Non-refrigeration high-performance infrared detector
By introducing field emission true space gaps into infrared photodetectors, blocking thermal noise current and forming detection signals through tunneling field emission, the problem of dark current and excessive noise of infrared photodetectors is solved, and the signal-to-noise ratio and specific detection are improved.
Patent Information
- Application Number
- CN202422214637.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-10
- Publication Date
- 2025-06-13
- Estimated Expiration
- 2034-09-10
AI Technical Summary
The dark current and noise of existing infrared photodetectors are too high, resulting in insufficient signal-to-noise ratio and specific detection.
An infrared detector based on the true space gap is adopted to introduce a field emission true space gap into the narrow band gap semiconductor pn structure to block the thermal noise current caused by ambient temperature, and to form a detection signal through the tunneling field emission of photogenerated electrons.
It effectively reduces dark current and noise, improves detection signal response, and enhances signal-to-noise ratio and specific detection.
Smart Images
Figure CN222978944U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to low-noise and high-sensitivity infrared detection technology, belonging to the field of optoelectronic detection technology, and particularly relates to an uncooled infrared detector. Background Art
[0002] The function of an infrared detector is to convert the incident infrared signal into an electrical signal. Its working mechanism and physical process are very similar to those of visible light detection. However, due to the longer wavelength and lower photon energy of infrared rays, compared with visible light detection, the infrared detector has its particularity. Since the infrared photon energy is low, a semiconductor with a very narrow bandgap (≤1.4 eV) needs to be selected as the infrared detection active material so as to meet the requirement that the incident photon energy is greater than the bandgap. However, when the energy bandgap of the active semiconductor is very small, the energy fluctuation caused by the ambient temperature will cause some electrons to jump from the valence band across the narrow bandgap to the conduction band, thus forming a noise current. Therefore, even with a pn structure, the signal-to-noise ratio and specific detectivity of the infrared detector are not high enough. In order to improve the signal-to-noise ratio and specific detectivity of the infrared detector, it is proposed to use a Stirling cooler 1, a cooler mounting flange 2, a vacuum dewar 3, a cooler mounting flange 4, and an optical input window 5 shown in Fig. 1(a) to make the infrared detection chip work in a low-temperature environment (tens of K temperature) to reduce the detection noise.
[0003] Although cooling the working environment can effectively reduce the infrared detection noise current and improve the detection sensitivity, it can be seen from the cooled detector structures shown in Fig. 1(a) and Fig. 1(b) that the detection system is very complex. In addition to the cooler 1 and the vacuum dewar 3, it also requires an optical window 5, a getter 6, an infrared focal plane sensor 7, a cooling filter 8, a cooling filter 9, a cooling shield 10, a cooling shield 11, a cooling disk 12, and a cooling rod 13. The whole infrared detector is large in volume and weight and has low integration. Therefore, there is an important need to develop an uncooled infrared detector. Generally speaking, an infrared thermoelectric detector does not require a cooled working environment, but its visible resolution, response speed, etc. are much lower than those of infrared optoelectronic detection. Therefore, improving the signal-to-noise ratio and specific detectivity of infrared optoelectronic detection under uncooled conditions has been the direction that people have been working hard on. Summary of the Utility Model
[0004] The object of the present utility model is to provide a low-noise infrared photodetector based on a vacuum gap for the problems of excessive dark current and noise in existing infrared 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 infrared light irradiates the detector, under the action of the built-in electric field of the pn junction, photo-generated electrons drift and accumulate towards the vacuum gap side, 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 uncooled infrared detector based on the vacuum gap proposed by the present utility model can not only effectively reduce the dark current and noise, but also obtain a large detection signal responsivity.
