Research On GaN Regrowth Interface

GaN has great application prospects in the field of high-frequency and high-voltage electronic components because of its excellent material properties.With the development of GaN single crystal substrate technology,homoepitaxy has become a hot topic of research.GaN homoepitaxy has impurity aggregation at the interface,which limits the development of GaN homogenous devices.In power electronics,the secondary growth interface is an uncontrollable secondary channel.The thickness of the secondary growth interface is in the tens or even hundreds of nanometers,and the characteristics of impurity accumulation affect the square distribution of the resonant cavity in the structure of the nitride-based laser.Based on the metal organic compound chemical vapor deposition(MOCVD)equipment,the problem of impurity aggregation of the secondary growth interface of GaN was studied,the main contents of which are as follows:1.Research on the source of impurities in the secondary growth interface.The relationship between substrate preservation,preservation time and impurity content in the secondary growth boundary was studied by MOCVD to prepare the composite substrate of nitride on sapphire substrate.Changing the background Si content of GaN substrate itself,the relationship between background Si content and interface impurity content was studied.Comparing the free-standing substrate with the composite substrate,the effect of the free-standing substrate N-face and sidewall on the interface impurity content in the epitaxy process was studied.Three sources of Si impurities in the GaN secondary growth interface were found:(1)Si impurities adsorbed on the surface during substrate preservation,(2)background Si in the surface of the substrate decomposition during the delay heating and thermal cleaning process,and(3)During the process of heating and thermal cleaning,Si,which free-standing N-face decomposition,gathers on the epitaxy surface.2.Research on the improvement of interface impurities.Through MOCVD in-place thermal cleaning,the problem of secondary growth interface C,H and O impurities aggregation was solved,and the distribution of Si aggregation was improved.For composite substrates and free-standing substrates,the effects of dry etching and wet corrosion in exoneration treatment were studied,and the Si content at the interface could be reduced by at least 1 magnitude or more.The wet corrosion process,including solution selection,temperature control,corrosion time control,composite substrate can achieve the best theoretical results after wet corrosion,free-standing GaN in the wet corrosion process,N surface will bring secondary contamination.The dry method etching process was studied,including the selection,power and etching time of etching gas,and the improvement effect of dry etching on two different substrates was the same,but the stability was not as high as wet corrosion.3.Study on the preservation of GaN substrate.GaN substrate was prepared on sapphire substrate by MOCVD,and the preservation effect of different methods on clean surface was studied.Conventional vacuum sealing,nitrogen protection cannot achieve the preservation effect.It was found that the liquid isolation can be used to ensure the cleaning effect of GaN substrate surface in a short time.