Diamond deep ultraviolet photoelectric detector based on low boron doping

Abstract

The invention discloses a diamond deep ultraviolet photoelectric detector based on low boron doping, and belongs to the technical field of semiconductor devices. A proper amount of acceptor energy level is introduced into diamond through low-boron doping, a p-type conducting channel is formed, the conducting channel provides an efficient transmission path for photon-generated carriers (electrons and holes) and improves light current, meanwhile, the number of thermal excitation carriers is reduced through low-boron doping, generation of dark current is restrained, and therefore the dark current is remarkably reduced; furthermore, by optimizing the boron doping concentration, the optimal balance is achieved between conductivity and dark current control, and the switch ratio of the detector is remarkably improved.

Description

Technical Field

[0001] The present invention relates to a deep ultraviolet photodetector based on low boron-doped diamond, belonging to the technical field of semiconductor devices. Background Art

[0002] Since the ozone layer in the atmosphere strongly absorbs deep ultraviolet light in the wavelength range of 200 nm to 280 nm, sunlight in this wavelength range cannot reach the Earth's surface. Therefore, photodetectors operating in this region have a low false alarm rate, a high signal-to-noise ratio, and the ability to detect weak signals, and can be used for flame detection, missile tracking, environmental safety, solar-blind imaging, and navigation positioning, etc.

[0003] As a wide-bandgap semiconductor material, diamond has a bandgap width of about 5.5 eV, which can effectively absorb deep ultraviolet light, resulting in a low false alarm rate in deep ultraviolet detection. At the same time, diamond carriers have a high mobility and can quickly respond to rapidly changing optical signals. Therefore, diamond is often used as the detection medium for deep ultraviolet photodetectors.

[0004] In the existing research solutions, a photodetector based on hydrogen-terminated diamond is provided. By introducing hydrogen atoms on the diamond surface to form a two-dimensional hole gas (2DHG), the conductivity of the diamond surface is significantly improved, enabling it to effectively transport and collect photo-generated carriers, thereby improving the responsivity of the photodetector. Moreover, hydrogen termination passivates the surface defect states and reduces the generation of thermally excited carriers, thereby reducing the dark current. However, due to the instability of hydrogen termination (being easily affected by environmental temperature), photodetectors based on hydrogen-terminated diamond are difficult to apply. Summary of the Invention

[0005] In order to solve the problems existing in current diamond deep ultraviolet photodetectors, the present invention provides a deep ultraviolet photodetector based on low boron-doped diamond. A conductive channel layer is formed by low boron doping. The on-off ratio of the detector designed based on this technology can reach 10 10 or more, showing excellent performance.

[0006] The first object of the present invention is to provide a deep ultraviolet photodetector based on low boron-doped diamond. The photodetector includes an intrinsic layer, a low boron-doped layer, an oxide gate layer, and a drain, a source, and a gate. Among them, the intrinsic layer uses undoped diamond for device support and insulation. The low boron-doped layer uses an ion implantation process to implant boron ions with a concentration of 1e 13 -1e 16 cm -3 on the surface of the intrinsic layer to form a conductive channel for receiving ultraviolet light irradiation and generating photo-generated electron-hole pairs. The oxide gate layer is used to separate the gate from the drain, the source, and the conductive channel between the drain and the source.

[0007] Optionally, the thickness range of the intrinsic layer is 50 - 150 μm.

[0008] Optionally, the depth range of the low boron doped layer is 5 - 500 nm, preferably 20 nm.

[0009] Optionally, the oxidation gate layer is alumina, silicon nitride or silicon oxide.

[0010] Optionally, the thickness of the oxidation gate layer is 5 - 20 nm.

[0011] Optionally, the drain and source electrodes are made of Ti / Pt / Au or Ti / Ru. When using Ti / Pt / Au, the thickness is 30 - 200 nm / 30 - 200 nm / 50 - 500 nm. When using Ti / Ru, the thickness is 50 - 200 / 50 - 200 nm; the gate metal is Al with a thickness of 100 - 500 nm.

