Abstract
This study investigated carrier compensation induced by thermal annealing in sputtered ZnO:Al (Al2O3: 0.25, 0.5, 1.0, and 2.0 wt %) films. The films were post-annealed in a N2 atmosphere at low (1 × 10−23 atm) and high (1 × 10−4 atm) oxygen partial pressures (PO2). In ZnO:Al films with low Al contents (i.e., 0.25 wt %), the carrier density (n) began to decrease at annealing temperatures (Ta) of 600 °C at low PO2. At higher PO2 and/or Al contents, n values began to decrease significantly at lower Ta (ca. 400 °C). In addition, Zn became desorbed from the films during heating in a high vacuum (i.e., <1 × 10−7 Pa). These results suggest the following: (i) Zn interstitials and Zn vacancies are created in the ZnO lattice during post-annealing treatments, thereby leading to carrier compensation by acceptor-type Zn vacancies; (ii) The compensation behavior is significantly enhanced for ZnO:Al films with high Al contents.
Highlights
Transparent conducting oxide (TCO) films have been widely used as window electrodes in optoelectronic devices such as flat panel displays and solar cells
ZnO films have been used in thin-film solar cell applications [1], they typically exhibit low conductivity compared to In2 O3 -based TCO [2]
Was reported to be ~0.3 at % [13], the ZnO:Al films fabricated in this study are metastable from a thermodynamic point of view, and a supersaturated solid solution occurs as a result of the highly non-equilibrium growth process
Summary
Transparent conducting oxide (TCO) films have been widely used as window electrodes in optoelectronic devices such as flat panel displays and solar cells. ZnO films exhibit higher conductivity than SnO2 films at relatively low growth temperatures. ZnO films have been used in thin-film solar cell applications [1], they typically exhibit low conductivity compared to In2 O3 -based TCO [2]. The most important properties of TCO films for use as window electrodes are their conductivity and absorption coefficient. Both of these parameters are related to the carrier density (n) and mobility (μ) [3]
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