Determination of the indirect bandgap of lattice-matched SiGeSn on Ge

The first experimental results for the indirect bandgap of SiGeSn, lattice-matched on Ge are reported. The necessary condition for lattice-matching on Ge is a constant ratio of Si/Sn = 3.67. Thus, the investigated composition range is cSn={5.0,7.5,10.0}% and precisely investigated using secondary ion mass spectroscopy. The bandgap determination is based on the extraction of the built-in voltage of a SiGeSn pn++ junction utilizing the so-called capacitance-voltage intercept method. Detailed calculations of the band diagram of the pn++ junction to be investigated, including first level approximations for the effective density of states in the valence and conduction band were performed. The results show that the composition of the alloy strongly influences its bandgap and is Eg,SiGeSnL={0.588,0.704,0.413}eV, respectively.