Understanding phase separation in ZnCdO by a combination of structural and optical analysis

A phenomenon of wurtzite (w), zincblende (zb), and rock-salt (rs) phase separation was investigated in ZnCdO films having Cd contents in the range of 0%--60% settling a discussion on the phase stability issues in ZnCdO. First, low-Cd-content ({}17%) ZnCdO was realized preferentially in a w matrix determining optimal Zn-lean conditions by tuning the precursor decomposition rates during synthesis. However, more detailed analysis of x-ray diffraction and photoluminescence (PL) data revealed that the w single-phase stability range is likely to be as narrow as 0%--2% Cd, while samples containing 7%--17% of Cd exhibit a mixture of w and zb phases. Second, high-Cd-content (32%--60%) ZnCdO samples were realized, supplying more of the Cd precursor utilizing Zn-lean growth conditions, however, resulting in a mixture of w, zb, and rs phases. Characteristic PL signatures at 2.54 and 2.31 eV were attributed to zb-ZnCdO and rs-CdO, respectively, while the band gap variation in w-Zn_1-xCdₓO is given by (3.36--0.063x) as determined at 10 K. The phase separation is interpreted in terms of corresponding changes in the charge distribution and reduced stacking fault energy.