Low-noise photoelectric detector based on vacuum gap and preparation method thereof

Abstract

The invention discloses a low-noise photoelectric detector based on a vacuum gap and a preparation method thereof. The sensor is composed of a semiconductor pn junction sensing unit and a field emission vacuum gap, a left-end metal electrode is arranged at the left end of a pn junction, a thin vacuum gap is arranged at the right end of the pn junction, and a right-end metal electrode is arranged at the right end of the vacuum gap; a nano structure is arranged on the right end surface of the pn junction; and a bias power supply is arranged between the left end electrode and the right end electrode, and the detection current is read. According to the invention, the vacuum gap with very high insulativity is introduced, so that dark current and noise current can be greatly inhibited. In addition, a metal or semiconductor nanostructure is arranged on the right end face of the pn junction, the field emission effect of the vacuum gap is enhanced, and the responsivity of photoelectric detection is improved.

Description

Technical Field

[0001] The invention relates to a low-noise, high-sensitivity detection technology, belonging to the field of photoelectric detection technology, and in particular to a low-noise photoelectric detector based on a vacuum gap and a preparation method thereof. Background Art

[0002] With the development of information technology, photodetection has important applications in image acquisition, optical communication and other fields. Most photodetectors use the photoelectric effect of semiconductors to convert absorbed photons into photogenerated electron / hole pairs, which then form detection photocurrent. Noise and responsivity are two important performance parameters of photodetectors. In order to obtain excellent detection results, the noise of the detector is required to be as small as possible, and a sufficiently high photocurrent is also required. Photoconductive detectors are a type of photodetector with a simple structure, such as Figure 1a As shown. It deposits a left-end metal electrode 2 and a right-end metal electrode 3 at both ends of the photoconductive semiconductor 1. When incident light irradiates the photoconductive semiconductor, photogenerated electron / hole pairs are generated through the photoelectric effect. They are separated and transported under the action of the bias electric field, and finally collected by the metal electrodes at both ends to form a photocurrent. Since the photoconductor itself has a certain conductivity, even if there is no incident light irradiation, a certain current will pass through the electrodes at both ends of the detector under the action of the bias electric field. This detection current in the dark state is called dark current. Due to the influence of temperature, electromagnetic interference, etc., a larger dark current often generates a larger noise current. In order to suppress dark current and noise current, people have proposed photodiode detector structures, such as Figure 1b As shown. Compared with the photoconductive detector, the photodiode constructs a pn junction (composed of an n-type layer 5 and a p-type layer 6) by doping in a photoconductive semiconductor, and a built-in electric field exists in the depletion layer of the pn junction. The photodiode operates under a reverse bias voltage, at which time the bias electric field enhances the built-in electric field and prevents dark state carriers from being injected into the detector from the electrodes at both ends, thereby reducing the dark current and noise current. When the incident light irradiates the photodiode, the photogenerated electron / hole pairs generated in the depletion layer and its vicinity are separated under the action of the built-in electric field, and the electrons and holes drift to the electrodes at both ends respectively, and the photodiode still has a high detection response.

[0003] Compared with photoconductive detectors, the dark current of photodiodes can generally be reduced by more than one order of magnitude, and their noise current is also suppressed. However, under some harsh working conditions, such as low-light detection and high-energy X-ray detection, the incident light signal is very weak, and the photocurrent density generated in the semiconductor is often less than μA / cm 2, which may be in the same order of magnitude as the noise current. Under such working conditions, even if a high-gain signal amplifier is used, the photodiode still cannot effectively identify the signal generated by the incident light due to the low signal-to-noise ratio of the detection signal. Therefore, further reducing the dark current and noise and improving the detector's responsiveness are the directions that people have been working on. Summary of the invention

