Lasing of Excitons in ZnO Thin Films.

A high quality ZnO thin film was grown by the laser molecular beam epitaxial technique. Under high-density excitation, the exciton-exciton collision process (P line) was observed at room temperature in ZnO thin films where the exciton binding energy is 60 meV. From the edge of the sample, a rapid increase in the P line was observed with increasing excitation power. A fine structure originating from the cavity mode was also observed. These facts suggest the lasing of the exciton at room temperature. Crystal growth of the ZnMgO mixed crystal and the stability of the ZnO/ZnMgO heterostructure were discussed. Optical properties of the ZnO/Zn0.8Mg0.2O multi-quantum-well show that the electrons and holes are well confined in this heterostructure.