Lifetime and Drift Mobility of Holes in AgBr

Abstract

Holes with free lifetimes greater than 50 \ensuremath{\mu}sec have been found in silver bromide at temperatures above 200\ifmmode^\circ\else\textdegree\fi{}K. The long hole lifetimes are observed only in strained pure crystals, apparently because of the precipitation on dislocations of point defects which are traps for holes. The drift mobility follows an approximately ${T}^{\ensuremath{-}2}$ temperature dependence from 300 to 250\ifmmode^\circ\else\textdegree\fi{}K before falling off because of multiple trapping of the holes by a low density (\ensuremath{\sim}${10}^{9}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) of large-cross-section (\ensuremath{\sim}${10}^{\ensuremath{-}10}$ ${\mathrm{cm}}^{2}$) hole traps. The data suggest intermediate coupling of the hole to the lattice, and a hole polaron mass greater than that of the electron. The relevance of polaron theory to the present results is unclear because of possible high-temperature effects not included in the theory.