Bias-dependent electron velocity and short-channel effect in scaling sub-100 nm InAlN/GaN HFETs

This work reports on the extraction and simulation of the electron velocity-gate voltages relationship for sub-100 nm InAlN/GaN heterojunction field-effect transistors (HFETs). A peak electron velocity (v(e)) at an electron density (n(s)) of 0.41 x 10(13) cm(-2) was observed at 1.06 x 10(7) cm/s in an InAlN/GaN HFET with 60 nm gate length (L-g) by delay time analysis. The v(e) at a high n(s) of 1.5 x 10(13) cm(-2) was observed at 0.6 x 10(7) cm/s. This peak v(e) behavior is explained by polarization Coulomb field (PCF) scattering and optical phonon scattering based on a Monte Carlo method. As L-g scaled from 350 to 60 nm, the current gain cutoff frequency (f(T)) and transconductance (g(m)) were improved. However, the thermal performance was degraded with a bad figure of merit P-150 degrees C. Although a weakening of the control capability of V-gs on n(s) (Delta n(s)/Delta V-gs) was observed in the shorter L-g device, which leads to a decrease in device g(m), the larger electron velocity by the increased lateral electric field (E) and the larger Delta v(e)/Delta V-gs by the increased PCF scattering still enhance the peak g(m). Results indicate that the enhancement of Delta v(e)/Delta V-gs is a vital method to strengthen the modulation of the gate on current and to suppress the short channel effect in GaN HFET. Our work supports a deeper understanding and analysis of sub-100 nm InAlN/GaN HFET device performance and physical mechanisms.