Wide-gap layered oxychalcogenide semiconductors: Materials, electronic structures and optoelectronic properties

Applying the concept of materials design for transparent conductive oxides to layeredoxychalcogenides, several p-type and n-type layered oxychalcogenides were proposed aswide-gap semiconductors and examined their basic optical and electrical properties. The layeredoxychalcogenides are composed of ionic oxide layers and covalent chalcogenide layers, whichbring wide-gap and conductive properties to these materials, respectively. The electronicstructures of the materials were examined by normal/inverse photoemission spectroscopy andenergy band calculations. The results of the examinations suggested that these materials possessunique features more than simple wide gap semiconductors. Namely, the layeredoxychalcogenides are considered to be extremely thin quantum wells composed of the oxide andchalcogenide layers or 2D chalcogenide crystals/molecules embedded in an oxide matrix.Observation of step-like absorption edges, large band gap energy and large exciton bindingenergy demonstrated these features originating from 2D density of states and quantum sizeeffects in these layered materials.