Study On Epitaxial Lateral Overgrowth Of InGan/GaN Heterostructures And Nanowire LEDs

?-nitride materials are the most important semiconductors ever after silicon.They have been widely applied into various lighting and display devices owing to their excellent optical and electrical properties.InGaN/GaN hetrostructure is the most promising structures as its emitting spectrum covers a rather wide range from ultraviolet to infrared.The industry developed on the base of ?-nitride brought a revolution for the field of lighting and display.The Nobel Prize in Physics 2014 was awarded jointly to Isamu Akasaki,Hiroshi Amano and Shuji Nakamura for the invention of efficient blue light-emitting diodes based on ?-nitride which has enabled bright and energy-saving white light sources".Metal Organic Chemical Vapor Deposition?MOCVD?is the most common growth method for ?-nitride materials with high quality.However,it is not easy for obtaining GaN or InGaN crystal with satisfying quality due to the nature of such materials like threading dislocations?TD?and mismatch of the lattice.Such problems would a disaster for the upcoming device manufacture.Epitaxial lateral overgrowth?ELO?is one of the most widely used method for optimizing the quality of ?-nitride materials.Although it has been proved that ELO is able to reduce the dislocation density effectively,the unavoidable problems like the inhomogeneous of the doping and strain are still unsolved.In this study,we focused on ELO growth process of InGaN/GaN heterostructures.Scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and cathodoluminescence?CL?were involved in the characterization of the obtaining crystals.We studied deeply the influence factors in the ELO growth process of InGaN/GaN heterostructures by MOCVD in order to perfect the growth of InGaN/GaN heterostructures.The specific studies are as follows:1.We analyzed kinetic model for the ELO growth of ?-nitride materials by MOCVD.Various reactions which would possibly take place during the growth process of MOCVD were listed.We also studied the mechanism of the ELO with the gas phase diffusion model as well as the surface migration model.2.We grew InGaN/GaN heterostructure with the help of growth template and studied the influence from window orientations and dislocations.Growth template for ELO with different window orientations and window widths was built with the help of electron beam lithography?EBL?and InGaN/GaN heterostructure stripes were obtained by ELO.It was found that the morphology and indium composition varied with the change of the window orientations.After that,uneven substrate was used to obtain stripes with asymmetric distribution of dislocations.It was found that the spatial distribution of indium composition on the stripe can be related to the dislocation density,as dislocation played an important role in the diffusion of the metal atoms?In and Ga atoms?during the growth.3.InGaN/GaN multiple-quantum-well?MQW?nanowires were obtained and the influence from surface polarity was studied.SnO₂ nanowires were employed for the fabrication of the nano-scaled growth template for ELO and InGaN/GaN MQW nanowires were grown by ELO.It was found that the morphology would change greatly when the scale of the windows was down to nano-scale and growth time decreased simultaneously.Continuously plane-changed semi-polar InGaN/GaN quantum well was also realized by this special fabrication method.The CL results showed that metal atoms?In and Ga atoms?would rearrange along the semi-circle nanowire surface due to the difference of the surface properties.4.InGaN/GaN MQW nanowires light-emitting-diodes?LEDs?were also fabricated on the n-GaN/sapphire substrate with the nano-patterned growth templates.A strong cathodoluminescence emission peak related to InGaN/GaN MQW is observed located at 461 nm.In addition,InGaN/GaN MQW nanowire LED shows typical p-n junction characteristics with a low turn-on voltage,and its electroluminescence displays purplish.