Dopants In Thin Films Research Articles

Correlation of Coexistent Charge Transfer States in F4TCNQ-Doped P3HT with Microstructure.

Understanding the interaction between organic semiconductors (OSCs) and dopants in thin films is critical for device optimization. The proclivity of a doped OSC to form free charges is predicated on the chemical and electronic interactions that occur between dopant and host. To date, doping has been assumed to occur via one of two mechanistic pathways: an integer charge transfer (ICT) between the OSC and dopant or hybridization of the frontier orbitals of both molecules to form a partial charge transfer complex (CPX). Using a combination of spectroscopies, we demonstrate that CPX and ICT states are present simultaneously in F4TCNQ-doped P3HT films and that the nature of the charge transfer interaction is strongly dependent on the local energetic environment. Our results suggest a multiphase model, where the local charge transfer mechanism is defined by the electronic driving force, governed by local microstructure in regioregular and regiorandom P3HT.

Systematic comparison of different dopants in thin film hematite (α-Fe2O3) photoanodes for solar water splitting

Thin (~50 nm) film hematite photoanodes doped with different dopants at a concentration of 1 cation% display internal solar to chemical (ISTC) conversion efficiency in the following order: Sn > Nb > Si > Pt > Zr > Ti > Zn > Ni > Mn.

Investigation of phosphorus and arsenic as dopants in polycrystalline thin films of zinc oxide

The use of implanted phosphorus and arsenic has been systematically investigated and compared with implanted boron as n-type dopants in thin films of polycrystalline zinc oxide. For a given heat-treatment schedule and without fluorine co-doping, the steady-state resistivity of the phosphorus-doped ZnO is found to be consistently lower than that of the boron-doped ZnO. Both are in turn lower than that of the arsenic-doped ZnO. A resistivity of 3 mΩ cm has been obtained for a phosphorus dose of 1016/cm2, if activated at 500 °C for 5 min in nitrogen. Direct exposure to an oxidizing ambience during a heat-treatment resulted in an increase in the resistivity of the phosphorus- or arsenic-doped zinc oxide thin films. However, the kinetics of the oxidation and reduction of arsenic in zinc oxide are found to be significantly slower than those of phosphorus or boron. Thin-film transistors with self-aligned phosphorus-doped source/drain regions and channel-lengths as short as 2 μm have been realized and characterized.

Unrelaxed processes in photostimulable energy transfer to the dopant in thin films of alkali halides

In thin films of alkali halides the primary process of defect production takes place in the near vicinity of the dopant ion in a ps-time range forming a close pair {F, dopant hole centre} due to capturing of an unrelaxed H-centre by the dopant ion. Only in nanostructures of doped alkali halides the unrelaxed H-centres are able to escape from the surface producing in the grains of nanostructure an interacting F-centre chain (or a channel). It is concluded that specific interaction of unrelaxed H-centres and electrons with the F-centre chain leads to a temperature-independent exciton and electron transport via the chain at any distances. The systems are available as active highly sensitive storage media for fast and multifunctional optical data processing in miniaturised optoelectronic and photonic devices (including optical chips).

BF3-doped amorphous silicon thin films

BF3 has been used as a p-type dopant in thin films of hydrogenated amorphous silicon (a-Si:H). The films were deposited in a capacitively coupled radio frequency (13.56 MHz) glow discharge system in which silane (SiH4) was the principal gaseous component. The boron content in the films was measured by secondary ion mass spectroscopy (SIMS) using a calibrated boron-implanted silicon standard. The optical and transport properties of these films were measured and compared with films of similar boron film content deposited using B2H6 BF3-doped films showed less sub-band gap absorption (as determined by photothermal deflection spectroscopy), no band gap narrowing, and higher conductivity prefactors σo for low doping levels compared to B2H6-doped films. The possible utility of lightly BF3-doped a-Si:H as the i-layer in a p/i/n photovoltaic device is suggested.