Impact Ionization, Breakdown, and Photoinduced Switching in CdSe

Abstract

Measurements of conductivity, Hall coefficient, and mobility of CdSe single crystals have been made in the temperature range 4.2-300 \ifmmode^\circ\else\textdegree\fi{}K. For the sample with the lowest carrier concentration of 2.8\ifmmode\times\else\texttimes\fi{}${10}^{15}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, the donor ionization energy of 18 meV is obtained. This is in good agreement with the calculated hydrogenic value of 19 meV. Above 100 \ifmmode^\circ\else\textdegree\fi{}K, the electron---polar-optical-phonon interaction determines the mobility. Below 100 \ifmmode^\circ\else\textdegree\fi{}K, ionized- and neutral-impurity scattering also contribute to the mobility, and for $T<50$ \ifmmode^\circ\else\textdegree\fi{}K dominate the mobility. At relatively low fields, nonlinear $I\ensuremath{-}V$ characteristics are observed. The samples show breakdown around 100 V/cm (varies somewhat with carrier concentration), resulting in a region of current-controlled negative resistance. The conductivity, Hall coefficient, and mobility of the samples are measured in the high-field region. The samples which show current-controlled negative resistance can be switched from a low- to a high-conductivity state under illumination below the threshold field in the dark. The higher the intensity of illumination, the lower is the threshold field for switching. These results are discussed in terms of various models.