We report an experimental study of the band-gap photoluminescence from strain-adjusted ${\mathrm{Si}}_{\mathit{m}}$${\mathrm{Ge}}_{\mathit{n}}$ (m=9,6,3; n=6,4,2) superlattices under applied hydrostatic pressure. The strain adjustment was achieved by a thick, step-graded ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ buffer layer resulting in an improved quality of the superlattice with respect to dislocation density. The no-phonon (NP) lines shift linearly under applied hydrostatic pressure in all superlattices to lower energies. The stress dependence was modeled using an approach based on deformation potentials and effective-mass theory. Under the assumptions made a close resemblance between experiment and theory was found. From the slopes of the stress shifts and amplitudes under various pressures, further evidence is given to an earlier assignment of the NP lines as arising from band-to-band recombination.

• Received 5 August 1993

DOI:https://doi.org/10.1103/PhysRevB.49.2615