Research On High Performance Hexagonal Boron Nitride Deep Ultraviolet Photodetector

In recent years,hexagonal boron nitride(hBN),as an emerging III-V semiconductor material,has gradually entered the attention of researchers due to its excellent material properties.hBN has extremely high resistivity,low dielectric constant,excellent thermal stability,chemical stability and radiation resistance,with a band gap of about 6 e V,an intrinsic absorption edge located around 210 nm,and a extremely high absorption coefficient(about 7.0×10~5cm^-1)has great potential in the field of deep ultraviolet photodetection.However,there is still insufficient research on the preparation of large-area and high-quality hBN thin films at home and abroad,and the prepared hBN deep ultraviolet photodetectors generally have the following problems:(1)low responsivity;(2)long cut-off wavelength;(3)The leakage current is large(4)The response speed is slow.In this paper,hBN thin films were prepared by radio frequency magnetron sputtering method,the preparation process was optimized,and the performance of hBN deep ultraviolet photodetectors was improved by optimizing the device structure and electrodes.The main research results obtained in the main research content of the paper include:1.Using two methods of RF magnetron sputtering hBN target and reactive magnetron sputtering B target,high-quality hBN thin films were prepared on sapphire substrates,and the working gas composition,substrate temperature and sputtering were optimized.process parameters such as radiation power.The experimental results show that with the increase of substrate temperature,sputtering power and N₂ composition,the quality of the film is significantly improved,and the half-peak width of the Raman characteristic peak corresponding to the E_2g mode decreases from 42.6 cm^-1 At 22.9 cm^-1,the absorption cut-off wavelength is red-shifted from 212.6 nm to 217.3 nm,the optical band gap is reduced from 5.93 e V to 5.81 e V,and the maximum average lateral grain size is increased from 43 nm to about 100 nm.The increase of the average grain size is beneficial to the collection of photogenerated carriers and the improvement of the responsivity of the detector.Based on the method of reactive magnetron sputtering of boron target,the film quality was the best under the conditions of 100sccm pure nitrogen atmosphere,substrate temperature of 600?,and sputtering power of 200W.2.Based on hBN thin films grown by an optimized process,a deep ultraviolet photodetector with a conventional metal-semiconductor-metal(MSM)structure was fabricated.The effects of different interdigital electrode width/interdigital spacing(100?m/100?m,20?m/20?m,10?m/10?m)on the photoelectric characteristics of the detector were compared,and the results showed that the responsivity increased with the reduction of the interdigital electrode spacing.Under the irradiation of 184.9nm UV pen lamp and 300V,the responsivity of hBN deep UV photodetector with 10?m/10?m finger width/finger spacing is 18.90m A/W.3.The etching process of hBN thin film was studied,and the embedded MSM structure hBN deep ultraviolet photodetector was fabricated on this basis.The structure takes into account the anisotropy of carrier mobility within the hexagonal boron nitride layer,that is,the carrier mobility in the hexagonal boron nitride layer is much higher than the interlayer mobility,so the electrons generated between the interdigital-The hole pairs can be collected by the electrodes after being transported within the layer.And because the electrode is deposited in the groove etched by hBN,the electrode and hBN are combined more firmly,which can avoid the falling off and scratching of the electrode,increase the collection range of photogenerated carriers,and make the hBN deep ultraviolet photodetector photoelectric.Response is improved.Under the irradiation of 184.9nm UV pen lamp,at 300V,the responsivity of the embedded MSM structure hBN deep UV photodetector with 10?m/10?m finger width/finger spacing increased to 24.2m A/W.4.The enhancement of the surface plasmon resonance effect of the Al electrode on the responsivity of the hBN deep ultraviolet photodetector was found and verified,and a preliminary study was carried out.An embedded MSM structure hBN deep ultraviolet photodetector with a finger width/finger spacing of 10?m/10?m based on Ti/Al electrodes,under the irradiation of a UV lamp light source with a wavelength of184.9nm,the responsivity at 300V reaches 226.70m A/W,the response speed is faster,the rise time is 56ms,and the fall time is 54ms.After testing,the detector does not respond to light sources with wavelengths?254 nm.