InN MOVPE Via Indium Bilayer Control And H-induced Nitridation

As a kind of narrow bandgap semiconductor,InN has significant application prospect in fields of infrared light emission,light detecting and light absorption devices.Meanwhile,InN has theoretical ultrahigh carrier transport speed,which give InN huge potential of application in fields of high speed and high frequency electronic devices,too.But,even to this day people can not fabricate workable light emission device with InN yet because of its tremendous difficulty of epitaxial growth and doping.For workable InN-base light absorption device,the photoelectric conversion efficiency is pretty low.In the last decade,in the field of metal-organic vapor phase epitaxy(MOVPE),all the attempts which using regular ways to grow InN epilayer had not obtained ideal outcome.These issues root in a critical contradiction between the relative low temperature of InN decomposition and the high temperature requirement of nitrogen resource's thermal cracking and high surface adatoms'mobility.Therefore,what is needed now is to develop a new InN MOVPE method with novel thinking.In this thesis,the systematic theoretical study of surface atoms'dynamic behavior had been carried out and two new growth methods of InN MOVPE,indium bilayer control and hydrogen inducing penetrated nitridation,had been proposed and put it into practice.The major works are as follows:First,in the frame of first principle theory,we had studied the absorption and the diffusion of surface nitrogen and indium atoms during the process of InN epitaxy.We had discovered that when additional indium atoms had been deposited on the regular In-polar InN surface,these indium atoms could form a monolayer of good uniformity rapidly,constructing an indium bilayer.Theoretically,this indium bilayer had higher uniformity and flatness than regular N-In top structure.Meanwhile,in the later nitridation process,the indium atoms of top layer need not to lateral migrate and reconstruct,which benefited their uniformity too.Base on this theoretical prediction,we had designed a special control mode of atoms' transportation.In this mode,we deposited the indium atoms alone first.When the construction of indium bilayer was done,we start to deliver nitrogen atoms onto the surface and nitridated this indium bilayer.We had found the optimized parameters of indium bilayer controlling through indium resource mass flow tuning and sample characterization.The result of practical InN epitaxy had proved the superiority of this indium bilayer controlling method.However,we found that the coherency of samples' InN/GaN(substrate)boundary was week through the characterization of crystal structure and strain,which did not fulfilled our initial vision.Meanwhile,the growth rate of this method here is extremely low because of the pretty long duration of nitridation,which decreased its practical value in industry manufacture.Therefore,to improve this method,we needed to find additional supplementary mechanisms.Furthermore,our later theoretical study had discovered the positive role which hydrogen atom played during the nitridation process of indium bilayer.The hydrogen atom can be inset into the interval of indium bilayer by properly choosing the timing of hydrogen supply.Further simulation shown that at some sites of indium bilayer surface,the nitrogen atom could penetrate to the interval of indium bilayer free with the existent of these hydrogen atoms.The free vertical penetration of surface nitrogen atoms means the nitridation of indium bilayer would progress faster.On the other hand,the rapid penetration of nitrogen atoms could make them isolated from activated-nitrogen-atom-rich atmosphere faster,which would eliminate the runoff of nitrogen atoms.Besides,we studied the behavior of the "interval" hydrogen atom at the end of nitridation process,we found that these hydrogen atoms tended to escape from InN epilayer when the Top sites of indium bilayer interval were almost being occupied by nitrogen atoms.Base on the theoretical mechanism above,we had tried to pass over a small amount of hydrogen during the indium bilayer controlling process,then we characterized these grown InN samples with different hydrogen inlet flow.We had discovered that the compactness and flatness were extraordinary improved after the introducing of hydrogen.On the other hand,huge amount of compress stain had been observed in InN epilayer after the introducing of hydrogen.Theoretically,this significant strain can contain more misfit stress,which could maintain coherent interface better and eliminated defects.Meanwhile,the XRD characterization shown that the indium clusters had been eliminated too,which implied a more sufficient nitridation process.Finally,the optical characterization had shown that the introducing of hydrogen also broadened the bandgap of grown InN epilayer.Base the shift scales of grown InN sample's XRD diffraction peaks and Raman characteristic peak,we had calculated the corresponding strain-induced bandgap broadening of InN samples.Through the comparation of these two bandgap broadening tendency,we deduced that the changing of InN sample's bandgap was closely related to their inner strain.