[0005] To solve the above technical problems, the specific technical method of the present utility model is as follows:
[0006] An uncooled high-performance infrared detector includes an infrared sensing unit composed of a narrow-bandgap semiconductor pn junction and a field emission vacuum gap. The infrared sensing unit and the field emission vacuum gap are connected in series. The infrared sensing unit absorbs incident infrared photons and generates photo-generated carriers; the field emission vacuum gap first blocks the thermal noise current generated by the narrow-bandgap semiconductor due to the ambient temperature, converts the photo-generated carriers into vacuum field emission current, and forms a detection signal;
[0007] The infrared sensing unit is a photoconductive semiconductor with an energy bandgap less than 1.4 eV. An n-type layer is formed at the left end by doping, and a p-type layer is formed at the right end; in order to apply a bias voltage and collect the detection current, a left-end metal electrode is deposited at the left end of the n-type layer;
[0008] A bias power supply is arranged between the left-end metal electrode and the right-end metal electrode, and the detection current is read. The bias power supply applies a forward bias electric field to the narrow-bandgap semiconductor pn junction sensing 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 there is a gap between the right-end metal electrode and the right end of the p-type layer; the pn junction sensing unit and the right-end metal electrode are mounted together through a transparent shell, and through a vacuum exhaust process, a vacuum gap is formed between the right end of the p-type layer and the right-end metal electrode; a nanostructure is arranged at the right end of the p-type layer to improve its field emission ability;
[0010] The energy bandgap of the narrow-bandgap semiconductor pn junction sensing unit is less than the energy of the incident infrared photons, so the incident infrared photons are absorbed and electron / hole pairs are generated through the photoelectric effect;
[0011] The gap thickness between the right end of the p-type layer and the right-end metal electrode ≤ 100 nm.
[0012] Furthermore, the field emission vacuum gap is in a cut-off state at room temperature. The thermally generated noise carriers of the narrow bandgap semiconductor are blocked by this gap and cannot reach the right-end electrode to form a current. When incident infrared photons irradiate the pn junction sensing unit of the narrow bandgap semiconductor, due to the action of photo-generated carriers, the field emission vacuum gap is in a state where electrons can tunnel through, and an infrared detection signal is formed through the vacuum field emission current.
[0013] Furthermore, the nanostructure provided at the right end of the p-type layer has metallic properties and a work function of ≤ 4 eV to facilitate field emission of electrons.
[0014] Furthermore, the nanostructure provided at the right end of the p-type layer has semiconductor properties and an electron affinity of ≤ 3.5 eV.
[0015] Furthermore, the aspect ratio of the nanostructure provided at the right end of the p-type layer is ≥ 20, reducing the threshold field strength of field emission.
[0016] Furthermore, the transparent shell has light-transmitting properties, and incident light passes through the shell and irradiates the pn junction sensing unit; the transparent shell has vacuum sealing properties, and through the vacuum exhaust process, the vacuum degree inside the transparent shell is maintained at ≤ 10 -6 Torr.
[0017] A non-cooled high-performance infrared detector of the present utility model has the following advantages:
[0018] 1. The present utility model introduces a field emission vacuum gap on the basis of a pn junction infrared photodiode detector. Since the potential barrier between the vacuum gap and the infrared sensing pn junction is very high, the injection of dark-state carriers is effectively blocked. Therefore, the dark current of the non-cooled high-performance infrared detector proposed by the present utility model is very small, and the noise current is also suppressed.
