arXiv subjects

Subhasis Ghosh

Publications and source records attributed to Subhasis Ghosh.

25 records · Page 2Linked to original sources

arXiv2004

Dark and Bright Excitonic States in Nitride Quantum Dots

Formation of excitonic states in quantum dots of nitride based III-V semiconductors GaN and AlN including coulomb and exchange interactions are investigated. Dark exciton formation is found to occur for both GaN quantum dots(QDs) with wurtzite structure having positive crystal field splitting and GaN and AlN QDs with zero crystal field splitting with a transition from dark to bright exciton at about 40Å. In wurtzite AlN QDs with negative crystal field splitting the splitting between the dark and bright excitonic states is very small and vanishes at about 15Å.

cond-mat.mes-hall↗

arXiv2004

A Device Structure for Electronic Transport Through Individual Molecules with Strong Coupling to Metallic Electrodes

We present a simple and reliable method for making electrical contacts to small organic molecules with thiol endgroups. Nanometer-scale gaps between metallic electrodes have been fabricated by passing a large current through a lithographically-patterned Au-line with appropriate thickness. Under appropriate conditions, the passage of current breaks the Au-line, creating two opposite facing electrodes separated by a gap comparable to the length of small organic molecules. Current-voltage characteristics have been measured both before and after deposition of short organic molecules. The resistance of single 1,4-benzenedithiol and 1,4-bezenedimethanedithiol molecules were found to be 9M$Ω$ and 26M$Ω$, respectively. The experimental results indicate strong electronic copuling to the contacts and are discussed using a relatively simple model of mesoscopic transport. The use of electrodes formed on an insulating surface by lithography and electromigration provides a stable structure suitable for integrated circuit applications.

cond-mat.mes-hall↗

arXiv2004

Photoluminescence Spectroscopy of many-body Effects in Heavily Doped Al$_x$Ga$_{1-x}$As

We present an experimental investigation of heavy doping-induced many-body effects such as band gap narrowing(BGN) and Fermi edge singularity(FES) in Al$_x$Ga$_{1-x}$As using photoluminescence(PL) spectroscopy. The band-to-band transition energy shifts to lower energies and FES-like feature in PL spectra grows with increasing electron concentration. We show that FES-like feature is a nonmonotonic function of temperature and excitation intensity. Our data lead us to suggest that a small concentration of nonequilibrated holes is required to enhance the FES-like feature in the PL spectra.

cond-mat.mtrl-sci↗

arXiv2004

Energy Levels in Spheroidal Quantum Dot

The effect of non-sphericity of the quantum dot on the eigenvalues and eigenfunctions has been investigated for the case of both the finite and infinite barrier. The ground and excited state energies have been calculated for prolate and oblate spheroids as a function of eccentricity of the spheroid. The analytic wavefunctions giving the admixture of higher angular momentum states have been obtained as a function of eccentricity.

cond-mat.mes-hall↗

arXiv2003

Role of Correlation on Charge Carrier Transport in Organic Molecular Semiconductors

We have investigated the charge carrier transport in organic molecular semiconductors. It has been found that mobility is a function of electric field and temperature due to hopping conduction. Several theoretical models for charge transport in disordered solids have been debated over the role of spatial and energetic correlation in these systems and such correlations have been recently shown to explain the universal electric field dependence of mobility. We have compared and evaluated the applicability of different theoretically proposed models using very simple experimental results and based on our extensive analysis, we have found that correlation is important to explain the electrical transport in these systems.

cond-mat.mtrl-sci↗

arXiv2003

Nature of Charge Carriers in Disordered Organic Molecular Semiconductors

Understanding the charge carrier transport in the disordered organic molecular semiconductors is a fascinating and still unresolved problem in modern condensed-matter physics, yet has an extremely important bearing on their application in ``plastic'' based field effect transistor, light emitting diodes and lasers. The most contentious issue in this subject is the nature of the charge carriers i.e. whether they are bare electrons or dressed electrons, known as polarons. Here we show for the first time, by means of simple experiments that polaron moving in static disorder is responsible for charge carrier transport in disordered molecular semiconductors.

cond-mat.mtrl-sci↗

arXiv2003

Is Correlation Important in Explaining the Charge Transport in Disordered Molecular Solids ?

We have examined the electrical transport in disordered molecular solids. It has been found that mobility is a function of electric field and temperature due to hopping conduction. Several theoretical models for charge transport in disordered solids have been debated over the role of spatial and energetic correlation in these systems and such correlations have been recently shown to explain the universal electric field dependence of mobility. We have compared and evaluated the applicability of different theoretically proposed models using very simple experimental results and based on our extensive analysis, we have found that correlation is important to explain the electrical transport in these systems.

cond-mat.mtrl-sci↗