Tunability of bipolar conductivity in GaAs doping superlattices

Abstract

In GaAs doping superlattices the conductivity parallel to the constituent layers is tunable over wide ranges by injection or extraction of free carriers via selective electrodes. The transport simultaneously involves electrons in the n layers and holes in the p layers. The tunability of bipolar conductivity depending on temperature in the range 10 to 300 K and on the design parameters of the superlattice configuration is analyzed in detail. The carrier concentrations and mobilities as a function of bias Unp are determined independently from Hall effect measurements. The observed tunability of carrier concentration is in good agreement with calculations based on a simplified semiclassical approach. The carrier mobility is found to be strongly influenced by the carrier concentration and correspondingly by the effective thickness of the constituent superlattice layers. This behavior is analyzed in terms of the classical size effect. Only a minor influence of the temperature on the carrier mobility is detected. The temperature dependence of the carrier concentration is solely determined by the temperature dependence of the threshold voltage. The present detailed investigation is of importance for application of GaAs doping superlattices in bulk multijunction field effect transistors.