Band offset in calcium hydroxide mediated CaO-ZnO heterointerfaces

Chemical routes for synthesizing semiconductor heterostructures (SHs) from viewpoints of improved band energetics in an optoelectronic device continue to be a lucrative area. Here we report on the experimental and theoretical band alignment correlated by XPS and UV-DRS analysis at the n-n nanointerfaces of CaO-ZnO heterostructure. A wet synthesis route was utilized to obtain SHs by zinc hydroxide carbonate (Zn5(CO3)2(OH)6) conversion to ZnO using Ca(OH)2 at near room temperature and by calcination method. The heterostructures achieved by reacting Zn5(CO3)2(OH)6 with Ca(OH)2 at near room temperature and by calcination method are referred to as Ca-ZMS and CaO-ZnO, respectively. The band gaps of individual components namely, CaO and ZnO were found to be 4.67 and 3.32 eV, respectively. In each case, band alignment was found to be of type II (staggered) in contrast to what is reported in the literature as type I (straddled). This change was attributed to the presence of nanostructured CaO. An interfacial valence band and conduction band offset of −1.37 and 2.72 eV was observed in Ca-ZMS, while CaO-ZnO demonstrated valence band and conduction band offset of −0.67 and 2.02 eV, respectively.