A procedure for temperature-dependent, differential van der Pauw measurements

Abstract

A two-step procedure is presented for temperature-dependent carrier-concentration and mobility profiling of InP and GaAs epitaxially grown on Si. Carrier concentrations and mobilities are determined by the van der Pauw technique between 14 and 300 K using a refrigerator-cooled cryostat. Anodic oxidation and oxide stripping by chemical etching were selected for the subsequent removal of controlled thin sublayers. By the combination of differential and temperature-dependent van der Pauw measurements, mobilities and carrier concentrations in dependence on depth and temperature have been extracted whereby the carrier-concentration profile at room temperature agrees very well with the results obtained by the electrochemical C/V technique. For InP/Si at a distance of more than 0.7 μm away from the heterointerface, the dependence of the carrier mobility on the concentration at room temperature is essentially the same as for InP/InP layers. At low temperatures, e.g., 77 K, scattering by dislocations results in a mobility reduction in InP/Si and GaAs/Si with respect to homoepitaxy. Due to the nonuniform distribution of impurities and dislocations the temperature dependences of carrier concentration and mobility vary considerably with depth, thus strongly recommending the use of the differential technique.