut off the floating gate 200 and the floating gate 201, as shown in FIG4 , and an independent isolation gate is adopted and a negative DC bias is applied. The width of the independent isolation gate is about 100 nm, which is much smaller than the line width of the sub-gratings 100 and 101, and thus has no significant effect on the photon screening function.

Embodiment 3

In order to realize high-sensitivity detection of terahertz photons of four different target photons (λ ₁ , λ ₂ , λ ₃ , λ ₄ ), this embodiment adopts a supercell structure in a two-dimensional plane, and each supercell contains four resonant structures of different sizes (as shown in FIG. 5 ).

In summary, when the technical solution is applied in practice (such as microscope applications), it is only necessary to focus and collect the entire incident light beam without considering the different photon compositions of the incident light beam; and the light signal intensity information corresponding to multiple photons can be obtained from a single device in a time sequence.

The photon screening terahertz optical transistor proposed in the technical solution can break through the limit of less than 1/n detection efficiency of each single photon in the existing multi-photon detection technology, and can simultaneously perform multi-photon detection devices in the same photosensitive detection area without the need for prior spatial splitting, and there is no need to perform separate optical path optimization calibration for multiple photons in the application; in addition, by adopting a phototransistor structure with a transconductance amplification function, the multi-photon photoelectric gain amplification function can be realized simultaneously, thereby realizing multi-photon synchronous high-sensitivity detection of single-pixel multi-photons; in terms of manufacturing process, mature materials and device processes can be used to realize monolithic integrated multi-photon single-pixel detection devices.

Claims (9)

1. A multi-photon detection method, applied to a photon screening type terahertz optical transistor, characterized in that the photon screening type terahertz optical transistor comprises a coupling grating layer, a photosensitive floating gate layer and a channel layer which are arranged in sequence from top to bottom, the coupling grating layer comprises a plurality of sub-gratings for coupling and enhancing different target terahertz photons, the photosensitive floating gate layer is used to correspondingly absorb photons enhanced by coupling of the sub-grating structure, so as to change the electrochemical potential and thus change the conductivity of the channel layer, one end of the channel layer is connected to the source electrode, and the other end of the channel layer is connected to the drain electrode; The multiphoton detection method comprises the following steps: S1. According to the detection requirements of multi-target photons, a supercellular grating structure with multiple sub-gratings is designed and constructed to obtain a coupled grating layer; S2, designing and constructing a plurality of phototransistor floating gates that match the plurality of sub-gratings and have corresponding terahertz band response capabilities to obtain a photosensitive floating gate layer; S3, arranging the coupling grating layer and the photosensitive floating gate layer corresponding to each other up and down, and arranging a channel layer below the photosensitive floating gate layer, connecting the two ends of the channel layer to the source and the drain respectively, to manufacture a monolithic integrated photon screening type terahertz optical transistor structure; S4, connect the source and drain to an external ammeter, connect the source to a potential and detect the path current at the same time; Applying reset electrical pulse signals with different timings to the multiple sub-gratings respectively; According to the synchronous changes of the current on the source and the drain, the signal intensities of multiple different photons are obtained. 2. A multi-photon detection method according to claim 1, characterized in that the coupling grating layer specifically adopts a periodic metamaterial structure with multi-periodic characteristics. 3. A multi-photon detection method according to claim 1, characterized in that reset electrical pulse signals with different timings are applied to different sub-gratings in the coupled grating layer. 4. A multi-photon detection method according to claim 1, characterized in that the photosensitive floating gate layer is located in the near field range just below the coupling grating layer so as to be able to directly absorb the photons enhanced by the corresponding sub-grating coupling. 5 . A multi-photon detection method according to claim 1 , characterized in that the photosensitive floating gate layer comprises a plurality of phototransistor floating gates corresponding to different sub-gratings, and the plurality of phototransistor floating gates are electrically isolated from each other. 6 . The multi-photon detection method according to claim 1 , wherein the source and the drain are both composite metal electrodes. 7 . The multi-photon detection method according to claim 1 , wherein a capacitive coupling relationship is formed between the photosensitive floating gate layer and the channel layer. 8. A multi-photon detection method according to claim 1, characterized in that the step S1 specifically adopts an electromagnetic field numerical calculation simulation method to design a supercellular grating structure with multiple sub-gratings, wherein the electromagnetic field numerical calculation simulation method includes a finite time-domain difference method and a finite element method. 9 . The multi-photon detection method according to claim 1 , wherein the step S2 specifically adopts a semiconductor band engineering design method to design a plurality of phototransistor floating gates.