Performance investigation of elevated source EBG TFET based photosensor for near-infrared light sensing applications

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In this manuscript, an elevated source TFET with extended back gate (ES-EBG-TFET) based photosensor is designed to offer improvement in optical performance for detecting incident light of narrow-spaced wavelengths (∼100 nm) and low luminous intensity (<0.9 W/cm2) in the near-infrared (IR) range. The proposed photosensor combines the advantages provided by both the elevated top gate and extended back gate in the sense of increasing the line tunneling region at the source-channel (S–C) interface, resulting to improvement in illumination current (ILight), threshold voltage (Vth) and average subthreshold swing (SSavg) under the light state. Furthermore, the inclusion of an L-shaped pocket around the source region helps to reduce the corner effects at S–C interface in the sub-threshold region, thereby improving the signal-to-noise ratio (SNR) of the proposed photosensor for on-chip applications. Due to improved optical generation in the photosensing gate, a high spectral sensitivity (Sn) of ∼54 is achieved for ES-EBG-TFET based photosensor because the variation in wavelength (λ) of incident light from 1050 to 750 nm shows a two order change in ILight (ID at Vgs = 0.2V under light state) from 3.1 × 10−15 A/μm to 1.72 × 10−13 A/μm, respectively. Since the elevated source provides a space to create larger illumination window above the channel region, a high optical generation rate is observed for the proposed photosensor under the incident light with low intensity (<0.9 W/cm2). The maximum value of SNR is observed to be 66.4 dB at a λ of 750 nm, while the quantum efficiency (ƞ) and responsivity (R) are reported to be 74% and 0.59 A/W, respectively, around λ of 1050 nm. Moreover, an optimum length of back-gate underlap with drain (LBGUD) is found to enhance the magnitude of SNR (at λ of 750 nm) and Sn (750–1050 nm) from 25.6 to 63.1 dB and 14 to 52.8, respectively when the photosensor is operated at the ambipolar state (Vgs = −0.6 V and Vds = 0.5 V). Finally, the photosensing parameters such as Sn and SNR are analyzed under the presence of acceptor and donor interface traps and it is found that there is insignificant degradation in the optical performance of the proposed photosensor.