arXiv subjects

Shaili Sett

Publications and source records attributed to Shaili Sett.

7 recordsLinked to original sources

arXiv2026

Polarization engineered all 2D Graphene/Ferroelectric hybrid for persistence-free photoresponse

Graphene-based van der Waals hybrid photodetectors typically work on trap-mediated photogating mechanism, exhibiting high sensitivity, but under-perform in the fast detection of repetitive optical signals. Designing photodetectors that are simultaneously fast and highly sensitive has therefore remained difficult. In this work, we realize both attributes by integrating atomically thin sliding ferroelectrics in the design architecture, thereby uniting semiconducting properties with intrinsic polarization fields capable of efficiently governing interfacial photocarrier dynamics. We report a bilayer graphene-bilayer MoS2 (with MoS2 in a rhombohedrally stacked (3R) configuration) van der Waals photodetector with edge-contacted dual-gated field-effect transistor architecture. The photo-induced modulation in spontaneous out-of-plane polarization of 3R-MoS2 and selective confinement of charge carriers in bilayer graphene under an out-of-plane displacement field results in a tunable persistence-free photoresponse. Here, the photoinduced polarization change in 3R-MoS2 produces an optically controlled gating effect that alters the electrostatic environment of bilayer graphene, resulting in a temperature-independent photoresponse with rapid response times of the order of 10's of milliseconds (limited by the measurement instrument). We demonstrate reproducible detection of optical signals and examine the photon-counting resolution of this structure in high-sensitivity regimes, where we determine its internal quantum efficiency to be 10 percent with minimum detectable photon number of 31 in single shot measurements. This work highlights the functionality of 3R-MoS2 in manipulating the interfacial charge dynamics and establishes the hybrid of graphene and ferroelectric 3R-MoS2 as a promising platform for ultra-sensitive optoelectronic devices.

cond-mat.mes-hall↗

arXiv2025

Moire-Engineered Ferroelectric Transistors for Nearly Trap-free, Low-Power and Non-Volatile 2D Electronics

Long-range moire patterns in twisted WSe2 enable a built-in, moire-length-scale ferroelectric polarization that can be directly harnessed in electronic devices. Such a built-in ferroic landscape offers a compelling means to enable ultralow-voltage and non-volatile electronic functionality in two-dimensional materials; however, achieving stable polarization control without charge trapping has remained a persistent challenge. Here, we demonstrate a moire-engineered ferroelectric field-effect transistor (FeFET) utilizing twisted WSe2 bilayers that leverages atomically clean van der Waals interfaces to achieve efficient polarization-channel coupling and trap-suppressed, ultralow-voltage operation (subthreshold swing of 64 mV per decade). The device exhibits a stable non-volatile memory window of 0.10 V and high mobility, exceeding the performance of previously reported two-dimensional FeFET and matching that of advanced silicon-based devices. In addition, capacitance-voltage spectroscopy, corroborated by self-consistent Landau-Ginzburg-Devonshire modeling, indicates ultrafast ferroelectric switching (~0.5 microseconds). These results establish moire-engineered ferroelectricity as a practical and scalable route toward ultraclean, low-power, and non-volatile 2D electronics, bridging atomistic lattice engineering with functional device architectures for next-generation memory and logic technologies.

cond-mat.mtrl-sci↗

arXiv2024

Emergent inhomogeneity and non-locality in a graphene field-effect transistor on a near-parallel moire superlattice of transition metal dichalcogenides

At near-parallel orientation, twisted bilayer of transition metal dichalcogenides exhibit inter-layer charge transfer-driven out-of-plane ferroelectricity that may lead to unique electronic device architectures. Here we report detailed electrical transport in a dual-gated graphene field-effect transistor placed on 3R stacked twisted bilayer of WSe2 at a twist angle of 2.1 degree. We observe hysteretic transfer characteristics and an emergent charge inhomogeneity with multiple local Dirac points as the electric displacement field (D) is increased. Concomitantly, we also observe a strong non-local voltage signal at D = 0 V/nm that decreases rapidly with increasing D. A linear scaling of the non-local signal with longitudinal resistance suggests edge mode transport, which we attribute to the breaking of valley symmetry of the graphene channel due to the spatially fluctuating electric field from the moire domains of the underlying twisted WSe2. A quantitative analysis connecting the non-locality and channel inhomogeneity suggests emergence of finite-size domains in the graphene channel that modulate the charge and the valley currents simultaneously. This work underlines efficient control and impact of interfacial ferroelectricity that can trigger a new genre of devices for twistronic applications.

