Resistive properties of indium and indium-gallium contacts to CdS

Abstract The contact resistance of wiped-on InGa, evaporated In, and ion-plated In contacts on low-resistivity CdS single crystals both with and without an insulating surface layer have been examined. Resistance-voltage characteristics were measured for applied voltages of 1 mV to ∼ 10 V. On etched crystals (without insulating layer) low-resistance ohmic contacts ( 2 ) are obtained with InGa and evaporated In, whereas the ion-plated In contacts are ohmic but have apparent resistivities of ∼ 3.6 Ω-cm 2 . On unetched crystals (with insulating layer) contacts of InGa and evaporated In are highly resistive (2 × 10 2 to 2 × 10 6 Ω-cm 2 ) and non-ohmic, but the ion-plated contacts have approximately the same characteristics as those applied to etched samples. It is concluded that the high-resistivity surface layer on low-resistivity CdS crystals must be removed or altered in order to make low-resistance ohmic contacts, and that constant R-V (or linear I-V) characteristics are a necessary but not a sufficient condition for neglecting contact resistance in two-terminal measurements of the bulk electrical properties of CdS.