Elaboration and characterization of thin layers of SiP lamellar alloys
Résumé
In contrast to III-V or II-VI semiconductor alloys, group IV-V alloys have been the subject of much less attention up to now. Theoretical calculations have shown that bulk SiP is an indirect bandgap semiconductor which becomes direct in its 2D form. Moreover, bulk SiP is a lamellar alloy that can be exfoliated, which is of particular interest for new applications in optoelectronics. In this work, we investigate SiPx thin films prepared by evaporation under high vacuum. The films were prepared by co-evaporation of Si from an e-beam gun and P from a GaP decomposition source. The structural and optical properties were investigated by means of X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), vibrational spectroscopies (Infrared and Raman) and photoluminescence spectroscopy. After annealing at 1100°C, the structural characterizations reveal the presence of lamellar SiP grains crystallizing in an orthorhombic structure which coexist with Si polycrystals. To further characterize the SiP alloy, DFT calculations have been carried out to get a better understanding of the features observed in both infrared and Raman spectra. The calculated spectra are found to be in excellent agreement with the experimental results. Moreover, temperature dependent photoluminescence measurements strongly suggest that SiP is an indirect bandgap semiconductor with a bandgap energy of 1.47 eV. The obtained value is in good agreement with theoretical values found in the literature.