Simulation Study of Photosensitive Characteristics of a Junctionless Heterostructure (GaAs-Ge) TFET for Near Infra-Red Sensing Application

Abstract

Tunnel Field Effect Transistor has proved to be an inexpensive electronic device in the application of low power VLSI Design systems owing to its low operational voltages, high ION/IOFF ratio and very steep sub-threshold slope. However, due to their typical requirements of degenerate doping concentrations and sharp doping gradient profiles at the junctions, TFETs pose difficulties like Random Dopant Fluctuations (RDFs), increased process complexity and raised thermal budget. In this thesis, a germanium gate-junctionless-hetero (GaAs-Ge) device structure, working on the principle of band-to-band tunneling mechanism, has been designed and simulated to exhibit sensitivity to near-infrared (NIR) wavelengths (1–1.5 μm). Therefore the device can be utilized for NIR optical detecting applications in the field of biosensing, life science and medical imaging. In order to address the issues of RDFs, increased process complexity and raised thermal budget associated with TFETs, recently studied techniques like junctionless structure and dopingless concepts have been incorporated in the device design. Also, in recent studies, these techniques were reported to exhibit improved electrostatic characteristics. The use of the dopingless technique is realised by electrostatic doping to induce carrieroconcentration of required high concentrations within the source and drain regions that is capable to allow dynamic configuration (same device able to perform as n-type and p-type based on requirement). In order to elevate the on current level, sandwiching of III-V groups compound material with group IV semiconductor material is done for hetero-junction channel. A subthreshold swing of less than 60 mv/decade (~30mV/dec) has been achieved. VTH increased by 42 mV for the variation of incident illumination photon wavelength from 1 μm to 1.5 μm at a gate doping level of 1×1018 cm−3 . With such a level of sensitivity to NIR wavelengths and such steep SS value, the proposed device can serve as a potential candidate for near-infrared biosensing and imaging applications.