Dresden 2003 – wissenschaftliches Programm
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SYOC: Optical coating in information technology, light management and other areas
SYOC 1: Optical coating in information technology, light management and other areas I
SYOC 1.2: Hauptvortrag
Dienstag, 25. März 2003, 10:05–10:40, HSZ/01
Transparent and Conductive Oxides - Challenging Materials for Optoelectronic Applications — •Bernd Szyszka — Fraunhofer Institute for Surface Engineering and Thin Films (IST), Bienroder Weg 54 E, 38108 Braunschweig, Germany
Transparent and conductive oxide films such as In2O3:Sn, SnO2:(Sb, F) or ZnO:Al combine the optical properties of dielectric layers with metal-like electrical conductivity. The conductivity of the film is due to electron degeneracy at high doping levels, e. g. due to the substitution of cations or anions with higher or lower valence in respect to the transparent matrix. The need for optimal performance puts strong demands on the control of phase composition and defect chemistry at high doping level up to several at %. In addition to optical and electrical properties, the devices to be realized put strong demands on other properties such as temperature and chemical stability, surface morphology and etching characteristics. Devices such as transparent OLEDs, CIS solar cells and flexible displays are sensitive to high temperature or energetic sputter processes. As a consequence, the development of low temperature - soft growth processes is mandatory. For a-Si:H solar cells, special etch treatment is necessary to increase the light scattering. This paper gives an outline on the material science of TCO films with special emphasize on ZnO:Al films. These films can be deposited at low temperature by reactive AC magnetron sputtering from metallic Zn:Al targets. They are a cost effective alternative for front electrodes of a-Si:H solar cells and also for ITO for flat panel displays. Films with resistivity of ρ < 270 µ Ω cm and low absorption (k at 550 nm < 2 x 10−3) have been grown on 100 × 60 cm2 glass substrates. The optical properties of these films are characterized by ellipsometry and spectral photometry. Advanced models based on the Gerlach Grosse theory are implemented for the evaluation of free electron properties. Structural investigations are performed using XRD, SEM and HRTEM.