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 and fiber lasers, and space applications. Many of these applications require high reliability and predictability of 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 for revealing defects that nucleate during a laser diode's useful life, how these evolve under further operation, and the type and location of defects that can lead to device failure.
For 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 comprise 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., the need for higher drive currents to maintain a constant output power. However, while laser diodes exhibit only these dark spots, catastrophic failure is avoided. Dark lines can be observed through the laser stripe in devices that exhibited catastrophic failures (b and c). 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, the latter inclined 45° towards the laser stripe.
