Structural, optical and electrical properties of the novel semiconductor alloy ZnO_xTe_(1-x)

摘要

Epitaxial films of undoped ZnO_xTe_(1-x) have been prepared on double-side polished c-axis oriented sapphire substrates with pulsed laser deposition. The method of epitaxial growth is expected to have the same domain matching epitaxial relationship with sapphire as does pure ZnO, where six lattice planes of ZnO_xTe_(1-x) match with seven lattice planes of sapphire. High quality, single crystal, epitaxial alloys with around 4% Te have been grown that demonstrate excellent optical properties and a pronounced, sharp excitonic peak, in optical transmission. The incorporation of Te makes the compound more covalent, and less ionic than pure ZnO. Transmission electron microscopy (TEM) demonstrates single-crystal growth with a sharp interface. The low-resolution X-ray diffraction (XRD) pattern of ZnO_xTe_(1-x) films is almost indistinguishable from those of pure ZnO, except a usually diminished intensity of the (0004) peak. The incorporation of Te in ZnO was verified by a shift in excitonic peak position in absorption, and through a shift in cathodoluminescence (CL) peak. X-ray photoelectron spectroscopy (XPS) data verifies incorporation of telluride chemical state of tellurium atoms. Rutherford backscattering/channeling (RBS/C) confirmed crystal quality for the pure ZnO films. Hot-point probe measurements indicate as-grown, undoped films to be somewhat higher in resistivity than pure ZnO with inconclusive carrier type, as compared to the naturally n-type ZnO. This may be a consequence of the more covalent bonding between Zn and Te and suggests a possible strategy for p-type doping.