Compensation Dependence of Impurity Conduction in Antimony-Doped Germanium

Abstract

A study has been made of the compensation dependence of impurity conduction in $n$-type germanium containing between 7\ifmmode\times\else\texttimes\fi{}${10}^{15}$ and 2\ifmmode\times\else\texttimes\fi{}${10}^{17}$ antimony atoms ${\mathrm{cm}}^{\ensuremath{-}3}$, the compensation being changed by fastneutron irradiation. Activation energies ${\ensuremath{\epsilon}}_{1}$, ${\ensuremath{\epsilon}}_{2}$, and ${\ensuremath{\epsilon}}_{3}$, characteristic of the resistivity-temperature curves, change continuously with increasing compensation. The energies ${\ensuremath{\epsilon}}_{1}$ and ${\ensuremath{\epsilon}}_{2}$ increase monotonically with compensation, while ${\ensuremath{\epsilon}}_{3}$ passes through a minimum value. The compensation dependence of ${\ensuremath{\epsilon}}_{2}$ is in qualitative agreement with the suggestions that this activation energy is associated with the thermal excitation of electrons from the donor ground state to a band that arises from the interaction of negatively charged donors. For small donor concentrations, the value of the compensation at which ${\ensuremath{\epsilon}}_{3}$ is a minimum is 0.5, in agreement with the Miller-Abrahams theory. At higher donor concentrations, this minimum occurs at smaller compensations. It is suggested that this occurs because the effective compensation at low temperatures is greater than that determined at room temperature, the increase arising because electrons on neutral donors are lost not only to acceptor sites but also to the negatively charged donor band.