Ohmic contacts on p-GaN (Part I): investigation of different contact metals and their thermal treatment

The changes in contact resistivity and I-V curve linearity after annealing of Pd, Ni/Au, Cr/Au, Co/Au, Pt and Au contacts on p-GaN after tempering bel ow and above 500 degreesC have been investigated. CTLM-layered structures o n p-GaN were thermally stressed and electrically analyzed. The I-V curve li nearity as a measure of ohmic behavior has been derived from the correlatio n coefficient of the I-V curves. Below 500 degreesC the Pd, Ni/Au, Cr/Au an d Co/Au contacts become ohmic after annealing. The best final values of the specific contact resistance rho (c) after annealing increase in the sequen ce Ni/Au, Pd, Co/Au, Cr/Au, Au and Pt. After annealing above 500 degreesC t he contact resistance increases for all contact materials and the linearity decreases. A competition between the formation of reaction phases at the i nterface and the decomposition of the p-GaN epi-layer is a probable reason for this behavior. (C) 2001 Elsevier Science Ltd. All rights reserved.