[0012] The second object of the present invention is to provide a preparation method of a diamond deep ultraviolet photodetector based on low boron doping, and the method includes:

[0013] Step (1): Select high-quality MPCVD diamond material. After cutting, the thickness of the diamond is 50 - 150 μm, and the surface is polished to make the surface roughness Ra < 1 nm;

[0014] Step (2): Pickle the diamond polished in step (1), and then clean it thoroughly with ultrasonic waves in distilled water;

[0015] Step (3): Adopt ion implantation technology to implant boron ions on the surface of the cleaned diamond. The implantation depth is 5 - 500 nm, and the boron ion concentration is 1e 13 -1e 16 cm -3 , and then anneal;

[0016] Step (4): After pickling the diamond material implanted with boron ions, use photolithography, electron beam evaporation coating and stripping technology to deposit a Ti / Pt / Au or Ti / Ru metal stack layer on the diamond surface as the drain and source electrodes, and then perform annealing treatment to form an ohmic contact;

[0017] Step (5): Use photolithography, electron beam evaporation coating and stripping technology to deposit an oxidation gate layer, and then anneal to achieve an interface without Fermi pinning effect; the oxidation gate layer is alumina, silicon nitride or silicon oxide;

[0018] Step (6): Use photolithography, electron beam evaporation coating and stripping technology to deposit a gate metal aluminum layer as the gate electrode, and then anneal.

[0019] Optionally, when pickling the diamond in step (2), the diamond is boiled in a solution of sulfuric acid, nitric acid and perchloric acid.

[0020] The third object of the present invention is to provide a detection method for a deep ultraviolet photodetector based on low-boron-doped diamond. The method places the above-mentioned deep ultraviolet photodetector based on low-boron-doped diamond in a detection environment, grounds its source S and gate G, the intrinsic layer is grounded together with the source S, and the drain D is connected to a negative voltage.

[0021] The beneficial effects of the present invention are as follows:

[0022] By introducing an appropriate amount of acceptor energy levels in diamond through low-boron doping, a p-type conductive channel is formed. This conductive channel provides an efficient transmission path for photo-generated carriers (electrons and holes), increases the photocurrent. At the same time, low-boron doping reduces the number of thermally excited carriers and suppresses the generation of dark current, thus significantly reducing the dark current. Further, the present invention optimizes the boron doping concentration to achieve the best balance between conductivity and dark current control, significantly improving the on-off ratio of the detector. Further, when using the prepared deep ultraviolet photodetector based on low-boron-doped diamond, by grounding the diamond intrinsic layer and the source together, when a reverse voltage is applied to the drain, the pn junction formed by the low-boron-doped layer and the intrinsic layer is reverse-biased, and the drain leakage current decreases; when a reverse voltage is applied to the gate, the effect is particularly significant, and the on-off ratio is as high as 10 10 ; moreover, under the action of a gate 0V bias voltage, the device is in an off state and has low power consumption. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 is a flowchart of the preparation of a deep ultraviolet photodetector based on low-boron-doped diamond provided by an embodiment of the present invention;

[0025] Figure 2 is a working circuit diagram of a deep ultraviolet photodetector based on low-boron-doped diamond provided by an embodiment of the present invention;

[0026] Figure 3A is a simulation diagram of the dark current and photocurrent of a deep ultraviolet photodetector based on low-boron-doped diamond provided by an embodiment of the present invention when the intrinsic layer is suspended and not connected to the source under a -5V drain bias;

[0027] Figure 3B This is the simulation diagram of the dark current and photocurrent when the intrinsic layer of the deep ultraviolet photodetector based on low boron-doped diamond provided by the embodiment of the present invention is connected to the source electrode and grounded under a drain bias of -5V. Detailed implementation manners

[0028] To make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0029] Embodiment 1:

[0030] This embodiment provides a deep ultraviolet photodetector based on low boron-doped diamond and a preparation method thereof. The photodetector includes an intrinsic layer, a low boron-doped layer, an oxide gate layer, as well as a drain electrode, a source electrode and a gate electrode. Among them, the intrinsic layer uses undoped diamond for device support and insulation; the low boron-doped layer uses an ion implantation process to implant boron ions with a concentration of 1e 13 -1e 16 cm -3 on the surface of the intrinsic layer to form a conductive channel for receiving ultraviolet light irradiation and generating photoinduced electron-hole pairs; the oxide gate layer uses alumina, silicon nitride or silicon oxide to separate the gate electrode from the drain electrode, the source electrode and the conductive channel between the drain electrodes.

[0031] The thickness range of the intrinsic layer is 50 - 150 μm; the depth range of the low boron-doped layer is 5 - 500 nm, preferably 20 nm. The thickness of the alumina is 5 - 20 nm; the drain and source electrodes use Ti / Pt / Au or Ti / Ru. When using Ti / Pt / Au, the thickness is 30 - 200 nm / 30 - 200 nm / 50 - 500 nm, and when using Ti / Ru, the thickness is 50 - 200 / 50 - 200 nm; the gate metal uses Al with a thickness of 100 - 500 nm.

