Excitonic line broadening in PbSrSe thin films grown by molecular beam epitaxy

Pb 1−x Sr x Se thin films grown by molecular beam epitaxy have been investigated by x-ray diffraction and temperature-dependent photoluminescence measurements with the Sr composition as high as 0.276. Temperature and composition dependent excitonic line broadening effects in PbSrSe thin films have been studied on the basis of the proposed theoretical models and the experimentally obtained lattice constant, excitonic energy gap and effective mass as a function of the alloy composition. The exciton-longitudinal optical phonon coupling model has been employed successfully for PbSrSe with a coupling strength of 51.0 meV, which can be well explained by the proposed theoretical approach. The lattice deformation may have played a key role in the composition dependent broadening in PbSrSe at low temperature, rather than the normally observed alloy disorder effect in III–V and II–VI semiconductor materials.