[0004] The purpose of the present invention is to provide a low-noise photodetector based on a vacuum gap and a method for preparing the same in order to address the problem of excessive dark current and noise in existing photodetectors. Since the conductivity of the vacuum gap is almost zero, the dark current of the detector in the dark state is also almost zero, thereby suppressing its noise current. When incident light irradiates the detector, under the action of the built-in electric field of the pn junction, the photogenerated electrons drift and gather to one side of the vacuum gap, thereby enhancing the electric field strength at both ends of the vacuum gap. When the electric field strength at both ends of the vacuum gap exceeds the threshold field strength, tunneling field emission occurs and a detection current is formed. Therefore, the photodetector based on a vacuum gap and a method for preparing the same proposed by the present invention can not only effectively reduce dark current and noise, but also obtain a greater detection signal responsiveness.

[0005] In order to solve the above technical problems, the specific technical methods of the present invention are as follows:

[0006] A low-noise photodetector based on a vacuum gap comprises a pn junction sensing unit and a field emission vacuum gap, the pn junction sensing unit and the field emission vacuum gap are connected in series, the pn junction sensing unit absorbs incident photons and generates photogenerated carriers, the field emission vacuum gap converts the photogenerated carriers into a vacuum field emission current, and forms a detection signal;

[0007] The pn junction sensing unit is a photoconductive semiconductor, which is doped to form an n-type layer at the left end and a p-type layer at the right end. In order to apply bias voltage and collect detection current, a left-end metal electrode is deposited at the left end of the n-type layer.

[0008] A bias power supply is set between the left-end metal electrode and the right-end metal electrode, and the detection current is read, and the bias power supply applies a forward bias electric field to the pn junction sensor unit;

[0009] The field emission vacuum gap includes a nanostructure, a vacuum gap and a right-end metal electrode; a right-end metal electrode is arranged at the right end of the p-type layer, and a gap is arranged between the right-end metal electrode and the right end of the p-type layer; a pn junction sensing unit and the right-end metal electrode are mounted together through a transparent tube shell, and a vacuum gap is formed between the right end of the p-type layer and the right-end metal electrode through processes such as vacuum exhaust; a nanostructure is arranged at the right end of the p-type layer to improve its field emission capability.

[0010] Furthermore, the energy band gap of the pn junction sensing unit is smaller than the energy of the incident light photon, so the incident light photon can be absorbed and generate electron / hole pairs through the photoelectric effect, which means that after the semiconductor absorbs the energy of the incident photon, the electron jumps from the valence band to the conduction band, leaving a hole in the valence band.

[0011] Furthermore, the thickness of the gap between the right end of the p-type layer and the right end metal electrode is ≤100 nm.

[0012] Furthermore, the nanostructure disposed at the right end of the p-type layer is metallic in nature and has a work function of ≤4 eV to facilitate field emission of electrons.

[0013] Furthermore, the nanostructure disposed at the right end of the p-type layer has semiconductor characteristics and has an electron affinity of ≤3.5 eV.

[0014] Furthermore, the aspect ratio of the nanostructure disposed at the right end of the p-type layer is ≥20, which reduces the threshold field strength of the field emission.

[0015] Furthermore, the transparent tube shell has a light-transmitting property, and the incident light passes through the tube shell and irradiates the pn junction sensing unit; the transparent tube shell has a vacuum sealing property, and through the vacuum exhaust process, the vacuum degree in the transparent tube shell is maintained at ≤10 -6 Torr.

[0016] The present invention also discloses a method for preparing a low-noise photodetector based on a vacuum gap, comprising the following steps:

[0017] Step 1: Prepare a pn junction sensing unit using a photodetector preparation process, without depositing a metal electrode at the right end of the p-type layer;

[0018] Step 2: a right-end metal electrode is arranged at the right end of the p-type layer by clamping with an insulating rod, and a gap is arranged between the right-end metal electrode and the right end of the p-type layer;

[0019] Step 3, mounting the pn junction sensing unit and the right-end metal electrode to the transparent tube shell through the tube core;

[0020] Step 4: Connect the mounted transparent tube shell, the pn junction sensor unit, and the right-end metal electrode to the vacuum exhaust table, and maintain the vacuum degree in the transparent tube shell through vacuum exhaust, baking and separation processes;

[0021] Step 5: In order to reduce the field emission threshold voltage, a nanostructure is prepared at the right end of the p-type layer.

