Bias and temperature dependence of tunneling phenomena in GaAs Schottky-barrier junctions

Abstract

The bias and temperature dependence of tunneling structure was studied in Zn-doped $p$-type GaAs Schottky-barrier junctions over a doping range of 5.4 \ifmmode\times\else\texttimes\fi{} ${10}^{18}$-1.4 \ifmmode\times\else\texttimes\fi{} ${10}^{19}$ Zn/${\mathrm{cm}}^{3}$. An increase in conductance with increasing temperature at the bias polarity for electron injection into the semiconductor is considered to be a consequence of impurity-assisted (two-step) tunneling via acceptor impurities. The reduction in the lifetime of electrons localized on acceptor sites by stimulated emission in a thermally populated phonon field is responsible for the temperature dependence. An enhancement of phonon-induced structure in the tunneling characteristics by Ar-ion bombardment of the semiconductor surface is observed. The magnitude of the zero-bias conductance minimum is found to vary as the logarithm of both bias voltage and temperature of higher biases and temperature, but to saturate at low values of these parameters. The magnitude of the conductance minimum depends strongly upon doping, but its functional dependence upon bias and temperature varies only slightly over the doping range investigated. These results and the observations of others are the basis for objections to the major models dealing with the conductance minimum. The strong correlation between the magnitude of the conductance minimum and impurity-band localization observed by others and the similarity of the bias and temperature dependence of the conductance minimum to that of the Appelbaum conductance maximum suggest the possibility of some form of exchange interaction as the cause of the conductance minimum.