Compositionally-tuned epitaxial cubic MgxZn1−xO on Si(100) for deep ultraviolet photodetectors

Abstract

We report on the epitaxialgrowth of wide-band-gap cubic-phase Mg x Zn 1−x O thin films on Si(100) by pulsed-laser deposition and fabrication of oxide-semiconductor-based ultraviolet photodetectors. The challenges of large lattice and thermal expansion mismatch between Si and Mg x Zn 1−x O have been overcome by using a thin SrTiO 3 buffer layer. The heteroepitaxy of cubic-phase Mg x Zn 1−x O on Si was established with epitaxial relationship of Mg x Zn 1−x O (100)// SrTiO 3 (100)// Si (100) and Mg x Zn 1−x O [100]// SrTiO 3 [100]// Si [110]. The minimum yield of the Rutherford backscattering ion channeling in Mg x Zn 1−x O layer was only 4%, indicating good crystalline quality of the film. Smooth surface morphology with rms roughness of 0.6 nm was observed using atomic force microscopy. Photodetectors fabricated on Mg 0.68 Zn 0.32 O/SrTiO 3 / Si show peak photoresponse at 225 nm, which is in the deep UV region.