J.M. Marshall

Improved thin films of pentacene via pulsed laser deposition at elevated substrate temperatures

Thin films of pentacene were deposited by thermal evaporation and by pulsed laser deposition (PLD). Surface characterization using atomic force microscopy shows that PLD leads to a reduction in surface roughness, which can be reduced further using heated substrates. Observation of enhanced field‐effect carrier mobilities in the PLD films, together with increased electrical conductivity and reduced activation energy for electrical conduction, is consistent with increased molecular ordering in the pentacene films and suggests a direct correlation between molecular ordering in the bulk and surface roughness.

Optoelectronic properties of highly conductive microcrystalline SiC produced by laser crystallisation of amorphous SiC

The optoelectronic properties of undoped and doped microcrystalline silicon carbide thin films, prepared by excimer (ArF) laser crystallisation of plasma enhanced chemical vapour deposited hydrogenated amorphous silicon carbide, are analysed. All films show more than six orders of magnitude increase relative to the conductivities before the laser crystallisation. It is shown that the increase in conductivity is not predominantly due to the activation of dopant atoms. However, dopant sites, but not carbon content (up to 30 at%), play an important role in electrical transport in μc-SiC. We also report the observation of blue photoluminescence at room temperature from the undoped laser irradiated samples having a carbon content of 35 at%. The spectrum exhibits two visible peaks (1.8 eV and 2.6 eV), while the as-deposited films show only the 1.8 eV peak.

Photovoltaic and photoactive materials - properties, technology and applications

Preface. Invited Papers. Large-Area Smart Glass and Integrated Photovoltaics C.M. Lampert. Photovoltaic Materials, an Overview of Historical Development, Current State of the Art and Future Scope D. Dimova-Malinovska. Electronic Characterisation and Modelling of Disordered Semiconductors J.M. Marshall. Measurement Methods for Photoactive Materials and Solar Cells G.S. Popkirov. Structural and Optical Properties of Microcrystalline Silicon for Solar Cell Applications R. Carius. Crystalline Silicon p-n Junction Solar Cells - Efficiency Limits and Low-Cost Fabrication Technology J. Szlufcik. Application of III-V Compounds in Solar Cells V.M. Andreev. Micro-/Poly-Crystalline Silicon Materials for Thin Film Photovoltaic Devices: Deposition Processes and Growth Mechanisms J.K. Rath. Micro-/Poly-Crystalline Silicon Materials for Thin Film Photovoltaic Devices: Physical Properties J.K. Rath. Micro-/Poly-Crystalline Silicon Materials for Thin Film Photovoltaic Devices: Application in Solar Cells J.K. Rath. Organic Materials and Devices for Photovoltaic Applications J.-M. Nunzi. Photovoltaic Applications M. Palfy. Past, Actual and Future EU-Funded Research, Technological Development and Demonstration Actions in the Field of Photovoltaics T.L. DEstaintot. Contributed Papers. Evaluation of the Gap State Distribution in a-Si:H by SCLC Measurements A. Eray, G. Nobile. Creation and Annealing of Light Induced Metastable Defects in a-Si1-xCx:H A.O. Dodolbas, O. Oktu. Potential PV Materials Based on InN Polycrystalline Films: Growth, Structural and Optical Properties V.Ya. Malakhov. Light Soaking Effect in a-Si:H Based n-i-p and p-i-n Solar Cells G. Nobile, M. Morana. Accelerated Ageing Test of Solar Cells and Encapsulations V. Saly, et al. DifferentialSpectral Responsivity of c-Si:H Solar Cells M. Sendova-Vassileva, et al. Temperature and Compositional Dependence of Raman Scattering and Photoluminescence Emission in CuxGaySe2 Thin Films C. Xue, et al. Enhancement of the Photovoltaic Efficiency of Ge0.2Si0.8/Si Photodiodes M.M. Pociask, et al. Charge Carrier Transport and Photovoltage in Layers Based on Poly(3,3Phthalidylidene-4,4 Biphenylilene) A.R. Tameev, et al. Diagnostics of Large-Area Solar Cell Homogeneity by Local Irradiation V. Benda. Determination of Trap Parameters from Photocurrent Decay Measurements: Metal-Free Phthalocyanine Films I. Zhivkov, et al. Luminescent Properties of Li2GBP/YYGBP4O7 (LTB) Polycrystals at the Deviation from Stoichiometry B.M. Hunda, et al. Influence of Solution Resistivity and Postanodizing Treatment of PS Films on the Electrical and Optical Properties of Metal/Ps/Si Photodiodes K. Ait-Hamouda, et al. Study of Sol-Gel Derived Very Thin Films of Mixed Titanium Dioxide and Vanadium Oxide T. Ivanova, et al. Photoelectrochemical Characterization of Some Argyrodite-Type Materials Yu. Stasyuk, et al. Optical Absorption in APCVD Metal Oxide Thin Films K.A. Gesheva, et al. Extrinsic Surface Photovoltage Spectroscopy -- An Alternative Approach to Deep Level Characterisation in Semiconductors K. Germanova, et al. CELLO: An Advanced LBIC Measurement Technique for Solar Cell Local Characterisation J. Carstensen, et al. The Behaviour of PV Module Parameters as a Function of Solar Cell Temperature in Hot Climates P. Vitanov, et al. Application of SiO2: Re Layers for Improvement of the UV Sensitivity of a-Si:H Solar Cells M. Sendova-Vassileva, et al. Cost-Effective Porous Silicon Technology for Solar Cell Industrial

EXCIMER LASER CRYSTALLIZATION AND DOPING OF SOURCE AND DRAIN REGIONS IN HIGH QUALITY AMORPHOUS SILICON THIN FILM TRANSISTORS

A method has been proposed to fabricate a bottom gate hydrogenated amorphous silicon thin film transistor with highly conductive polycrystalline silicon source and drain regions. Dopant atoms were supplied during selective crystallization of the amorphous silicon layer, via a spin‐on‐dopant film coated on top of it. A suitably patterned thin layer of silicon nitride served to restrict laser‐induced crystallization and doping of the amorphous silicon to the required source and drain regions. The sheet resistance of the resulting doped polycrystalline areas of the film was found to be 1.8 kΩ/⧠. The fabricated transistors had a room temperature field effect mobility of up to 1.35 cm2u2009V−1u2009s−1 and featured on/off current ratios of more than 106.

