ZnO thin films were grown homoepitaxially on O-face ZnO single crystals by pulsed-laser deposition. The ZnO substrates grown by the hydrothermal method were heat-treated in oxygen ambient at 1000 °C for 2 h prior to deposition. After the thermal treatment the substrates show bilayer steps between 200–400 nm wide terraces and a considerably improved crystalline structure. Thin film surfaces exhibit closed loop spirals and show steps of c /2 or c. The FWHM of the (0002) rocking curve of the best sample is 29″. Similar to the substrates used, Al is contained in the thin films (<1014 cm–3) as photoluminescence (PL) and thermal admittance spectroscopy suggest. However, deep levels between 200 and 400 meV below the conduction band are the dominant donors at room temperature. Low temperature PL is dominated by (Al0,X) (I6, FWHM: 200 µeV) and extremely homogeneous (σ ≈ 1%).
AFM amplitude error image (scale: 0–10 mV) of homoepitaxial PLD thin film grown at Tg ∼ 650 °C and p = 0.016 mbar. The step height is c (cf. Fig. 1f).
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