Effect Of Interfaces On Electron Mobility In Wurtzite Al_xGa_1-xN Heterostructures

Influence from scattering of interface optical (IF) phonons and interface roughness on electron mobility of AlxGa1-xN heterostructures is discussed.Firstly, the influence from IF phonons on electron mobility in wurtzite AlN/AlxGa1-xN/AlN quantum wells (QWs) is discussed.Adopting a numerical method to solve self-consistently the Schrodinger equation and Poisson equation for wurtzite AlN/AlxGa1-xN/AlN QWs including ternary mixed crystal (TMC) effect, the eigenstates and eigenenergies of electrons in two-dimensional electron gas (2DEG) are obtained. Using the Lei-Ting balance equation, the influence of IF phonon scattering on electron mobility is discussed. In our calculation, the modified random element isodisplacement (MREI) model is adopted to obtain frequencies of LO phonons, whereas TO phonons in AlxGa1-xN are fitted by the linear fit function (LF) and by quadratic polynomial function (QPF) respectively to calculate the interface phonon scattering on an electron. The results show that the electron mobility calculated by LF method is higher than that by QPF method. The results of electron mobility obtained by the two methods increase monotonically with increasing Al composition, and their varying trends are similar. There exist maximum points in both results by the two methods at appropriate Al compositions.Then, as a prophase work for electron mobility, the influence from interface roughness on the distribution of2DEGs in wurtzite AlxGa1-xN/AlN hetero-structures is discussed.Adopting a numerical method to solve self-consistently the Schrodinger equation and Poisson equation for wurtzite AlxGa1-xN/AlN heterostructures including TMC effect, the eigenstates and eigenenergies of electrons in a2DEG are obtained. The influences from the piezoelectric polarization charges induced by the ideal and non-ideal interfaces are compared. The results show that the main contribution of the interface roughness is to produce body-piezoelectric charges, which decay from the contact interface to its internal sides according to an index law, and the decay depth is about2nm. When x=0.5, the equivalent surface charges of interface roughness is about2times of ideal interface charges. The interface roughness has a great influence on the distribution of a2DEG.