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We report a detailed investigation of the electrical properties of organic field-effect transistors (OFETs) and metal-insulator-semiconductor (MIS) capacitors formed from highly ordered thin films of C60 as the active semiconductor and divinyltetramethyl disiloxane-bis(benzocyclobutene) (BCB) as the gate dielectric. Current-voltage measurements show the OFETs to be n-channel devices characterized by a high electron mobility (∼6 cm2/V s). An equivalent circuit model is developed which describes well both the frequency and voltage dependences of the small-signal admittance data obtained from the corresponding MIS capacitors. By fitting the circuit response to experimental data, we deduce that increasing gate voltages increases the injection of extrinsic charge carriers (electrons) into the C60. Simultaneously, the insulation resistance of the BCB decreases, presumably by electron injection into the insulator. Furthermore, the admittance spectra suggest that the capacitance-voltage (C-V) behavior originates from a parasitic, lateral conduction effect occurring at the perimeter of the capacitor, rather than from the formation of a conventional depletion region. [ABSTRACT FROM AUTHOR]

A comparative study of steady-state and time-resolved photoluminescence of para-sexiphenyl (PSP) films grown by organic molecular beam epitaxy (OMBE) and hot wall epitaxy (HWE) under comparable conditions is presented. Using different template substrates [mica(001) and KCl(001) surfaces] as well as different OMBE growth conditions has enabled us to vary greatly the morphology of the PSP crystallites while keeping their chemical structure virtually untouched. We prove that the broad redshifted emission band has a structure-related origin rather than being due to monomolecular oxidative defects. We conclude that the growth conditions and type of template substrate impacts substantially on the film morphology (measured by atomic force microscopy) and emission properties of the PSP films. The relative intensity of the defect emission band observed in the delayed spectra was found to correlate with the structural quality of PSP crystallites. In particular, the defect emission has been found to be drastically suppressed when (i) a KCl template substrate was used instead of mica in HWE-grown films, and (ii) in the OMBE-grown films dominated by growth mounds composed of upright standing molecules as opposed to the films consisting of crystallites formed by molecules lying parallel to the substrate. [ABSTRACT FROM AUTHOR]

In this article we present the Fourier analysis of kinetic reflectometry spectra acquired during metalorganic chemical vapor deposition. We can show that offset errors due to background radiation can be completely removed by the method itself without using filters or lock-in amplifiers. Additionally, calibration of the reflected intensity is needed as long as the response of the detector is linear to the reflected intensity of the sample. By analyzing the time dependent part of the signal growth rate, layer thickness and the refractive index of the growing layer can be deduced. We demonstrate that, by applying the method to the GaN:Mg δ-doping process, it is possible to obtain accurate information about the time, optical properties, and thickness of the grown multilayers with a resolution down to the monolayer range. [ABSTRACT FROM AUTHOR]

We report on the morphological and nonlinear optical properties of highly ordered para-sexiphenyl nanofibers grown by hot-wall epitaxy on muscovite mica. For suitable substrate temperatures and deposition times, needle-shaped aggregates are obtained. These nanoaggregates, which are formed by regrouping of small islands of the material, can support optical waveguiding and amplification of the deep-blue emission of para-sexiphenyl. We show evidence of low-threshold coherent random lasing in ensembles of nanofibers and study the dependence of lasing on the nanofibers’ film thickness. We also present spatially resolved lasing measurements on individual nanofiber segments. The achievement of isolated nanofibers with suitable morphology and low optical losses could open the route to unprecedented photonic and optoelectronic devices at the submicrometric scale. [ABSTRACT FROM AUTHOR]

Analysis of the coherent dynamics of excitons in Zn(1 - x)Cd(sub x)Se/ZnSe multiple quantum well structures using spectrally combined and resolved four-wave mixing reveals relaxation times longer than those seen in the strained, binary ZnSe layers. During concurrent excitation of the heavy- and light-hole exciton resonance, a beating of the four-wave mixing signal is seen. This beating period fails to fit exactly to the energetic split for free-exciton resonances, until calculations include a bound-exciton state.

The characteristics of p-type CdTe epilayers grown by the hot-wall-beam epitaxy technique were investigated. The results showed that within the range p=4x10(super 14) to 2x10(super 18)cm(super -3), doping levels can be controlled. The hole concentration determined the Hall mobility. The growth rate was decreased while the incorporation of dopants was enhanced by photoassisted growth.

Discusses a study which examined the use of a combination of deep level transient spectroscopy and electron spin resonance measurements to determine the energy level of substitutional manganese in silicon. Benefits from the combination; Problem in the physics of deep levels; Impact of large electron correlation effects in transition-metals.

Presents comparative optical investigations on zinc selenide (ZnSe)/gallium arsenide (GaAs) epilayers grown by molecular beam epitaxy (MBE) and hot-wall epitaxy (HWE). Information on a reliable means of analyzing the dominant impurity-related excitonic transitions in ZnSe epilayers; Comparison of the efficiency of MBE and HWE in obtaining ZnSe epilayers with reliable properties.

Presents information on a study that investigated the coherent dynamics of excitons in Zn[sub1-x]Cd[subx]Se/ZnSe multiple quantum wells. Experimental procedure; Results and discussion on the study; Conclusion.