Doped Gallium Nitride grown by Phase Shift Epitaxy, fabrication and characterization of Gallium Nitride:Europium LED.

摘要

A novel growth and doping scheme in Molecular Beam Epitaxy (MBE) named Phase Shift Epitaxy (PSE) is developed and described in this thesis. PSE is a periodic and dynamic growth scheme which desynchronizes the host material growth and the dopant incorporation by adjusting delays between shutter operations. PSE frees the doping procedure from the limited growth conditions of the host material, making it a very effective technique for determining the optimum surface condition for a particular dopant. In order to demonstrate its advantages over traditional MBE growth, PSE techniques were applied to the doping of GaN (activated layer of GaN:Eu LED) and Mg doping of GaN (p-type). The optimum PSE condition for GaN:Eu with Eu doped in a Ga-rich surface condition, was shown to lead to over 50% enhancement of the photoluminescence efficiency of Eu ions compared with the optimum traditional MBE condition. Luminescence from a specific Eu location was significantly increased. With the PSE growth of p-type GaN:Mg, Mg self-compensation effect was significantly suppressed at high Mg concentration when Mg is doped in an N-rich condition. A high hole concentration (2.4E18cm-3) is achieved with the optimum PSE condition for Mg doping. Even with a relatively high compensation donor level and a relatively poor template quality, this hole concentration result is comparable to the highest concentration, thanks to the self-compensating effect of PSE. Phase Shift Epitaxy is thus demonstrated to be a very effective tool in the doping of GaN, as well as other compound semiconductors. The PSE-grown active layer (GaN:Eu) and the p-type layer are also tested in devices such as GaN p-n junction and GaN:Eu LED in order to prove its feasibility in device fabrication.