La2O3 gate dielectrics for AlGaN/GaN HEMT

• One is the presence of negative charges at the interface of La2O3 gate dielectrics and AlGaN layer to shift the threshold voltage to positive direction. This is the prominent feature of La2O3/AlGaN interface.
• Another is a high k-value of 27 can be obtained with La2O3 gate dielectrics with suppressed gate leakage current which limits the reduction of gate capacitance.
• The other is that La2O3 gate dielectrics can prevent the 2DEG from mobility degradation associated with annealing processes, which is commonly observed with metal Schottky gate.

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 (Vth) 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.