Simulation study of device physics and design of GeOI TFET with PNN structure and buried layer for high performance

Large threshold voltage and small on-state current are the main limitations of the normal tunneling field effect transistor (TFET). In this paper, a novel TFET with gate-controlled P⁺N⁺N⁺ structure based on partially depleted GeOI (PD-GeOI) substrate is proposed. With the buried P⁺-doped layer (BP layer) introduced under P⁺N⁺N⁺ structure, the proposed device behaves as a two-tunneling line device and can be shut off by the BP junction, resulting in a high on-state current and low threshold voltage. Simulation results show that the on-state current density I_on of the proposed TFET can be as large as 3.4 × 10⁻⁴ A/μm, and the average subthreshold swing (SS) is 55 mV/decade. Moreover, both of I_on and SS can be optimized by lengthening channel and buried P⁺ layer. The off-state current density of TTP TFET is 4.4 × 10⁻¹⁰ A/μm, and the threshold voltage is 0.13 V, showing better performance than normal germanium-based TFET. Furthermore, the physics and device design of this novel structure are explored in detail.