Fabrication Of 4H-SiC Nanoarrays By Electrochemical Etching And Their Photoelectrocatalytic Properties

Si C is a third-generation semiconductor material with high critical breakdown electric field,high thermal conductivity,high electron saturation mobility,and excellent chemical stability,which offer them significant advantages to be utilized in the development of optoelectronic devices for service in harsh environments,especially those with high temperature,high pressure,and high power.SiC low-dimensional materials are provided with unique surface effects and size effects,exhibit much better physical properties than traditional materials,which can promote the miniaturization and integration of devices,providing opportunities for the development of novel and highly efficient next-generation optoelectronic devices.In this work,we reported the controllable and repeatable large-scale fabrication of well-aligned,free-standing and transparent 4H-SiC nanostructure arrays via anodic oxidation of SiC wafers at room temperature,together with atmospheric pressure conditions.In the meantime,the diameters,wall thickness and depth of the nanostructures could be modulated through the customization of the cycle times.According to the comprehensive work of this thesis,the main research results are as follows:?1?Governable preparetion of SiC nanostructure arrays via electrochemical etching at room temperature and under atmospheric pressure conditions.Meanwhile,the diameters,wall thickness and depth of the nanoholes could be modulated through the customization of the cycle times.?2?SiC nanoarrays were utilized for photoelectrochemical?PEC?water splitting.The SiC nanoarray photoanode exhibited a photocurrent density of 1mA cm^-22 at 1 V?versus Ag/AgCl electrode?bias and light excitation(simulated solar and optical power 100 mW cm^-2)in 1 mol/L neutral Na₂SO₄ solution,and the 2000 s continuous photocurrent density is always maintained,presenting excellent photoelectrocatalytic stability.?3?Atomic layer deposition?ALD?technology was applied to modificate SiC nano-arrays surface to construct heterojunction?SiC@Ti O₂?.SiC@TiO₂heterojunction nanoarrays exhibited significantly higher photocurrent density than the SiC nanoarray electrodes,producing an unprecedented photocurrent of1.7 mA cm^-22 at 1 V?versus Ag/Ag Cl electrode?bias under simulated sunlight(optical power 100 mW cm^-2)in 1 mol/L neutral Na₂SO₄ solution,which is increased by 70%than SiC nanoarrays.The dark current of SiC@Ti O₂heterojunction nanoarrays were almost zero,and the photocurrent density of the electrode rapidly recovers to 1.7 mA cm^-22 when illuminated again,indicating that the SiC@Ti O₂ nanoarray process a fast response speed.Meantime,compared with SiC nanoarrays,SiC@Ti O₂ heterojunction nanoarrays exhibited smaller impedances.It was concluded that the higher PEC performance should be attributed to constructed Si C@TiO₂ heterojunction nanoarrays can significantly enhance charge separation and improve transportation of carriers.