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Growth and properties of nonpolar and polar MgZnO/ZnO quantum structures

Spectacular breakthroughs have been achieved in optoelectronics with the use of ZnO as a source for light-emitting diodes (LED) and quantum wells (QWs). In particular, atomically flat surfaces were obtained in Zn-polar growth, which led to the fabrication of Mg-rich Mg0.37Zn0.67O/ZnO QWs with sharp heterointerfaces between MgZnO and ZnO. μ-PL spectroscopy revealed that excitons were efficiently confined in the wells at room temperature. Excitonic emissions from Zn-polar QWs did not have a linear polarization effect, although polarized lights were clearly observed in M-nonpolar Mg0.12Zn0.88O/ZnO QWs. From the optical selection rule, the polarized lights of excitonic emissions were based on A- and C-excitonic transitions under E⊥c and E//c configurations. Furthermore, the anisotropic surface morphology was self-organized on the M-nonpolar ZnO layer surfaces, which allowed examination of the relationship between electron transport and surface morphology. The observed transport anisotropy correlated with the surface morphology. On the other hand, Zn-polar QWs resulted in isotropic electron transport because of two-dimensional surfaces. In this presentation, we introduce the detailed growth and various properties of Zn-polar and M-nonpolar QWs.