Electrical and microstructure analysis of Ni/Ge/n-GaAs interface

Ni(27 nm)/Ge(23 nm) and Ni(10 nm)/Ge(40 nm) layers deposited onto n-type GaAs by electron beam evaporation were studied structurally and electrically. The samples were annealed for 20 min at different temperatures in flowing forming gas-H-2:N-2 (5%:95%) -in tube furnace. The current-voltage characteristics of the samples annealed at 600 degrees C show ohmic character. The contact resistance was found to be a minimum of 5.1 x 10(-5) Omega cm(2) after annealing at 600 degrees C. The alloying behaviour of the specimens were investigated by electron microscopy. The contacts show a mixed structure in the case of as-deposited samples. In the sample annealed at 550 degrees C, there appeared deep pyramidal pits of 20-30 nm size. The structural characterization was carried out by cross-sectional transmission electron microscope (XTEM) equipped with energy dispersive system (EDS). The composition investigations showed that the pits contained of Ga, As, Ni and Ge. The upper layer of the metal was very thin and rich in Ga. The layer between the semiconductor and the upper layer was a Ni-Ge(Ga, As) mixed one. (C) 1998 Elsevier Science S.A. All rights reserved.