Degradation of gate-recessed MOS-HEMTs and conventional HEMTs under DC electrical stress

The performance degradation of gate-recessed metal–oxide–semiconductor high electron mobility transistor(MOSHEMT)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.

The Instability of Terahertz Plasma Waves in Two Dimensional Gated and Ungated Quantum Electron Gas

The instability of terahertz（THz）plasma waves in two-dimensional（2D）quantum electron gas in a nanometer field effect transistor（FET）with asymmetrical boundary conditions has been investigated.We analyze THz plasma waves of two parts of the 2D quantum electron gas：gated and ungated regions.The results show that the radiation frequency and the increment（radiation power）in 2D ungated quantum electron gas are much higher than that in 2D gated quantum electron gas.The quantum effects always enhance the radiation power and enlarge the region of instability in both cases.This allows us to conclude that 2D quantum electron gas in the transistor channel is important for the emission and detection process and both gated and ungated parts take part in that process.

Tuning of the Electron Spin Relaxation Anisotropy via Optical Gating in GaAs/AlGaAs Quantum Wells

The carrier-density-dependent spin relaxation dynamics for modulation-doped GaAs/Al0.3 Gao,TAs quantum wells is studied using the time-resolved magneto-Kerr rotation measurements. The electron spin relaxation time and its in-plane anisotropy are studied as a function of the optically injected electron density, Moreover, the relative strength of the Rashba and the Dresselhaus spin-rbit coupling fields, and thus the observed spin relaxation time anisotropy, is further tuned by the additional excitation of a 532nm continuous wave laser, demonstrating an effective spin relaxation manipulation via an optical gating method.