Hole transport in the rare-gas solids Ne, Ar, Kr, and Xe

Abstract

This paper reports an investigation of the drift mobility of excess holes in solid Ne, Ar, Kr, and Xe. Thin-crystal specimens (50-500 \ensuremath{\mu}m thick) were grown from the liquid between parallel-plate electrodes in a chamber attached to a miniature cryostat after purification of the starting gas. As in previous work on the electron transport in rare-gas solids and liquids, an electron-beam technique was used to generate excess carriers near one of the electrodes. Holes were extracted by the applied field and their transit time was measured directly, leading to the drift mobility ${\ensuremath{\mu}}_{h}$. Close to the triple points, ${\ensuremath{\mu}}_{h}$ values in the above crystals lie between 1 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}2}$ and 4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}2}$ ${\mathrm{cm}}^{2}$ ${\mathrm{V}}^{\ensuremath{-}1}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, several orders of magnitude lower than the corresponding electron mobilities. The form of the temperature dependence of ${\ensuremath{\mu}}_{h}$ changes progressively from $\mathrm{Xe} ({\ensuremath{\mu}}_{h}\ensuremath{\propto}{T}^{\ensuremath{-}1.6})$ to an essentially activated mobility in Ar and Ne. The experimental results have been analyzed in terms of small-polaron theory, using both the adiabatic and nonadiabatic approximations. The theory can account for the different forms of the temperature dependence and possible ranges of values for the predominant phonon energy, the polaron binding energy and the transfer energy for holes have been deduced in each case. These quantities, characterizing the hole hopping transport, vary systematically from Xe to Ne and their correlation is discussed in some detail.