TMAH-based wet surface pre-treatment for reduction of leakage current in AlGaN/GaN MIS-HEMTs

Abstract

The pre-passivation surface treatment process with tetramethylammonium hydroxide (TMAH)-based wet solution was proposed for the minimization of the leakage current (Ileak) in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs). This process step contributes to the simultaneous decrease of the surface current (Isurf) in the active region of device and mesa-isolated region by removing the surface states and traps related to nitrogen (N) vacancy, Ga-oxide, and dangling bonds. Using the surface treatment, the fabricated device achieves a lower off-state current (Ioff) of ∼10−12A/mm, a higher on/off current ratio (Ion/Ioff) of ∼1011, a small subthreshold swing (SS) of 68.4mV/dec. The reduced Ileak also improves breakdown voltage (BV). In addition, the interface trap density (Dit) between the SiN layer and the AlGaN surface was extracted to evaluate the quality of the SiN/GaN interface, which showed that the treatment decreases the Dit with reduction of the surface defects.