Tracking the emergence of defect in light emitting semiconductor diodes with two-photon excitation microscopy and spectral microthermography

摘要

We demonstrate a multifunctional optical technique for tracking the evolution of defects in live 605 nm LEDs. Photocurrent images, electroluminescence, and spectral reflectance maps are simultaneously acquired and utilized to evaluate LED performance at different injection currents. Free-carrier density profiles in the active region are constructed from photocurrent images that are generated via two-photon excitation (2PE) at 800 nm. A device defect is induced by electrical stress and ripples are observed in the density distribution by 2PE microscopy. The microscopic stress patterns are not revealed with linear excitation. We investigate the local thermal activity in the active region by measuring the spectral reflectance change with injection current. Spectral unmixing separates the electroluminescence and reflectance signals and high-resolution background-free thermal maps are derived to determine the device operational limits and possible connections between structural defect and thermal activity.