Effect of antimony doping on the energy of optical transitions in n-Ge layers grown on Si (001) and Ge (001) substrates

Abstract

Comparative studies of the bandgap narrowing in antimony doped Ge layers grown on Si(001) and Ge(001) substrates are reported. The doping level in Ge:Sb layers was varied in such a way as to obtain structures with both full and partial electrical activation of the impurity atoms. It was shown that the direct bandgap narrowing as a function of electron concentration can be fitted rather well by a root power dependence in Ge layers grown on both types of substrates. Taking into account the doping-induced deformation of Ge lattices and a careful determination of electron concentration made it possible to accurately distinguish the “structural” contribution to the bandgap narrowing caused by the embedding of large Sb atoms into the Ge matrix and the “electrical” one caused by the interaction of charge carriers. The presented results shed light on some optical properties of heavily and ultra-heavily doped n-Ge and, thus, can be useful for the development of Ge-based electronic or photonic devices.