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15 February 2008 Properties of homoepitaxial ZnO and ZnO:P thin films grown by pulsed-laser deposition
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We have investigated the morphology, crystalline quality, the transport and electronic properties of homoepitaxial ZnO and ZnO:P thin films grown by pulsed-laser deposition. Atomic surface steps are visible for growth temperatures of 650°C and higher. The unit cell volume of undoped thin films is smaller than that of the hydrothermal substrates. Phosphorous doping increases the unit cell volume such that a perfect lattice match is achieved for a nominal phosphorous content of 0.01 wt.%. Undoped thin films have a net doping concentration below 1015 cm-3, whereas the phosphorous doping increases the free electron concentration at room temperature to 1017 cm-3 and above. Temperature dependent Hall effect measurements show that interstitial zinc with a thermal activation energy of 34 meV is a dominant donor in homoepitaxial ZnO:P thin films. The Hall mobility of such samples is similar to ZnO single crystals grown by seeded chemical vapor transport. Low temperature photoluminescence measurements reveal recombination of free excitons and excitons bound to interstitial zinc and excitons bound to neutral and ionized aluminum donors. Defect related deep luminescence is not observed for undoped homoepitaxial thin films. In contrast phosphorous doping introduces two broad recombination bands centered at 2.9 eV and 1.9 eV.
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H. von Wenckstern, M. Brandt, H. Schmidt, G. Benndorf, J. Zippel, H. Hochmuth, M. Lorenz, and M. Grundmann "Properties of homoepitaxial ZnO and ZnO:P thin films grown by pulsed-laser deposition", Proc. SPIE 6895, Zinc Oxide Materials and Devices III, 689505 (15 February 2008);

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