[0022] Furthermore, the nanostructure is a molybdenum micro-cone, and the preparation method thereof is:

[0023] Deposit an insulating layer on the right end of the p-type layer by PECVD or sputtering deposition;

[0024] An array microcavity structure is prepared on the insulating layer by exposure and etching;

[0025] Molybdenum metal atoms are deposited in the microcavity structure by a dual-source deposition method, and molybdenum micro-cones are formed through adaptive stacking.

[0026] Furthermore, the nanostructure is a carbon nanotube, and the preparation method thereof is:

[0027] A metal catalyst layer is sputter-deposited on the right end of the p-type layer;

[0028] Forming a patterned metal catalyst by exposure and etching;

[0029] The PECVD method was used to grow the carbon nanotube array, and the length of the carbon nanotube was controlled by the growth time to avoid short circuit between the carbon nanotube and the right end metal electrode.

[0030] A low-noise photodetector based on a vacuum gap and a preparation method thereof of the present invention have the following advantages:

[0031] (1) The present invention introduces a field emission vacuum gap based on a pn junction photodiode detector. Since the potential barrier between the vacuum gap and the pn junction sensing unit is very high, the injection of dark state carriers is effectively blocked. Therefore, the dark state current of the vacuum gap-based photodetector proposed by the present invention is very small, and the noise current is also suppressed.

[0032] (2) When incident light irradiates the detector, under the action of the built-in electric field of the pn junction sensing unit, the photogenerated electrons drift to the interface between the pn junction sensing unit and the vacuum gap, and form negative charge accumulation, which increases the electric field strength of the vacuum gap. When the electric field strength exceeds the threshold field strength, tunneling field emission occurs and a detection photocurrent is formed. Therefore, the vacuum gap-based photodetector proposed in the present invention can suppress dark current and noise while also achieving a higher detection response. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1( a ) is a schematic diagram of the structure of a conventional photoconductive detector;

[0034] Figure 1(b) is a schematic diagram of the structure of a conventional photodiode detector;

[0035] Figure 2 It is a schematic diagram of the structure of a low-noise photodetector based on a vacuum gap of the present invention;

[0036] Figure 3 It is a partial enlarged schematic diagram of the vacuum gap part of the low-noise photodetector based on the vacuum gap of the present invention;

[0037] FIG4( a ) is a schematic diagram of the energy band structure of a conventional pn junction photodiode of a photodetector;

[0038] FIG4( b ) is a schematic diagram of the energy band structure of the vacuum gap photodetector according to the present invention;

[0039] FIG5( a ) is a diagram showing the axial one-dimensional electric field distribution obtained by numerical calculation based on the vacuum gap photodetector of the present invention;

[0040] FIG5(b) is a cross-sectional two-dimensional electric field distribution diagram obtained by numerical calculation based on the vacuum gap photodetector of the present invention.

[0041] FIG6( a ) is a diagram showing the energy band distribution of the vacuum gap-based photodetector when incident light is irradiated under a relatively small bias electric field;

[0042] FIG6( b ) is a diagram showing the energy band distribution of the vacuum gap-based photodetector when the bias electric field exceeds the threshold value when incident light is irradiated on the photodetector;

[0043] FIG. 7( a ) is a charge density distribution diagram of the axial one-dimensional space obtained by numerical calculation of the vacuum gap-based photodetector of the present invention;

[0044] FIG. 7( b ) is a cross-sectional two-dimensional spatial charge density distribution diagram obtained by numerical calculation of the photodetector based on the vacuum gap of the present invention.

