Low-temperature thermal evaporation deposition tellurium / germanium heterojunction photoelectric detector and preparation method thereof

Abstract

The invention belongs to the technical field of semiconductor materials and devices, and discloses a low-temperature thermal evaporation deposition tellurium / germanium heterojunction photoelectric detector and a preparation method thereof. The photoelectric detector comprises a germanium substrate, a tellurium thin film, a metal top electrode and a metal bottom electrode, the tellurium thin film is a polycrystalline tellurium film layer containing a micron-sized large domain, the surface roughness is lower than 1nm, and the tellurium thin film is in close contact with the germanium substrate to form a heterojunction; the metal top electrode is a platinum / gold laminated electrode, and the metal bottom electrode is an indium gallium alloy / copper foil electrode. The tellurium thin film with large crystal domain and low roughness grows on the germanium substrate through a-low temperature (-80 DEG C to-160 DEG C) thermal evaporation deposition process, and the electrode is prepared by combining a micro-nano processing technology. Compared with traditional molecular beam epitaxy, pulse laser deposition and other methods, the method is low in process cost and compatible with the integrated circuit technology, and the obtained heterojunction photoelectric detector has the excellent rectification characteristic and infrared light response and is suitable for large-scale preparation and practical application.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor materials and optoelectronic devices, and more specifically, relates to a tellurium / germanium heterojunction photodetector based on sub-zero low-temperature thermal evaporation deposition and a preparation method thereof. Background Art

[0002] The construction of semiconductor heterostructures is the cornerstone of functional electronic and optoelectronic devices. In the field of photodetection, the integration of heterostructures plays an indispensable role in achieving high-performance, functional applications such as broadband detection, fast light response, high detectivity, and flexible detectors. In addition, the construction of large-scale heterojunctions and their heterogeneous integration with readout circuits are the basis for realizing large-scale detection arrays and imaging applications. However, the growth temperature of most commercial three-dimensional materials and two-dimensional transition metal chalcogenides is generally higher than 400°C, which severely limits the choice of substrate materials. Temperature-sensitive materials, such as flexible polyester fiber substrates and silicon-based readout circuits, will fail at high temperatures, thus limiting the heterogeneous integration of materials.

[0003] Commercial germanium single crystals play an indispensable role in infrared photodetection. However, due to their narrow bandgap of 0.67 eV, their response wavelength is limited to ~2 μm, making them difficult to detect mid-wave infrared light. To improve germanium's detection performance and broaden its detection wavelength, heterojunctions can be formed with materials with narrower bandgap values. However, traditional commercial narrow-bandgap materials, such as indium gallium arsenide and mercury cadmium telluride, exhibit significant lattice mismatch with germanium and require high growth temperatures, making high-quality heterojunctions difficult to construct. Low-temperature growth methods can be used to construct heterojunctions, minimizing damage to the substrate material. Current research into low-temperature fabrication processes for two-dimensional (2D) materials paves the way for high-quality heterojunction integration. Among the many low-temperature-gap 2D materials, tellurium (T) offers the potential for high-performance mid-wave infrared detection due to its narrow bandgap of 0.33 eV and high hole mobility. It can be formed into heterojunctions with Ge for broadband detection. However, current large-scale tellurium-based growth generally adopts complex and high-cost methods such as molecular beam epitaxy, atomic layer deposition, and pulsed laser deposition, and its room-temperature preparation process usually results in smaller grains and higher surface roughness.

[0004] Therefore, there is an urgent need to explore effective methods to construct low-cost, large-area, high-quality tellurium / germanium heterojunctions and process photodetection devices. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvements in the prior art, the present invention aims to provide a tellurium / germanium heterojunction photodetector based on sub-zero thermal evaporation deposition and a method for its fabrication. The heterojunction is formed by depositing a tellurium thin film on a sub-zero germanium substrate (below -80°C) using thermal evaporation, and then fabricating the heterojunction photodetector through micro-nanofabrication. The present invention utilizes thermal evaporation to produce a low-roughness, large-domain tellurium thin film on a sub-zero germanium substrate. Furthermore, the heterojunction photodetector fabricated in this manner exhibits excellent rectification characteristics and infrared light response, is cost-effective, and can be easily manufactured on a large scale, thus possessing significant potential for practical applications.

