A Thermomechanical Approach to the Formation of Dark Defects in High Power Laser Diodes
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1195-B02-04
A Thermomechanical Approach to the Formation of Dark Defects in High Power Laser Diodes Alonso Martín-Martín1,2, Pilar Iniguez2, Juan Jimenez1, Myriam Oudart3 and Julien Nagle4 1 GdS Optronlab, Universidad de Valladolid, Paseo de Belén 1, ed. i+d, 47011 Valladolid, Spain. 2 Dpto. de Física Teórica, Atómica y Óptica, Universidad de Valladolid, 47011 Valladolid, Spain. 3 Alcatel-Thales 3-5lab, RD 128, 91767 Palaiseau, France. 4 Thales Research and Technology (TRT), RD 128, 91767 Palaiseau, France. ABSTRACT A thermomechanical model to explain the formation of dark defects in AlGaAs high power laser bars is presented. The local heating at facet defects due to nonradiative recombination and self-absorption of photons induces thermal stresses capable of producing a local plastic deformation and subsequent degradation of the device. The output power density thresholds calculated are in agreement with the data reported in the literature for these lasers. INTRODUCTION Great efforts are devoted to improve the optical power and the reliability of high power broad area, multi-emitter laser cm-bars, in order to extend the range of applications (solid-state laser pumping, materials processing, optical communications, medical applications, printing machines…) [1,2]. The research on the degradation mechanisms of these devices is a critical matter to improve their performance and reliability. The increase of the optical power induces the heating of the active parts, quantum well (QW) and surrounding layers, especially at the mirror facet where energy losses can be the ultimate cause of the catastrophic optical damage (COD) [3,4]. COD begins by nonradiative recombination at facet defects which can transfer heat locally to the lattice increasing the local temperature at this zone of the facet with the concomitant band gap shrinkage, which enhances the laser light self-absorption; besides, nonradiative recombination can transfer energy to the surrounding lattice assisting defect formation and motion by the mechanism of recombination enhanced defect reactions (REDRs) [5]. These two processes feedback the local temperature increase during the laser operation. Finally a thermal runaway process led to the catastrophic degradation of the device. Efficient heat sinks are needed for removing the heat generated during laser operation; generally, the laser bar is soldered with the junction side down to the heat sink. This soldering introduces mechanical stresses that arise from the differences in the thermal expansion coefficients of the heat sink, the solder and the chip [6]. A model providing a comprehensive description of the laser degradation process is needed. An incomparable tool to investigate the defect signatures in degraded devices and so the main defects generated during laser operation is cathodoluminescence (CL). CL images of degraded devices unveil the presence of dark defects at the facet together with extended defects in the active layers of the laser [7]. The examination of those defects provides crucial informatio
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