[0045] Explanation of the marks in the figure: 1. photoconductive semiconductor; 2. left metal electrode; 3. right metal electrode; 4. first bias power supply; 5. n-type layer; 6. p-type layer; 7. transparent tube shell; 8. vacuum gap; 9. second bias power supply; 10. nanostructure; 11. conduction band bottom CBM; 12. quasi-hole Fermi level; 13. quasi-electron Fermi level; 14. valence band top VBM. DETAILED DESCRIPTION

[0046] In order to better understand the purpose, structure and function of the present invention, the following is a further detailed description of a low-noise photodetector based on a vacuum gap and a preparation method thereof in conjunction with the accompanying drawings.

[0047] A photodetector based on a vacuum gap comprises a pn junction sensing unit and a field emission vacuum gap, wherein the pn junction sensing unit and the field emission vacuum gap are connected in series, the pn junction sensing unit absorbs incident photons and generates photogenerated carriers, and the field emission vacuum gap converts the photogenerated carriers into a vacuum field emission current and forms a detection signal;

[0048] The pn junction sensing unit is a photoconductive semiconductor 1, which is doped to form an n-type layer 5 at the left end and a p-type layer 6 at the right end; in order to apply a bias voltage and collect a detection current, a left-end metal electrode 2 is deposited at the left end of the n-type layer 5;

[0049] The field emission vacuum gap includes a nanostructure 10, a vacuum gap 8 and a right-end metal electrode 3; the right-end metal electrode 3 is arranged at the right end of the p-type layer 6, and a gap is arranged between the right-end metal electrode 3 and the right end of the p-type layer 6; the pn junction sensing unit and the right-end metal electrode 3 are mounted together through a transparent tube shell 7, and a vacuum gap 8 is formed between the right end of the p-type layer 6 and the right-end metal electrode 3 through a vacuum exhaust process; the nanostructure 10 is arranged at the right end of the p-type layer 6 to improve its field emission capability.

[0050] exist Figure 2 In the photodetector structure shown, first, as with a conventional photodiode, an N-type layer 5 and a P-type layer 6 are prepared; a left-end metal electrode 2 is deposited at the left end of the n-type layer 5, and a distance is separated from the right end of the P-type layer 6, which is usually required to be less than 500nm, and in this embodiment is ≤100nm; a right-end metal electrode 3 is set; a transparent tube shell 7, such as glass or quartz, is used to encapsulate the photodetector, and the tube shell is evacuated by a vacuum pump to form a vacuum gap 8 between the p-type layer 6 and the right-end electrode 3. If there is no transparent tube shell 7, the gap is air instead of vacuum, and the field-induced emission electrons will be blocked by air molecules and no detection current can be formed. A second bias power supply 9 is set between the left-end metal electrode 2 and the right-end metal electrode 3. Different from the first bias power supply 4 in Figure 1, the second bias power supply 9 applies a forward bias electric field to the pn junction sensor unit, that is, the left-end metal electrode 2 is grounded and the right-end metal electrode 3 is connected to a forward bias voltage.

[0051] Since the conductivity of the vacuum gap 8 is almost zero, Figure 2 The dark state current of the vacuum gap photodetector shown is also almost zero. When incident light irradiates the pn junction sensing unit, in order to obtain a larger light response, the present invention sets a metal or semiconductor nanostructure 10 at the right end of the p-type layer 6, such as Figure 3 As shown. These nanostructures can be nanowires, nanopillars or nanocones with a scale of tens of nanometers. They have a high aspect ratio and can effectively enhance the electric field strength at the tip of the nanostructure. In addition, these metal or semiconductor nanostructures should have a low work function or electron affinity, so that the photoelectrons accumulated at the right end of the p-type layer can easily tunnel through the vacuum barrier, form field emission, and constitute photocurrent.

