In2O3 gap states in amorphous and poly-crystalline phases: Band tail and defect level characterization by subgap photocurrent spectroscopy

A nanometer-thick indium oxide (In2O3) layer is studied in terms of gap states, by means of subgap photocurrent spectroscopy. The In2O3 layer is prepared by atomic layer deposition, where its nanostructure is changed from an amorphous to poly-crystalline phase, via changing the layer thickness. Two groups of gap states are distinguished: shallow and deep levels, reflecting the valence band (VB) tail and a specific type of defects, respectively. The VB tail is clearly broadened for the amorphous phase, where the broadening is characterized by the Urbach energy, e.g., 326 ±30 meV. The deep-level defect states are recognized at ≈ 2.3 eV from the conduction band edge, with a distribution of ≲110 meV. Interestingly, the energy level and distribution are not strongly changed, regardless of an amorphous or poly-crystalline structure.