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The polarity control of ZnO films grown on (0001) Al 2 O 3 substrates by plasmaassisted molecular-beam epitaxy (P-MBE) was achieved by using a novel CrN buffer layer. Zn-polar ZnO films were obtained by using a Zn-terminated CrN buffer layer, while O-polar ZnO films were achieved by using a Cr 2 O 3 layer formed by O-plasma exposure of a CrN layer. The mechanism of polarity control was proposed. Optical and structural quality of ZnO films was characterized by high-resolution X-ray diffraction and photoluminescence (PL) spectroscopy. Low-temperature PL spectra of Zn-polar and O-polar samples show dominant bound exciton (I 8 ) and strong free exciton emissions. Finally, one-dimensional periodic structures consisting of Zn-polar and O-polar ZnO films were simultaneously grown on the same substrate. The periodic inversion of polarity was confirmed in terms of growth rate, surface morphology, and piezo response microscopy (PRM) measurement.

We report the characteristics of chemical lift-off method using metallic buffer layer and its application to the real light emitting devices.Recently, differently from the conventional method, metallic buffer layer was introduced for the GaN growth 1 .We fabricated GaN-based light-emitting diodes (LEDs) by metal-organic vapor-phase epitaxy on two different GaN templates with the same LED structure: one on thin GaN template with LT-GaN buffer layer grown by MOVPE, and the other on GaN template with CrN buffer layer by HVPE. Compared with the metal buffer GaN