The purpose of this study is to explore the possibility of phosphor-free white-emitting LED？s based in the gallium nitride material system. The structures are to be grown using mixed source hydride vapor phase epitaxy (MS-HVPE). It is unique crystal growth technology different from conventional HVPE and MOCVD system using mixed metal source of aluminum, indium and gallium.
The first step in this project is the optimization of MS-HVPE growth process. This was achieved successfully, as binary, ternary and quaternary films are demonstrated. Successful n and p-type doping are also demonstrated introducing Te and Mg.
The second step in this project is fabricating broadband spectrum emitting device of phosphor-free white LED by MS-HVPE. The device structure consisted of conventional double-hetero (DH) structure, which was the undoped InAlGaN active layer and n, p-AlGaN cladding layers. We observed that the device of AlInGaN quarternary active grown by MS-HVPE emitted multi spectrum from UV to red area. We also found that its spectrum was variable as indium mole fraction and controllable. It was nano phase epitaxy phenomenon being only observed in HS-HVPE process. An extensive growth study of GaN based material was also carried out. The effects of several growth parameters on emission characteristics were presented. PL emission wavelengths for each structure were demonstrated. And EL emission wavelengths were also demonstrated after wafer fabrication process. Additionally, x-ray diffraction and x-ray photoelectron spectroscopy (XPS) showed to verify crystal quality of MS-HVPE.
The dissertation presented herein demonstrates achieving phosphor-free solid-state white lighting. But it still has unknown physical characteristics. Continuation of this study will lead to future industry. And hopefully it will be commercialized and applied to residential illumination due to this technology.