Studying Fabzrication And Characteristic Of ZnO/GaN Heterojunction LEDs

ZnO is a common wide direct bandgap semiconductor material,which is the hotspot in third generation semiconductors.ZnO has a exciton energy of 60 me V at room temperature,and a bandgap of 3.37 e V.It can be widely used in the field of short wavelength optoelectronic devices and optical detector,etc.However,the stability of the p-ZnO materials is still a difficult problem in the industry nowadays,greatly restricting the development of ZnO based photoelectric device.Similarly,GaN is a widely-used third generation semiconductor.GaN and ZnO have a very small lattice mismatch?1.8%?,close forbidden band width and the electron affinity.So p-GaN/n-ZnO heterojunction is often used in optoelectronic devices.In this paper,I grew the ZnO layer on the p-GaN/c-Al2O3 substrates by metal organic chemical vapor deposition?MOCVD?technology,and observed the change of the ZnO layer's morphology and quality in different conditions.Otherwise,I optimized the structure of light emitting diodes?LED?based on n-ZnO/p-GaN heterojunction to raise the performance of devices.The main research is as follows.1.I etched the GaN substrates for different time?30 s,5 min,15 min,30 min?,grew ZnO layers on the substrates,and observed the surface morphology,crystal quality,and the optical property of different ZnO layers.The results show that the size of ZnO nanorods changes with the size of pyramids on the substrate.As the etching time of GaN become longer,the diameter of ZnO nanorod becomes longer,the crystal quality becomes worse,and optical quality becomes better.2.During the ZnO growth process by MOCVD,I chose different O₂ flows?150 sccm,200 sccm,250 sccm,300 sccm?,and observed the surface morphology,crystal quality,optical property of ZnO layers.The results are shown as follow: with the O₂ flows increasing,the holes on the ZnO surface decrease,the surface tends to be flat,and the optical property tends worse.When O₂ flow comes to 250 sccm,the crystal quality is the best.3.I adopt SiO₂ insertion layers in different thickness?10 nm,30 nm?to prepare n-ZnO/SiO₂/p-GaN LEDs.It is found that SiO₂ insertion layers can raise the luminous efficiency effectively.The device with the 10-nm insertion layer performs best optical properties.4.I inserted distributed Bragg reflector?DBR?under the p-GaN layer to fabricate LED.We found that the DBR layer can effectively improve the n-ZnO/p-GaN heterojunction luminous efficiency.The luminous intensity of the device increased about 1.8 times compared the device without DBR.