Articles you may be interested inInvestigation of the crystallinity of N and Te codoped Zn-polar ZnO films grown by plasma-assisted molecularbeam epitaxy J. Appl. Phys. 108, 093518 (2010); 10.1063/1.3498800Effects of two-step growth by employing Zn-rich and O-rich growth conditions on properties of ( 11 2 ¯ 0 ) ZnO films grown by plasma-assisted molecular beam epitaxy on sapphire Optical and electrical properties of highly nitrogen-doped ZnO thin films grown by plasma-assisted molecular beam epitaxy Origin of green luminescence in ZnO thin film grown by molecular-beam epitaxy J. Appl. Phys. 98, 073502 (2005); 10.1063/1.2064308Ga-doped ZnO films grown on GaN templates by plasma-assisted molecular-beam epitaxyThe influence of rf power and aperture plate configuration on the growth of ZnO thin films using plasma-assisted molecular beam epitaxy was investigated. It was found that by changing the aperture plate geometry from 276 to 25 holes, an increase of growth rate was observed, suggesting that the latter is more efficient for ZnO growth. The structural, electrical, and optical properties were also improved as measured by in situ electron diffraction, single field Hall effect, and photoluminescence. A background carrier concentration of 1 ϫ 10 18 cm −3 and a mobility of 52 cm 2 / V s were measured, and a room-temperature band edge peak 200 times the defect band intensity was observed. Optical emission spectroscopy shows significantly different behavior in plasma generated using the two plates and suggests that more than increased atomic oxygen production is occurring.
The dependence of characteristics of plasma-assisted molecular beam epitaxygrown ZnO thin films on different postgrowth annealing conditions was investigated. It was found that, under oxygen atmosphere, annealing temperature can profoundly affect the morphological, electrical, and optical properties of ZnO thin films. In particular, the surface morphology changed from a relatively smooth surface before annealing to various island morphologies after annealing above 800°C for samples grown directly on sapphire without a buffer layer. It is speculated that intrinsic stress due to lattice mismatch drives the island formation and the high temperature provides the energy needed for this surface rearrangement. Single-field Hall-effect measurement showed that the carrier concentration improved by an order of magnitude and the mobility increased from about 30 cm 2 /Vs to ;70 cm 2 /Vs by annealing at 750°C. Variablefield Hall effect shows that a model with two carriers, one a degenerate lowmobility electron and the other a higher mobility non-degenerate electron, is needed to explain the transport properties of the thin film. Analysis indicates that annealing at 750°C decreased the carrier concentration and increased the mobility for the high-mobility carrier. Annealing also led to a significant improvement in photoluminescence, with temperatures of ;750-850°C yielding the best results.
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