Microscopic electroluminescence images of 850 nm oxide-confined VCSELs during burn-in

Abstract 850 nm vertical-cavity surface-emitting laser (VCSEL) samples with an oxide aperture of 6 µ m diameter are studied during operation by means of reverse current–voltage ( I–V) characteristics, as well as various modes of a confocal scanning optical microscope, such as reverse bias electroluminescence (ReBEL). Reverse I–V characteristics exhibit avalanche breakdown, which enables an estimation of the electric field in the active region as a function of applied bias. ReBEL emission is observed at locations where the avalanche breakthrough current has its maximum. The oxide-confined VCSELs in this study are characterized before and after high current operation. Virgin devices, where defects are absent, have a homogeneous device center in ReBEL images. Upon a short high-current burn-in, VCSELs evolved a homogeneous ring at the oxide-aperture perimeter, which is observable in ReBEL images. This ring structure decays into two point-like areas after long-term current stress. These results can be understood by local current crowding, based on device simulations, which produces highest injection current densities at the oxide aperture perimeter, where the formation of non-radiative recombination centers during accelerated aging is triggered. Microscopic ReBEL spectra unveil spectral emission portions from both active quantum wells and AlGaAs barriers. Spectrally filtered ReBEL images show identical spatial distributions of both emissions.