Browsing by Author "Arunandan Kumar"

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Dependence of charge carrier mobility of 4,4′,4″-tris(N-3- methylphenyl-N-phenylamino)triphenylamine on doping concentration of tetrafluoro-tetracyano-quinodimethane
(Elsevier B.V., 2012) Gayatri Chauhan; Ritu Srivastava; Arunandan Kumar; Omwati Rana; P.C. Srivastava; M.N. Kamalasanan
Electrical transport of pure and tetrafluoro-tetracyano-quinodimethane doped 4,4′,4″-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (m-MTDATA) films have been studied at various temperatures and doping concentrations. Pure films show space charge limited conduction with field and temperature dependent mobility. The J-V characteristics of doped m-MTDATA were ohmic at low voltages due to thermally released carriers from dopant states. At higher voltages the current density increases nonlinearly due to field dependent mobility and carrier concentration thereby filling of tail states of HOMO of the host. The conductivity of doped films were analysed using the Unified Gaussian Disorder Model (UGDM). The carrier concentration obtained from the fitting show a non-linear dependence on doping concentration which may be due to a combined effect of thermally activated carrier generation and increased carrier mobility. © 2011 Elsevier B.V. All rights reserved.
Thermally activated field assisted carrier generation and transport in N, N′ -di-[(1-naphthalenyl)- N, N′ -diphenyl]-(1, 1′ biphenyl)- 4, 4′ -diamine doped with 2,3,5,6-tetrafluoro- 7, 7′,8, 8′ -tetracyanoquinodimethane
(2008) Gayatri Chauhan; Ritu Srivastava; Virendra Kumar Rai; Arunandan Kumar; S.S. Bawa; P.C. Srivastava; M.N. Kamalasanan
Current density-voltage (J-V) characteristics of N, N′ -di-[(1-naphthalenyl)- N, N′ -diphenyl]-(1. 1′ biphenyl)- 4, 4′ -diamine (α-NPD) doped with 2,3,5,6-tetrafluoro- 7, 7′,8, 8′ -tetracyanoquinodimethane have been studied as a function of doping concentration (0-0.8 wt %) and temperature (105-300 K). The current density was found to increase with increase in doping concentration. In the doped samples as field increases above 3.3× 104 V/cm the current abruptly starts increasing at a higher rate, which is ascribed as due to increased free charge carrier generation in the bulk. The enhanced free charge carrier generation is due to field assisted thermal dissociation of donor-acceptor pairs (Poole-Frenkel process) as well as charge injection at the interface. The released carriers increase the charge carrier density which brings the Fermi level near the highest occupied molecular orbital level of the α-NPD and reduces the space charge region near the interface favoring the tunneling of charge carrier across the interface, which is enough to support Ohmic conduction. The carrier generation has been found to be a thermally activated process. At higher fields (i.e., above 1.52× 105 V/cm) the nonlinear J-V characteristics have been explained as due to field dependent mobility of holes. © 2008 American Institute of Physics.