Interfacial reactions in the Nb/GaAs system

Solid-state reactions between niobium and gallium arsenide in both thin film and bulk forms were studied in the temperature range 400 to 1000 °C using transmission electron microscopy (TEM), metallography, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Initially Nb₄As₃ and Nb₅Ga₃ formed at the interface and grew very slowly. Following an incubation period, NbAs and NbGa, nucleated and grew at rates several orders of magnitude faster than the initial phases. The resulting metastable diffusion path, Nb/NbGa₃/NbAs/GaAs, was observed even after relatively long-term annealing and is believed to be kinetically stabilized. Formation of the other Nb–Ga binary compounds as predicted by the phase diagram was inhibited by nucleation and kinetic barriers. The observed reaction sequence is discussed considering the thermodynamics, kinetics, and possible growth mechanisms involved in the reaction.