arXiv subjects

D. Saha

Publications and source records attributed to D. Saha.

7 recordsLinked to original sources

arXiv2023

Numerical simulation of defect states and electron transport mechanisms in amorphous oxide thin film transistors

Physics based numerical simulation has been carried out to probe the sub-gap density of states (DOS) and underlying electron transport properties of amorphous oxide based thin film transistors (TFTs). The DOS model of TFTs consists of exponential band tails, Gaussian shallow donor levels and deep acceptor states. Electrical transport and various TFT performance parameters are found to be critically dependent on the sub-gap DOS. At low gate bias, when Fermi level lies below the conduction band mobility edge, defect states mediated trap limited conduction is found to be the dominant transport mechanism. However, at relatively higher gate bias, percolation conduction above the mobility edge becomes prevalent. Such possible crossover of electron transport is well corroborated by gate bias dependent band bending and induced free electron density in the channel layer. Such studies are important to unravel the critical role of sub-gap DOS on the electrical performance and charge transport processes of disordered amorphous oxide TFTs.

physics.app-ph↗

arXiv2017

Evidence for an excitonic insulator phase in a zero-gap InAs/GaSb bilayer

Many-body interactions can produce novel ground states in a condensed-matter system. For example, interacting electrons and holes can spontaneously form excitons, a neutral bound state, provided that the exciton binding energy exceeds the energy separation between the single particle states. Here we report on electrical transport measurements on spatially separated two-dimensional electron and hole gases with nominally degenerate energy subbands, realized in an InAs(10 nm)/GaSb(5 nm) coupled quantum well. We observe a narrow and intense maximum (~500 kΩ) in the four-terminal resistivity in the charge neutrality region, separating the electron-like and hole-like regimes, with a strong activated temperature-dependence above T = 7 K and perfect stability against quantizing magnetic fields. By quantitatively comparing our data with early theoretical predictions, we show that such unexpectedly large resistance in our nominally zero-gap semi-metal system is probably due to the formation of an excitonic insulator state.

cond-mat.mtrl-sci↗

arXiv2016

Comprehensive investigation on the correlation of growth, structural and optical properties of GaN nanowires grown on Si(111) substrates by plasma assisted molecular beam epitaxy technique

The present study elucidates the correlation between the structural and optical properties of GaN nanowires grown on Si(111) substrate by plasma assisted molecular beam epitaxy (PA-MBE) technique under various growth conditions. GaN NWs exhibiting different shapes, sizes and distribution were grown at various substrate temperatures with same Ga-N (III-V) ratio of 0.4. We observe that sample grown at lower substrate temperature (~700 degC) results 2-dimensional island like structure with almost very little (~30%) circularity while increasing substrate temperature (>770 degC) leads to growth of individual GaN NW (>80% circularity) with excellent structural properties. The temperature dependent photoluminescence measurement together with analysis of RAMAN active modes provides legitimate evidences of strong correlation between the structure and optical properties GaN nanowires grown on Si substrates.

cond-mat.mtrl-sci↗

arXiv2015

An unconditional experimental test of Nonclassicality

We theoretically introduce and experimentally demonstrate the realization of a nonclassicality test that allows for arbitrarily low detection efficiency without invoking any extra assumptions as independence of the devices. Our test and its implementation is set in a prepare-and-measure scenario with an upper limit on the communication capacity of the channel through which the systems are communicated. The essence for our novel test is the use of two preparation and two measurement devices, which are randomly paired in each round. Our work opens up the possibility of experimental realizations of device independent protocols with current off-the-shelf technology.

quant-ph↗

arXiv2014

Intrinsic Noise Induced Coherence Resonance in a Glow discharge Plasma

Experimental evidence of intrinsic noise induced coherence resonance in a glow discharge plasma is being reported. Initially the system is started at a discharge voltage (DV) where it exhibited fixed point dynamics, and then with the subsequent increase in the DV spikes were excited which were few in number and with further increase of DV the number of spikes as well as their regularity increased. The regularity in the interspike interval of the spikes is estimated using normalized variance (NV). Coherence resonance was determined using normalized variance curve and also corroborated by Hurst exponent and power spectrum plots. We show that the regularity of the excitable spikes in the floating potential fluctuation increases with the increase in the DV, upto a particular value of DV. Using a Wiener filter, we separated the noise component which was observed to increase with DV and hence conjectured that noise can be playing an important role in the generation of the coherence resonance. From an anharmonic oscillator equation describing ion acoustic oscillations, we have been able to obtain a FHN like model which has been used to understand the excitable dynamics of glow discharge plasma in the presence of noise. The numerical results agree quite well with the experimental results.

physics.plasm-ph↗

arXiv2013

Disorder-driven carrier transport in atomic layer deposited ZnO thin films

This paper addresses the effect of disorder on the carrier transport mechanism of atomic layer deposited ZnO thin films as has been investigated by temperature dependent electrical resistivity measurements in the temperature range of 4.2K to 300K. Films were grown on (0001) sapphire substrate at different substrate temperatures varying from 150 to 350 C. The defects and structural disorder in the films were found to be strongly dependent on their growth temperature. The films grown at 150, 300 and 350 C were found to be semiconductor-like in the whole measurement temperature range of resistivity due to the enhanced disorder in these films. However, a metal to semiconductor transition (MST) at low temperature has been observed in the films grown at 200 and 250 C. It was also observed that the film grown at 250 C with higher residual resistivity, the transition temperature shifted towards the higher value due to the increased disorder in this film as compared to that grown at 200 C. The upturn in resistivity below the transition temperature has been well explained by considering quantum corrections to the Boltzmanns conductivity which includes the effect of weak localization and coulomb electron-electron interactions related to the existence of disorder in these films.

cond-mat.mtrl-sci↗

arXiv2008

Electronic transport driven spin-dynamics

We propose a model to explore the dynamics of spin-systems coupled by exchange interaction to the conduction band electrons of a semiconductor material that forms the channel in a ferromagnet/semiconductor/ferromagnet spin-valve structure. We show that recent observation of the novel transient transport signature in a MnAs/GaAs/MnAs spin-valve structure with paramagnetic Mn impurities [D. Saha et al., Phys. Rev. Lett., 100, 196603 (2008)] can be quantitatively understood in terms of current driven dynamical polarization of Mn spins. Using our model of spin polarized transport through Schottky barriers at the two ferromagnet/semiconductor junctions in a spin-valve structure and a dynamical equation describing the paramagnetic impurities coupled to conduction band electrons we explain the scaling behaviour of observed transient features such as the magnitude and time-scale with temperature.

cond-mat.mes-hall↗