Ge concentration in regrown GaAs for ohmic contacts

Abstract

Dissociation and solid phase epitaxial regrowth of GaAs in Ti/Ge/Ni/GaAs were investigated using the transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS) of x-rays with spatial resolution approaching 2 nm. A ternary Ni2.4GaAs phase, ∼130 nm thick, was formed by 300 °C in situ anneals of 65 nm Ni film on GaAs. After this in situ anneal, films of 30 nm Ge and 20 nm Ti were deposited in sequence. The EDS analysis showed that Ni2.4GaAs transformed into Ni–As and Ni–Ga binaries after annealing at 500 °C for 5 min, while ∼30 nm of GaAs regrew by solid phase epitaxial regrowth from decomposition of the binary phases. High spatial resolution microanalysis allowed detection of ∼1×1020 cm−3 Ge in the regrown GaAs. This confirms that Ge is incorporated into GaAs during regrowth for ohmic contact formation.