[0052] In order to further analyze the working mechanism of the low-noise photodetector based on the vacuum gap, the energy band distribution of the photodetector is first obtained by numerical calculation, as shown in Figure 4(a) and Figure 4(b). Figure 4(a) is the energy band structure of a conventional pn junction photodiode. It can be seen that due to the effect of the pn junction, the bottom of the conduction band CBM11, the top of the valence band VBM14, the quasi-electron Fermi level 13 and the quasi-hole Fermi level 12 are all bent in the junction region. Due to the depletion layer of the pn junction, the quasi-electron Fermi level 13 and the quasi-hole Fermi level 12 have potential barriers at both ends of the junction region. The quasi-hole Fermi level barrier prevents holes from being injected from the left electrode, and the quasi-electron Fermi level barrier prevents electrons from being injected from the right electrode. However, the height of this barrier is relatively low (generally less than 1eV), so a certain amount of dark current and noise may still appear under the action of a strong bias electric field. FIG4( b ) is an energy band structure of a vacuum gap photodetector. Since the vacuum energy level is very high, there is a potential barrier with a height of several electron volts between the vacuum gap and the p-type layer 6, which prevents the injection of dark state electrons and holes at the same time. Therefore, the dark state current of the detector is almost zero.

[0053] In order to analyze the transport of photogenerated carriers, in addition to the energy band structure of the detector, it is also necessary to understand the electric field distribution of the detector. Figure 5(a) and Figure 5(b) are the calculated electric field distributions of the photodetector based on the vacuum gap. From this electric field distribution, it can be seen that the electric field strength in the vacuum gap is very high. This is because the resistance of the vacuum gap is very large, so the bias voltage falls on the vacuum gap. However, it can also be seen from Figure 5(a) and Figure 5(b) that in addition to the high field strength area of ​​the vacuum gap, there is another area with slightly higher electric field strength in the middle of the detector. This electric field strength is formed by the built-in electric field of the pn junction, which plays a vital role in the separation of photogenerated electron / hole pairs.

[0054] When incident light hits the photodetector based on the vacuum gap, its electric field distribution is shown in Figure 5(a) and Figure 5(b). The incident photon is absorbed by the semiconductor material, and electron / hole pairs are generated through the photoelectric effect, in which the electrons jump to the bottom of the conduction band, as shown in Figure 6(a) and Figure 6(b). Since there is a built-in electric field in the pn junction sensor unit, the photogenerated holes drift to the left electrode under the action of the built-in electric field, while the photogenerated electrons drift to the right end of the pn junction. However, since the potential barrier of the vacuum gap is very high, the energy of the photogenerated electrons is not enough to cross this barrier, so the photogenerated electrons gather at the right end of the pn junction sensor unit. The gathering of a large number of electrons will cause the electric field intensity of the vacuum gap to become higher and higher. When this electric field intensity exceeds the threshold field intensity, a tunneling effect occurs between the right end of the pn junction sensor unit and the vacuum gap, that is, the vacuum gap potential barrier becomes lower and thinner, and a large number of electrons tunnel through the vacuum barrier from the right end of the pn junction to form field emission and form a detection photocurrent. Figure 7 is the spatial charge density distribution based on the vacuum gap photodetector. It can be seen that there is a depletion layer in the middle of the detector, and a large amount of negative charges (electrons) are gathered at the interface between the pn junction sensor unit and the vacuum gap. This spatial charge density distribution confirms the aforementioned detector working process from another aspect.

[0055] When incident light irradiates the detector through the transparent tube shell 7, photogenerated electron / hole pairs are generated in the pn junction sensing unit, and the built-in electric field of the pn junction sensing unit is used to separate the photogenerated electron / hole pairs, forming a negative charge (electron) accumulation on the right end surface of the pn junction; under the combined action of the bias power supply and the photogenerated electron accumulation, tunneling field emission occurs in the vacuum gap, and a detection photocurrent is formed.

