Anisotropic optical gains in a-plane ZnO/Zn0.8Mg0.2O multiple quantum wells grown via pulsed-laser deposition
High periodicity non-polar ten-pair ZnO/Zn0.8Mg0.2O multiple quantum wells (MQWs), with a binding energy of approximately 69.8 meV, on r-plane sapphire were prepared via pulsed-laser deposition. The a-plane ZnO/Zn0.8Mg0.2O MQWs exhibit anisotropic optical properties, which demonstrate an energy difference of approximately 15 meV between the two splitting valence bands via photoluminescence measurement.Through the optical pump of the Q-switched laser, the amplified spontaneous emission (ASE) from both the side and surface normal of the non-polar MQWs shows a higher slope efficiency and gain coefficient under a perpendicular pump (Ep ⊥ c) than those under a parallel pump condition (Ep //c). Owing to the gain-guiding effect, the linealy polarized ASE from the side of the non-polar ZnO/Zn0.8Mg0.2O MQWs has been demonstrated with a degree of polarization (DOP) ~ 89 %. For the surface normal ASE, the P2 band emission from exciton-exciton (ex-ex) scattering is recognized as the dominant mechanism. Through the temperature-dependent ASE, the P band emission peak reveals an evident red shift as the temperature increases. Moreover, a higher characteristic temperature of ~ 124 K, which indicates the temperature-insensitive property, is obtained.