In this paper, a novel structure of double gate tunnel FET has been proposed and simulated for biosensing applications. The device uses III-V compound semiconductors and an n+ doped pocket at the source channel junction. Biomolecules of different dielectric constants (K) with different charge densities (Nbio), both negative and positive, are inserted in the nano-gap cavities (15 nm $\times1.5$ nm) that have been created under gates near source channel junction to capture biomolecules. From extensive 2D simulations, ION sensitivity of ${4.351} \times {10}<^>{{8}}/{1.03} \times {10}<^>{{8}}/{1.514} \times {10}<^>{{9}}$ , subthreshold swing sensitivity of 15.67/20.21/18.57 mV/dec, and threshold voltage sensitivity of 18/12/23 mV for neutral (K = 12)/negatively charged biomolecules ( $\text{N}_{\text {bio}} = - {1} \times {10}<^>{{12}}$ C/cm2, K = 12)/positively charged biomolecules ( $\text{N}_{\text {bio}} = + {1} \times {10}<^>{{12}}$ C/cm2, K = 12) respectively has been observed. Also, transconductance sensitivity of ${9.74} \times {10}<^>{{7}}$ and ION/IOFF sensitivity of ${5.255} \times {10}<^>{{8}}$ for neutral biomolecules (K = 12) has been calculated. Furthermore, the device performance with one-third filled cavities, two-third filled cavities and fully filled cavities has also been studied. The performance of the proposed biosensor has been compared with the previously published work and it has been observed that the sensitivity of the proposed biosensor is 100 times better than the best reported biosensor.
