Study On Photoelectrochemical Etching Technology Of Gallium Nitride

The third-generation semiconductor-Gallium Nitride(GaN)has excellent characteristics such as wide band gap(3.4 eV),strong radiation resistance,high breakdown voltage and thermal conductivity.It has an irreplaceable role in the fields of electronics and optoelectronics.At present,the manufacture of GaN-based devices mainly adopts dry etching,which requires the application of expensive equipment and complicated processes.Simple wet photoelectrochemical(PEC)etching can avoid the above shortcomings,but the use of the existing PEC method to process chemically inert GaN is slow,and crystal defects and uneven doping will seriously affect surface quality.How to achieve high-quality and high-efficiency processing of GaN by PEC etching is a problem that needs to be solved urgently.In this regard,understanding the key scientific issues such as the photoelectrochemical reaction and process of the GaN surface interface is the prerequisite for the development of new PEC etching technology.This thesis first solves the problems of slow processing of low-doped GaN and the inability to etch highly-doped GaN by the photovoltaic etching method currently used in the industry,and develops a composite salt of potassium hydrogen persulfate(K2SO4·KHSO4·2KHSO5,PMS)as The new system of photoelectrochemical etching with oxidant replaces the traditional potassium persulfate(K2S208,PS)oxidant system,and clarifies the processing mechanism that the new system can achieve high-efficiency and high-quality etching.At the same time,in order to clarify the complex reaction process of the semiconductor/oxide film/electrolyte interface(ie:the oxide film is always in a dynamic state),an innovative semiconductor tribo-photoelectrochemical research method was proposed,which was designed and constructed by itself.The relevant experimental device has realized the timely removal or stable control of the oxide film layer.According to this device,the internal connection and influence law between the photoelectrochemical reaction and the surface morphology have been systematically investigated.In the third chapter of the thesis,a new PMS etching solution and process that can be applied to industrial photovoltaic etching processing is proposed,and it is characterized in detail by electrochemistry,Electron Spin Resonance and other techniques.and the effects of additives,rotation and other conditions on the photoelectrochemical etching rate and surface quality of different doped GaN are systematically explored,and the following conclusions are drawn:1.Platinum(Pt)catalyzes PMS to produce singlet oxygen,and its reduction potential on the Pt surface is+0.85 V(vs.SCE),which is much higher than the reduction potential of PS on the Pt surface(+0.00 V).Since the etching speed of the photovoltaic etching method depends on the reduction potential of the oxidant in the etching solution on the metal Pt mask,the more positive the potential and the greater the potential difference between the GaN photoanode,the faster the etching is driven.Therefore,The performance of the PMS/Pt etching system is stronger than that of the traditional PS/Pt system.The new PMS/Pt etching system can etch low-doped(<5× 1017 cm-3)and high-doped(>1×1018 cm-3)Ga-GaN with high-efficiency and high-quality etching.The etching rate(material removal rate,MRR)reached 9.67 and 8.15 nm/min,and the facet surface roughness(Ra)was 10.51 nm and 6.31 nm(5 ×5 μm2),respectively.However,the PS/Pt system cannot etch highly-doped NGaN,and the rate of etching low-doped GaN is only 3.42 nm/min.2.The surface oxide layer is closely related to the etching quality.The lower the pH of the etching solution,the thinner the oxide layer,and the faster the etching rate;GaN wafer rotation etching can maintain the balance of the material and pH on the surface of the GaN photoanode,and reduce the Ra of the facet.For example,if a rotation speed of 1200 rpm is used,Ra can be as low as 1.43 nm(5 × 5 μm2).Chapter 4 of the thesis proposes a new research method of semiconductor tribophotoelectrochemistry,designing and constructing a force-photoelectrochemical research platform that can effectively combine tribological and photoelectrochemical research.And under friction conditions,using cyclic voltammetry on the photoelectrochemical properties of self-supporting Ga surface-GaN was carried out.At the same time,the influence of factors such as potential and pH on the photoelectrochemical response and surface morphology of GaN photoanodes was investigated,and the following results were obtained:1.Under acidic,neutral and alkaline conditions,as the potential increases,the surface oxidation of a GaN photoanode will undergo five different processes:non-oxidation,activation,passivation,transition and overpassivation.The thicker the oxide layer,the more positive the initial oxidation potential;the light intensity will not affect the passivation potential,but the greater the light intensity,the higher the peak current of overpassivation;when the light intensity is larger and the friction ability is weak,the high potential Oxidation increases Ra and produces a triangular pyramid structure;when the light intensity is weak,the oxidation potential is high,and the friction is strong,the facet quality is higher,because the high potential can effectively prevent the electron-hole pairs from recombining at the defect.2.Potential and solution pH are the key parameters that affect etching:the lower the pH,the thinner the surface oxide layer,the higher the current density,and the facet Ra is lower.For example:pH=1.0,Ea=1.5 V(vs.SCE),Ra can reach 0.08 nm(5 × 5 μm2).