Impact of Ge Substrate Thicknesses and Epitaxy Growth Conditions on the Optical and Material Properties of Ge- and GaAs-Based VCSELs

A comparative study is presented on the dependence of optical and material properties of VCSELs on Ge and GaAs substrate thicknesses as well as epitaxy process conditions. It was found that adjusting the Ge substrate thickness and optimizing the epitaxy process can shift the stopband center and cavity resonance wavelength by several nanometers. Ge-based VCSELs exhibit improved epitaxial uniformity, smaller deviations from design specifications, reduced stoichiometry variations, and strain magnitudes comparable to those of GaAs-based counterparts. In the selected 46.92 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> sample area, no defects were observed in the quantum well (QW) regions of Ge-based VCSELs, and the threading dislocation density (TDD) was measured to be below 2.13×106 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup>. These results highlight the potential of Ge substrates as promising candidates for advanced VCSELs.