Electroluminescence from Ge_1-ySn_y diodes with degenerate pn junctions

The light emission properties of GeSn pn diodes were investigated as a function of alloy composition and doping levels. Very sharp interfaces between contiguous ultra-highly doped p- and n-layers were obtained using in situ doping with B₂H₆ and P(SiH₃)₃ in a chemical vapor deposition environment, yielding nearly ideal model systems for systematic studies. Changes in the doping levels and layer Sn concentrations are shown to greatly affect the electroluminescence spectra. This sensitivity should make it possible to optimize the emission efficiency for these structures in the interesting quasi-direct regime, for which direct gap luminescence is observed due to the proximity of the conduction band quasi-Fermi level to the minimum of the conduction band at the center of the Brillouin zone. Such structures represent the basic building block of Ge-based electrically pumped lasers.