MBE Epitaxy Of GaN Based Materials And The Preparation And Characterization Of Light Emitting Devices

? Nitrides,a kind of direct band gap semiconductor,have a wide band gap which can cover ultraviolet-visible-near infrared and are widely used in solid-state lighting devices and ultraviolet electronic devices.Compared with traditional lighting sources,GaN based LEDs has great advantages in energy saving and environmental protection.After decades of development,thanks to the continuous improvement of material quality and the design of new device structure,the luminous efficiency of LEDs has been improved effectively,which is widely used in lighting,backlight and other fields.However,how to improve the luminous efficiency of long wavelength GaN based LEDs and apply it to high-resolution display,visible light communication and other fields is still one of the frontier issues concerned by researchers.In this paper,molecular beam epitaxy(MBE)is used to improve the luminous efficiency of long wavelength LEDs,"Bottom-up"and"top-down"methods were used to prepare micro-LEDs and InGaN/GaN multi quantum well nanowire structure.The mechanism of epitaxial growth and the photoelectric characteristics of the device are carefully studied.Conclusions are obtained as follow:1.In order to solve the problem of the dislocations at the interface of GaN epilayer,the techniques of surface Ga atomic layer control,N-plasma assisted thermal decomposition and N-plasma cycle etching are studied in this paper.The results show that:the introduction of surface Ga atomic layer control technology accurately controls the thickness of metal atomic layer on the surface of sample substrate during epitaxial process;the research of N-plasma assisted thermal decomposition technology effectively solves the existence of oxide layer on the surface of sample substrate;the exploration of N-plasma cyclic etching technology successfully inhibits the formation of undesired microstructure at the epitaxial interface.The characterization and analysis of RHEED and TEM showed that the dislocation density of GaN epilayer on free-standing GaN substrate can be reduced to 5×10⁵ cm^-2.2.In order to solve the problem of low luminous efficiency of green LEDs devices,GaN epitaxial layer with n⁺⁺/n⁺structure is epitaxial on green LEDs epitaxial chip with PA-MBE,which forms p⁺/n⁺⁺/n⁺tunnel junction with p⁺-GaN at the top of commercial LEDs epitaxial chip.Taking advantage of MBE's advantages in controlling the interface of epitaxial layers and by heavily doping GaN epitaxial layers(?10²⁰/cm³),the length tunnel junction is effectively reduced and the probability of inter band tunneling is improved.Compared with traditional micro-LEDs,the introduction of tunnel junction not only simplifies the fabrication process of the device,but also improves the device luminous efficiency.When the injection current density is 32 A/cm²,the droop attenuation ratio of tunnel junction micro LEDs and traditional micro-LEDs are 75%and 53%,respectively.3.The self-assembled GaN nanorods and the long wavelength InGaN/GaN MQWsstructures were epitaxial grown on Si(111)substrates by PA-MBE technique.High temperature annealing and nitriding technology is proposed to treat the low temperature deposited Al in order to inhibit the growth of parasitic GaN at the bottom of GaN nanorods.The kinetic diffusion model of Ga adsorbed atom under this growth condition is analyzed and proposed.The effects of growth temperature and Ga/N ratio on the morphology of self-assembled GaN nanorods were investigated.By controlling the growth temperature of different quantum wells,the long wavelength InGaN/GaN multi-quantum well structure nanorods with the wavelength in the range of orange and red light is realized.