O3-sourced atomic layer deposition of high quality Al2O3 gate dielectric for normally-off GaN metal-insulator-semiconductor high-electron-mobility transistors

Abstract

High quality Al₂O₃ film grown by atomic layer deposition (ALD), with ozone (O₃) as oxygen source, is demonstrated for fabrication of normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Significant suppression of Al–O–H and Al–Al bonds in ALD-Al₂O₃ has been realized by substituting conventional H₂O source with O₃. A high dielectric breakdown E-field of 8.5 MV/cm and good TDDB behavior are achieved in a gate dielectric stack consisting of 13-nm O₃-Al₂O₃ and 2-nm H₂O-Al₂O₃ interfacial layer on recessed GaN. By using this 15-nm gate dielectric and a high-temperature gate-recess technique, the density of positive bulk/interface charges in normally-off AlGaN/GaN MIS-HEMTs is remarkably suppressed to as low as 0.9 × 10¹²cm⁻², contributing to the realization of normally-off operation with a high threshold voltage of +1.6 V and a low specific ON-resistance R_ON,sp of 0.49 mΩ cm².