(Invited) Universal Alignment of Surface and Bulk Oxygen Levels in Semiconductors

Abstract

Lattices of most semiconductors have a large density of intrinsic and extrinsic defects which gives rise to effects such as surface Fermi level (EF) pinning, dopant compensation, asymmetrical p versus n-doping, and device degradation. Oxygen and hydrogen are the two most important impurities in semiconductors because of their ubiquitous presence in growth and device processing environments and consequently their incorporation strongly influences electronic and electrical properties. Therefore, a deeper understanding of the interaction of these species with the semiconductor surface and bulk defects is necessary for enabling the development of devices based on them such as photovoltaic and photocatalytic systems, fuel cells, and many others. Analysis of the reported surface work function values and the substitutional bulk O-defect energies show that the surface Fermi level of position in a broad range of group IV, III-V, II-VI, and I-III-VI2 semiconductors with physisorbed O2 lies universally at approximately -5.1 eV below the vacuum level. Similarly, results show that the energy of the bulk substitutional O-related amphoteric defects incorporated during crystal growth also has a universal energy of ~ -5.0 eV with respect to the vacuum level for most of the investigated semiconductors. It is shown that the process of ‘surface transfer doping’ that involves an adsorbed nanoscale water film on the semiconductor surface is likely responsible for the universal alignment of oxygen levels. Figure 1