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The performance degradation of gate-recessed metal–oxide–semiconductor high electron mobility transistor (MOS-HEMT) is compared with that of conventional high electron mobility transistor (HEMT) under direct current (DC) stress, and the degradation mechanism is studied. Under the channel hot electron injection stress, the degradation of gate-recessed MOS-HEMT is more serious than that of conventional HEMT devices due to the combined effect of traps in the barrier layer, and that under the gate dielectric of the device. The threshold voltage of conventional HEMT shows a reduction under the gate electron injection stress, which is caused by the barrier layer traps trapping the injected electrons and releasing them into the channel. However, because of defects under gate dielectrics which can trap the electrons injected from gate and deplete part of the channel, the threshold voltage of gate-recessed MOS-HEMT first increases and then decreases as the conventional HEMT. The saturation phenomenon of threshold voltage degradation under high field stress verifies the existence of threshold voltage reduction effect caused by gate electron injection. [ABSTRACT FROM AUTHOR]

Double-peak N-shaped negative differential resistance (NDR) with a high peak-to-valley ratio is observed in the output characteristics of a GaAs-based modulation-doped field effect transistor with InAs quantum dots in the barrier layer (QDFET). One NDR peak with a higher source-drain voltage VDS is explained as the real-space transfer (RST) of high-mobility electrons in the channel into the quantum dots layer, while the other with a lower VDS is caused by the high-mobility RST electrons in the channel into the modulation-doped AlGaAs barrier layer on the other side. We depict a point how a thinner Schottky barrier layer provides a stronger potential, opening a possibility of two-directional channel electron transfer when a much higher VG is applied. The result suggests that the QDFET can be an attractive candidate for high-speed logic application and memory devices [ABSTRACT FROM AUTHOR]