First Principle Study On Rare Earth Doped Gan

Wide band gap semiconductor materials have been attracting people’s attention duo to theirspecial physical and chemical properties. GaN has excellent optoelectric properties and wideband gap and is also a new semiconductor materials which can be used to develop themicroelectronic and optoelectronic device. Over the past decades, it was found that the propertiesare changed by doping different element into GaN. RE-doped GaN in optical and magneticproperties have attracted considerable interest due to rare earth’s particular properties. In thisthesis, Electronic structure, optical properties and magnetic properties of rare earth doping inGaN are investigated using first principle theory mathod. The contents are as follow.Based on density functional theory by the play wave pepseudopotential method, theelectronic structure and optical properties of GaN, GaN with an nitrogen vacancy and GaN withan gallium vacancy were investigated and the results were in agreement with others’. Thensupercell model was employed to investigate the vacancy of GaN. The results show that VNhaslower formation energy for p-type GaN. VNis a donor defect and introduces shallow donorlevels from N-2p states and Ga-4p states hybridization. VGahas lower formation energy forn-type GaN. VGais a acceptor defect and introduct three acceptor levels derived from N-2p states.VGaleads to spin polarization and the magnetic moment is3. In addition, the vacancy makesthe band gap of GaN increase and influence the optical properties.Based on density function theory by PBE+U method, the electronic structures and opticalproperties of substitutional Ce and Pr doping GaN were investigated. The results show that theCeGa introduces impurity levels derived from Ce-4f states in the bandgap. The PrGa introducesimpurity levels from Pr-4f ststes near the valence band maximum(VBM). After doping Ce and Primpurities, the GaN:Ce and GaN:Pr becomes indirect band gap semiconductor and have themagnetic order and the magnetic moment of1and2, respectively. Additionally, the opticalproperties are changed. For GaN:Ce, a new dielectric peak and absorption peak appears in thelow energy region, which comes from the transition between impurity level and conductor band minimun(CBM). For GaN:Pr, first dielectric peak and optical absoption edge has a red shift dueto the band gap narrowing. Furthermore, comparing with pure GaN, the static dielectricconstants both increase after Ce and Pr doping GaN, which will be the theory basis in developingnew materials.We further studied the effects of the complex defects CeGa-VNand CeGa-VGaon the electronicstructural and optical properties of GaN:Ce. The results show that the vacancy introducesshallow levels. VNintroduces shallow donor leves and makes the magnetic moment decrease to0.67. While VGaintroduces acceptor levels and makes the magnetic moment increase to2.The optical properties have a little change. Comparing with GaN:Ce, the position of dielectricpeak and absorption peak slightly shift. Finally, the maginetic properties of Gd doping GaN alsowere calculated. The results show that the coupling of Gd atoms is antiferromagnetic. It becomesferromagnetic when enough holes are present in the system. The interstitial N and O defects arethe origin for the colossal magnetic moment of GaN:Gd system but Ga vacancy not.