All-optical nonreciprocity due to valley polarization pumping in transition metal dichalcogenides

Nonreciprocity and nonreciprocal optical devices play a vital role in modern photonic technologies by enforcing one-way propagation of light. Here, we demonstrate an all-optical approach to nonreciprocity based on valley-selective response in transition metal dichalcogenides (TMDs). This approach overcomes the limitations of magnetic materials and it does not require an external magnetic field. We provide experimental evidence of photoinduced nonreciprocity in a monolayer WS2 pumped by circularly polarized (CP) light. Nonreciprocity stems from valley-selective exciton population, giving rise to nonlinear circular dichroism controlled by CP pump fields. Our experimental results reveal a significant effect even at room temperature, despite considerable intervalley-scattering, showing promising potential for practical applications in magnetic-free nonreciprocal platforms. As an example, here we propose a device scheme to realize an optical isolator based on a pass-through silicon nitride (SiN) ring resonator integrating the optically biased TMD monolayer.

Physics and Modelling of Tri-Layered Strained Channel for Development of Double Gate n-channel FET

The strain silicon technology with FET is a dominant technology providing enrichment in carrier velocity in nanoscaled device by change of band structure arrangement. Leakage reduction while enhancement in drain current is another major objective therefore, designing a nano-regime double gate FET with strained channel is perceived. So, design and implementation of a double gate strained heterostructure on insulator (DG-SHOI) FET with tri-layered channel (s-Si/s-SiGe/s-Si) is the core. Biaxial strain is created in channel by inculcating three layers with optimal thicknesses while narrow channel depletion regions are strongly controlled by equipotential gates. Consequently, maximum charge carriers accumulate in channel due to quantum carrier confinement instigating ballistic transport across the 22 nm channel length device leading to lessening of intervalley scattering. In comparison to existing 22 nm DGSOI FET, drain current augmentation of 56% and transconductance amplification of 87.6% is observed while DIBL is prudently reduced for this newly designed and implemented DG-SHOI FET, signifying advancement in microelectronic technology.

Direct observation and manipulation of hot electrons at room temperature

In modern electronics and optoelectronics, hot electron behaviors are highly concerned since they determine the performance limit of a device or system, like the associated thermal or power constraint of chips, the Shockley-Queisser limit for solar cell efficiency. Up-to-date, however, the manipulation of hot electrons is mostly based on conceptual interpretations rather than a direct observation. The problem arises from a fundamental fact that energy-differential electrons are mixed up in real-space, making it hard to distinguish them from each other by standard measurements. Here we demonstrate a distinct approach to artificially (spatially) separate hot electrons from cold ones in semiconductor nanowire transistors, which thus offers a unique opportunity to observe and modulate electron occupied state, energy, mobility, and even its path. Such a process is accomplished through the scanning-photocurrent-microscopy (SPCM) measurements by activating the intervalley-scattering events and one-dimensional charge-neutrality rule. Findings discovered here may provide a new degree of freedom in manipulating nonequilibrium electrons for both electronic and optoelectronic applications.