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

TL;DR

This study compares how Ge and GaAs substrates and epitaxy conditions affect VCSEL properties, showing Ge substrates can improve uniformity, reduce defects, and tune optical characteristics, indicating their potential for advanced VCSELs.

Contribution

It provides a detailed comparison of Ge and GaAs substrates and epitaxy conditions, revealing Ge's advantages in VCSEL performance and fabrication.

Findings

Ge substrate thickness influences stopband and resonance wavelengths.

Ge-based VCSELs show higher epitaxial uniformity and fewer defects.

Threading dislocation density in Ge VCSELs is below 2.13e6 per cm².

Abstract

We present a comparative study of the optical and material property dependences of VCSELs on Ge or GaAs substrate thicknesses and 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 square micron 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 2.13e6 per square cm. These results highlight the potential of Ge substrates as promising candidates for advanced VCSELs.