Direct-current and radio-frequency characteristics of passivated AlGaN/GaN/Si high electron mobility transistors

• Passivation of the HEMT by SiO2/SiN is made in order to reduce the trapping.
• We have investigated the effects of SiO2/SiN passivation on the transport properties of GaN HEMTs.
• The electrical behavior of the transistor devices is characterized by using DLTS, DC pulsed C–V and RF.

AlGaN/GaN/Si HEMTs grown by molecular beam epitaxy have been investigated using spectroscopy capacitance, direct and pulse current–voltage and small-signal microwave measurements. Passivation of the HEMT devices by SiO2/SiN with NH3 and N2O pretreatments is made in order to reduce the trapping effects. As has been found from DLTS data, some of electron traps are eliminated after passivation. This has led to an improvement in the drain current. To describe the electron transport, we have developed a charge-control model by including the deep traps observed from DLTS experiments. The thermal and trapping effects have been, on the other hand, studied from a comparison between direct-current and pulsed conditions. As a result, a gate-lag and a drain-lag were revealed indicating the presence of deep lying centers in the gate-drain spacing. Finally, small-signal microwave results have shown that the radio-frequency parameters of the AlGaN/GaN/Si transistors are improved by SiO2/SiN passivation and more increasingly with N2O pretreatment.