Impurity States In Strained GaN/Al_xGa_1-xN Rectangle Quantum Dots And Bound Polarons

Within the effective-mass approximation, the binding energy of a hydrogenic donor impurity state in a strained GaN/AlxGa1-xN rectangular quantum dot under hydrostatic pressure and the bound polaron in a GaN rectangular quantum dot are investigated,.Firstly, the binding energies of hydrogenic impurity states in strained GaN/AlxGa1-xN rectangular quantum dots are studied by considering the influence of strong built-in electric field effect due to the spontaneous and piezoelectric polarizations, pressure modification to the parameters of materials. The numerical results show that the binding energy decreases with increasing the dot size, but increases with increasing pressure. Moreover, we also compare the binding energy with and without strain. It is found that the binding energy with the strain effect is higher than that without the strain effect when the size of the quantum dot is small, but the situation becomes opposite when the size becomes large.Secondly, the binding energy of a bound polaron in a GaN rectangular quantum dot is studied without considering the strain and pressure for simplification. The longitudinal-like (LO-like) and transverse-like (TO-like) optical phonons which are particular to the wurtzite structure are adopted as an approximation for the phonon modes. The numerical results show that the binding energy of bound polaron always decreases monotonically with increasing the size of a quantum dot. The phonons lower significantly binding energies of impurity states under consideration of the interaction between an impurity and phonons, and the interaction between an impurity and phonons is stronger than that between an electron and phonons. In addition, we also find the binding energy of a bound polaron increases with increasing anisotropy angle.