| Hexagonal boron nitride is a typical wide bandgap ?-? compound semiconductor with a bandgap of 5.97 eV,and it has piezoelectric effect and good ultraviolet characteristics.In addition,it has high thermal conductivity,high thermal stability,good chemical stability and low coefficient of thermal expansion,so it is very suitable for the preparation of ultraviolet photodetectors,surface acoustic wave devices,and substrate materials for semiconductor devices.However,the preparation of high-quality hBN films is still not well solved,and research on hBN is still in its initial stage.For example,the bandgap type of hBN is still controversial,the work function of hBN and the metal-semiconductor contact characteristics are unknown.These problems seriously hinder the application of hBN in various fields,especially ultraviolet photodetectors.This paper will focus on the bandgap characteristics of hBN,the preparation of high-quality hBN film and hBN deep ultraviolet detector.The contents and results of this thesis are as follows:(1)We calculated the bandgap structure of single layer,double layer,triple layer and bulk material hBN by the first principles method,and we find they are all indirect bandgaps,and the band gap of the bulk material hBN is 6.0 eV with a scissors operator,it is close to the actual hBN bandgap.We calculated the effect of sulfur doping on the bandgap and spectral properties of hBN.It was found that hBN become an N-type semiconductor with a band gap of 4.3 eV when doped by S element with a concentration of 1.56%.And the band gap will decreases as the doping concentration increases,this proves that S is an excellent N-type dopant.(2)The hBN film was made by magnetron sputtering process and the prepared films were characterized by FT-IR,XPS,UV-Vis and AFM to determine the quality of the deposited film.The effects of the composition of the working gas on the quality of the film was studied.We found that the nitrogen-hydrogen mixed gas can effectively improve the film quality compared with the nitrogen-argon mixed gas.(3)An hBN ultraviolet photodetector with a device size of 1 × 0.5cm was made by photolithography and magnetron sputtering metal technology.Firstly,we studied the metal-semi contact of the device:the work function of hBN is measured by the Kelvin probe station,and the ideal bandgap diagram of the contact between hBN and Al metal was given.We found the contact characteristics of Al-hBN meet the characteristics of the Schottky model.Secondly,we built a test system for the UV detector and tested the detection performance of the device.We found the dark current is extremely small,only 1.25 × 10-100A at 40V;the device can detect the 214nm deep ultraviolet light(switching ratio is more than 24 times at 40V),and device has goods stability;It has strong absorption for 214nm ultraviolet light and almost no absorption for visible light.It has excellent UV-visible suppression ratio(over 100).The rise time and fall time of the device arer 0.25s and 0.32s,respectively.The reason why the response speed of the device is fast is that the junction structure detector has a fast response speed when compared with the photoconductive detector. |
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