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Tail States (tail + states)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Charge carrier density dependence of the hole mobility in poly(p -phenylene vinylene)

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2004
C. Tanase
Abstract The hole transport in various poly(p -phenylene vinylene) (PPV) derivatives has been investigated in field-effect transistors (FETs) and light-emitting diodes (LEDs) as a function of temperature and applied bias. The discrepancy between the experimental hole mobilities extracted from FETs and LEDs based on a single disordered polymeric semiconductor originates from the strong dependence of the hole mobility on the charge carrier density. The microscopic charge transport parameters are directly related to the chemical composition of the analysed polymers. By chemically modifying the PPV, the hole mobility in both FETs and LEDs can be changed by orders of magnitude. For highly disordered PPVs it is demonstrated that the exponential density of states (DOS), which is used to describe the charge transport in FETs, is a good approximation of the tail states of the Gaussian DOS, which describes the charge transport in LEDs. Increase of the directional order in the PPV film enhances the mobility but also induces a strong anisotropy in the charge transport, thereby obscuring a direct comparison between sandwich and field-effect devices. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Optically pumped lasing and gain formation properties in blue Inx Ga1,x N MQWs

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004
K. Kojima
Abstract Lasing and gain formation properties have been studied in an InxGaN1,x multiple quantum wells lasing at around 460 nm by employing the modified variable stripe length method (VSLM) and pump and probe spectroscopy (P&P). It was found that the spontaneous emission (Esp) appeared far below absorption edge (Ea) that is observed as a photo-bleaching negative-peak in P&P, indicating the formation of localized tail states. Lasing peaks appeared in between Esp and Ea with wide spectral distribution. This is consistent with the results where VSLM revealed the broad feature of optical gain spectra associated with rapid peak saturation of lasing even just above the threshold photo-pumping power density. Such mechanism observed in In-rich InxGa1,xN MQWs is contributed not only from the broad distribution of localized density-of-states but also from hot carrier distribution (determined by Maxwell,Boltzmann statistics), temperature of which is raised up due to long energy relaxation time to localized tail states. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Lifetime distribution of photoluminescence and radiative recombination rate of electron-hole pairs in a-Si:H

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010
Chisato Ogihara
Abstract Temperature variations of radiative recombination rates of electron-hole pairs responsible for photoluminescence in a-Si:H films have been analysed from the intensity, I, and the characteristic value of the lifetime, ,, obtained from frequency resolved spectroscopy. In a defective a-Si:H film, the radiative recombinationrate increases with increasing temperature because of thermal excitation of the electrons and holes from the tail states to more ex-tended tail states. In the case of a high-quality a-Si:H film, the temperature variation of I,,1 is explained by contributions from regions in the vicinity of the defects and the regions not affected by the defects (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effect of As alloying on the valence band tail states in a-Se

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010
Mohammed L. Benkhedir
Abstract Transient photocurrent (TPC) measurements have been carried out on evaporated a-Se doped with either 0.2% or 0.5% of As and compared with analogous measurements on undoped and Cl doped a-Se. These measurements show that As doping of a-Se suppresses the shallow defects linked to the dihedral angle variations in a-Se chains, and makes the valence band tail states distribution steeper. These changes in the a-Se density of states increase the relative importance of the deep defect levels in As-doped a-Se and thus explain the widely reported hole lifetime shortening with As addition. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Structural and optical properties of polycrystalline MgxZn1,xO and ZnO:Mn films prepared by chemical spray pyrolysis

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006
Tomoaki Terasako
Abstract Polycrystalline MgxZn1,xO (0.00 , x , 0.21) and ZnO:Mn films prepared by chemical spray pyrolysis were characterized by X-ray diffraction, optical transmittance, photoacoustic (PA) spectroscopy and photoluminescence (PL). Successful growth of the MgxZn1,xO (0.00 , x , 0.21) films was confirmed by the blue shift of both the near-band-edge PL peak and absorption edge with increasing the alloy composition x. However, the influence of the tail states caused by the deviation from stoichiometric compsosition and/or the spatial fluctuation of the alloy composition x was observed on the PA and PL spectra. Both the transmittance and PA spectra for the ZnO:Mn films showed the absorption band due to the d-d transitions in Mn2+ ion. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Thermalization and recombination in exponential band tail states

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
M. Niehus
Abstract We present an analytical model that combines the complementary experimental evidence of spatial dispersion (DAP recombination) and energetic dispersion (band tails). The model describes the competition between thermalization and recombination of excess carriers trapped in exponentially distributed (in energy), discrete localized (in space) states. We use the energy dependence of the relaxation rates to derive the energy and time dependence of sub gap photoluminescence. The model predicts that the yellow luminescence band (YLB) and blue luminescence band (BLB) commonly observed in GaN are not separate entities, but reflect the competition of thermalization and recombination. A distinct kink is observed in transient PL in the microsecond range, in the limiting cases of strong tailing and/or low temperatures, indicating the transition from thermalization-limited to (radiative) recombination-limited excess carrier relaxation. Both prediction are in line with experiment, and able to resolve interpretational difficulties. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]