[0019] 2. When incident infrared light irradiates the detector, under the action of the built-in electric field of the pn junction, photo-generated electrons drift towards the interface between the pn junction and the vacuum gap and form a negative charge accumulation, increasing the electric field strength of the vacuum gap. When this electric field strength exceeds the threshold field strength, tunneling field-induced electron emission occurs and a detected photocurrent is formed. Therefore, the non-cooled high-performance infrared detector proposed by the present utility model can obtain a high detection responsivity while suppressing dark current and noise. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1(a) is a schematic structural diagram of a cooled infrared detector;
[0021] FIG. 1(b) is a schematic diagram of the mounting head of an infrared sensing chip;
[0022] Figure 2 is a schematic structural diagram of the non-cooled high-performance infrared detector of the present utility model;
[0023] Figure 3 Partial enlarged schematic diagram of the vacuum gap part of the uncooled high-performance infrared detector of the present invention;
[0024] Figure 4(a) is a schematic diagram of the energy band structure of a conventional pn junction photodiode of a photodetector;
[0025] Figure 4(b) is a schematic diagram of the energy band structure of the uncooled high-performance infrared detector of the present invention;
[0026] Figure 5(a) is an axial one-dimensional electric field distribution diagram obtained by numerical calculation of the uncooled high-performance infrared detector of the present invention;
[0027] Figure 5(b) is a cross-sectional two-dimensional electric field distribution diagram obtained by numerical calculation of the uncooled high-performance infrared detector of the present invention
[0028] Figure 6(a) is an energy band distribution diagram of the uncooled high-performance infrared detector of the present invention when irradiated by incident light under a small bias electric field;
[0029] Figure 6(b) is an energy band distribution diagram of the uncooled high-performance infrared detector of the present invention when irradiated by incident light after the bias electric field exceeds the threshold;
[0030] Figure 7(a) is an axial one-dimensional space charge density distribution diagram obtained by numerical calculation of the uncooled high-performance infrared detector of the present invention;
[0031] Figure 7(b) is a cross-sectional two-dimensional space charge density distribution diagram obtained by numerical calculation of the uncooled high-performance infrared detector of the present invention. Marking description in the figure: 1. Refrigerator; 2. Refrigerator mounting flange; 3. Dewar; 4. Focal plane sensor mounting table; 5. Optical input window; 6. Getter; 7. Infrared focal plane sensor; 8. Refrigeration filter; 9. Infrared window; 10. Refrigeration shield; 11. Electrical insulation ring; 12. Refrigeration plate; 13. Refrigeration rod; 14. Left-end metal electrode; 15. Bias power supply; 16. n-type layer; 17. P-type layer; 18. Vacuum gap; 19. Right-end metal electrode; 20. Transparent shell; 21. Nanostructure; 22. Conduction band bottom CBM; 23. Quasi-hole Fermi level; 24. Quasi-electron Fermi level; 25. Valence band top VBM. Detailed implementation manners
[0032] In order to better understand the purpose, structure and function of the present invention, the following further describes in detail a non-cooled high-performance infrared detector of the present invention with reference to the accompanying drawings.
[0033] A non-cooled high-performance infrared detector includes an infrared sensing unit composed of a narrow-bandgap semiconductor pn junction and a field emission vacuum gap. The infrared sensing unit and the field emission vacuum gap are connected in series. The infrared sensing unit absorbs incident infrared photons and generates photo-generated carriers, and the field emission vacuum gap converts the photo-generated carriers into a vacuum field emission current and forms a detection signal.
[0034] The infrared sensing unit is a photoconductive semiconductor with a very small energy bandgap. An n-type layer 16 is formed at the left end by doping, and a p-type layer 17 is formed at the right end. In order to apply a bias voltage and collect the detection current, a left-end metal electrode 14 is deposited at the left end of the n-type layer 5.
[0035] The field emission vacuum gap includes a nanostructure 21, a vacuum gap 18, and a right-end metal electrode 19. A right-end metal electrode 19 is provided at the right end of the p-type layer 17, and there is a gap between the right-end metal electrode 19 and the right end of the p-type layer 17. The narrow-bandgap pn junction infrared sensing unit and the right-end metal electrode 19 are mounted together through a transparent shell 20. Through a vacuum evacuation process, a vacuum gap 18 is formed between the right end of the p-type layer 17 and the right-end metal electrode 19. A nanostructure 21 is provided at the right end of the p-type layer 17 to improve its field emission ability.
[0036] In Figure 2 In the infrared detector structure shown, first, like a conventional photodiode, an N-type layer 16 and a P-type layer 17 are fabricated. A left-end metal electrode 14 is deposited at the left end of the n-type layer 16, and at the right end of the P-type layer 17, there is a distance, which is usually required to be less than 500 nm, and in this embodiment, ≤100 nm. A right-end metal electrode 19 is provided. A transparent shell 20, such as glass or quartz, is used to encapsulate the photodetector, and the inside of the shell is evacuated by a vacuum pump so that a vacuum gap 18 is formed between the p-type layer 17 and the right-end electrode 19. Without the transparent shell 20, the gap is air instead of vacuum, and the field emission electrons will be blocked by air molecules and no detection current can be formed. A bias power supply 15 is provided between the left-end metal electrode 14 and the right-end metal electrode 19 to apply a forward bias electric field to the infrared sensing unit, that is, the left-end metal electrode 14 is grounded and the right-end metal electrode 19 is connected to a positive bias voltage.
