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Hole Density (hole + density)
Selected AbstractsControllable Molecular Doping and Charge Transport in Solution-Processed Polymer Semiconducting LayersADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Yuan Zhang Abstract Here, controlled p-type doping of poly(2-methoxy-5-(2,-ethylhexyloxy)- p -phenylene vinylene) (MEH-PPV) deposited from solution using tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) as a dopant is presented. By using a co-solvent, aggregation in solution can be prevented and doped films can be deposited. Upon doping the current,voltage characteristics of MEH-PPV-based hole-only devices are increased by several orders of magnitude and a clear Ohmic behavior is observed at low bias. Taking the density dependence of the hole mobility into account the free hole concentration due to doping can be derived. It is found that a molar doping ratio of 1 F4-TCNQ dopant per 600 repeat units of MEH-PPV leads to a free carrier density of 4,×,1022,m,3. Neglecting the density-dependent mobility would lead to an overestimation of the free hole density by an order of magnitude. The free hole densities are further confirmed by impedance measurements on Schottky diodes based on F4-TCNQ doped MEH-PPV and a silver electrode. [source] Control of Carrier Density by a Solution Method in Carbon-Nanotube Devices,ADVANCED MATERIALS, Issue 20 2005T. Takenobu A new method for controlling the hole density in single-walled carbon nanotube field-effect transistors (SWCNT-FETs) by solution-based chemical doping is presented. The use of organic molecules that adsorb onto SWCNTs from solution is investigated. The transfer characteristics of the SWCNT-FETs exhibit continuous and precise shifts in threshold voltages (see Figure) upon doping with F4TCNQ molecules, even in air. [source] Nitride-based quantum structures and devices on modified GaN substratesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009Piotr Perlin Abstract We have studied the properties of InGaN layers and quantum wells grown on gallium nitride substrates with intentional surface misorientation with respect to its crystalline c -axis. Misorientation varied in the range from 0 up to 2 degree. The indium content was changed by using the different growth temperature (between 750 °C and 820 °C) during metalorganic vapor phase epitaxy. With increasing misorientation angle the average indium content decreased significantly. This effect was accompanied by the strong increase of the emission line bandwidth suggesting more pronounced indium segregation. The results of cathodoluminescence measurements show that these effects correspond to different number of atomic steps/terraces existing on the surface of gallium nitride substrate. Very interesting result is also demonstrated concerning p-type GaN layers. With increasing misorientation, the free hole density drastically increases above 1018 cm,3. This improvement in p-type doping is not related to the increased Mg concentration but to the reduction in the compensating donor density. Using this advantage we demonstrate nitride light emitters with improved electrical properties. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of water vapor introduction during Cu(In1,xGax)Se2 deposition on thin film properties and solar cell performancePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006S. Ishizuka Abstract The effects of water vapor introduction during the growth of Cu(In1,xGax)Se2, specifically CuInSe2 (CISe), Cu(In,Ga)Se2 (CIGSe), and CuGaSe2 (CGSe) thin films were studied. We have developed thus far a novel technique to improve CIGSe (x , 0.5) cell performance by means of water vapor introduction during CIGSe deposition. In this study, we have examined the effectiveness of water vapor introduction for other x -compositions (CISe and CGSe). Variations in the electrical properties observed in CIGSe (x , 0.5), that is, increasing hole density and conductivity with water vapor introduction, were also observed in CISe and CGSe. Water vapor introduction affected solar cell performance as well; open circuit voltages, short circuit current densities, and efficiencies were improved. The improvements in cell performance are thought to be related to annihilation of donor defects arising from Se-vacancies by incorporation of oxygen from the water vapor. In addition to this, the sodium content in the CIGSe layers was found to depend on the partial pressure of water vapor during deposition. This result suggests that the improvement mechanism is also related with the so-called ,Na-effects'. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Predominant point defects in tellurium saturated CdTePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006P. Fochuk Abstract High temperature Hall effect measurements at 570,1070 K under well defined Te vapor pressure in CdTe single crystals grown by THM and Bridgman techniques were made. Both the free carrier density versus Te vapour pressure value and temperature dependencies were studied. At heating up till ,870 K the hole density was Te vapor pressure independent, but it varied in different samples from 1 × 1016 to 1 × 1017 cm,3. At higher temperatures the conductivity becomes of intrinsic type, turning then into n-type one. A theoretical analysis of native point defects contents at different conditions in the framework of Krögers quasichemical formalism was performed. It resulted in the impossibility of mutual compensation of native donors and acceptors proposed by different authors. The results were explained assuming the presence of an electrically active foreign point defect , the oxygen interstitial acceptor. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||