Plasma-Enhanced Atomic Layer Deposition of AlN Epitaxial Thin Film for AlN/GaN Heterostructure TFTs

AlN/GaN heterostructures were realized by growing AlN thin film with low-thermal-budget (300 ^°C) plasma-enhanced atomic layer deposition (ALD) on a semi-insulating GaN-on-sapphire template. Thin-film transistors (TFTs) have been successfully fabricated using in situ ALD-grown Al₂O₃ as the gate dielectric. The proposed TFTs exhibit good gate control with a low subthreshold swing of ~ 85 mV/decade and a low-field mobility of ~ 27 cm²/(V·s). This mobility is one order of magnitude higher than that obtained in AlN/GaN heterostructures grown by magnetron sputtering. The enhanced device performance is attributed to a high-quality ALD-AlN/GaN interface obtained by in situ remote-plasma predeposition cleaning and the subsequent epitaxial growth of AlN thin film by plasma-enhanced ALD.