One-dimensional confinement effects on miniband transport in a semiconductor superlattice

We analyze steady-state miniband conduction for a superlattice subject to transverse confinement in one direction. Force and energy balance equations are presented for these asymmetric, nonparabolic band systems, taking account of impurity, acoustic-phonon, and polar-optic phonon scatterings. Four transverse subbands are included in the numerical calculations. Nonlinear drift velocity and electron temperature are examined as functions of the applied electric field at lattice temperatures between 45 and 300 K, for a series of confined superlattices with miniband widths Δ ranging from 50 to 900 K. Negative differential velocity is manifested in all cases investigated. We find that as lateral extension increases, the linear mobility rises, the critical field decreases, and the nonlinear velocity-field curves become steeper. When the lateral extension ${\mathit{d}}_{\mathit{x}}$ varies from 5 to 45 nm, almost all transport properties monotonically approach the corresponding three-dimensional values, except at low temperature (T=45 K), where the peak drift velocity exhibits moderate oscillations. The velocity-field behavior of the Δ=900-K and ${\mathit{d}}_{\mathit{x}}$=45-nm system appears to be particularly well suited for use in high-frequency oscillators.