UV and visible photoconductivity of undoped diamond films: morphology and related electrical transport phenomena

UV and visible photoconductivity and electrical features of undoped diamond thin films grown by microwave plasma-assisted chemical vapour deposition (MP-CVD) on silicon and copper substrates are studied. The results are correlated with morphology properties analysed by atomic force microscopy (AFM) and micro-Raman. The photoconductivity presents several bands from 1.8 to 3.8 eV that are dependent on the substrate used to grow the samples in spite of some common bands observed. The J-V curve tin DC) in samples grown on Si has a rectifier behaviour (Schottky emission) in opposition to the samples grown on Cu that have no rectification (SCLC conduction). With these results we can conclude that diamond based optoelectronic devices behaviour is controlled by two kinds of structural defects localized in microcrystal and in its boundaries. A general structure model for the optoelectronic behaviour is discussed. (C) 2000 Elsevier Science S.A. All rights reserved.

Charge transport in poly(3-methylthiophene) schottky barrier diodes

Schottky-barrier devices were formed from electropolymerised films of poly (3-methylthiophene) (PMeT). Thermal annealing of a partially undoped film led to diodes with rectification ratios as high as 5900 at 1 V and 50,000 at 2.5 V and ideality factors slightly above 2. The temperature dependence of ac loss tangent and forward currents are identical suggesting that bulk effects dominate device behaviour event at very low forward voltages. Below 250 K forward currents are essentially independent of temperature. Preliminary TSC measurements show the presence of at least two trapping levels in the devices. © 1993.