The lack of high power conversion efficiency in RF passive rectifier circuits at sub-µW power levels with current MOSFET technologies is directly related with the difficulty of the transistors in conducting the required level of current at low voltage values. With a different carrier injection mechanism, the superior electrical characteristics of the Tunnel FET devices at low voltage values (sub-0.25 V) can outperform the process of energy conversion at ultra-low power, thus improving the operation range of RF energy harvesting circuits. In this work, a simulation study on the doping profile and material selection of Tunnel FET devices shows the impact of device properties in rectifier circuit efficiency.