Ultra Steep Ge-source Dopingless Tunnelling Field Effect Transistor with Enhanced Drive Current

Ge-source dopingless tunnelling field effect transistor (Ge-source DLTFET) with the optimization of dielectric oxide thickness under the source and the gate contacts is proposed and investigated by calibrated 2D TCAD device simulation. As the structure is realized using dopingless technique, this enables lower thermal budget, higher immunity towards the random dopant fluctuations (RDFs) effects and velocity degradation effects. The optimization of dielectric thickness has been done to tune the carrier concentrations induced in source and channel regions in order to improve the device performance. The drive current is magnificently enhanced along with ION/IOFF ratio, peak transconductance and ultra-steep subthreshold slope (SS) is reported for the optimized Si-DLTFET. In addition to this by deploying Ge-source instead of Si source in optimized Si-DLTFET increases ON current slightly and OFF current gets reduced by the order of two as compared to the optimized Si-DLTFET. This improves the ION/IOFF ratio,the reported drive current for Ge-source DLTFET is 5.1×10− 4 A/µm, along with ION/IOFF ratio as 1.54×1013, peak transconductance as 1.26 mS/µm and ultra-steep SS as 1.69 mV/decade. Further, the analog, RF and linearity performance parameters have also been investigated for both the structures and demonstrated notable improvement. The energy efficiency investigationreveals a significant reduction in energy-delay product. This paper indicates thepotentials of optimized Si-DLTFET and Ge-source DLTFET as promising candidates for low power analog and RF applications and Ge-source DLTFET hasbetter device dc performance.

Ultrasensitive negative capacitance phototransistors

Sensitive photodetection is crucial for modern optoelectronic technology. Two-dimensional molybdenum disulfide (MoS2) with unique crystal structure, and extraordinary electrical and optical properties is a promising candidate for ultrasensitive photodetection. Previously reported methods to improve the performance of MoS2 photodetectors have focused on complex hybrid systems in which leakage paths and dark currents inevitably increase, thereby reducing the photodetectivity. Here, we report an ultrasensitive negative capacitance (NC) MoS2 phototransistor with a layer of ferroelectric hafnium zirconium oxide film in the gate dielectric stack. The prototype photodetectors demonstrate a hysteresis-free ultra-steep subthreshold slope of 17.64 mV/dec and ultrahigh photodetectivity of 4.75 × 1014 cm Hz1/2 W−1 at room temperature. The enhanced performance benefits from the combined action of the strong photogating effect induced by ferroelectric local electrostatic field and the voltage amplification based on ferroelectric NC effect. These results address the key challenges for MoS2 photodetectors and offer inspiration for the development of other optoelectronic devices.

Positive non-linear capacitance: the origin of the steep subthreshold-slope in ferroelectric FETs

We show that the non-linear positive capacitance (PC) of ferroelectrics (FE) can explain the steep subthreshold-slope (SS) observed in FE based MOSFETs and often attributed to the existence of a negative capacitance in FE capacitors. Physically attainable and unattainable regions of the S-shape curve used in the negative capacitance theory are investigated by self-consistently solving Landau-Khalatnikov and Maxwell equations and by experimental validation. Finally, the conditions for attaining a steep SS in FE based MOSFETs assuming only positive capacitances are discussed.