Photoelectrochemical And Laser Processing Of N-type 4H-SiC Surface And Their Applications

Silicon carbide(SiC)crystals are one of the most promising semiconductor materials for low-loss high-power electronic devices due to their excellent physical properties such as high breakdown electric field,high saturation electron drift rate,high thermal conductivity,and high hardness.However,it is also because of the outstanding chemical stability of SiC that chemical corrosion at room temperature becomes much more difficult.In the 1990s,systematic research into the electrochemical etching of SiC began.Today,electrochemical etching can be used to identify the polarity and type of SiC and is an important device fabrication process for the preparation of devices with smooth surfaces.Based on the above research background,this thesis delves into the controlled electrochemical processing of SiC surface microstructures,explores the differences in electrochemical etching on different polar surfaces,and prepares surface-enhanced Raman scattering(SERS)substrates that work stably under harsh conditions in combination with metal nanostructures.Finally,the UV laser processing and wetting of 4HSiC surfaces were investigated.The main experimental drugs,instruments,and test methods are introduced in Chapter 2;the photoelectrochemical etching and porous surface preparation of 4H-SiC polar surfaces are presented in Chapter 3;the Raman properties of porous 4H-SiC modified with gold nanoparticles(AuNPs)are investigated in Chapter 4;the UV laser processing and wettability of 4H-SiC surfaces are investigated in Chapter 5;the conclusions and outlook are presented in Chapter 6.The main studies and conclusions are as follows:(1)The polar structure of n-type 4H-SiC,the methods for determining the polar surface,and surface microstructure processing techniques are outlined.We then discuss the surfaceenhanced Raman scattering theory and the effects of surface morphology and chemical composition on wettability.Then the research objectives and proposed solutions of this paper are presented.(2)The anodic photoelectrochemical oxidation mechanism of n-type 4H-SiC with different polar surfaces is investigated;the differences between C-V and i-t curves in etching SiC with and without light and under different electrolyte conditions are explored;the variation of pore shape and size of SiC polar surfaces with photoelectrochemical(PEC)etching time is studied using KOH as the electrolyte.(3)SERS substrates of uniformly porous n-type 4H-SiC compounded with gold nanoparticles were developed using photoelectrochemical anodic etching,surface sputtering deposition,and thermal annealing methods.The substrate parameters were experimentally optimized to achieve single molecule capability for the detection of the dye rhodamine 6G at concentrations as low as 10-12 M with an enhancement factor(EF)of 2.0 × 107.The substrate has excellent SERS reproducibility and outstanding stability against corrosion,wear,and UV irradiation.The SERS substrate also supports the detection of bovine serum albumin(BSA)at a concentration of 0.5 mg/ml.Finally,the SERS enhancement mechanism of heterostructured AuNPs/pSiC substrates was explored in combination with electromagnetic and chemical enhancement mechanisms.(4)The mechanism of the action of the 355 nm UV nanosecond laser on SiC was investigated in the context of nonlinear optical theory.After UV laser processing,micron-sized patterned 4H-SiC with a micro-convex square structure was obtained to explore the change in wettability of the material surface before and after processing under UV illumination.In summary,we achieved controlled microstructure processing and metal nanoparticle preparation on the surface of crystalline 4H-SiC to achieve effective enhancement of the SERS effect of AuNPs/pSiC substrates obtained by photoelectrochemical etching on R6G and BSA;the corrosion process and SERS results are discussed in the context of semiconductor/electrolyte interface theory(SEI)and Raman enhancement mechanism;finally,the optically assisted exploration of the wettability of laser processed patterned SiC.