Effects of ammonia and oxygen plasma treatment on interface traps in AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors

A HfO2/Al2O3/AlN stack deposited in a plasma-enhanced atomic layer deposition system is used as the gate dielectric for GaN metal-insulator-semiconductor structures. Prior to the deposition, in situ remote plasma pretreatments (RPPs) with O-2, NH3, and NH3-O-2 (in sequence) were carried out. Frequency-dependent capacitance-voltage (C-V) measurements reveal that for all the RPP-treated samples, the interface trap density D-it was significantly reduced compared to the sample without RPP. In particular, the NH3-treated sample exhibits an extremely low D-it of similar to 10(11) cm(-2)<middle dot>eV(-1) from E-C - 0.31 eV to E-C - 0.46 eV. To characterize the interface traps at deeper levels, the transfer pulsed I-V measurement was employed further. In the energy range of E-C - E-T > 0.54 eV, the interface trap charge density Q(it) of various samples demonstrates the following order: NH3 RPP < NH3-O-2 RPP < O-2 RPP < without RPP. By adjusting multiple pulse widths, the D-it derived from the Q(it) result matches the C-V measurement precisely. Moreover, X-ray photoelectron spectroscopy analysis of the Ga 3d core-level indicates that NH3 RPP facilitates the conversion of Ga2O into GaN at high RF power of 2500 W, whereas O-2 RPP mainly oxidizes GaN to relatively stable Ga2O3. Combined with the C-V and pulsed I-V measurements, it is confirmed that a strong positive correlation exists between Ga2O and the interface traps, rather than Ga2O3.