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We fabricated double-gate vertical GaAsSb/InGaAs tunnel FETs (TFETs). The characteristics of these TFETs were improved by changing the gate electrode evaporation from the electron beam to thermal evaporation. Furthermore, by changing the insulator from Al2O3/HfO2 to Al2O3/ZrO2, the steepest subthreshold slope (SS) = 56 mV dec−1 at VDS = 0.2 V was achieved. We analyzed these devices in two ways. First, to investigate the influence of trap-assisted tunneling (TAT), we conducted low-temperature measurements and found that TAT was suppressed through thermal evaporation. Next, to estimate the limitation of the SS, the energy decay parameter E0 was estimated from the negative differential resistance characteristics. Energy decay parameter E0 is determined by the impurity level and becomes a leak component of the TFET. However, we found that energy decay parameter E0 is both process and temperature-dependent.

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In this study, we fabricated MOSFETs with Al2O3/InGaAs or HfO2/Al2O3/InGaAs gate stacks. The surface was subjected to nitrogen plasma and trimethylaluminum cleaning prior to low-temperature atomic layer deposition. Electron mobility was extracted using the capacitance–gate voltage (C–VG) and drain current–gate voltage (ID–VG) characteristics. We determined that the mobility decreased when the gate voltage sweeping width increased during C–VG and ID–VG measurements. In addition, we determined that the lowering of the deposition temperature to 120 °C improved the mobility of MOSFETs with HfO2/Al2O3/InGaAs gate stacks as compared with that corresponding to deposition at 300 °C. Furthermore, HfO2/Al2O3/InGaAs gate stacks with various Al2O3 thicknesses were fabricated. When the number of Al2O3 deposition cycles was more than 4, the mobility of MOSFETs with HfO2/Al2O3/InGaAs gate stacks improved, reaching the value of the Al2O3/InGaAs gate stack.