Structural and optical properties of SiP thin films
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. Very recently, however, alloyed SiPx thin films have gained an increasing interest. Indeed, it was predicted theoretically that a monolayer of SiP is a direct bandgap semiconductor which could be promising for the development of 2D blue light emitting diodes. 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), Fourier transform infrared absorption spectroscopy (FTIR), Raman and photoluminescence spectroscopies. After annealing at 1100°C, the structural characterizations reveal the presence of 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 FTIR 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.