Size-dependent optical edge shifts and electrical conduction behaviour of RF magnetron sputtered CdTe nanocrystals:TiO2composite thin films
- 6 October 2000
- journal article
- Published by IOP Publishing in Semiconductor Science and Technology
- Vol. 15 (11), 1011-1021
- https://doi.org/10.1088/0268-1242/15/11/301
Abstract
CdTe nanocrystals sequestered and passivated in an amorphous TiO2 thin film matrix have been prepared by RF sputtering from a composite TiO2:CdTe target. The CdTe nanocrystal size and volume fraction increases from 15 to 40 nm and 2 to 20% respectively as the film thickness increases, typically from 0.05 to 0.25 µm. A systematic dependence of the optical band edge on the CdTe nanocrystal size shows a strong quantum confinement effect. The optical edge shifts are significantly higher than the theoretical prediction based on single-particle confinement of decoupled electrons and holes. This is understood on the basis of nucleation-controlled growth of CdTe nanocrystals by direct vapour phase condensation, in which small nuclei are rapidly passivated by TiO2 depositing at much higher rates. The nano-sized CdTe growth island thus formed comprises of several TiO2 passivated nanocrystals. Electrical conduction behaviour of these films show that tunnelling between the CdTe nanocrystals is not a dominant mechanism, as a three-dimensional network is not realized due to small thickness and lower coverage. The current transport is essentially space-charge-limited. The injection of electrons from nano-sized CdTe crystals follows spherical radial space charge flow which modifies the usual power law dependence from quadratic to 3/2. The analytical description of the current conduction process in composite CdTe:TiO2 is discussed.This publication has 25 references indexed in Scilit:
- The dissociative adsorption of hydrogen sulfide over nanophase titanium dioxideJournal of Materials Research, 1992
- Melting in Semiconductor NanocrystalsScience, 1992
- Optical Properties of CdS Microcrystallite-Doped SiO2 Glass Thin FilmsJapanese Journal of Applied Physics, 1990
- Nonlinear Optical Properties of Quantum Confined Semiconductor MicrocrystallitesPhysica Status Solidi (b), 1990
- Third-order optical nonlinearities in semiconductor microstructuresPhysical Review B, 1988
- Quantum size effects in optical properties of CdS-glass compositesPhysical Review B, 1988
- Determination of kinetic parameters from steady-state microdisk voltammogramsThe Journal of Physical Chemistry, 1988
- Degenerate four-wave mixing of CdS/polymer compositeOptics Communications, 1987
- Gas phase reactions of iron clusters with hydrogen. I. KineticsThe Journal of Chemical Physics, 1985
- Photochemistry of colloidal metal sulfides. 3. Photoelectron emission from cadmium sulfide and cadmium sulfide-zinc sulfide cocolloidsThe Journal of Physical Chemistry, 1982