An Actively-Passivated p-GaN Gate HEMT With Screening Effect Against Surface Traps

An active-passivation p-GaN gate HEMT (AP-HEMT), featuring an active p-GaN passivation layer extending into the drain-side access region, is demonstrated on a commercial E-mode p-GaN/AlGaN/GaN heterostructure wafer. The active passivation layer (APL) is electrically connected to the p-GaN gate, and thus can supply/release mobile holes through gate electrode. The mobile holes in the APL effectively shields the overlaying surface traps from depleting the underlying 2DEG channel, and thus results in a much improved dynamic <tex-math notation="LaTeX">Rₒₙ </tex-math> . After a 10-ms 650-V <tex-math notation="LaTeX">VDS </tex-math> stress, the measured dynamic <tex-math notation="LaTeX">Rₒₙ </tex-math> /static <tex-math notation="LaTeX">Rₒₙ </tex-math> is 4.30 for Conv-HEMT, but only 1.39 for AP-HEMT. Specially designed HEMTs with a surface testing electrode (ST) in the access region are fabricated to verify the screening effect. A negative <tex-math notation="LaTeX">VST </tex-math> mimics the virtual gate effect caused by negative surface charges, resulting in a reduced drain current in conventional HEMT (Conv-HEMT). In the AP-HEMT, a negative <tex-math notation="LaTeX">VST </tex-math> is shown to induce no change in the drain current, indicating an effective screening of the trap states. On the other hand, under a positive <tex-math notation="LaTeX">VST </tex-math> stress applied to a Conv-HEMT, electrons in the 2DEG channel are pulled over the AlGaN barrier and get trapped at the surface, resulting in a sharply decreased drain current after positive <tex-math notation="LaTeX">VST </tex-math> is removed. For the AP-HEMT, the drain current remain unchanged after the positive <tex-math notation="LaTeX">VST </tex-math> is removed. The actively passivated HEMT exhibits the highly desired suppression of surface trap induced dynamic <tex-math notation="LaTeX">Rₒₙ </tex-math> degradation.