Formation mechanism of In sub(x)Ga sub(1-x)As ohmic contacts to n-type GaAs prepared by radio frequency sputtering

• Published in: Journal of electronic materials Vol. 23; no. 9; pp. 983 - 989
• Main Authors: Uchibori, C J, Okunishi, M, Oku, T, Otsuki, A, Ono, N, Murakami, M
• Format: Journal Article
• Language: English
• Published: 01-01-1994
• ISSN: 0361-5235

The formation mechanisms of InAs/Ni/W ohmic contacts to n-type GaAs prepared by radio-frequency (rf) sputtering were studied by measuring contact resistances (R sub(c)) using a transmission line method and by analyzing the interfacial structure mainly by x-ray diffraction and transmission electron microscopy. Current-voltage characteristics of the InAs/Ni/W contacts after annealing at temperatures above 600 degree C showed 'ohmic-like behavior.' In order to obtain the 'ohmic' behavior in the contacts, pre-heating at 300 degree C prior to high temperature annealing was found to be essential. The contacts showed ohmic behavior after annealing at temperatures in the range of 500 approximately 850 degree C and contact resistance values of as low as approximately 0.3 Omega -mm were obtained. By analyzing the interfacial structures of these contacts, In sub(x)Ga sub(1-x)As layers with low density of misfit dislocations at the In sub(x)Ga sub(1-x)As and GaAs interface were observed to grow epitaxially on the GaAs substrate upon heating at high temperatures. This intermediate In sub(x)Ga sub(1-x)As layer is believed to divide the high energy barrier at the contact metal and GaAs interface into two low barriers, resulting in reduction of the contact resistance. In addition, Ni was found to play a key role to relax a strain in the In sub(x)Ga sub(1-x)As layer (introduced due to lattice mismatch between the In sub(x)Ga sub(1-x)As and GaAs) by forming an intermediate Ni sub(x)GaAs layer on the GaAs surface prior to formation of the In sub(x)Ga sub(1-x)xAs layer.