Ohmic contacts to p-type GaP

Abstract

The objective of thisresearch was to develop ohmic contact schemes of low resistance, i.e. in the mid10-1 QCM2, to p-type Gallium Phosphide by the mechanism of solid-phase regrowth. The contact resistivityof the samples fabricated in this work was measured by the Cox-Strack method. Ohmic contacts based on the Zn/Pd system were developed. The Zn(350A)/Pd(IOOA)/p-GaP and Zn(350A)/Pd(IOOA)/p-GaP gave rather high values of the contact resistivity, 3-8xl 0-4 f2CM2. An improvement in the contact resistivity was achieved by developing the Si(750A)/Pd(400A)/Zn(xA)/Pd(IOOA)/p-GaP scheme. Values of the contact resistivity in the range of 3xlO-5 to 7xlO-' nCM2 were obtained. It was found that the optimum Zn layer thickness is 30 A for the Pd and Si thickness used in this scheme. The samples were annealed for I @n at temperatures ranging from 3 5 0 to 4 5 0 'C. Lower values of the contact resistivity than those of the Si/Pd/Zn/Pd/p-GaP scheme were achieved by depositing an Aluminum layer on the top of the Si/Pd/Zn/Pd/p-GaP system. Values of the contact resistivity in the range of 2xl 0-5 f2CM2 to 5xlO-5 flcM2 were achieved for the contacts AI(IOOOA)/Si(750A)/Pd(400A)/Zn(30A)/Pd(IOOA)/p-GaPand AI(200A)/Si(750A)/Pd(400A)/Zn(30A)/Pd(IOOA)/p-GaP, respectively. The low values of the contact resistivity were attributed to the formation of a heavilydoped surface layer beneath the contact area. The doping concentration of this surface layer was estimated by using theoretical plots of the contact resisvity versus doping concentration.