cond-mat.mes-hall↗

arXiv2022

Tuning exciton complexes in twisted bilayer WSe2 at intermediate misorientation

Twist angle modifies the band alignment, screening, and interlayer (IL) coupling in twisted bilayers (tBLs) of transition metal dichalcogenides. Intermediate misorientation (twist angles > 15 degrees) bilayers (BLs) offer a unique opportunity to tune excitonic behavior within these concurrent physical mechanisms but are seldom studied. In this paper, we measure many-body excitonic complexes in monolayer (ML), natural BL, and tBL WSe2. Neutral biexciton (XX) is observed in tBL, while being undetected in nonencapsulated ML and BL, demonstrating unique effects of disorder screening in tBLs. The XX as well as charged biexciton are robust to thermal dissociation and are controllable by electrostatic doping. Vanishing of momentum-indirect IL excitons with increasing electron doping is demonstrated in tBL, resulting from the near alignment of Q-K and K-K valleys. Intermediate misorientation samples offer a high degree of control of excitonic complexes while offering possibilities for studying exciton-phonon coupling, band alignment, and screening.

physics.optics↗

arXiv2020

Effective separation of photogenerated electron-hole pairs by radial field facilitates ultrahigh photoresponse in single semiconductor nanowire photodetectors

We report an investigation on the observation of ultrahigh photoresponse (photogain, G_Pc>106) in single nanowire photodetectors of diameter < 100 nm. The investigation which is a combination of experimental observations and a theoretical analysis of the ultrahigh optical response of semiconductor nanowires, has been carried out with emphasis on Ge nanowires. Semiconductor nanowire photodetectors show a signature of photogating where G_Pc rolls-off with increasing illumination intensity. We show that surface band bending due to depleted surface layers in nanowires induces a strong radial field (~ 108 V/m at the nanowire surface) which causes physical separation of photogenerated electron-hole pairs. This was established quantitatively through a self-consistent theoretical model based on coupled Schrodinger and Poisson Equations. It shows that carrier separation slows down the surface recombination velocity to a low value (< 1 cm/s) thus reducing the carrier recombination rate and extending the recombination lifetime by few orders of magnitude. An important outcome of the model is the prediction of G_Pc ~ 106 in a single Ge nanowire (with diameter 60 nm), which matches well with our experimental observation. The model also shows an inverse dependence of G_Pc on the diameter that has been observed experimentally. Though carried out in context of Ge nanowires, the physical model developed has general applicability in other semiconductor nanowires as well.

cond-mat.mtrl-sci↗

arXiv2020

Broad Band Single Germanium Nanowire Photodetectors with Surface Oxide Controlled High Optical Gain

We have investigated photoconductive properties of single Germanium Nanowires(NWs)of diameter less than 100 nm in the spectral range of 300 to 1100 nm showing ultra large peak Responsivity in excess of 10^{7}AW^{-1}.The NWs were grown by Vapor Liquid Solid method using Au nanoparticle as catalyst. In this report we discuss the likely origin of the ultra large responsivity that may arise from a combination of various physical effects which are a): Ge and GeO_{x} interface states which act as scavengers of electrons from the photo-generated pairs,leaving the holes free to reach the electrodes,b) Schottky barrier at the metal and NW interface which gets lowered substantially due to carrier diffusion in contact region and (c) photodetector length being small (approximately few μm), negligible loss of photogenerated carriers due to recombination at defect sites. We have observed from power dependence of the optical gain that the gain is controlled by trap states. We find that the surface of the nanowire has presence of a thin layer of GeO_{x} (as evidenced from HRTEM study) which provide interface states. It is observed that these state play a crucial role to provide a radial field for separation of photogenerated electron and hole pair which in turn leads to very high effective photoconductive gain that reaches a very high at low illumination density.

physics.app-ph↗

arXiv2020

Enhanced broad band photoresponse of a partially suspended horizontal array of Silicon microlines fabricated on Silicon-On-Insulator wafers

We report a high Responsivity broad band photo-detector working in the wavelength range 400 nm to 1100 nm in a horizontal array of Si microlines (line width ~1 micron) fabricated on a Silicon-on-Insulator (SOI) wafer. The array was made using a combination of plasma etching, wet etching and electron beam lithography. It forms a partially suspended (nearly free) Silicon microstructure on SOI. The array detector under full illumination of the device shows a peak Responsivity of 18 A/W at 800 nm, at a bias of 1V which is more than an order of magnitude of the Responsivity in a commercial Si detector. In a broad band of 400 nm to 1000 nm the Responsivity of the detector is in excess of 10A/W. We found that the suspension of the microlines in the array is necessary to obtain such high Responsivity. The suspension isolates the microlines from the bulk of the wafer and inhibits carrier recombination by the underlying oxide layer leading to enhanced photo-response. This has been validated through simulation. By using focused illumination of selected parts of a single microline of the array, we could isolate the contributions of the different parts of the microline to the photo-current.

physics.app-ph↗