Photoluminescence processes in Si1−xGex/Si disordered superlattices grown on Si(001) substrate

Abstract

Photoluminescence (PL) properties of Si1−xGex/Si disordered superlattices (d-SLs) are investigated. Two types of d-SLs with various Ge compositions (x<0.55) and various averaged superlattice periods are grown for experiments. The PL intensity ratio I(d-SL)/I(o-SL), the redshift energy, and the characteristic temperature T0 are strongly affected with Ge composition variation but not with averaged superlattice period variation. Small improvement of the ratio of no-phonon (NP)/TO-phonon assisted PL intensities by the Si1−xGex/Si disordered structure suggests that the disorder effect on the increase in NP recombination probability is not as large as expected by other disordered superlattices. The reasons are (1) the weak electron localization and (2) the difference in the directions between momentum ambiguity caused by the localization and the momentum required for recombination. Thus, improved PL properties for SiGe/Si d-SL are mainly owing to the strong hole localization by increased valence-band offset.