Structural and electrical transport properties of excimer (ArF)-laser-crystallized silicon carbide

Abstract The structural and electrical properties of undoped and doped microcrystalline silicon carbide (μc-SiC) thin films prepared by excimer (ArF) laser crystallization of plasma-enhanced chemical vapour deposited hydrogenated amorphous silicon carbide (a-SiC: H) have been analysed. Using transmission electron microscopy this material is shown to possess partial β-SiC structure. Bonding configurations have also been characterized by infrared spectroscopy. It is shown that a-SiC:H films having a carbon content as large as 30 at.% can be crystallized by this novel method. After crystallization, all films show greater than six orders of magnitude increase in dark conductivity [sgrave]dc. The temperature dependences of [sgrave]dc for undoped, n- and p-type μc-SiC exhibit different characteristic shapes. For all samples, it is shown that the increase in [sgrave]dc is not predominantly due to the activation of dopant atoms. Instead, the change is associated with the formation of a microcrystalline structure....

a-SiC:H thin film visible light-emitting diodes with highly conductive wide band gap a-SiC:H as the carrier injection layers

Abstract Highly conductive (∼10 −4 (Ωcm) −1 ) and wide band gap (∼2.0eV) carrier injection layers of a-SiC:H have been prepared by rf plasma enhanced chemical vapour deposition (PECVD) using the hydrogen dilution technique. These materials have been utilized in the fabrication of a-SiC:H based thin film light emitting diodes (TFLEDs) as hole and electron injectors and have also been crystallized using an excimer (ArF) laser. The conductivity of these materials increased by up to six orders of magnitude after the laser crystallization. The TFLEDs developed have a structure of glass/ tin oxide (TO)/ i (a-SiC:H) / n (a-SiC:H) and glass/TO/ p (a-SiC:H)/ i (a-SiC:H)/ n (a-SiC:H). Visible yellowish orange light emissions have been observed in these junctions at room temperature. The properties of the carrier injection material as well as device characteristics are reported.

A comparative study of photoconductivity and carrier transport in oligomeric films

Abstract DC conductivity and transient photoconductivity (TPC) measurements on 1 μm films of pentacene and thienylene-vinylene oligomers deposited by thermal evaporation (TE) and by laser ablation are reported. Conduction properties are found to be relatively insensitive to both chemical composition and deposition method. DC conductivity prefactor magnitudes of order 0.1 S cm−1, and the observation of field-dependent conduction, are indicative of hopping transport. In all formulations we observed a two-power-law photocurrent decay, consistent with transport initially by hopping down in energy in an exponential distribution of localised states followed by thermal excitation and multiple-trapping (MT). The temperature-dependence of photocurrent decay has been studied for pentacene and yields an exponential tail slope of 650 K (56 meV). A maximum mobility of 10−5 cm2 V−1 s−1 is estimated from the TPC data, 2–3 orders less than field-effect mobilities reported previously. This discrepancy may be due to differences between surface and interior conduction processes.

Optoelectronic properties of polycrystalline silicon produced by low-temperature (600°C) solid-phase crystallization of hydrogenated amorphous silicon

Abstract We present novel data on optoelectronic properties observed in the amorphous-to-polycrystalline silicon (polysilicon) phase transition, and the effect on as-crystallized films of a simple post-hydrogenation treatment. The polysilicon thin films were produced by low-temperature (600°C) furnace crystallization of undoped hydrogenated amorphous silicon (a-Si: H). Other parameters, such as the onset of crystallization, degree of amorphization and average grain size were determined by ultraviolet reflectivity and electron microscopy. The grain size is found to increase with decreasing a-Si: H substrate temperature, and a maximum areal grain size of 0.4 μm2 is obtained. Optical absorption, d.c. conductivity and transient photoconductivity measurements are employed to examine carrier transport mechanisms. We observe a Meyer-Neldel relationship between the d.c. conductivity pre-factor [sgrave]0 and activation energy E[sgrave] . A plasma hydrogenation treatment of the as-crystallized films results in an o...

Carbazolyalkyl substituted cyclosiloxanes: Synthesis and properties

Abstract Carbazolylalkyl substituted oligosiloxanes undergo anodic oxidation to give electrochromic thin films which are characterised by two redox processes. These processes are well defined when the carbazole groups are separated from the oligosiloxane core by long spacer groups, a feature which has been observed previously for analogous polymers.

Polysilicon produced by excimer (ArF) laser crystallisation and low-temperature (600°C) furnace crystallisation of hydrogenated amorphous silicon (a-Si:H)

Abstract We report on the opto-electronic and structural properties of polysilicon produced by excimer (ArF) laser crystallisation of undoped hydrogenated amorphous silicon (a-Si:H). Micro structure and average grain size are determined by TEM and electron diffraction. A maximum areal grain size of 0.1 μm2 is observed in excimer (ArF) laser crystallised polysilicon. UV reflectivity and FTIR spectroscopy are employed to investigate the degree of crystallinity and atomic bonding configurations. These data are compared with studies of low-temperature (600 °C) furnace crystallised polysilicon.