[0032] As Figure 1 shown, the preparation method of the photodetector includes:

[0033] Step 1: Select high-quality MPCVD diamond material with a thickness of 50 μm after cutting, polish and grind the surface to make the surface roughness Ra < 1 nm.

[0034] Step 2: Before plasma implantation, boil the diamond in a solution of sulfuric acid, nitric acid and perchloric acid for 2 hours to thoroughly clean the diamond surface; then, clean it thoroughly with ultrasonic waves in distilled water.

[0035] Step 3: Adopt the ion implantation technology to implant boron ions on the surface of the cleaned diamond with an implantation depth of 100 nm and a boron ion concentration of about 1e 14 cm -3 , and then anneal for 3 hours.

[0036] In Step 4, after pickling the diamond material, a Ti / Pt / Au metal stack layer with a thickness of 30 / 30 / 50 nm is deposited on the diamond surface as the drain and source electrodes by means of photolithography, electron beam evaporation coating, and lift-off technology. Subsequently, annealing is carried out in an argon environment at 450 °C for about 50 minutes to form an ohmic contact.

[0037] In Step 5, after pickling the diamond material, an oxide gate layer with a thickness of 5 nm is deposited by means of photolithography, electron beam evaporation coating, and lift-off technology. Subsequently, post-annealing is carried out at 350 °C in a vacuum for 30 minutes to achieve an interface without the Fermi pinning effect; the oxide gate layer is alumina, silicon nitride, or silicon oxide.

[0038] In Step 6, a gate metal aluminum layer with a thickness of 100 nm is deposited as the gate electrode by means of photolithography, electron beam evaporation coating, and lift-off technology at 450 °C. Subsequently, post-annealing is carried out at 450 °C for 30 minutes.

[0039] The diamond deep ultraviolet photodetector provided by the present invention introduces an appropriate amount of acceptor levels in the diamond through low boron doping, forming a p-type conductive channel. This conductive channel provides an efficient transmission path for photo-generated carriers (electrons and holes), increasing the photocurrent. At the same time, low boron doping reduces the number of thermally excited carriers, suppressing the generation of dark current, thereby significantly reducing the dark current, and thus enabling a switching ratio as high as 10 10 。

[0040] Generally, high boron doping will lead to an increase in carrier scattering and an increase in recombination centers, reducing the carrier mobility and lifetime. At the same time, it may introduce more thermally excited carriers, increasing the dark current; while undoped diamond has poor conductivity and it is difficult to form an effective conductive channel, resulting in low photocurrent and switching ratio. Therefore, the present invention optimizes the boron doping concentration, achieving an optimal balance between conductivity and dark current control, and significantly improving the switching ratio of the detector.

[0041] Example Two

[0042] This example provides a detection method for a diamond deep ultraviolet photodetector based on low boron doping. The diamond deep ultraviolet photodetector based on low boron doping is placed in a detection environment, and its source S and gate G are grounded according to the circuit connection method shown in Figure 2 , and the drain D is connected to a negative voltage. In particular, when using the diamond deep ultraviolet photodetector with low boron doping provided by the present invention for detection, its intrinsic layer is grounded together with the source.

[0043] To highlight the effect of the method of grounding the intrinsic layer and the source in the present invention, this example simulates its photocurrent and dark current using deep ultraviolet light with a wavelength of 213 nm. Figure 3AWhen the intrinsic layer is suspended and not connected to the source electrode, it is a simulation diagram of dark current and photocurrent under a drain bias of -5V. It can be seen that when the gate-source voltage is lower than 2V, a large leakage current is generated in the detector. Only when the gate-source voltage is higher than 2V, the forward bias applied by the gate reduces the hole concentration under the gate, so that the leakage current remains at a low level; Figure 3B When the intrinsic layer is connected to the source electrode and grounded together, it is the dark current and photocurrent under a drain bias of -5V. It can be seen that when the gate-source voltage is higher than -6V, the leakage current of the detector is already at a low level; The reason for such a big difference is that when the intrinsic layer and the source electrode of the diamond deep ultraviolet photodetector based on low boron doping provided by the present invention are grounded together, under the reverse bias applied to the drain, the pn junction formed by the low boron doping layer and the intrinsic layer is reverse biased, and the drain leakage current decreases; When a reverse bias is applied to the gate, the effect is particularly significant, and the on-off ratio is as high as 10 10 .

