Unveiling optical FoMs of DSTC-VTFET for visible spectrum photosensor

Abstract

This study used TCAD simulations to assess the electrical properties of a symmetrical vertical TFET with double germanium source regions and a T-shaped silicon channel (DSTC-VTFET) for very low power and photodetector devices. Enhanced switching performance is achieved through the inclusion of highly doped N⁺ epitaxial layers adjacent to the germanium sources. The photodetector's spectral response is evaluated under SiO₂ and HfO₂ gate oxides across varying wavelengths within the near-visible spectrum (300–700 nm), with optimized pocket doping levels. The DSTC-VTFET shows remarkable enhancements in ON-current (I_on), subthreshold swing (SS_avg), and dark current (I_Dark). These improvements boost optical performance metrics like responsivity (R), quantum efficiency (ƞ), signal-to-noise ratio (SNR), and spectral sensitivity (S_n). Devices with HfO₂ show superior carrier transport tunneling at the source-channel interface, achieving better I_on and SS_avg than SiO₂, particularly in the wavelength range of 300–700 nm. A reliability study, accounting for the influence of interface-trap impurities at the oxide-semiconductor boundary, indicates little SNR decrease when using SiO₂.The device demonstrates impressive performance with f_T of 175.42 GHz, SS_avg of 23.28 mV/dec, I_on of 8.38 × 10⁻⁸ A/μm, SNR of 90 dB, quantum efficiency reaching 85 %, and a spectral sensitivity of approximately 2 × 10⁴, showcasing its effectiveness in photodetection.