[0056] When there is no light, since the resistance of the vacuum gap is close to infinity, even if a forward bias voltage is applied to the pn junction, the dark current and noise current of the detector are close to zero; when the incident light irradiates the detector, the semiconductor absorbs the incident photons and generates photogenerated electron / hole pairs. Under the action of the built-in electric field in the pn junction depletion layer, the photogenerated electrons drift to the right end face of the pn junction. Blocked by the vacuum gap barrier, these photogenerated electrons will gather at the right end face of the pn junction, increasing the electric field strength at both ends of the vacuum gap. When the electric field strength at both ends of the vacuum gap exceeds the threshold, field emission is generated due to the tunneling effect. At this time, the field emission current collected by the electrode is proportional to the intensity of the incident light, forming a detection of the incident light signal. Compared with conventional semiconductor photoconductors or photodiode detectors, the present invention can greatly suppress dark current and noise current because it introduces a vacuum gap with high insulation. In addition, the present invention proposes to set a metal or semiconductor nanostructure on the right end face of the pn junction, which enhances the field emission effect of the vacuum gap and improves the responsiveness of photoelectric detection.

[0057] The present invention also discloses a method for preparing a low-noise photodetector based on a vacuum gap, comprising the following steps:

[0058] 1) A pn ​​junction photodiode is prepared using a conventional photodetector preparation process, but no metal electrode is deposited at the right end of the p-type layer;

[0059] 2) Install the right-end metal electrode at a certain distance from the right end surface of the pn junction by means of insulating rod clamping or the like. This electrode is separated from the pn junction sensing unit by a certain distance, so it has no electrical connection with the pn junction sensing unit. In order to more easily realize field emission, the distance between the pn junction sensing unit and the right-end metal electrode is very small, and the typical gap thickness is less than 100nm;

[0060] 3) Mount the pn junction sensing unit and the right-end metal electrode through the tube core to a transparent tube shell, such as glass, quartz, etc. The transparent tube shell must first have vacuum sealing performance, secondly, it must have good light transmittance to the incident light, and finally, it must be able to withstand a baking temperature above 300°C;

[0061] 4) Connect the mounted transparent tube shell, pn junction sensor unit, and metal electrode to the vacuum exhaust table, and maintain a high vacuum degree in the transparent tube shell through conventional vacuum exhaust, baking, and separation processes. Considering the high voltage sparking problem that field emission devices are prone to, the vacuum degree in the tube shell is generally better than 10 -6 Torr;

[0062] 5) In order to reduce the field emission threshold voltage, some nanostructures can be prepared on the right end of the pn junction and used as electron field emitters. Taking typical molybdenum micro-cones and carbon nanotubes as examples, the preparation method is as follows;

[0063] Molybdenum micro-cone preparation:

[0064] 1. Deposit an insulating layer on the right end surface of the pn junction sensing unit by PECVD or sputtering deposition;

[0065] 2. Prepare an array microcavity structure on the insulating layer by exposure and etching;

[0066] 3. Molybdenum metal atoms are deposited in the microcavity using a conventional dual-source deposition method, and molybdenum micro-cones are formed through adaptive stacking.

[0067] Carbon nanotube preparation:

[0068] 1. Sputtering and depositing a metal catalyst layer on the right end surface of the pn junction sensing unit;

[0069] 2. Forming a patterned metal catalyst by exposure and etching;

[0070] 3. Use the conventional PECVD method to grow the carbon nanotube array, and control the length of the carbon nanotube by the growth time to avoid short circuit between the carbon nanotube and the right end metal electrode.

