Zinc oxide,a wide band-gap semiconductor,has shown extensive potential applications in high-efficiency semiconductor photoelectronic devices,semiconductor photocatalysis,and diluted magnetic semiconductors.Due to the undisputed lattice integrity,ZnO single crystals are essential for the fabrication of high-quality ZnO-based photoelectronic devices,and also believed to be ideal research subjects for understanding the underlying mechanisms of semiconductor photocatalysis and diluted magnetic semiconductors.This review,which is organized in two main parts,introduces the recent progress in growth,basic characterization,and device development of ZnO single crystals,and some related works in our group.The first part begins from the growth of ZnO single crystal,and summarizes the fundamental and applied investigations based on ZnO single crystals.These works are composed of the fabrication of homoepitaxial ZnO-based photoelectronic devices,the research on the photocatalysis mechanism,and dilute magnetic mechanism.The second part describes the fabrication of highly thermostable n-type ZnO with high mobility and high electron concentration through intentional doping.More importantly,in this part,a conceptual approach for fabricating highly thermostable p-type ZnO materials with high mobility through an integrated three-step treatment is proposed on the basis of the preliminary research.
Phosphorus was diffused into CVT grown undoped ZnO bulk single crystals at 550 and 800℃ in a closed quartz tube. The P-diffused ZnO single crystals were characterized by the Hall effect, X-ray photoelectron spectroscopy （XPS）, photoluminescence spectroscopy （PL）, and Raman scattering. The P-diffused ZnO single crystals are n-type and have higher free electron concentration than undoped ZnO, especially for the sample diffused at 800℃. The PL measurement reveals defect related visible broad emissions in the range of 420-550nm in the P-diffused ZnO samples. The XPS result suggests that most of the P atoms substitute in the Zn site after they diffuse into the ZnO single crystal at 550℃ ,while the P atom seems to occupy the O site in the ZnO samples diffused at 800℃. A high concentration of shallow donor defect forms in the P-diffused ZnO,resulting in an apparent increase of free electron concentration.
