Impurity States And Their Pressure Effect In Strained GaN/Al_xGa_1-xN Heterojunctions With Finite Thick Potential Barriers

In recent years, the low-dimensional structures consisting of wurtzite and zinc-blende groupâ…¢-â…¤nitride semiconductors such as GaN, AlN and InN have been paid much attention owing to their promising application in microelectronic devices and optoelectronic devices due to their wide band gap and favorable photoelectric characteristics. The investigation in stained semiconductor heteroj unction materials has an important practical significance to improve their physical properties and to speed up theoretical development, and can provide guidance and new ideas for the design of semiconductor devices.A variational method and a numerical computation method are used respectively to investigate binding energies of donor impurity states in strained AlxGa1-xN/GaN heterojunctions with finite thick potential barriers and furthermore, the effect of hydrostatic pressure by adopting a simplified coherent potential approximation to take into account the effects of ternary mixed crystals and internal electric fields. The thesis is organized as two main parts.Firstly, the binding energies of impurity states in strained wurtzite AlxGa1-xN/GaN heterojunctions with GaN substrates are calculated with a variational method by considering finite thick potential barrier for ideal interfaces. The influences of the barrier width, the impurity position and the Al component on the binding energy are discussed and compared with that of a heterojunction with an infinite thick barrier. The results indicate: the binding energy for a heterojunction with a finite thick barrier is obviously greater than that with an infinite thick barrier when the barrier width and Al component are small and the impurity locates in the channel near the interface of the heterojunction. That the binding energies increase nearly linearly with pressure is similar to the case of an infinite thick barrier.The second part of the thesis improves the variational method adopted in the first part to deal with the binding energies of impurity states using the wave function at z direction obtained by numerical computation in order to improve the accuracy. It is found that binding energies using numerical calculated wave functions are obviously greater than that of using variational wave functions when impurities locate in the channel near the interface of a heterojunction. Nevertheless, binding energies using numerical calculated wave functions are obviously less than that of using variational wave functions when impurities locate in the channel far from an interface. The binding energies still increase nearly linearly with hydrostatic pressure. But the change is not obviously in comparison with that obtained by variational wave functions.