Suppression of kink phenomenon in ultra-high-speed strained InAs- inserted E-mode HEMTs with a new 0.1 μm Y-shaped Pt-buried gate and their impacts on device performance

Kink phenomenon has been carefully investigated in InP-based HEMTs with a highly strained InAs channel. Although this narrow band-gap (ΔE_g) InAs channel layer with high hall mobility was effective to improve device speed characteristics, it also degraded high frequency power-gain severely in a depletion-mode operation (D-mode), mainly owing to the increased interactions associated with the impact-ionization induced holes. By operating InAs-based HEMT in an enhancement-mode (E-mode), Kink effect in I-V curve could be remarkably suppressed because the applied positive gate potential prevented the impact-ionization-induced holes from reacting with surface states, which also led to the improvements on high frequency gain (f_max), on-state breakdown voltage (BV_ds.on) and low-frequency transconductance (G_m) dispersion characteristics. Pt-buried gate technology was used to operate InAs-based HEMT in E-mode region, and a new Y-shaped gate structure with 0.1 μm gate length (L_g) was successfully developed to enhance device cutoff frequency (f_T) to the utmost by etching middle PMGI layer in tri-layer e-beam resist stack (ZEP520/PMGI/ZEP520).