[0037] Since the conductivity of the vacuum gap 18 is almost zero, the dark current of the vacuum-gap-based photodetector shown is also almost zero in the absence of light. When incident light irradiates the narrow-bandgap pn junction infrared sensing unit, in order to obtain a large optical responsivity, in the present invention, a nanostructure 21 of metal or semiconductor is provided at the right end of the p-type layer 17, such as Figure 2 shown Figure 3As shown. These nanostructures can be nanowires, nanorods, or nanocones with a scale of dozens of nanometers. They have a high aspect ratio and can effectively enhance the electric field strength at the tip of the nanostructure. Additionally, these metal or semiconductor nanostructures should have a low work function or electron affinity, enabling the photoelectrons accumulated at the right end of the p-type layer to easily tunnel through the vacuum barrier, forming field emission and constituting a photocurrent.
[0038] To further analyze the working mechanism of the uncooled high-performance infrared detector, first, the energy band distribution of the infrared detector is obtained by numerical calculation, as shown in Figs. 4(a) and 4(b). Fig. 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 conduction band bottom CBM21, valence band top VBM25, quasi-electron Fermi level 23, and quasi-hole Fermi level 24 are all bent in the junction region. Due to the existence of a depletion layer in the pn-junction, there are potential barriers at both ends of the junction region for the quasi-electron Fermi level 23 and quasi-hole Fermi level 24. The potential barrier of the quasi-hole Fermi level prevents holes from being injected from the left electrode, and the potential barrier of the quasi-electron Fermi level prevents electrons from being injected from the right electrode. However, the height of this potential barrier is relatively low (generally less than 1 eV), so there may still be a certain amount of dark current and noise under the action of a strong bias electric field. Fig. 4(b) is the 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 17, which simultaneously prevents the injection of dark-state electrons and holes. Therefore, the dark-state current of this detector is almost zero.
[0039] To analyze the transport of photo-generated carriers, in addition to the energy band structure of the detector, the electric field distribution of the detector also needs to be understood. Figs. 5(a) and 5(b) are the calculated electric field distributions of the uncooled high-performance infrared detector. From this electric field distribution, it can be seen that the electric field strength in the vacuum gap is very high because the resistance of the vacuum gap is very large, so the bias voltage drops across the vacuum gap. However, it can also be seen from Figs. 5(a) and 5(b) that in addition to the high-field region of the vacuum gap, there is another region with a 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 and plays a crucial role in the separation of photo-generated electron / hole pairs.
[0040] When incident light irradiates a non-cooled infrared detector, its electric field distribution is shown in Figures 5(a) and 5(b). The incident infrared photons are absorbed by the semiconductor material, and electron / hole pairs are generated through the photoelectric effect, where electrons transition to the bottom of the conduction band, as shown in Figures 6(a) and 6(b). Due to the built-in electric field in the narrow-bandgap pn-junction infrared sensing unit, the photo-generated holes drift towards the left electrode under the action of the built-in electric field, while the photo-generated electrons drift towards the right end of the pn-junction. However, due to the high potential barrier of the vacuum gap, the energy of the photo-generated electrons is not sufficient to overcome this potential barrier at this time, so the photo-generated electrons accumulate at the right end of the pn-junction sensing unit. The accumulation of a large number of electrons will cause the electric field strength in the vacuum gap to become higher and higher. When this electric field strength exceeds the threshold field strength, a tunneling effect occurs at the right end of the pn-junction sensing unit and the vacuum gap, that is, the potential barrier of the vacuum gap becomes lower and thinner, and a large number of electrons tunnel through the vacuum potential barrier from the right end of the pn-junction to form field emission, and a detection photocurrent is formed. Figure 7 shows the space charge density distribution of the non-cooled infrared detector. It can be seen from it that there is a depletion layer in the middle of the detector, and a large number of negative charges (electrons) accumulate at the interface between the narrow-bandgap pn-junction infrared sensing unit and the vacuum gap. This space charge density distribution corroborates the aforementioned detector working process from another perspective.
