Optical and morphological properties of MBE grown wurtzite CdxZn1−xO thin films

Wurtzite CdxZn1−xO epilayers with cadmium concentrations ranging from x = 0.02 to 0.30 were investigated using photoluminescence, transmission/reflection spectroscopy, and atomic force microscopy. The CdxZn1−xO photoluminescence peak was found to shift through the visible region from 421 (2.95 eV) to 619 nm (2.0 eV) as the cadmium concentration was increased from 2% to 30%. An additional broad photoluminescence peak was observed and is attributed to deep levels – the center of the broad peak was found to shift from 675 to 750 nm as the cadmium concentration was increased. RMS roughness of the epilayers increased from 1.5 nm (x = 0.02) to 9.2 nm (x = 0.30), as determined from atomic force microscopy. The demonstrated visible wavelength tunability throughout the visible range verifies the viability of using wurtzite CdxZn1−xO compounds for visible light emission in future optoelectronic devices.