Study On AlGaN/GaN MOS-HEMT With High-k Gate Dielectric

High-performance GaN-based high-electron mobility transistors (HEMTs) have shown outstanding performance for high-temperature, high-power and high-frequency applications. However, they also have many questions, such as defect states, the larger gate leakage current and current collapse, which would seriously limit device reliability.To solve this problem, signifcant progress has been made on AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) using SiO2, Si3N4 as the gate dielectrics. However, as the size of device is reducing, in order to maintain good performance of the device, gate dielectric thickness also needs to be reduced, the resulting quantum tunneling effect will increase gate leakage current and power consumption. Then, the use of high dielectric constant materials is to be the trend of development. While maintaining the same gate capacitance, high-k gate dielectric can increase the physical thickness of gate dielectric layer, which can reduce the gate leakage current and improve the performance of the device.Firstly, this paper takes the simulation for AlGaN/GaN MOS-HEMT with high-k gate dielectric. Compared MOS-HEMT to conventional HEMT, MOS structure could get greater drain saturation current, higher cutoff frequency, but at the expense of a significant decrease in device transconductance and a large threshold voltage shift.Based on above mentioned simulation result, the authors also studied the same structure, different dielectric layer thickness, dielectric constant and temperature on the MOS-HEMT properties. The results showed that the decrease of oxide thickness can inhibit the threshold voltage shift, improve the transconductance and enhance the gate control ability. Usage of dielectrics with high-k could translate to more ef?cient gate modulation, thus a smaller decrease in transconductance and a moderate increase in the threshold voltage could be expected in MOS-HEMT with high-k gate dielectrics. With increasing temperature, the saturation current and transconductance decrease except slightly positive direction shift of the threshold voltage.Finally, a MOS-HEMT with Atomic Layer Deposition (ALD) 5nm HfSiO gate dielectric is manufactured. The results showed that the interface state density between the AlGaN film and the HfSiO insulating film was fairly low, the gate leakage current of MOS-HEMT is two orders lower as compared with the Schottky gate structure. With the insertion of dielectric layer , higher gate voltage will be applied to obtain higher maximum drain saturation current density. Otherwise, MOS-HEMT gained higher cut-off frequency and maximum frequency.