Defects and degradation of InGa(Al)As/GaAs high-power diode lasers

Abstract

High power diode lasers are mainly used for applications such as pumping of solid state lasers, direct material processing (i.e. welding, soldering, hardening, annealing) and printing. The outstanding characteristics of diode lasers are their compactness, their high efficiency and their reliability accompanied by a long lifetime. Since high power diode lasers are composed of an array of single emitters (multi-stripe or broad area) their lifetimes can widely differ from those of the corresponding single emitters. The lifetime of high power diode lasers depends on the driving current and the cooling temperature they are run with. Their degradation is caused by different degradation mechanisms which have not been definitively clarified up to now. Defects and degradation of InGa(Al)As/GaAs DQW diode laser bars mounted on copper micro channel heat sinks were investigated. The analytical techniques used for this investigation are optical microscopy, scanning electron microscopy, white light interference microscopy. The high power diode lasers were investigatively accompanied through the different phases of their setup process (i.e. mounting, characterization and burn-in). Afterwards a long-term lifetest was performed. The influence of a raised current and a raised cooling temperature on their degradation was investigated respectively. Changes in surface morphology and surface composition of the facets were detected as well as changes in the threshold current, slope efficiency and emission spectrum. Due to the degradation the threshold current increases and the slope efficiency decreases while the emission wavelengths are shifted to higher values showing a broadened spectral width. Formation of micro cracks and dislocations through the facets was also observed. The influence of these changes on performance and lifetime of the high power diode lasers will be discussed.