Thermomechanical modelling of high power laser diode degradation
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Thermomechanical modelling of high power laser diode degradation J. Anaya1, A.Martin-Martin1, J. Souto1, P.Iñiguez2, J. Jimenez1 1 Física de la Materia Condensada, Universidad de Valladolid, Paseo de Belén 1, ed.i+d, 47011 Valladolid, Spain 2 Física Teórica, Atómica y Optica, Universidad de Valladolid, 47011 Valladolid, Spain. ABSTRACT Catastrophic degradation of high power laser diodes is due to the generation of extended defects during the laser operation. The stress necessary for is induced by temperature gradients generated by local enhancement of the temperature due to non radiative recombination and subsequent laser self absorption. The thermal stresses induced by such temperature gradient are calculated using finite element methods, showing that the yield strength can be surpassed. The thermal conductivity of the laser structure is shown to play a relevant role in the process. INTRODUCTION The understanding of the degradation mechanisms of high power laser diodes is critical to improve their power and reliability. The degradation occurs because of the generation of crystal defects during the laser operation (1). The identification of these defects, as well as the understanding of the causes that contribute to their formation, are crucial for the improvement of the technological processes leading to the fabrication of reliable laser diode devices. We focus here on high power AlGaAs/GaAs based laser bars (808 nm); however, our analysis can be extended to other laser structures without loss of generality. Among the degradation modes of laser diodes, the catastrophic optical damage (COD) is associated with the generation and propagation of extended defects during the laser operation (2). The high output power can induce a non negligible heating of the active parts, quantum well (QW) and surrounding layers, particularly at the facet mirrors, where energy losses take place, producing a degradation of the output power, and eventually being responsible of COD (3,4). The observation of the crystal damage resulting of the degradation suggests that degradation is a local event, which the propagation is feedback by laser light self-absorption, as far as the laser is still lasing (2). The formation of extended defects points to bond breaking as the mechanism responsible for laser degradation. It is well known that the presence of dislocations in the active zone of the laser leads to irreversible damage, which is usually described by a thermal run away process (4). Extended defects generated during the fabrication process, usually are responsible for infant mortality. However, defects generated during the normal operation of the laser are hazardous, because of the difficult to screen them. It is important to understand how those defects can be formed during the normal operation of the laser. We present herein a thermo-mechanical analysis where we evidence that the conditions for dislocation generation in the active part of the laser can be achieved under laser operation provided that some factors contribute additively to i
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