Home About us Contact
|
Home About us Contact | ||
|
|
||
Trap States (trap + states)
Selected AbstractsTrap states in n-GaN grown on AlN/sapphire template by MOVPEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008T. Ito Abstract Using epitaxial AlN/sapphire templates, high crystalline quality GaN films are grown on them by metal organic chemical vapour deposition. The electron traps behaviour of these GaN films were observed by deep level transient spectroscopy (DLTS). Four distinct trap levels were ob-served in both n-GaN grown on AlN/sapphire template and on conventional low temperature buffer layer (LT-BL)/sapphire. The magnitude the of the DLTS signal E1 and E2 were almost same. It suggests that E1 is not only associate with dislocation density but also other defect. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photo-induced Charge Transfer and Relaxation of Persistent Charge Carriers in Polymer/Nanocrystal Composites for Applications in Hybrid Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Marc Daniel Heinemann Abstract The photo-induced charge transfer and the dynamics of persistent charge carriers in blends of semiconducting polymers and nanocrystals are investigated. Regioregular poly(3-hexylthiophene) (P3HT) is used as the electron donor material, while the acceptor moiety is established by CdSe nanocrystals (nc-CdSe) prepared via colloidal synthesis. As a reference system, organic blends of P3HT and [6,6]-phenyl C61 -butyric acid methyl ester (PCBM) are studied as well. The light-induced charge transfer between P3HT and the acceptor materials is studied by photoluminescence (PL), photo-induced absorption (PIA) and light-induced electron spin resonance spectroscopy (LESR). Compared to neat P3HT samples, both systems show an intensified formation of polarons in the polymer upon photo-excitation, pointing out successful separation of photogenerated charge carriers. Additionally, relaxation of the persistent charge carriers is investigated, and significant differences are found between the hybrid composite and the purely organic system. While relaxation, reflected in the transient signal decay of the polaron signal, is fast in the organic system, the hybrid blends exhibit long-term persistence. The appearance of a second, slow recombination channel indicates the existence of deep trap states in the hybrid system, which leads to the capture of a large fraction of charge carriers. A change of polymer conformation due to the presence of nc-CdSe is revealed by low temperature LESR measurements and microwave saturation techniques. The impact of the different recombination behavior on the photovoltaic efficiency of both systems is discussed. [source] Threshold Voltage Shifts in Organic Thin-Film Transistors Due to Self-Assembled Monolayers at the Dielectric SurfaceADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Stefan K. Possanner Abstract Recently, it has been shown by several groups that the electrical characteristics of organic thin-film transistors (OTFTs) can be significantly influenced by depositing self-assembled monolayers (SAMs) at the organic semiconductor/dielectric interface. In this work, the effect of such SAMs on the transfer characteristics and especially on the threshold voltage of OTFTs is investigated by means of two-dimensional drift-diffusion simulations. The impact of the SAM is modeled either by a permanent space charge layer that can result from chemical reactions with the active material, or by a dipole layer representing an array of ordered dipolar molecules. It is demonstrated that, in both model cases, the presence of the SAM significantly changes the transfer characteristics. In particular, it gives rise to a modified, effective gate voltage Veff that results in a rigid shift of the threshold voltage, ,Vth, relative to a SAM-free OTFT. The achievable amount of threshold voltage shift, however, strongly depends on the actual role of the SAM. While for the investigated device dimensions, an organic SAM acting as a dipole layer can realistically shift the threshold voltage only by a few volts, the changes in the threshold voltage can be more than an order of magnitude larger when the SAM leads to charges at the interface. Based on the analysis of the different cases, a route to experimentally discriminate between SAM-induced space charges and interface dipoles is proposed. The developed model allows for qualitative description of the behavior of organic transistors containing reactive interfacial layers; when incorporating rechargeable carrier trap states and a carrier density-dependent mobility, even a quantitative agreement between theory and recent experiments can be achieved. [source] Silicon Nanowires: A Review on Aspects of their Growth and their Electrical PropertiesADVANCED MATERIALS, Issue 25-26 2009Volker Schmidt Abstract This paper summarizes some of the essential aspects of silicon-nanowire growth and of their electrical properties. In the first part, a brief description of the different growth techniques is given, though the general focus of this work is on chemical vapor deposition of silicon nanowires. The advantages and disadvantages of the different catalyst materials for silicon-wire growth are discussed at length. Thereafter, in the second part, three thermodynamic aspects of silicon-wire growth via the vapor,liquid,solid mechanism are presented and discussed. These are the expansion of the base of epitaxially grown Si wires, a stability criterion regarding the surface tension of the catalyst droplet, and the consequences of the Gibbs,Thomson effect for the silicon wire growth velocity. The third part is dedicated to the electrical properties of silicon nanowires. First, different silicon nanowire doping techniques are discussed. Attention is then focused on the diameter dependence of dopant ionization and the influence of interface trap states on the charge carrier density in silicon nanowires. It is concluded by a section on charge carrier mobility and mobility measurements. [source] Trap state emission of water-soluble CdS nanocrystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009W. Lü Abstract We prepared water-soluble CdS nanocrystals (NCs) capped by the poly (ethylene glycol)-b-poly (2-(N,N -dimethylamino)ethyl methacrylate) chain. The photoluminescence (PL) properties of CdS NCs are investigated by time-resolved and temperature-dependent PL spectra. It is found that the PL band of CdS NCs is dominated by two trap state emissions, respectively. Due to the trap state emissions, fluorescent resonance energy transfer from CdS NCs to organic dyes (Texasred) can be observed, which suggests the potential application of trap states of CdS NCs for fabrication of biosensors. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Trap-sensitive relaxation of hot carriers in ZnO:Cu,AlPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006I. Konovalov Abstract Modulated photoconductivity measurements with x-ray excitation were performed on ZnO:Cu,Al thin films. We found a strong variation of the modulated photocurrent with temperature starting from the excitation energy approximately equal the binding energy of Cu 2p3 core electrons and above. Strong temperature sensitivity at ,280 K suggests participation of thermally activated trap states in the process of hot carrier relaxation. The shape of the temperature dependence was satisfactorily fitted by the respective calculation. No comparable deviations of the temperature sensitivity were observed when the Cu 2s electrons were excited. We explain the observations by assumption of fast local transitions from a valley in the conduction band into the trap state according to the symmetry selection rules. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||