Molecular Beam Epitaxy of Ge-VCSELs
Résumé
Vertical-cavity surface-emitting laser (VCSEL) structures emitting near 940 nm were grown by solid source molecular beam epitaxy (MBE) on GaAs/Ge(001) wafer templates grown by MOVPE. The epitaxial design comprised 35-pairs n-doped and 17-pairs p-doped Al 0.9 Ga 0.1 As/GaAs Distributed Bragg reflectors (DBRs), three In 0.1 Ga 0.9 As quantum wells, and an Al 0.98 Ga 0.02 As layer for lateral oxidation. In-situ growth monitoring methods were employed, namelymultispectral reflectometry, and magnification-inferred curvature imaging [1] for real-time stress analysis. Curvature measurements revealed progressive accumulated compressive stress with some indication of partial relaxation, while optical reflectometry data confirmed the good control of both the stopband center wavelength and the VCSEL cavity resonance. Post-growth reflectivity measurements showed a stopband centered at 942.7 nm with a bandwidth of 93.6 nm and cavity resonance at 944.21±1.15 nm over the 4" wafer. Atomic force microscopy revealed a continuous surface morphology without cracks over a 10x10 µm 2 surface. Fabricated devices with mesa diameters of 35-40 μm, corresponding to oxide apertures of approximately 11-16 μm, exhibited room-temperature lasing under continuous-wave bias with threshold currents below 3 mA. To the best of our knowledge, this is the first demonstration of monolithically integrated 940 nm VCSELs grown on Ge substrates by MBE, since all the work on AlGaAs VCSELs on Ge has to date been carried out using MOVPE [2-5]. These results confirm the viability of MBE-grown VCSELs on Ge, and the advantages of in-situ control tools for understanding growth-related phenomena and achieving the target specifications for the component.
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