Analysis of Ge-Si Heterojunction Nanowire Tunnel FET: Impact of Tunneling Window of Band-to-Band Tunneling Model

Abstract

Tunnel FET (TFET) has potential applications in the next generation ultra-low power transistor to substitute the conventional FETs. It can offer very steep inverse subthreshold swing slope to maintain a low leakage current, thus it can be very essential for limiting power consumption in MOSFETs. The carriers in TFET transport from source to channel by the band-to-band tunneling (BTBT) mechanisms. To realize high saturation currents of TFET, it critically depends on the transmission probability, T WKB . In indirect semiconductor, such as Si and Ge, the BTBT model is very crucial for designing and predicting the device performance. In this paper, we employed the nonlocal BTBT model applied to three-dimensional Ge-Si heterojunction TFET with gate length 10 nm compare with Si TFET by including quantum effects simulation. The results show that the Ge-Si TFET outperforms Si TFET because of the lower bandgap and larger tunneling windows. BTBT generation rates of Ge-Si TFET are higher than Si TFET in the on-state condition. The highest BTBT generation rates are located in the source and channel junction and its peaks close to the gate dielectric. Power dissipation is a primary concern for future nanoelectronics devices and switching systems.1 Reducing supply voltage (V DD ), while keeping leakage current very low is very essential for limiting power consumption in MOSFETs.2 As V DD is reduced, the overdrive factor (V DD -V TH ) must be remained high to meet performance requirements. On the other hand, reducing threshold voltage (V TH ) can cause the off-state current (I OFF ) increase exponentially. Therefore, subthreshold swing (SS) must be reduced to maintain a low I OFF . However, conventional MOSFETs cannot provide SS lower than 60 mV/dec at room temperature because of fundamental thermal limits. Charge injection in the MOSFETs occurs by thermionic emission over a potential barrier, is bound by an exponential tail of Fermi statistics. 3,4 In the nanoscale transistor, the cylindrical nanowire is the promising candidate in the ultra-low power vertical devices due to high device density, its negligible trapping and leakage from buffer layer, wrap-gated structure and possibility of very short gate length (below 20 nm).5 Moreover, cylindrical shape tunnel field-effect transistor (TFET) can offer a very steep inverse subthreshold slope for maintain a low leakage current. The TFET is a gated p-i-n transistor with a gate voltage that causes large band bending at the source junction. Hence, the carriers can be transported from source to channel by the band-to-band tunneling (BTBT) mechanism. 6 The carrier injection on the BTBT of electrons from a degenerate p+ source into the channel conduction band causes high-energy carrier are filtered out by the semiconductor bandgap. Thus, steeper subthreshold slopes can be achieved. 3Recent studies have reported many complex fabrication issues of TFETs because of asymmetric doping concentration in source and drain of planar horizontal TFET. For the mature material process like germaniu...

Investigation of the impact of mole-fraction on the digital benchmarking parameters as well as sensitivity in GaXIn1−XAs/GaYIn1−YSb vertical heterojunctionless tunneling field effect transistor

“…Equation 1 shows the probability of tunneling in a TFET device, in which Wentzel-Kramers-Brillouin approximation is used [12,16].…”

“…ε channel and ε oxide are relative permittivity of channel and gate dielectric, respectively. ∆φ is the energy difference between the valence band of the source and the conduction band of the channel, and m * is tunneling effective mass [16]. In fact, Equation 1 shows that both parameters E g and m * play an important role in the performance of the TFET device.…”

“…The reason is that the forbidden band width is so large that it reduces the electron tunneling probability in tunneling junction [6,11]. With the recent progress, the low ION problem in JLTFET has been resolved by various strategies, such as using small band gape materials [15,16] gate engineering [17,18]. and hetero-gate dielectric [11,19].…”

Performance investigation of a semi‐junctionless type II heterojunction tunnel field effect transistor in nanoscale regime

“…Band‐to‐band tunnelling is the main current mechanism of n‐channel SJTFET and occurs when the electron in the valence band of the source region tunnels across the bandgap into the conduction band of the channel region in the absence of traps. The potential barrier can be approximated by a triangular barrier and the tunnelling phenomena mainly depends on the transmission probability, T ( E ), that can be calculated by employing the Wentzel–Kramers–Brillouin approximation [11] where m * denotes the effective mass of carrier, q is the electric charge, h is the Planck constant and E g is the bandgap. In addition, λ presents the screening tunnelling length and demonstrates the spatial extension of the transition region at the source–channel interface that mainly depends on the device geometry.…”

Analog/RF Performance Analysis of Heterojunction Tunnel FET with Temperatute

“…The values of the device parameters have been provided in Table 1. Silicon on Insulator (SOI) has been utilized to suppress short channel effects [30][31][32].…”