TCAD-based optical FoM analysis of doping-less TFET photosensors with geometrically engineered channels for near-infrared (NIR) light detection

This work presents a comparative performance analysis of inverted T-shaped channel TFET (IT-DLTFET) and L-shaped channel TFET (L-DLTFET) based photosensors using a doping-less technique, designed for improved optical performance in detecting incident light with closely spaced wavelengths ($\sim$100 nm) and low luminous intensity ($<0.8$ W/cm²) in the near-infrared (NIR) region. Though a photo gate with the same footprint and position is placed near the source–channel (S–C) interface in both devices, differences in their geometrical design result in distinct electrostatics, leading to variations in sensing performance. Key optical figures of merit (FoMs), namely sensitivity ($S_n$), signal-to-noise ratio (SNR), quantum efficiency ($\eta$), and responsivity ($R$) are obtained from 2D TCAD simulation results, including transfer characteristics and optical generation contours, over the incident wavelength range of 700–1000 nm. The IT-DLTFET demonstrates superior FoM owing to its inverted T-shaped channel enabled by an elevated top gate and extended back gate, which enhances the tunneling region near the S–C interface. A higher illumination current ($I_{\text{Light}}$), improved average subthreshold swing ($S{S}_{\text{Avg}}$), and reduced dark current ($I_{\text{Dark}}$) in the IT-DLTFET contribute to a peak $S_n$ of $\sim$ 549.75, compared to $\sim$ 276.1 for the L-DLTFET at $\lambda =700\mathrm{nm}$. Moreover, the extended back gate near the drain–channel (D–C) interface improves electrostatic control and carrier confinement, enabling more efficient carrier injection and stronger photocurrent, which enhances the SNR to 89.7 compared to 56.7 in the L-DLTFET. Enhanced tunneling near the S–C interface increases the optical generation rate, improving sensitivity under low-intensity light and significantly boosting SNR, optimizing the device’s performance for on-chip applications. The dual-gate configuration of the IT-DLTFET further strengthens gate control over the elevated channel region, thereby enhancing the local electric field at the S–C interface and improving optical voltage ($V_{\text{OP}}$) development. Additionally, IT-DLTFET exhibits higher quantum efficiency ($\eta$), responsivity ($R$), and detectivity ($D$) even at longer wavelengths (e.g., 1000 nm), due to the enhanced generation of electron–hole pairs (EHPs) under illumination. The impact of interface traps on device performance is also analyzed, revealing that the IT-DLTFET shows better resilience to trap-induced degradation compared to the L-DLTFET.