Investigation of the direct band gaps in Ge1-xSnx alloys with strain control by photoreflectance spectroscopy

Unstrained and compressive-strained Ge1-xSnx alloys were grown on InGaAs buffer layers by molecular beam epitaxy. Photoreflectance at room temperature determines the direct bandgap energies of Ge1-xSnx alloys from the maxima of the light-and heavy-hole bands to the bottom of C valley. The lowest transition energies from photoreflectance are consistent with the energies derived from photoluminescence. The calculated bowing parameter is 2.42 +/- 0.04 eV for the direct band gap of Ge1-xSnx alloys. The dilational and shear deformation potentials of the direct band gap are -11.04 +/- 1.41 eV and -4.07 +/- 0.91 eV, respectively. These basic material parameters are important in designing optoelectronic devices based on Ge1-xSnx alloys. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3692735]