Requirements of epitaxially grown InGaAs channel layers for tunnel field-effect transistors

Abstract

The requirements of the epitaxially grown InGaAs channel layers for tunnel field-effect transistors (TFETs) have been studied by a comparison between the experimental results and technology computer-aided design (TCAD) simulations. It is observed that the threshold voltage (Vth) of InGaAs TFETs with high In contents is shifted more toward the negative bias direction and the off-characteristics are degraded more than that expected in simulation results. These results are attributable to the increase in n-type effective carrier concentration (Nch) in the InGaAs and InAs channels, which can be caused by lattice relaxation because of the large lattice mismatch between the epitaxial layer and the substrate. The use of a thin channel layer with high In content InGaAs and/or InAs can be a solution for achieving high on-current and low off-current simultaneously. It is found that p-type doping in the InGaAs and InAs channels can mitigate the degradation of the cut-off properties. Moreover, it is observed that increased Nch by unintentional Si impurity atoms at the epitaxial layer and the substrate interface can affect the performance of TFETs with thin InGaAs channels, which can be suppressed by introducing an insertional undoped buffer layer. The impact of Nch is also studied for the short channel devices by TCAD simulations. The p-type doping in InGaAs channels can also mitigate short channel effects in comparison to the n-type doping. The carefully controlled epitaxial growth of InGaAs and InAs channel layers with Nch <1 × 1017 cm−3 is required to realize superior performance InGaAs TFETs.