Preparation And Photoelectric Properties Of Graphene-SiC Materials

Graphene is a single atom layer material with honeycomb two-dimensional lattice structure formed by sp² hybridization covalent bond.It is the basic material for carbon nanotubes,fullerenes,and graphite.Graphene has a ballistic electron transport speed which is 10 to100 times faster than Si,and its mobility is as high as 2×10⁵cm²V^-1s^-1,making it possible to produce smaller,faster,higher-frequency products than silicon-based devices.Graphene has a zero band gap structure,making it generally behave as semi-metal.However,many evidence has shown that the band gap can be artificially modulated by doping,electrochemical modulation,and vertical gate voltage regulation to make it exhibit desired properties.In fact,due to its two-dimensional structure,adjustable bandgap,flexibility,and its excellent electrical properties,Graphene has a bright prospect in applications such as MOSFET and HEMT.In addition to the above characteristics,graphene also has excellent optical properties.It has superior light transmission in the visible to near-infrared wavelengths,its single layer transmittance is as high as 97.7%,the transmittance of each additional layer is reduced by2.3%,and even in the daily blind ultraviolet range it has more than 90%of the single Layer transmittance.Graphene is easily heterogeneously integrated with semiconductor materials or other two-dimensional materials,in addition to its flexibility and semi-metal properties,making it widely used in the field of optoelectronics.The following describes the focus of this article.Starting from the preparation and characterization of 4H-SiC epitaxial graphene,the effects of various parameters on the material quality during the preparation process of SiC epitaxial graphene were analyzed,the preparation process is finally determined,and the grown material is characterized by Raman spectroscopy.On this basis,a graphene-SiC Schottky ultraviolet photodetector was designed and fabricated.Two structures of epitaxial graphene and transferred graphene were attempted.Graphene-SiC junctions with epitaxial graphene structure do not exhibit rectification characteristic.Quasi-free standing structure was attempted to introduce rectification characteristic,but the result was not satisfactory.In order to avoid the effect of high temperature annealing on the Quasi-free Standing structure,the C surface of N⁺type4H-SiC was tried with low-temperature ohmic contact,but the result is still poor.Finally,an optimized solution is proposed for isolating and preparing the back electrode after epitaxy,and the specific process needs further exploration.Graphene-SiC junctions with transferred graphene structure exhibit significant rectification characteristic and maintain a dark current density of 1.0 nA/cm2 under a reverse bias within 6V.The tested response of0.035A/W is obtained with the illumination of 260nm wavelength light under the reverse bias of 1V.We believe that the size of the device size does not match the photoelectric test system in the short wavelength range of incident light,resulting in low responsivity of the tested data.Optimizing device structure can improve the performance of the device.Through the simulation of Sentaurus-TCAD software,it was found that as the thickness of the lightly doped layer increases and the doping concentration decreases,the peak value of the response of the device gradually increases,and the corresponding peak wave moves toward the long wavelength.In order to investigate the photoelectric characteristic of 4H-SiC Si surface epitaxial graphene in visible light band,a lateral structure photodetector based on 4H-SiC substrate and graphene channel transistor was designed,and the device preparation process was explored.Different sizes of devices were tested under the illumination of different wavelengths and power light,the responsivity from 405 nm to 635 nm wavelengths was gradually reduced,and there was no obvious saturation trend in the device's response with the incident light power up to several hundred milliwatts.The optical response current with illumination of 405nm wavelength 19.6mW power light is approximately 1/10 of dark current,and the responsivity is no less than 0.032mA/W.The location and the change of the Dirac point were observed through the top-gate control,so that the carrier transport mechanism was intuitively obtained.Photogenerated electrons transfer from SiC to graphene,which is opposite to the response mechanism of Schottky junction.