[0006] According to a first aspect of the present invention, a tellurium / germanium heterojunction photodetector is provided, comprising a germanium substrate and a tellurium thin film deposited on the surface of the germanium substrate, wherein the tellurium thin film is a polycrystalline tellurium film layer containing micron-scale crystal domains, has a surface roughness of less than 1 nm, and is in close contact with the germanium substrate to form a heterojunction; and further comprises a metal top electrode arranged above the tellurium thin film, and a metal bottom electrode arranged below the germanium substrate.

[0007] Preferably, the size of the crystal domain of the tellurium thin film is 1 μm to 10 μm.

[0008] Preferably, the metal top electrode is a platinum / gold stacked electrode, wherein the platinum layer directly contacts the tellurium thin film; and the metal bottom electrode is an indium gallium alloy / copper foil electrode, wherein the indium gallium alloy directly contacts the germanium substrate.

[0009] According to another aspect of the present invention, a method for preparing the tellurium / germanium heterojunction photodetector is provided, comprising the following steps: (1) Place the germanium substrate and tellurium powder in a vacuum thermal evaporation coating system, with the germanium substrate placed on the substrate substrate and the tellurium powder placed in a quartz crucible heater; (2) Vacuum filter the thermal evaporation coating system; (3) Cooling the substrate to below -80°C by external liquid nitrogen perfusion; (4) Heating tellurium powder under vacuum conditions for thermal evaporation deposition while keeping the substrate rotating to obtain a tellurium / germanium heterojunction; (5) Prepare the top electrode and the bottom electrode to obtain a tellurium / germanium heterojunction photodetector.

[0010] Preferably, in step (2), the vacuum filtration is to evacuate to a pressure lower than .

[0011] Preferably, the deposition rate is ≤ 2 Å / s.

[0012] Preferably, the thickness of the deposited layer is 30-50 nm.

[0013] Preferably, the substrate is cooled to -80°C to -160°C.

[0014] Preferably, in step (5), a platinum / gold top electrode is prepared on the tellurium thin film by photolithography, development and deposition processes; and then the tellurium thin film outside the metal top electrode area is removed by an etching process.

[0015] Preferably, in step (5), an indium gallium alloy is coated under the germanium substrate and a copper foil is attached to form a metal bottom electrode. The above technical solution conceived by the present invention can achieve the following beneficial effects compared with the prior art: (1) In the tellurium / germanium heterojunction obtained by the low-temperature method of the present invention, tellurium has the characteristics of large crystal domains and low roughness (roughness less than 1 nm). The maximum crystal domain size can reach ~10 μm, which is much larger than the nano-scale grains obtained by traditional room temperature or high temperature methods. In addition, the roughness can be as low as 0.87 nm, which is much lower than that of tellurium films grown at room temperature.

[0016] (2) The tellurium / germanium heterojunction photodetector obtained by the low-temperature method of the present invention exhibits excellent rectification characteristics and 1550nm infrared light response, wherein the rectification ratio is as high as ~1.47×10 4 , the light-to-dark current ratio is as high as 248.34 under -1V bias.

[0017] (3) The present invention is based on a tellurium / germanium heterojunction photodetector and its preparation method based on sub-zero low-temperature (below -80°C) thermal evaporation deposition. The photodetector is prepared by growing a tellurium thin film on a sub-zero low-temperature substrate and then performing micro-nanofabrication. The present invention uses a vacuum thermal evaporation coating process, which is significantly different from traditional methods such as molecular beam epitaxy, pulsed laser deposition, and atomic layer deposition, effectively avoiding the high cost and maintenance of equipment and cumbersome process flows.

[0018] (4) The micro-nano fabrication technology used in the present invention is compatible with the processes currently used in integrated circuits and is suitable for the preparation and application of large-scale array devices. The photodetector fabrication method of the present invention is simple, controllable, low-cost, and easy to manufacture on a large scale. The resulting photodetector has excellent photoelectric performance and therefore has great potential in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic structural diagram of the tellurium / germanium heterojunction photodetector based on sub-zero low-temperature thermal evaporation deposition according to the present invention.

[0020] Figure 2 This is a flow chart for preparing a tellurium / germanium heterojunction photodetector based on sub-zero low-temperature thermal evaporation deposition according to the present invention.

