High-Performance O- Band Photonic Power Converters Under Non-Uniform Laser Illumination

Photonic power converters designed and fabricated at Fraunhofer ISE for operation in the O-band were measured under non-uniform 1319 nm laser illumination with five spot sizes. Two 5.4 mm2 devices were studied. The first used lattice-matched InGaAsP on an InP substrate while the second used lattice-mismatched InGaAs grown on GaAs with a step-graded metamorphic buffer. The maximum measured efficiencies were 52.9% at a laser power of 353 m W and 48.8% at 413 mW for the lattice-matched and −mismatched designs respectively. Both maximal efficiencies were measured with a spot size of 2.3 mm, the largest and most uniform laser-spot applied in this study. The devices were insensitive to the illumination uniformity for input powers < 100 mW, exhibiting a logarithmic relationship between open-circuit voltage and short-circuit current density consistent with the non-ideal diode equation. At higher powers, deviations were observed from this trend and both devices exhibited better performance for larger spot sizes. Distributed circuit modeling (DCM), which uses a two-diode model and accounts for lateral current flow and resistive losses, was used to explore the mechanisms responsible for the measured beam-size dependence. Agreement was achieved between the DCM and experimental data measured under broadband uniform illumination. Under a Gaussian laser-illumination profile, comparison between the DCM and experimental data suggested that both resistive losses and localized heating likely contributed to the performance reductions under non-uniform illumination. Better performance at higher illumination powers could be achieved by engineering a more uniform illumination profile, optimizing the front metallization, or adopting multi-junction device architectures.