ALD TiN Schottky Gates for Improved Electrical and Thermal Stability in III-N Devices

TiN films were deposited by plasma-assisted atomic layer deposition on AlGaN/GaN structures to investigate the influence of impurities on the performance and stability of Schottky barrier diodes. Oxygen and carbon impurities were reduced, but not completely removed, with increasing TiN growth temperature up to 350 degrees C. However, the best films still had 4 at% O and 1 at% C impurities as-deposited. TiN films with lower impurity concentrations exhibited lower Schottky barrier heights, providing a way to tailor the properties for different device applications. Films were then exposed to sequential anneals from 400-800 degrees C in 200 degrees C increments. X-ray diffraction showed that increasing anneal temperature reduced compressive stress and resulted in higher crystalline quality films. All films maintained similar morphology up to 600 degrees C, but at 800 degrees C underwent complete relaxation through fracturing and grain growth that caused significantly rougher films. Despite the change in morphology, TiN gates showed stable operation and low leakage throughout the entire temperature range, while Ni/Au gates failed above 600 degrees C, suggesting ALD TiN gates could be used in applications where increased thermal stability is required.