High-temperature annealing characteristics of tungsten and tungsten nitride Schottky contacts to GaAs under different annealing conditions

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Abstract
We have systematically investigated the structural and electrical characteristics of thin‐film tungsten and reactively sputtered tungsten nitride (WNx) Schottky contacts to GaAs under high‐temperature annealing conditions (with annealing temperatures ranging from 700 to 850 °C) in an arsenic‐overpressure and flowing nitrogen ambient with and without a silicon dioxide capping layer. Compositions of the WNx films measured by Rutherford backscattering spectrometry and proton resonant scattering techniques indicate a linear relationship between x and the nitrogen partial pressure during sputtering. Glancing angle x‐ray diffraction studies revealed that for nonzero nitrogen partial pressure, the as‐deposited films were amorphous, and after annealing these films converted to polycrystalline W2 N and W phases. A surface layer of W2 As3 phase was also observed after As‐overpressure capless annealing and was believed to be the result of reactions between W and the ambient As gas. Electrical measurements showed that all WNx /GaAs contacts (with x=0–0.5) were thermally stable up to an annealing temperature of 850 °C. A diode edge effect is observed for WNx /GaAs diodes cap annealed in As overpressure at temperatures higher than 800 °C. The maximum achievable Schottky barrier heights for these contacts were found to be independent of the nitrogen content in the films but are influenced by the annealing conditions. We also explored the role played by nitrogen on the thermal stability and barrier height of the contacts.