We have demonstrated the operation of high on-off current ratio (I-on/I-off) and low subthreshold slope planar-type InGaAs tunnel field effect transistors (TFETs) with Zn-diffused source junctions. The solid-phase Zn diffusion process has been shown to form defect-less p(+)/n source junctions with steep profiles because of the inherent nature of Zn diffusion into InGaAs, which has significantly improved the TFET performance. The devices presented in this paper have exhibited a record low subthreshold slope of 64 mV/dec for planar-type III-V TFETs and a large I-on/I-off ratio of more than 10(6) at the same time. (C) 2015 AIP Publishing LLC.