Monolithic integration of substrate input/output resonant photodetectors and vertical-cavity lasers

We present theoretical and experimental results on monolithically integrated through-the-substrate input/output vertical-cavity lasers (VCLs) and resonant photodetectors that are compatible with substrate-side micro optics and flip-chip bonding. The required difference in bottom mirror reflectivity between the VCL and the detector is achieved by selective oxidation of a few high Al-content AlGaAs layers in the bottom mirror for the VCL. The modeling shows that using this approach makes it possible to individually design VCLs and resonant detectors from the same epitaxial structure without compromising performance of either device. Furthermore, since the oxidized layers are placed far enough from the active region, the VCL design is very robust with respect to uncertainties in the oxidized layers. For the detectors, we expect about 60% quantum efficiency, a 6-nm full-width at half-maximum optical bandwidth, and less than 1 nm difference in operating wavelength from the VCLs. Experimentally, VCLs and adjacent detectors with integrated microlenses have a difference of less than 0.5 nm in operating wavelength. The detectors have responsivities of 0.48 A/W, corresponding to 60% quantum efficiency and 7-nm optical bandwidths. Single-mode VCL´s exhibit threshold currents as low as 135 μA while maintaining differential efficiencies above 50%. Larger multimode VCLs have differential efficiencies exceeding 70% with threshold currents of 0.5 mA