Super-radiation processes of ZnO/Mg0.1Zn0.9O SQW under high-density excitation

ZnO /Mg0.1Zn0.9O single-quantum well (SQW) with 1.5 nm ZnO well width was grown on sapphire substrate by plasma-assisted molecular beam epitaxy. The absorption spectrum of the sample at room temperature (RT) shows a sharp absorption edge from MgZnO barrier layer in the ultraviolet region. A stronger exciton emission at 3.392 eV from the ZnO well layer was observed in the photoluminescence spectrum at RT, and the exciton binding energy of the ZnO well layer is 70.8 meV. In the PL spectra at 5 K, P2 band (one exciton was scattered into an excited state with a quantum number 2) located at 3.371 eV was observed. At excitation densities higher than 76 kW/cm2, the P band shows a typical super-radiation characteristic. With increasing the excitation density further, the P band converges gradually at the saturation value of 3.354 eV with significant narrowing. It was attributed to the gradually enhanced exciton-exciton scattering.