In this letter, we investigate the threshold voltage (V _TH ) shift in a p-GaN gate AlGaN/GaN transistor by designed gate-bias pulse measurements. It was found that the forward gate bias causes positive (V _TH ) shift. The dynamics of electron trapping was revealed from the dependences of the consequent (V _TH ) shift on the bias duration at different voltages. A time constant smaller than 0.1 ms for the (V _TH ) shift saturation at 6-V gate bias was obtained. It was also found that the (V _TH ) became inversely proportional to the gate-bias voltages exceeding 7 V. This inverse proportionality of the (V _TH ) shift resulted from the threshold of the hole-injection/electroluminescence (EL) and the sequential optical pumping effect on the electron traps. The EL emission was confirmed by a self- and in-situ photon detection measurement.

Linear magneto-resistance is observed in high magnetic field in topological insulator Bi₂Se₃ films. As revealed by tilted magnetic field measurement, this linear magneto-resistance is associated with the gapless topological surface states and of quantum origin. In the ultra-thin limit, the inter-surface tunneling induced surface state gap opening quenches the linear magneto-resistance. Instead, weak negative magneto-resistance is observed in high magnetic fields in ultra-thin films.

A low on-resistance normally-off GaN double-channel metal-oxide-semiconductor high-electronmobility transistor (DC-MOS-HEMT) is proposed and demonstrated in this letter, which features a 1.5-nm AlN insertion layer (ISL) located 6 nm below the conventional barrier/GaN interface, forming a second channel at the interface between the AlN-ISL and the underlying GaN. With gate recess terminated at the upper channel, normally-off operation was obtained with Vth of +0.5 V at ^I DS = 10 μA/mm or +1.4 V from the linear extrapolation of the transfer curve. The lower heterojunction channel is separated from the etched surface in the gate region, thereby maintaining its high field-effect mobility with a peak value of 1801 cm ² /(V·s). The on-resistance is as small as 6.9 Q·mm for a DC-MOS-HEMT with LG/LGS/ ^L GD = 1.5/2/15 μm, and the maximum drain current is 836 mA/mm. A high breakdown voltage (>700 V) and a steep subthreshold swing of 72 mV/decade are also obtained. Index Terms-Double-channel MOS-HEMT (DC-MOSHEMT), field-effect mobility, gate recess, normally-off.