[0021] Figure 3This is the Raman spectrum of the tellurium / germanium heterojunction prepared in Example 1.

[0022] Figure 4 This is a high-resolution scanning transmission electron microscope image of the tellurium / germanium heterojunction prepared in Example 1.

[0023] Figure 5 1 is a scanning transmission electron microscope image of the tellurium / germanium heterojunction prepared in Example 1 and its element distribution.

[0024] Figure 6 This is a polarizing microscope image of the surface tellurium film of the tellurium / germanium heterojunction prepared in Example 1.

[0025] Figure 7 This is an atomic force microscope image of the surface tellurium film of the tellurium / germanium heterojunction prepared in Example 1.

[0026] Figure 8 This is a current-voltage curve of dark current and photocurrent of the tellurium / germanium heterojunction photodetector based on sub-zero low-temperature thermal evaporation deposition prepared in Example 1.

[0027] Figure 9 This is a polarizing microscope image of the surface tellurium film of the tellurium / germanium heterojunction prepared in Example 2.

[0028] Figure 10 This is a polarizing microscope image of the surface tellurium film of the tellurium / germanium heterojunction prepared in Example 3.

[0029] Figure 11 This is an atomic force microscope image of the surface tellurium film of the tellurium / germanium heterojunction prepared in Comparative Example 1.

[0030] Figure 12 This is a scanning electron microscope image of the surface tellurium film of the tellurium / germanium heterojunction prepared in Comparative Example 1. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0032] The present invention discloses a tellurium / germanium heterojunction photodetector based on sub-zero low-temperature thermal evaporation deposition, comprising a germanium substrate and a tellurium thin film deposited on the surface of the germanium substrate. The tellurium thin film is a polycrystalline tellurium film layer containing micron-scale crystal domains, has a surface roughness of less than 1 nm, and is in close contact with the germanium substrate to form a heterojunction. The detector also comprises a metal top electrode disposed above the tellurium thin film and a metal bottom electrode disposed below the germanium substrate, wherein: As a further preferred embodiment of the present invention, the size of the crystal domain of the tellurium thin film is 1 μm to 10 μm; As a further preferred embodiment of the present invention, the resistivity of the germanium substrate is 5-10 Ωcm -1 ; As a further preferred embodiment of the present invention, the metal top electrode is a platinum / gold stacked electrode, and the platinum layer in the platinum / gold stacked electrode is used to directly contact the tellurium thin film; As a further preferred embodiment of the present invention, the metal bottom electrode is an indium gallium alloy / copper foil electrode, wherein the indium gallium alloy in the indium gallium alloy / copper foil electrode is used to directly contact the germanium substrate; The present invention provides a method for preparing the above-mentioned tellurium / germanium heterojunction photodetector based on sub-zero low-temperature thermal evaporation deposition, comprising the following steps: S1: Preparation of tellurium / germanium heterojunction, including the following sub-steps: (1) placing a germanium substrate and tellurium powder in a vacuum thermal evaporation coating system, wherein the germanium substrate is placed on a substrate substrate and the tellurium powder is placed in a quartz crucible heater; (2) subjecting the above vacuum thermal evaporation coating system to vacuum filtration; (3) cooling the substrate to a sub-zero temperature by external liquid nitrogen perfusion; (4) A tellurium thin film is deposited on the surface of a germanium substrate using a vacuum thermal evaporation coating process to obtain a tellurium / germanium heterojunction; the vacuum thermal evaporation coating process is specifically performed by heating tellurium powder under vacuum conditions to cause it to volatilize and deposit the tellurium. Specifically, during the deposition process, the temperature of the substrate is maintained at a sub-zero temperature, and the substrate is rotated; S2: On the tellurium / germanium heterojunction obtained in step S1, a metal top electrode is prepared by a micro-nano processing process, and a metal bottom electrode is prepared by coating an indium gallium alloy, thereby obtaining a tellurium / germanium heterojunction photodetector based on sub-zero low-temperature thermal evaporation deposition.

