Effect of optical phonons scattering on electron mobility in asymmetric AlGaN/GaN quantum wells

Based on the dielectric continuum model, uniaxial model and force balance equation, the electron mobility in asymmetric wurtzite AlxGa1-xN/GaN/AlyGa1-yN quantum wells (QWs) is investigated theoretically in consideration of optical phonon scattering and varieties of Al compositions x and y. The dispersion relations and potentials of interface, confssined, half space and propagation optical phonon modes are given by the transfer matrix method including the effect of two-mode transverse optical phonons. Contrary to symmetric QWs, one branch of interface optical phonons vanishes and transforms into half space or confined optical one in certain intervals of Al component, whereas the confined optical phonons exist in a wider Al component range. The electron mobility in asymmetric AlGaN/GaN QWs can be modulated to be higher than that in symmetric ones. It is found that the total electron mobility decreases at first, then induces steps and finally decreases as x increases for certain y. The electron mobility also shows strong temperature-dependence. A significant modification on electron mobility appears for a narrower GaN well layer. Our results indicate that the asymmetric AlGaN/GaN QWs can be modulated to exhibit better transport properties than symmetric ones.