(Invited) Applications of Electrochemistry Toward Blue/Green and SWIR-Wavelength VCSELs

Abstract

Unlike the more established edge-emitting lasers (EELs) with a horizontal Fabry-Perot (FB) cavity, VCSELs have a vertical cavity with highly reflective top and bottom mirrors sandwiching the active region. This design enables wafer-level testing, one- and two-dimensional arrayed integration, and scalability for low- and high-power applications. VCSELs are poised to surpass EELs as a more versatile and intelligent option for semiconductor lasers in the future.Currently commercially available VCSELs only cover the red to near-infrared (NIR) range of 700-1100nm, whereas EELs offer products across a wide spectral range. The optimal active regions for blue and short-wavelength infrared (SWIR) spectra are only supported on GaN and InP substrates, respectively. Lattice-matched, epitaxial mirrors compatible with these two substrates remain major challenges. As a solution, we propose the use of electrochemistry to engineer the refractive index of the material. The innovation is based on the recognition that nanoporous (NP) semiconductor layers can be considered a nanocomposite with nanoscale voids of air uniformly dispersed in a single-crystalline semiconductor, thus rendering a unique way to control the effective optical index with a tunability that is typically un-attainable through epitaxy.We have studied the electrochemistry of semiconductors for applications in photonics, beginning with GaN and most recently with InP. In both material systems, we have discovered a selective porosification process based on the doping concentration. Due to the doping selectivity in EC etching, layers with high doping concentration will be converted to low index nanoporous material with an unprecedented tunability in the refractive index depending on the porosity. Meanwhile, the lightly doped layers remain intact. As a result, highly reflective mirrors were fabricated on GaN and InP substrates with wide stopbands. In this talk, we will provide latest updates in the VCSEL performances in the blue/green and long-wavelength region.