La2O3 gate dielectrics for AlGaN/GaN HEMT

The annealing temperature dependent electrical characteristics of La₂O₃ gate dielectrics for W gated AlGaN/GaN high electron mobility transistors (HEMTs) have been characterized. The threshold voltage (V_th) has been found to shift to positive direction with higher temperature annealing, exceeding those of Schottky HEMTs, presumably attributed to the presence of negative fixed charges at the interface between La₂O₃ and AlGaN layers. At a high temperature annealing over 500 °C, a high dielectric constant (k-value) of 27 has been achieved with poly-crystallization of the La₂O₃ film, which is useful to limit the reduction in gate capacitance. A high k-value for La₂O₃ gate dielectrics and the presence of negative charges at the interface are attractive for AlGaN/GaN HEMTs with low gate leakage and normally-off operation.