Temperature, stress, disorder and crystallization effects in laser diodes: Measurements and impacts

Abstract

This paper reviews extensive Raman scattering, reflectance modulation and luminescence microprobe measurements made on GaInP/AlGaInP, GaAs/AlGaAs and InGaAs/AlGaAs ridge quantum well lasers to investigate (1) laser operating temperatures, (2) built-in mechanical stress, (3) atomic disorder in mirror facets, (4) Si recrystallization effects in mirror coatings, and (5) correlations of these parameters with laser performance and reliability data. Mirror temperatures have been found to depend sensitively on mirror treatment, mirror structure design, the geometry of a deposited heat spreader, the type of coupling of the laser to a heat sink, the number of active quantum wells, the type of cladding layer, and the strength of lattice disorder at the mirror surfaces. Axial temperatures drop from the hot mirror side along the cavity to low constant values within typically 10 μm. Degradation processes have been observed in real time by continuously monitoring the mirror temperature. Dark line defects formed during laser operation exhibit a temperature gradually increasing with time. The mirrors suffer catastrophic optical damage within seconds after having reached a critical temperature. Temperature maps show a striking localized hot spot within the optical near-field pattern. Strong structural and compositional lattice disorder have been identified as potential root causes of strong mirror heating. Disorder strongly suppresses the catastrophic optical mirror damage power limit. Ridge waveguide lasers show a characteristic camel hump-like stress profile, i.e. high compressive strain levels of up to 5 kbar near the ridge slopes and reduced compressive stress or even low tensile stress fields towards the ridge center. The measured stress fields affect the formation of defects and the optical near-field pattern. Ion-beam deposited amorphous Si layers in mirror coating stacks rapidly recrystallize under high power exposure. This reduces the reflectivity of the coating and increases the transmitted power. Model experiments demonstrate that the recrystallization can modify the effective kink-free optical output power. ©2004 Copyright SPIE - The International Society for Optical Engineering.