No abstract

We demonstrate improvement in fatigue resistance and other ferroelectric properties through cerium doping in sol–gel derived lead zirconate titanate thin films. We have studied frequency dependence of fatigue behavior and show that the loss of polarization due to fatigue follows a universal scaling behavior with N/f2, where N is the number of switching cycles and f the frequency. The origin of the scaling is attributed to the drift of oxygen vacancies, which is the rate limiting process in the growth of the interface layer responsible for fatigue. Empirical fits for both undoped and cerium-doped samples show that switchable polarization follows stretched exponential decay with time or N/f. Cerium doping is shown to improve fatigue resistance by impeding the motion of oxygen vacancies.

We demonstrate white organic light-emitting diodes (OLEDs) having spectral width of approximately 260 nm in electroluminescence (EL) in a simple bilayer structure, consisting of TPD and zinc benzothiazole, without taking recourse to complex strategies such as blending and doping. The EL is broader than the corresponding photoluminescence (PL) of both component materials and their structures. A deconvolution of PL and EL spectra shows that as large as 60% of the broad EL emission originates from multiple exciplexes formed at the interface during electrical excitation.

We have studied electrical activity of defects created by high-dose MeV heavy-ion implantation in n-silicon. Heavy damage induced by Ar+ and Au+ ions is embedded within depletion layers of Schottky diodes. The defects are characterized using capacitance–voltage (C–V), current–voltage (I–V), deep-level transient spectroscopy (DLTS) and time analyzed transient spectroscopy techniques. Large concentration of defects in the depletion layer of as-implanted device lead to unusual features in C–V and I–V characteristics. The damage layer is found to extend several microns beyond the ion range or the damage profile predicted by standard Monte Carlo simulation packages. The dominance of a single trap in the damaged region is established from hysteresis effect in C–V, space-charge-limited conduction in forward I–V and DLTS spectrum. With annealing in the temperature range of 400–600 °C, the observed changes in the defect profile indicate that the effective electrical interface between damaged and undamaged layer moves progressively towards the surface. From transient spectroscopic analysis the major defect is found to be a midgap trap whose energy is sensitive to the degree of disorder in the damaged layer. The experimental features in C–V characteristics have been simulated using model charge profiles taking into account crossing of the Fermi level with the midgap trap within the depletion layer. The simulations suggest the presence of a compensated region and a sharp negatively charged defect profile at a distance much larger than that expected from ion range. Our results constitute experimental evidence, in qualitative agreement with recent predictions of molecular dynamics simulations, of defect migration and clustering of interstitial related defects even at room temperature in the case of high-dose irradiation.

Buried damaged layers in n-silicon created by implantation of MeV heavy ions (Ar+) have been studied by capacitance and current measurements, and spectroscopic techniques such as deep level transient spectroscopy and constant capacitance time analyzed transient spectroscopy. We have isolated a new midgap acceptor level responsible for carrier compensation in samples irradiated with doses below amorphization threshold. This defect level is demonstrated to control hysteresis in capacitance-voltage characteristics, space charge limited current conduction, and premature termination of emission transients. The emission energy of the defect is observed to be sensitive to degree of disorder in the damaged layer controlled by irradiation dose, and relaxation induced by heat treatment.