Growth, characterization, and properties of bulk SnO sub(2) single crystals

SnO sub(2) is a semiconductor with a wide optical bandgap (3.5eV), which makes it an attractive transparent semiconducting oxide (TSO) for electronic and opto-electronic applications. At elevated temperatures it is, however, much more unstable than other TSOs (such as ZnO, Ga sub(2)O sub(3), or In sub(2)O sub(3)). This leads to a rapid decomposition even under very high oxygen pressures. Our experiments showed that stoichiometric SnO sub(2) does not melt up to 2100 degree C, in contradiction to earlier published data. Bulk SnO sub(2) single crystals, that could provide substrates for epitaxial growth, have not been reported so far. Hereby we report on truly bulk SnO sub(2) single crystals of 1inch diameter grown by physical vapor transport (PVT). The most volatile species during SnO sub(2) decomposition is, in addition to oxygen, SnO, which is stable in the gas phase at high temperature and reacts again with oxygen at lower temperatures to form SnO sub(2). We identified a relatively narrow temperature window, temperature gradients and a ratio of SnO/O sub(2) for providing the best conditions for SnO sub(2) single crystal growth. X-ray powder diffraction (XRD) proved the single SnO sub(2) phase. Moreover, by selecting a suitable SnO/O sub(2) ratio it was possible to obtain either n-type conductivity with electron concentrations up to 210 super(18)cm super(-3) and electron mobilities up to 200cm super(2)V super(-1)s super(-1), or insulating behavior. The crystals exhibited an optical absorption edge located at 330-355nm, depending on the crystal orientation, and a good transparency over visible and near infrared (NIR) spectra.