Papers by Keyword: Hole Mobility

Abstract: A single-carrier hole-only device of ITO/MoO₃/NPB/Al was used to measure the hole mobility of NPB layer, where NPB is a hole transport material. The hole mobility of NPB at different electric fields was obtained from the hole transit time (τ_dc) which was extracted from the negative differential susceptance (ΔB) as a function of frequency. To eliminate the impact of the contact resistance on the mobility measurement, an equivalent circuit model has been introduced to calculate the capacitance and the conductance of the NPB layer. By fitting the Nyquist plot of the impedance spectroscopy using the equivalent circuit, the contact resistance can be extracted from the impedance measurements. It is found that the mobility at low electric field is lower than what was reported in literature after the consideration of the contact resistance. It is also found that the calculated hole mobility of the NPB layer follows the Poole-Frenkels rule.

Abstract: Ps and radiolytic hydrogen yields anticorrelate in saturated hydrocarbons when molecular structure changes from a normal to a cyclic form. This fact is explained by much higher mobility of primary radical-cations in cyclic hydrocarbons than in normal ones.

Abstract: The Bässler’s energy and position disorder model is used to study the relationship between molecular structure of hole-transport materials and performance of the photoreceptor. The result shows that dipolar moments of hole-transport materials (HTM) are inverse proportion to the half decay exposures (E1/2) of the Organic photoreceptors (OPC) which closely related with the hole-mobility of hole-transport layer. In this article Marcus hopping theory and DFT method are also used to calculate the hole-mobility of four hole-transport materials (HTM). The compare of the half decay exposures of OPCs used these material as hole-transport layer and hole mobility, dipolar moments of these molecules show that the E1/2 increases with decrease of hole mobility and dipolar moment.

Abstract: Applying KP theory combined with deformation potential we obtained the valence band structure, and based on this result we calculated the orientation-dependent effective mass which is also called conductivity effective mass in strained Si_1-xGe_x/(001)Si in this research, and furthermore ,we established the scattering rate model by using the density-of-states effective mass. On the basis of conductivity effective mass and scattering rate model, utilizing analytical method and relaxation time approximation we obtained the dependence of the value of hole mobility on stress and doping concentration in strained Si_1-xGe_x/(001)Si along different crystal orientations. Compare to the unstrained Si, the anisotropy of hole mobility is more obvious in strained Si_1-xGe_x/(001)Si, for example, It shows that under the same stress and doping concentration (Ni=1x1014cm-3, x=0.4), the value of hole mobility along [010] crystal orientation is visibly higher than other crystal orientations. This result can provide valuable references to the research of hole mobility of strained Si1-xGex materials and the design of devices.

Abstract: Novel soluble three-component conjugated copolymers are synthesized by palladium- catalyzed Suzuki coupling reaction from 9,9-dioctylfluorene (DOF), 9-ethylhexylcarbazole (Cz) and 4,7-dithien-2-yl-2,1,3-benzothiadiazole (DBT) with Cz composition varying from 1-15 mol% in the copolymer. All of the polymers are soluble in common organic solvents and are highly photoluminescent. The electrochemical, optical, photoluminescent (PL) and electroluminescent (EL) properties of the copolymers were studied. When the hole transmitting material carbazole is introduced into the copolymer PFO-DBT, the hole mobility of the luminescent layer material is improved. The three-component copolymers compared with copolymer PFO-DBT15, Devices made up of these copolymers still emit saturated red light. The highest external quantum efficiency achieved in the device configuration ITO/PEDT/PFO-Cz-DBT15/Ba/Al is 1.81% for the copolymer for 10% Cz content, higher than that of the device made from PFO-DBT15.

Abstract: Crystalline recovery mechanism in the activation annealing process of Al implanted 4H-SiC crystals were experimentally investigated. Annealing temperature and annealing time dependence of acceptor activation and activated hole’s behavior were examined. Poly-type recovery from the implantation induced lattice disordering during the annealing was investigated. The existence of meta-stable crystalline states for acceptor activation, and related scattering centers due to annealing is reported To achieve 100% acceptor activation and to reduce strain after ion implantation, annealing at 2000°C for 10 min. was required.

Abstract: The total conductivity and oxygen deficiency of partially substituted strontium ferrite, SrFe0.9M0.1O3-δ (M=Cr, Ti, Al), at 700-950°C were measured depending on oxygen partial pressure varying in ranges 10-19-0.5 and 10-5-0.5 atm. The partial contributions of n- and p-type electronic charge carriers and oxygen ions to the electrical transport were determined analyzing the total conductivity vs. oxygen pressure dependencies. Additions of all dopants studied in this work are found to extend the cubic perovskite phase stability range and to improve oxygen transport in the intermediate-temperature range. The behavior of hole mobility suggests a polaron conduction mechanism. Doping with aluminum has a weak influence on the mobility level, while the incorporation of Cr and Ti cations into the ferrite lattice decreases hole mobility up to four times.

Abstract: The high sensitivity of the low temperature electrical properties of p-type pure tellurium (Te) to impurities, structural boundaries, point defects and dislocations allows to investigate the structural imperfection profiles in crystals grown under different conditions. Our interest was focused on studying the influence of grain boundaries on the electrical properties of the samples that were remelted and directionally solidified in space (µg) without a seed (W-µg), in comparison with the sample grown under the normal earth conditions (1g0) and a nanocluster sample obtained by filling with melted Te of dielectric opal matrix voids (Opal sample). The W-µg ingot of Te was prepared in the "Crystallizator" furnace under microgravity conditions aboard the "Mir" space station [1]. The concentration variation of electrically active defects and neutral defects along the samples were studied by galvanomagnetic methods (Hall effect and electrical resistivity) in a wide temperature range from 0.4 to 300 K. In these measurements, the following effects caused by the micro- and nano- crystalline structure were found: low hole mobility, high concentration of neutral defects, and anomalous positive magnetoresistance in low magnetic fields at low temperatures. Besides, the specific resistivity of the space sample was found to oscillate (up to 20%) along the length which can be correlated with the presence of a few contact points of the melt with the ampoule wall. This ingot was formed as a result of rapid homogeneous spontaneous solidification, accompanied by forming a micro-block structure. The appearance of the anomalous positive magnetoresistance was observed in the micro-block W- sample and the nanocluster Opal sample. It is a consequence of intensive hole scattering at the grain boundaries which leads to an increase of the intervalley transition probability and to a change of the spin sign of holes in a low symmetry Te crystal. According to the weak localization theory [2], the spin variation during the scattering results in a positive magnetoresistance of the sample in low magnetic fields, in contrast to bulk Te crystals.