Refractory metal nitride rectifying contacts on GaAs

The electrical characteristics of reactive-sputtered refractory metal nitride contacts on GaAs are investigated for their high-temperature stability after rapid-thermal annealed up to 850 °C for 10 s. It is observed that all the contacts studied, including ZrN/GaAs, TiN/GaAs, and NbN/GaAs systems, show improving rectifying characteristics with annealing temperatures up to 800–850 °C. Not only do they maintain excellent thermal stability and have ideality factors very close to unity, these refractory metal nitride/GaAs contacts actually exhibit a barrier height enhancement ranging from 0.13 eV for NbN/GaAs to 0.30 eV for ZrN/GaAs when contacts are annealed from 500 to 850 °C. Concomitantly, the small-signal capacitance of the contacts decreases with higher annealing temperature. The breakdown characteristics of these contacts become avalanche-like and the breakdown voltages increase by twofold. We have invoked the Shannon contact structure (i.e., metal/p+-GaAs/n-GaAs) to account for these high-temperature induced properties. The p+-GaAs layer formation is attributed to the incorporation of nitrogen into GaAs substrate during sputtering deposition. Comparison between pure refractory metals and their nitride contacts on GaAs are also made with electrical techniques (I–V, C–V) and material characterization techniques (Rutherford backscattering, scanning electron microscopy). Our study suggests that refractory metal nitrides have several advantageous properties for self-aligned GaAs metal–semiconductor field-effect transistor processes.