The multi-state photoluminescence and anisotropic properties of Al-catalyzed grown spherulite-like GeS thin films

Two photoluminescence (PL) peak centers, i.e. the principal GeS PL peak at 1.61 eV and the newly discovered PL peak at 1.36 eV, were obtained from the Al-catalyzed grown spherulite-like GeS thin films on SiO 2 /Si substrates, whereas no distinct PL peak at 1.36 eV was obtained from the grown GeS without applying Al catalyst layer. Anisotropic properties of Raman spectra were observed in one domain of spherulite-like GeS without using a polarized Raman microscope, which corresponded to the observed Maltese-extinction cross pattern. Density functional theory calculations suggest that the 1.36 eV PL peak likely results from defect-to-band PL in Al-doped GeS, attributed to orbital hybridization among Al, Ge and S atoms.