Thermal stability of MISFET with low-temp molecular-beam epitaxy-grown GaAs and Al/sub 0.3/Ga/sub 0.7/As gate ins

GaAs and Al/sub 0.3/Ga/sub 0.7/As epilayers grown at LT by MBE were used as insulators in the fabrication of MISFET devices. Parametric changes were used to evaluate the thermal stability of MISFET, to identify failure mechanisms and validate the reliability of these devices. The LT-Al/sub 0.3/Ga/sub 0.7/As MISFET showed superior thermal stability. The degradation in the performance of MISFET with 1000 /spl Aring/ thick LT-GaAs gate insulator was worse than those of the MESFET. On the other hand, MISFET with 250 /spl Aring/ thick LT-GaAs gate insulators exhibited stable characteristics with thermal stressing, LF (low frequency) noise studies on the TLM structures of MISFET layers exhibited 1/f noise in the LT-Al/sub 0.3/Ga/sub 0.7/As samples and 250 /spl Aring/ LT-GaAs samples; whereas the 1000 /spl Aring/ thick LT-GaAs samples exhibited 1/f/sup 3/2/ noise, which was attributed to: (i) the thermal noise generated at the interface of the insulator, and (ii) the active layer due to the outdiffused metallic arsenic. Reverse gate-drain current degradation experiments were carried out at 120/spl deg/C, 160/spl deg/C, 200/spl deg/C, and 240/spl deg/C. Transconductance frequency dispersion studies were carried out before and after thermal stress on these MISFET. The transconductance of MISFET with 1000 /spl Aring/ LT-GaAs gate insulators was degraded by 40% at 100 kHz after thermal stress. The rest of the samples exhibited stable characteristics. These results indicate that composition changes had occurred at the interface in thicker LT-GaAs MISFET structures. Thinner LT-layers are ideal for achieving higher transconductance and better thermal stability without sacrificing the power capability of MISFET.