Anisotropic charge transport in nonpolar GaN quantum wells: Polarization induced line charge and interface roughness scattering

Charge transport in GaN quantum well devices grown in the nonpolar direction is theoretically investigated. Emergence of a different form of anisotropic line charge scattering mechanism originating from anisotropic rough-surface morphology in conjunction with in-plane built-in polarization is proposed. It is shown that such scattering leads to a large anisotropy in carrier transport properties, which is partially reduced by strong isotropic optical phonon scattering.

Figure 1

Nonpolar GaN quantum well: (a) QW of width $a$ sandwiched between AlN barriers, (b) schematic of interface roughness at GaN/AlN interface, (c) polarization-induced line charge at each step edge of roughness.

Figure 2

(Color online) (a) Angle- $\left(\theta \right)$ dependent scattering time for line charge and IR scattering. (b) RI scattering time as a function of angle $\left(\psi \right)$ between initial and final wave vectors of scattering.

Figure 3

(Color online) (a) IR scattering vs in-plane correlation length $\Lambda$ for various carrier densities (Fermi energies), (b) electron mobility along two principal directions $x$ and $y$ as a function of temperatures. The dashed blue line is the longitudinal mobility using variational technique.

Figure 4

(Color online) Electron mobility along two principal axes $x$ and $y$—(a) as a function of carrier densities and (b) as a function of well width. Note that mobility anisotropy decreases with increasing carrier density or well width. Dashed blue curves represent longitudinal mobility calculated using variational technique.