Valence Band Dispersion of Perovskite Single Crystal Observed by Angle-resolved Photoemission Spectroscopy

The electronic structure of the cleaved perovskite (CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbBr$_{\mathrm{3}})$ single crystal was studied in an ultra-high vacuum (UHV) system by angle-resolved photoemission spectroscopy (ARPES) and inverse photoelectron spectroscopy (IPES). Highly reproducible dispersive features of the valence bands were observed with nice symmetry about the Brillouin zone center and boundaries. The largest dispersion width was found to be about 0.73 eV and 0.98 eV along the $\Gamma X$ and $\Gamma M$ directions, respectively. The measured band dispersions correspond to an effective hole mass as about 0.59$ m_{0}$ and a lower limit of the hole mobility of 33.90 cm$^{\mathrm{2}}$V$^{\mathrm{-1}}$s$^{\mathrm{-1}}$ from the tight-binding fitting. The quality of the surface was verified by atomic force microscopy (AFM) and scanning electron microscope (SEM). The elemental composition was investigated by high resolution x-ray photoelectron spectroscopy (XPS). The experimental electronic structure shows a good agreement with the theoretical calculation.