Study On The Gallium Nitride-based Heterostructures By Metal Organic Chemical Vapor Deposition

Indium nitride(In N),Gallium nitride(Ga N),Aluminum nitride(Al N)and their alloys compounds in group III nitride are the most widely researched in the third generation semiconductor materials,which collectively as Ga N-based semiconductor material.The bandgap of the Ga N-based semiconductor material was adjusted from 0.7 e V(In N)to 6.2e V(Al N).Meanwhile,the Ga N-based semiconductor material has some good performances such as high heat conductivity,high electron saturation drift velocity,easy to form the heterojunction,easy to form the two dimensional electron gas(2DEG)in channel.At present,Ga N-based semiconductor is widely used in high temperature,high power,high frequency microwave,laser,LED lighting and other power electronic and optoelectronic devices,and these materials are usually used to make the device in the form of heterostructures.Al Ga N/Ga N and In Al N/Ga N heterostructures have been widely studied among all heterostructures.There are some shortcomings for Al Ga N/Ga N and In Al N/Ga N heterostructures.On the one hand,Al Ga N/Ga N heterostructures cannot have both thin barrier and high surface density.On the other hand,In Al N materials with heterogeneous structure of In Al N/Ga N are difficult to grow.Therefore,the Ga N-based heterostructures need to be further studied.In this paper,Ga N based semiconductor materials were prepared by MOCVD epitaxy technology.Ga N-based heterostructures are studied from three parts in this paper,and various properties of the heterostructures are explored by changing the barrier materials.Main work contents include:1.The effects of the growth temperature of low temperature Ga N nucleation layer and the introduction of Al N thin layer on the morphology,crystallization quality and electrical properties of Al Ga N/Ga N epitaxial structure have been studied.First,Al_0.30Ga_0.70N/Ga N heterostructures were prepared on an undoped Ga N template with the nucleation temperature of 580?and 600?.The morphology,structure and electrical properties of the materials were analyzed.The results show that,compared with the nucleation temperature of 580?,the Al_0.30Ga_0.70N/Ga N heterostructures prepared on the undoped Ga N template with the nucleation temperature of 600?have better properties,and the level of dislocation density of the undoped Ga N template is lower,namely the order of magnitude is 10⁸ cm^-2.Secondly,1 nm Al N thin layer was introduced into the Al_0.30Ga_0.70N/Ga N heterostructure,and the effect of Al N insertion layer on the whole Al_0.30Ga_0.70N/Ga N heterostructure was studied.The results show that the introduction of Al N thin layer into Al_0.30Ga_0.70N/Ga N heterostructure can improve the 2DEG sheet density and 2DEG electron mobility.Meanwhile,the average sheetresistance of Al_0.30Ga_0.70N/Al N/Ga N heterostructures is significantly lower than that of Al_0.30Ga_0.70N/Ga N heterostructures without Al N insertion layer,and its transport characteristics are better.2.The effects of the different epitaxial temperatures of In Al N films on the structure and electrical properties of the In Al N/Ga N heterostructures were investigated.Three different In Al N/Ga N epitaxial materials were prepared by setting the growth temperature of In Al N barrier material as 920?,890?and 860?.The results show that when the growth temperature of In Al N decreases from 920?to 860?,the level of dislocation density of the whole heterostructure decreases,and the RMS roughness value of the structure surface decreases gradually,that is,the morphology of In Al N material gradually becomes better and the crystal quality is better.Meanwhile,with the decrease of the growth temperature of In Al N layer,the 2DEG mobility of In Al N layer increases gradually.3.Ga N-based heterostructures with In Al N/Al Ga N bilayer barriers have been prepared and studied.First,In Al N barriers of different components were prepared on Al_0.40Ga_0.60N/Al N/Ga N structure by changing the In flow of 1400 sccm and 1000 sccm.Secondly,In Al N barriers of different components were prepared on Al_0.43Ga_0.57N/Al N/Ga N structure by changing In flow of 1200 sccm and 800 sccm.Results show that the surface morphology in Ga N-based heterostructures with In Al N/Al Ga N double barrier are improved with the decrease of In flow,and the electron mobility and sheet density are increased.