Controlled Growth Of ZnO Nanostructures And Investigated The Optical Properties Of Heterojunction

Zinc Oxide(ZnO)as a excellent photoelectric material with a 3.37 eV bandgap and a large exciton binding energy of 60 meV under room temperature,ZnO is considered as a very promising candidate for Ultraviolet Light Emitting Diodes and Lasing Diodes with low threshold and high efficiency.However,it's difficult to synthesize high crystalline quality p-type ZnO thin films,thus,high-ultraviolet light-emitting LEDs is the focus of research in the past twenty year.In this article,we realized the density controlled ZnO nanowires growth by introduced seed layer,and analyzed its optical characteristic.Finally,we have prepared ZnO-based heterojunction LEDs with the high ultraviolet emission intensity,and analyzed its photoelectric properties.At the same time,the energy band model was constructed to study the luminescence mechanism.(1)Explored the controllable growth method of ZnO nanostructure: Compared ZnO nanowires density of which with and without covered different annealed temperature of ZnO seed layer on GaN substrate.Seed layer with 400 °C annealed,the density of ZnO increased double and the PL intensity increased double;with annealed temperature increased to 500 °C,the density of ZnO nanowires increased to 8 times,the 376 nm peak intensity increased to 3 times.This condition is used as the growth method of ZnO nanowires in ZnO based LEDs.(2)Photoluminescence studies of core-shell ZnO/ZnS nanostructure: Solid-phase Sulfide and Chemical Bath Deposition to synthesize ZnO/ZnS core-shell structure.As the dose of sulfur increased,Solid-phase Sulfide method introduced considerable Si in ZnO nanowires which seriously increased the defect emission,caused the UV emission weaker and weaker.For the CBD method,ZnS introduced local states in ZnO surface,which lead to the peak position blue shift to 376 nm,and the intensity firstly increase then decreases,and the maximum value is four cycles,which is four times than ZnO NWs.(3)Based on the first two results,we carried out research on ZnO heterojunction LED characteristics.In order to realize high-ultraviolet electroluminescence of ZnO-based heterojunction,combination with an energy band model we constructed a GaN/MgO/ZnO/ZnS heterojunction structure.Firstly,with ZnO thin film structure,the GaN/MgO/ZnO/ZnS heterojunction was prepared.It was found that the UV emission intensity increased by nearly 26 times.After replacing ZnO film with ZnO nanowires,the UV intensity heterojunction continues increase to nearly 50 times.Finally,the preparation of ZnO-based heterojunction LEDs with high UV emission intensity was realized,and the mechanism of the heterojunction luminescence was studied.