[0071] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A low-noise photodetector based on a vacuum gap, characterized in that: It includes a pn junction sensing unit and a field emission vacuum gap, the pn junction sensing unit and the field emission vacuum gap are connected in series, the pn junction sensing unit absorbs incident photons and generates photogenerated carriers, the field emission vacuum gap converts the photogenerated carriers into vacuum field emission currents, and forms detection signals; The pn junction sensing unit is a photoconductive semiconductor, which is doped to form an n-type layer at the left end and a p-type layer at the right end. In order to apply bias voltage and collect detection current, a left-end metal electrode is deposited at the left end of the n-type layer. A bias power supply is set between the left-end metal electrode and the right-end metal electrode, and the detection current is read, and the bias power supply applies a forward bias electric field to the pn junction sensor unit; The field emission vacuum gap includes a nanostructure, a vacuum gap and a right-end metal electrode; a right-end metal electrode is arranged at the right end of the p-type layer, and a gap is arranged between the right-end metal electrode and the right end of the p-type layer; a pn junction sensing unit and the right-end metal electrode are mounted together through a transparent tube shell, and a vacuum gap is formed between the right end of the p-type layer and the right-end metal electrode through a vacuum exhaust process; a nanostructure is arranged at the right end of the p-type layer to improve its field emission capability.

2. The vacuum gap based low noise photodetector according to claim 1, characterized in that: The energy band gap of the pn junction sensing unit is smaller than the energy of the incident light photon, so the incident light photon can be absorbed and generate electron / hole pairs through the photoelectric effect.

3. The low-noise photodetector based on vacuum gap according to claim 2, characterized in that: The thickness of the gap between the right end of the p-type layer and the right end metal electrode is ≤100nm.

4. The vacuum gap based low noise photodetector according to claim 1, characterized in that: The nanostructure disposed at the right end of the p-type layer is metallic in nature and has a work function of ≤4 eV to facilitate field emission of electrons.

5. The vacuum gap based low noise photodetector according to claim 1, characterized in that: The nanostructure provided at the right end of the p-type layer has semiconductor characteristics and has an electron affinity of ≤3.5 eV.

6. The vacuum gap based low noise photodetector according to claim 1, characterized in that: The aspect ratio of the nanostructure arranged at the right end of the p-type layer is ≥20, which reduces the threshold field intensity of field emission.

7. The vacuum gap based low noise photodetector according to claim 1, characterized in that: The transparent tube shell has the property of light transmission, and the incident light passes through the tube shell to irradiate the pn junction sensor unit; the transparent tube shell has the property of vacuum sealing, and through the vacuum exhaust process, the vacuum degree in the transparent tube shell is maintained at ≤10 -6 Torr.

8. A method for preparing a low-noise photodetector based on a vacuum gap as claimed in any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: Prepare a pn junction sensing unit using a photodetector preparation process, without depositing a metal electrode at the right end of the p-type layer; Step 2: a right-end metal electrode is arranged at the right end of the p-type layer by clamping with an insulating rod, and a gap is arranged between the right-end metal electrode and the right end of the p-type layer; Step 3, mounting the pn junction sensing unit and the right-end metal electrode to the transparent tube shell through the tube core; Step 4: Connect the mounted transparent tube shell, the pn junction sensor unit, and the right-end metal electrode to the vacuum exhaust table, and maintain the vacuum degree in the transparent tube shell through vacuum exhaust, baking and separation processes; Step 5: In order to reduce the field emission threshold voltage, a nanostructure is prepared at the right end of the p-type layer.

9. A method for preparing the low-noise photodetector based on vacuum gap as claimed in claim 8, characterized in that: The nanostructure is a molybdenum micro-cone, and the preparation method thereof is as follows: Deposit an insulating layer on the right end of the p-type layer by PECVD or sputtering deposition; An array microcavity structure is prepared on the insulating layer by exposure and etching; Molybdenum metal atoms are deposited in the microcavity structure by a dual-source deposition method, and molybdenum micro-cones are formed through adaptive stacking.

10. A method for preparing the low-noise photodetector based on vacuum gap according to claim 8, characterized in that: The nanostructure is a carbon nanotube, and the preparation method thereof is: A metal catalyst layer is sputter-deposited on the right end of the p-type layer; Forming a patterned metal catalyst by exposure and etching; The PECVD method was used to grow the carbon nanotube array, and the length of the carbon nanotube was controlled by the growth time to avoid short circuit between the carbon nanotube and the right end metal electrode.

Images