Substitutional Donors and Core Excitons in Many-Valley Semiconductors

Abstract

The shallow-deep instability of substitutional donors and core excitons is discussed, with inclusion of all intervalley interactions. Shallow levels result in Si for a screened point-charge potential, because intervalley overlap and kinetic energy balance the potential-energy terms, which are severely reduced, at substitutional sites, by umklapp effects. Contrary to recent claims based on consideration of potential energy only, many-valley interactions cannot therefore be invoked to predict deep core-exciton levels in Si.