[0044] Because the diamond deep ultraviolet photodetector based on low boron doping provided by the present invention has an on-off ratio as high as 10 10 , it has higher sensitivity to weak optical signals. In deep ultraviolet communication, it can detect optical signals at a farther distance or with weaker intensity; Since the photocurrent is much larger than the dark current, the signal-to-noise ratio (SNR) of the detector is higher. Therefore, in deep ultraviolet imaging, a clearer image can be obtained, and in spectral analysis, characteristic peaks can be identified more accurately; Because of its extremely low dark current, the detector has a lower noise level. In scientific research, more accurate experimental data can be obtained, and in medical detection, the diagnostic accuracy can be improved; The detector has low power consumption, thus saving energy and can be applied to portable devices.

[0045] Some steps in the embodiments of the present invention can be implemented by software, and the corresponding software program can be stored in a readable storage medium, such as an optical disc or a hard disk, etc.

[0046] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-boron-doped diamond deep ultraviolet photodetector, characterized in that: The photodetector comprises an intrinsic layer, a low-boron doped layer, an oxide gate layer, a drain electrode, a source electrode and a gate electrode; wherein the intrinsic layer is made of undoped diamond for device support and insulation; the low-boron doped layer is made of ion implantation technology, and the concentration of the implantation is 1e 13 -1e 16 cm -3 The boron ions form a conductive channel for receiving ultraviolet light and generating photogenerated electron-hole pairs; the gate oxide layer is used to separate the gate from the drain, the source, and the conductive channel between the drain.

2. The detector according to claim 1, characterized in that: The thickness of the intrinsic layer is in the range of 50-150 μm.

3. The detector according to claim 1, characterized in that: The depth of the low boron doping layer is in the range of 5-500 nm, preferably 20 nm.

4. The detector according to claim 1, characterized in that: The gate oxide layer is aluminum oxide, silicon nitride or silicon oxide.

5. The detector according to claim 1, characterized in that: The gate oxide layer has a thickness of 5-20 nm.

6. The detector according to claim 1, characterized in that: The drain and source electrodes are made of Ti / Pt / Au or Ti / Ru. When Ti / Pt / Au is used, the thickness is 30-200nm / 30-200nm / 50-500nm, and when Ti / Ru is used, the thickness is 50-200 / 50-200nm; the gate metal is Al, and the thickness is 100-500nm.

7. A method for preparing a low-boron-doped diamond deep ultraviolet photodetector, characterized in that: The method comprises: Step (1) Select high-quality MPCVD diamond material, the thickness of the diamond after cutting is 50-150 μm, and polish the surface to make the surface roughness Ra <1 nm; Step (2) acid-washing the polished diamond in step (1), and then fully cleaning it in distilled water using ultrasonic waves; Step (3) uses ion implantation technology to implant boron ions into the cleaned diamond surface, with an implantation depth of 5-500nm and a boron ion concentration of 1e 13 -1e 16 cm -3 , then annealing; Step (4) After acid washing the diamond material after the boron ion injection, Ti / Pt / Au or Ti / Ru metal stacking layers are deposited on the diamond surface as drain and source electrodes by using photolithography, electron beam evaporation coating and stripping technology, and then annealing is performed to form an ohmic contact; Step (5) depositing a gate oxide layer by photolithography, electron beam evaporation coating and stripping technology, and then annealing to achieve an interface without Fermi pinning effect; the gate oxide layer is aluminum oxide, silicon nitride or silicon oxide; Step (6) deposits a gate metal aluminum layer as a gate electrode using photolithography, electron beam evaporation coating and lift-off technology, followed by annealing.

8. The method according to claim 7, characterized in that In the step (2), the diamond is pickled by boiling the diamond in a solution of sulfuric acid, nitric acid and perchloric acid.

9. The method according to claim 7, characterized in that: When ion implantation is performed on the diamond surface in step (3), the ion implantation energy range is 30-170 keV.

10. A detection method based on a low-boron-doped diamond deep ultraviolet photodetector, characterized in that: The method places the low-boron-doped diamond deep ultraviolet photodetector according to any one of claims 1 to 6 in a detection environment, grounds its source S and gate G, shares a common ground with the source S, and connects the drain D to a negative voltage.

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