Photoluminescence of Mg2Si films fabricated by magnetron sputtering

Abstract

To understand the photoluminescence mechanisms and optimize the design of Mg2Si-based light-emitting devices, Mg2Si films were fabricated on silicon (111) and glass substrates by magnetron sputtering technique, and the influences of different substrates on the photoelectric properties of Mg2Si films were investigated systematically. The crystal structure, cross-sectional morphology, composition ratios and temperature-dependent photoluminescence (PL) of the Mg2Si films were examined using X-ray diffraction (XRD), Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and PL measurement system, respectively. XRD results indicate that the Mg2Si film on Si (111) displays polycrystalline structure, whereas Mg2Si film on glass substrate is of like-monocrystalline structure.SEM results show that Mg2Si film on glass substrate is very compact with a typical dense columnar structure, and the film on Si substrate represents slight delamination phenomenon. EDS results suggest that the stoichiometry of Mg and Si is approximately 2:1. Photoluminescence (PL) of Mg2Si films was observed for the first time. The PL emission wavelengths of Mg2Si are almost independence on temperature in the range of 77–300K. The PL intensity decreases gradually with increasing temperature. The PL intensity of Mg2Si films on glass substrate is much larger than that of Mg2Si film on Si (111) substrate. The activation energy of 18meV is determined from the quenching of major luminescence peak(1342nm) as a function of temperature in the Mg2Si film grown on Si (111) substrate, which is much smaller than that deduced in the sample grown on glass substrate (about 25meV). The small activation energy can be attributed to the additional nonradiative centers originated from relatively poor crystal quality.The physical mechanism responsible for the measured ∼1342nm and other three longer wavelengths emissions may be respectively result from strong Mgi donor level to valence band transitions and other defect-related radiative recombination occurred in the Mg2Si films.