Current flow by metallic shunts in alloyed ohmic contacts to wide-gap semiconductors

Abstract

A mechanism of current flow across alloyed ohmic contacts in lightly doped wide-gap A3B5 semiconductors has been investigated experimentally. Changes in the current–voltage and capacity–voltage characteristics of semiconductor–metal structures have been retraced on continuous heating, the semiconductors being GaAs and GaP and the metals In and Au. Furthermore, the temperature dependence of specific resistance has been studied in the 77–450 K range for In–GaN–In, In–GaP–In and In–GaAs–In ohmic contacts. A new mechanism of current flow across ohmic contacts has been proposed that lies in the suggestion that ohmic contacts in the In–GaN and In–GaP structures containing high-density dislocations should be formed by conducting metallic shunts that are connected across the space-charge layer. The shunts originate due to indium-atom precipitation on dislocations or other imperfections, the specific contact resistance being increased with temperature. In contrast, the shunts are of no importance at low dislocation density, for instance in In–GaAs structures, and the current flow mechanism is typical of Schottky diodes (thermionic or field emission at a certain carrier concentration in semiconductors).