Molecular Beam Epitaxy of High Magnesium Content Single-Phase Wurzite Mg_xZn_1-xO Alloys ($x\simeq 0.5$) and Their Application to Solar-Blind Region Photodetectors

Abstract

A series of single-phase wurzite MgxZn1-xO alloys from x=0 to 0.5 were successfully obtained by molecular beam epitaxial growth on sapphire substrates, resulting in artificial tuning of band gap energy Eg from 3.3 to 4.5 eV which covers UV-A, UV-B, and solar-blind spectral regions. The problem of phase separation ever reported in the growth of MgxZn1-xO with higher Mg content, e.g., x>0.4 and Eg>3.9 eV, has been overcome by using a ZnO buffer layer. The Mg0.5Zn0.5O layers have been applied to a planar geometry Schottky type metal-semiconductor-metal photodetector, exhibiting the photoresponse for the wavelength shorter than 270 nm which correspond to the solar-blind region.