Paper EH-WeM2
Atomic Structure and Intrinsic Electronic States of the In₂O₃(111) surface

Wednesday, December 10, 2014, 8:20 am, Room Lehua

Indium oxide as transparent semiconductor is one of the most promising materials for contact layers in photovoltaic applications. Neverthless, due to the delicate fabrication process for single crystals only a few intrinsic properties are known about In₂O₃, yet. Especially the storage under air conditions may influence the surface properties. Hence it is hard to decide, which properties are intrinsic and which ones are influenced by physisorbed and/or chemisorbed atoms and molecules from the ambient air.

In this contribution for the first time we studied high quality single crystals at their freshly UHV-cleaved (111) surfaces by scanning tunneling microscopy (STM) and spectroscopy (STS). From these investigations we achieve knowledge about the atomic configuration at the surface. This configuration fits well with recent density functional theory calculations, and indicate a local charge enhancement within the surface unit cell. Furthermore, STS reveals intrinsic electronic sturface states within the fundamental band gap. The Fermi level is also enegetically located within the fundamental bulk band gap, which leads to the assumption that previously reported electron accumulation at this surface is not an intrinsic property, but related to extrinsic effects, such as e.g., non-stoichiometric material reorganization. After oxidation of the In₂O₃(111) surfaces outside the UHV their structural as well as their electronic properties look quite different: astonishingly both show much more metallic bevahiour as the freshly cleaved ones kept under UHV-conditions. The processes leading to such an behaviour are still under discussions, but the data fits much better to previous observations.