Undoped and Al-doped ZnO films with tuned properties by pulsed laser deposition

Evie L. Papadopoulou 1Maria Varda 1Kostas Kouroupis-Agalou 1Maria G. Androulidaki 2Ekaterina Chikoidze 3Guido Huyberechts 6Mircea Modreanu 4Elias Aperathitis 5

1. IESL, FORTH, P.O. Box 1527, Vassilika Vouton, Heraklion 71110, Greece
2. Microelectronics Research Group, Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, and University of Crete, Physics Department (MRG), Heraklion 71110, Greece
3. University of Versailles CNRS (GEMAC), 1, Place A. Briand, Meudon 92195, France
4. University College Cork, Tyndall National Institute (TYNDALL), Lee Maltings, Prospect Row, Cork, Ireland
5. Microelectronics Research Group, Institute of Electronic Structure and Laser, Foundation for Research and Technology – Hellas, P.O. Box 1527, 71110 Heraklion, Crete, Greece, P.O. Box 1527, Heraklion 71110, Greece
6. Umicore Group Research and Development, Kasteelstraat 7 B-2250, Olen B-2250, Belgium

Abstract

Zinc oxide (ZnO) has been the focus of intense investigation due to the unique properties it possesses. It is a transparent, wide band gap semiconductor (Eg~3.4eV) with high exciton binding energy (~60 meV). Its conductivity, if properly doped, approaches the high value of the widely used n-type indium-tin-oxide (ITO), and if it could also be reproducibly of p-type, ZnO would be the ideal material for many emerging transparent optoelectronic applications.
However, if ZnO is to be used as an active layer in optoelectronic devices, it must have electrical and optical properties within a wide range of values. Thus, it would be of paramount technological importance if ZnO films can be fabricated with tuned properties by adjusting the deposition parameters.
In this investigation the properties of undoped and Al-doped ZnO films fabricated by pulsed laser deposition (PLD) on UV-grade fused silica and Si substrates are presented. The ZnO and ZnO:Al(2%) target were ablated by a 248 excimer laser and the films were deposited in a wide range of PLD parameters, including substrate temperature (up to 500oC), oxygen pressure (from 10-2 to 10-5 mbar) and at different target-substrate distances. Polycrystalline films having the wurtzite structure were fabricated, with carrier concentration between 1015 and 1021 cm-3, resistivity from 100 to 3x10-4 Ωcm and Eg spanning from 3.2 to 3.7eV. Sharp emission excitonic peak at 353.6nm was observed for highly conductive (3.3x10-4 Ωcm) ZnO:Al films.
The properties of the ZnO films were investigated using atomic force microscopy (AFM), Hall-effect measurements and various spectroscopic techniques such as UV-NIR optical measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) as well as low temperature photoluminescence (PL) for identifying excitonic emission peaks and band gap defects. The use of the ZnO films, fabricated in this investigation, in optoelectronic devices like LEDs, TFTs, etc., will also be addressed.

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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium H, by Evie L. Papadopoulou
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-21 11:04
Revised:   2009-06-07 00:44
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