Regensburg 2004 – scientific programme
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DS: Dünne Schichten
DS 22: Postersitzung
DS 22.58: Poster
Tuesday, March 9, 2004, 14:30–17:00, Poster B
Modulation Doping as a Means to Overcome the Mobility Limitation of Zinc Oxide Transparent Electrodes? — •Goetz Vollweiler und Klaus Ellmer — Hahn-Meitner-Institut, Solar Energy Research, Glienicker Straße 100, 14109 Berlin
Heavily doped ZnO, which belongs to the material class of transparent conductive oxides, finds an important application as transparent electrode in thin film solar cells. As recent reviews have shown, there exists a lower limit in the range of 1.4 to 2.0 × 10−4 Ωcm concerning the resistivity of this material, which is caused by a low mobility due to ionized impurity scattering. The aim of this work is to proof a concept to overcome this limitation. The idea is, to create a system consisting of small adjacent domains with undoped and doped ZnO, a so-called modulation doped structure. Charge carriers from the doped areas with low mobility would diffuse to the undoped domains with low ionized impurity scattering and consequently high mobility. For the film preparation magnetron sputtering from two different targets has been used to grow multi-sandwich films of thin doped and undoped ZnO-films on sapphire substrates. In order to widen the bandgap of the doped films, which is a prerequisite for the modulation doping principle, MgO was added. The electrical parameters carrier concentration and Hall mobility and the crytallographic quality of the films will be given in dependence of the deposition parameters.