Hole drift velocity in silicon

Abstract

Drift velocities for holes in high-purity Si were measured for fields between about 3 and 5\ifmmode\times\else\texttimes\fi{}${10}^{4}$ V/cm and temperatures between 6 and 300\ifmmode^\circ\else\textdegree\fi{}K for the crystallogrphic directions $〈100〉$, $〈110〉$, and $〈111〉$. The Ohmic mobility is theoretically interpreted on the basis of a two-band model consisting of a spherical parabolic and a spherical nonparabolic band, and the relaxation-time approximation. The low-temperature Ohmic mobility is strongly influenced by the nonparabolicity of the heavy-hole band. The high-field region ($E\ensuremath{\ge}{10}^{3}$ V/cm) was analyzed using a single warped heavy-hole band model and a Monte Carlo technique. Anisotropy of hot-hole drift velocity is associated with warping of the valence band. Optical- and acoustic-scattering mechanisms are found to be of comparable strength.