Polarization doping of wurtzite III-nitride ternary alloys

Polarization doping, which can be applied in numerous III-nitride devices such as lasers, light-emitting diodes, and high electron mobility transistors, produces temperature-independent three-dimensional electron and hole gases. However, current polarization doping models are far from perfect, ignoring some key issues and great potential. We have greatly enriched the model using first-principles calculations on ternary group-III nitride alloys. We find that the polarization charge density depends on the polarization change rate as a function of composition and tensile strain, as well as on the grading speed as a function of grading range, nonlinearity, and thickness. The polarization change rate varies significantly for all materials studied except AlGaN, which is very advantageous for achieving large carrier densities and novel device structures. We have also experimentally verified our proposed theoretical model by experimentally characterizing the rates of III-polar AlGaN and N-polar InGaN samples in good agreement with our theoretical calculations. The significance of our work can greatly contribute to the development of polarization doping applications of a III-nitride system.