THERMALLY STABLE ZNO FILMS DEPOSITED ON GAAS SUBSTRATES WITH A SIO2 THIN BUFFER LAYER

SiO2 thin films (1000-angstrom thick) were sputter deposited on GaAs substrates as a buffer layer in order to alleviate a thermal mismatching problem between ZnO films and GaAs substrates. Thermal stability of sputter-deposited ZnO films (0.5-2.0 mum thick) was tested on such a buffered GaAs substrate with a postdeposition heat treatment at 430-degrees-C for 10 min, which is similar to a standard ohmic contact alloying condition. The films sustained the heat treatment well, not showing any crumbling, which has usually been a problem when a ZnO film is deposited directly on a GaAs substrate. The postdeposition anneal treatment also dramatically enhances c-axis orientation of the ZnO films and relieves intrinsic stress almost completely. These improvements are attributed to a reduction of grain boundaries and voids with the anneal treatment as supported by the scanning electron microscopy and x-ray diffraction measurement results.