Study Of Epitaxial Growth And Device Fabrication Of Nonpolar ZnO/AlGaN Heterostructure Ultraviolet LED

Zinc oxide(ZnO)is one of the wide bandgap semiconductor with a wide direct bandgap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature.ZnO has a broad prospect in optoelectronic devices,especially for light emitting diode and laser diode.However,up to now,there are two obstacles hindering the development of ZnO.The reproducible p-type doping of ZnO is still difficult to realize.Meanwhile,polar ZnO suffers huge built-in electric fields along c-direction due to strong spontaneous and piezoelectric polarization,which will decrease the internal quantum efficiency of ZnO-based LEDs.To solve the above problems,in this thesis,we prepared nonpolar a-plane n-ZnO/p-AlGaN heterostructure ultraviolet LED.The polarization-induced built-in electric fields can be avoided,by growing ZnO along the nonpolar direction.Meanwhile,we substitute p-type AlGaN to unavilable p-type ZnO,whose lattice constants are close to ZnO.Furthermore,nonpolar ZnO-based materials are proper to realize polarization-sensitive optoelectric devices,because of the natural anisotropy of optical properties.In this work,we firstly designed the structure of the ZnO/AlGaN heterostructure LED,then we grew the p-AlGaN,n-ZnO in sequence.Finally,the heterostructure devices are producted and characterized.The main work included:(1)The structure of nonpolar a-plane ZnO-based heterosturecture ultraviolet LED was designed theoretically.By studying the energy band structure and properties of electronic transport,a special nonpolar a-plane n-ZnO/i-ZnO/p-AlGaN heterostructure ultraviolet LED was built.On one hand,the employment of p-type AlGaN in place of p-type GaN could prevent electrons from n-ZnO leaking to the p-type layer.On the other hand,the insertion of i-ZnO could further confine electrons in ZnO layer,promoting the recombination in ZnO.(2)The effects of nitridation of r-plane sapphire on the growth of nonpolar a-plane materials were investigated,and a model was built to describe the physical mechanism.The effects of growth temperature on the deposition of nonpolar a-plane AlN were studied.Through the optimization of growth process,high-quality nonpolar a-plane GaN film was obtained,which was a proper template for the subsequent growth.(3)The in-situ grown SiNx interlayers were introduced in the growth of nonpolar a-plane AlGaN materials to reduce the threading dislocation and stacking faults.Through optimizing the growth time of SiNx interlayers,the crystal quality of nonpolar a-plane AlGaN was improved obviously.The mechanism for dislocation reduction with SiNx interlayer was explained with a newly established model.(4)High-quality nonpolar a-plane p-type AlGaN was obtained by MOCVD.The growth temperature,?/?,source flow and annealing temperature were optimized.(5)The effects of different templates on the growth of nonpolar a-plane ZnO were studied by PLD.Then nonpolar a-plane n-type ZnO was prepared.Nonpolar a-plane MgZnO films were deposited on different templates and the carrier localization in nonpolar MgZnO films was investigated in detail.(6)Nonpolar a-plane n-ZnO/i-ZnO/p-AlGaN heterostructure ultraviolet LED was prepared.The effects of i-ZnO interlayer on the device performance were studied.The luminous mechanism of the n-ZnO/i-ZnO/p-AlGaN heterostructure ultraviolet LED under reverse bias was studied.The optical anisotropy of the device was characterized by polarized EL and PL,and the DOPs were 0.23 and 0.33,respectively.