Investigation of the electronic structure of amorphous SnO film using X-ray absorption spectroscopy

The electronic structure of an amorphous SnO (a-SnO) thin film was examined by using spectroscopic methods including tender and soft X-ray absorption spectroscopies (XAS) and spectroscopic ellipsometry (SE). XAS at the Sn L₁-, L₃-, and O K-edges revealed that in a-SnO, the Sn 5p_x/y orbital states, which comprise the conduction band minimum (CBM), are broadened significantly compared to the case of crystalline SnO, whereas the hybridized Sn 5sp_z-O 2p states above the CBM are persistent. A lowering of the 5p_x/y states at the CBM by-0.4 eV and a reduction of the indirect bandgap were also observed. These orbital-dependent evolutions upon amorphization were caused by weakened interlayer couplings in the disordered quasi-2-dimensional semiconductor. However, the functionality of a-SnO as a p-type semiconductor would not be degraded significantly because the isotropic Sn 5s orbital states dominate in the valence band states.