[0033] As a further preferred embodiment of the present invention, the vacuum filtration pressure in sub-step (2) is reduced to the following; As a further preferred embodiment of the present invention, in sub-step (3), the substrate is cooled to below -80°C; As a further preferred embodiment of the present invention, in sub-step (4), the deposition rate of tellurium powder is maintained below 2Å / s, and the deposition thickness is 30-50nm; As a further preferred embodiment of the present invention, step S2 is to first form a metal top electrode pattern by photolithography, and then deposit a metal top electrode material after development; Next, an etching pattern is formed by photolithography, and after development, an etching process is used to remove the tellurium film outside the metal top electrode area; Wherein, the photolithography adopts ultraviolet lithography, laser direct writing or electron beam exposure; the deposition adopts electron beam evaporation or dual ion beam sputtering; the etching process adopts reactive ion etching or plasma etching.

[0034] The following are specific examples: Example 1

[0035] Combine Figure 1 As shown, the structure of a tellurium / germanium heterojunction photodetector based on sub-zero low-temperature thermal evaporation deposition described in the present invention is: The bottom is an indium gallium alloy / copper foil bottom electrode, and above it is a tellurium / germanium heterojunction; the electrode for the surface tellurium is a platinum / gold electrode.

[0036] Its preparation process, such as Figure 2 As shown, the specific steps include: (1) Tellurium / Ge heterojunction preparation: N-type resistivity 5-10 Ωcm -1 A germanium substrate and 99.99% pure tellurium powder were placed in a vacuum thermal evaporation coating system, wherein the germanium substrate was placed on a substrate substrate and the tellurium powder was placed in a quartz crucible heater. The vacuum thermal evaporation coating system was vacuum filtered until the vacuum pressure dropped to 1.5×10 -4 Pa, the substrate was cooled to -120°C by external liquid nitrogen perfusion, and the substrate was rotated at a rate of 10 rpm. Tellurium powder was heated to evaporate into a gaseous state. When the gaseous tellurium molecules reached the sub-zero low-temperature substrate, they were deposited. The deposition rate was maintained between 1.0±0.5 Å / s, and the deposited thickness was 40nm. After the deposition was completed, the substrate was allowed to naturally warm to room temperature, and a tellurium / germanium heterojunction sample was formed.

[0037] A series of characterizations were performed on the tellurium / germanium heterojunction samples obtained in this step, such as Figure 3 As shown in Figure 2, Raman spectroscopy characterization revealed three obvious tellurium peaks and one germanium peak, as shown in Figure 2. Figure 4 As shown, high-resolution scanning electron microscopy images show the successful construction of the Germanium Telluride heterojunction, as shown in Figure 5 As shown in Figure 2, scanning electron microscopy images and corresponding element distribution further demonstrate the construction of high-quality tellurium / germanium heterojunction. Figure 6The polarized microscope image of the tellurium film on the surface of the tellurium / germanium heterojunction shows that the tellurium film has a crystal domain size of up to ~10μm. Figure 7 Atomic force microscopy images show that the roughness can be as low as 0.87nm, proving the growth of high-quality tellurium films and the construction of tellurium / germanium heterojunctions.

[0038] (2) Preparation of metal top electrode: spin-coat PMMA electron beam glue, bake and use electron beam exposure to prepare the top electrode pattern mask, develop and deposit 60 / 100nm platinum / gold electrodes by dual ion beam sputtering, soak in acetone to remove glue, and clean with isopropyl alcohol to complete the preparation of metal top electrode.

[0039] (3) Etching excess material: spin-coat negative photoresist, pre-bake and then use ultraviolet laser direct writing to expose the mask, post-bake and develop. The mask protects the tellurium thin film material in the metal top electrode area, and the rest of the area is exposed after development. Use argon plasma etching to remove the tellurium thin film outside the metal top electrode area, soak in acetone to remove the glue, and clean with isopropyl alcohol.

[0040] (4) Preparation of bottom electrode: Coat the indium gallium alloy on the copper foil, and stick the prepared top electrode and etched tellurium / germanium heterojunction on the indium gallium alloy.

[0041] The dark current and photocurrent current-voltage curves of the tellurium / germanium heterojunction photodetector based on sub-zero low-temperature thermal evaporation deposition prepared in this embodiment are as follows: Figure 8 As shown, the device exhibits ~10 4 The rectification ratio is excellent, and the photoelectric performance is excellent, with a light-dark current ratio of up to 248.34. Calculation basis: Under the condition of no light, the current under the negative 1V bias is I off (-1V)=6.86×10 - 7 A, the current under positive 1V bias is I off (+1V)=0.01A, rectification ratio: I off (+1V) / I off (-1V)≈1.47×10 4 Under 235μW 1550nm infrared light irradiation, the current is I on (-1V) = 1.70 × 10 -7 A, light-dark current ratio I on (-1V) / I off (-1V)≈248.34.