[0041] When the incident infrared light irradiates the detector through the transparent housing 20, photo-generated electron / hole pairs are generated in the narrow-bandgap pn-junction infrared sensing unit, and the built-in electric field of the narrow-bandgap pn-junction infrared sensing unit is used to separate the photo-generated electron / hole pairs, and negative charges (electrons) accumulate on the right end face of the pn-junction; under the combined action of the bias power supply and the accumulation of photo-generated electrons, a tunneling field emission occurs in the vacuum gap, and a detection photocurrent is formed.
[0042] When there is no light illumination, 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 both close to zero; when incident light irradiates the detector, the semiconductor absorbs the incident photons and generates photo-generated electron / hole pairs. Under the action of the built-in electric field of the pn-junction depletion layer, the photo-generated electrons drift towards the right end face of the pn-junction. Blocked by the potential barrier of the vacuum gap, these photo-generated electrons will accumulate on 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, due to the tunneling effect, field emission occurs. At this time, the field emission current collected by the electrode is proportional to the incident light intensity, forming the detection of the incident light signal. Compared with conventional semiconductor photoconductive or photodiode detectors, since the present utility model introduces a vacuum gap with very high insulation, the dark current and noise current formed by the narrow-bandgap semiconductor due to the ambient temperature can be greatly suppressed. In addition, the present utility model proposes to set a metal or semiconductor nanostructure on the right end face of the pn-junction, enhancing the field emission effect of the vacuum gap and improving the responsivity of the photoelectric detection.
[0043] It can be understood that the present utility model is described through some embodiments. Those skilled in the art know that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present utility model. Additionally, under the teaching of the present utility model, these features and embodiments can be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present utility model. Therefore, the present utility model is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present utility model.
Claims
1. An uncooled high-performance infrared detector, characterized in that: The infrared sensing unit comprises an infrared sensing unit and a field emission vacuum gap formed by a narrow bandgap semiconductor pn structure, the infrared sensing unit and the field emission vacuum gap are connected in series, and the infrared sensing unit absorbs infrared incident photons and generates photogenerated carriers; The field emission vacuum gap blocks the thermal noise current generated by the narrow bandgap semiconductor due to the ambient temperature, converts the photogenerated carriers into vacuum field emission current, and forms a detection signal; The infrared sensing unit is a photoconductive semiconductor with an energy band gap of less than 1.4 eV. An n-type layer is formed at the left end and a p-type layer is formed at the right end by doping. 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 provided between the left-end metal electrode and the right-end metal electrode, and the detection current is read, wherein the bias power supply applies a forward bias electric field to the narrow bandgap semiconductor pn junction sensing 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 to form a vacuum gap between the right end of the p-type layer and the right-end metal electrode; a nanostructure is arranged at the right end of the p-type layer to improve its field emission capability; The energy band gap of the narrow bandgap semiconductor pn junction sensing unit is smaller than the energy of the incident infrared photon, and the incident infrared photon is absorbed and generates electron / hole pairs through the photoelectric effect; The thickness of the gap between the right end of the p-type layer and the right end metal electrode is ≤100nm.
2. The uncooled high-performance infrared detector according to claim 1, characterized in that: The field emission vacuum gap is in a cut-off state at room temperature, and the thermal noise carriers of the narrow-bandgap semiconductor are blocked by the gap and cannot reach the right-end electrode to form a current; when the incident infrared photons irradiate the narrow-bandgap semiconductor pn junction sensor unit, due to the action of photogenerated carriers, the field emission vacuum gap is in an electron tunneling state, and an infrared detection signal is formed through the vacuum field emission current.
3. The uncooled high-performance infrared detector 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.
4. The uncooled high-performance infrared detector 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.
5. The uncooled high-performance infrared detector 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.
6. The uncooled high-performance infrared detector 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.