Aging studies and failure analysis of laser diodes

Semiconductor lasers are important for many applications such as material processing, medical surgery, pumping of solid-state lasers and fiber lasers, and space applications. Many of these applications require high reliability and predictability of the lifetime due to the expense and/or difficulties in accessing their installation locations in environments like undersea fiber cables or satellite laser terminals.

Cathodoluminescence (CL) analysis is useful to reveal defects that nucleate during the useable life of a laser diode, how these evolve under further operation, plus the type and location of defects that can lead to the device failure.

As an example, CL images of three different broad area laser diodes (50 µm stripe width and 1.5 mm resonator length) at different stages of lifetime testing are shown below. The laser diodes consist of a GaAsP/AlGaAs single quantum well embedded in a 2 µm thick AlGaAs waveguide structure. The images show example images of laser diodes that exhibit (a) gradual degradation, (b) freak (early) failure, and (c) sudden failure after gradual degradation. During extended lifetime testing, an increasing concentration of dark spots can be observed from a CL image (e.g., images a and c). The dark spot contrast originates from newly nucleated dislocation loops, and the dislocation loop concentration correlates well with a gradual degradation in device performance, e.g., need for higher drive currents to maintain a constant output power. However, while laser diodes exhibit only these dark spots, catastrophic failure is avoided. In devices that exhibited catastrophic failures (b and c) you can observe dark lines through the laser stripe. These dark lines are extended dislocations formed by glide and climb processes of dislocation loops. The suddenly failed device (c) indicates dark lines running in [110] along the laser stripe, and in [100] directions, latter inclined 45° towards the laser stripe.

Images courtesy of Dr. U. Zeimer, Ferdinand-Braun-Institut, Berlin.