[0042] Example 2

[0043] As in Example 1, the difference is that the substrate is cooled to -80°C. Figure 9Shown is a polarizing microscope image of the tellurium thin film on the surface of a tellurium / germanium heterojunction, with crystal domain sizes as large as ~3μm.

[0044] Example 3

[0045] As in Example 1, the difference is that the substrate is cooled to -160°C. Figure 10 Shown is a polarizing microscope image of the tellurium thin film on the surface of a tellurium / germanium heterojunction, with crystal domain sizes as large as ~10μm.

[0046] Comparative Example 1

[0047] In this comparative example, a room temperature substrate was used to grow the heterojunction, and the other growth conditions were the same as in Example 1. The atomic force microscope image of the surface tellurium film of the obtained tellurium / germanium heterojunction is shown in FIG. Figure 11 As shown, its surface roughness is 3.85nm, which is much higher than that of the tellurium / germanium heterojunction deposited by sub-zero low-temperature thermal evaporation obtained in Example 1. The scanning electron microscope shows Figure 12 As shown, the crystal domain sizes are all below 80 nm, which is much lower than the micron-scale crystal domains achieved in the embodiment.

[0048] The above embodiments are merely examples. For example, the metal top electrode is not limited to being formed by dual ion beam sputtering.

[0049] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A tellurium / germanium heterojunction photodetector, characterized in that: It includes a germanium substrate and a tellurium thin film deposited on the surface of the germanium substrate. The tellurium thin film is a polycrystalline tellurium film layer containing micron-scale crystal domains, with a surface roughness of less than 1 nm, and is in close contact with the germanium substrate to form a heterojunction; it also includes a metal top electrode arranged above the tellurium thin film and a metal bottom electrode arranged below the germanium substrate.

2. The tellurium / germanium heterojunction photodetector according to claim 1, wherein: The size of the crystal domain of the tellurium thin film is 1 μm to 10 μm.

3. The tellurium / germanium heterojunction photodetector according to claim 1, wherein: The metal top electrode is a platinum / gold stacked electrode, wherein the platinum layer directly contacts the tellurium thin film; the metal bottom electrode is an indium gallium alloy / copper foil electrode, wherein the indium gallium alloy directly contacts the germanium substrate.

4. A method for preparing a tellurium / germanium heterojunction photodetector according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Place the germanium substrate and tellurium powder in a vacuum thermal evaporation coating system, with the germanium substrate placed on the substrate substrate and the tellurium powder placed in a quartz crucible heater; (2) Vacuum filter the thermal evaporation coating system; (3) Cooling the substrate to below -80°C by external liquid nitrogen perfusion; (4) Heating tellurium powder under vacuum conditions for thermal evaporation deposition while keeping the substrate rotating to obtain a tellurium / germanium heterojunction; (5) Prepare the top electrode and the bottom electrode to obtain a tellurium / germanium heterojunction photodetector.

5. The method for preparing a tellurium / germanium heterojunction photodetector according to claim 4, wherein: In step (2), the vacuum filtration is to evacuate the mixture to a pressure lower than .

6. The method for preparing a tellurium / germanium heterojunction photodetector according to claim 4, wherein: The deposition rate is ≤2 Å / s.

7. The method for preparing a tellurium / germanium heterojunction photodetector according to claim 4, wherein: The thickness of the deposit is 30-50 nm.

8. The method for preparing a tellurium / germanium heterojunction photodetector according to claim 4, wherein: The substrate is cooled to -80°C to -160°C.

9. The method for preparing a tellurium / germanium heterojunction photodetector according to claim 4, wherein: In step (5), a platinum / gold top electrode is prepared on the tellurium film by photolithography, development and deposition processes; and then the tellurium film outside the metal top electrode area is removed by an etching process.

10. The method for preparing a tellurium / germanium heterojunction photodetector according to claim 4, wherein: In step (5), an indium gallium alloy is coated under the germanium substrate and a copper foil is attached to form a metal bottom electrode.

Images