A Cathodoluminescence Study of the Defects Created by the Degradation of High Power AlGaAs/GaAs Multiemitter Laser Bars
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1108-A06-04
A Cathodoluminescence Study of the Defects Created by the Degradation of High Power AlGaAs/GaAs Multiemitter Laser Bars A. Martín-Martín1, M. Avella1, M. P. Iñiguez2, J. Jiménez1, M. Oudart3, J. Nagle4 1 Departamento de Física de la Materia Condensada, Universidad de Valladolid, Paseo de Belén 1, ed. i+d, 47011 Valladolid, Spain 2 Departamento 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, RD 128, 91767 Palaiseau, France ABSTRACT In this work we study the defects responsible for the degradation of high power AlGaAs based laser bars. The mirror and cavity degradations are studied by spectral cathodoluminescence (CL) imaging. Following the analysis of the CL images the main defects generated during the laser operation are revealed, both facet and intracavity defects are observed. A thermomechanical model is used to describe the very beginning of the defect formation. The defects are formed by a local plastic deformation induced by local heating at defects. INTRODUCTION The analysis of the degradation mechanisms of high power multi-emitter laser bars is a key issue to improve their optical power and reliability in order to extend the range of applications of these devices [1-3]. Very high power emission is achieved with multi-emitter laser cm-bars, supplying continuous wave optical output powers up to a few hundred watts. The high power of these devices induces a significant heating of the active parts of the device, especially at the mirror facet, where the energy losses are responsible for the catastrophic optical damage (COD) [4]. One of the key issues concerns the heat removal during laser operation. Increasing the optical power demands an improvement of the mounting and cooling techniques. The laser packaging leads to thermomechanical stresses, due to the difference in the thermal expansions of the semiconductor chips, the solder, and the submount [5]. It is a general consensus that such stresses play a relevant role in the degradation mechanisms; however, there is not a clear physical picture of such role. During the laser operation, crystal defects are generated; the understanding of the nature of these defects and their formation mechanisms are crucial steps towards the fabrication of reliable devices. CL is a powerful tool to study the crystal defects generated during the laser aging, both at the mirror facet and inside the cavity. The main defects revealed by CL imaging in degraded high power laser bars can be classified as dark spot defects (DSDs) inside the cavity and at the front facet, dark line defects (DLDs) along the cavity, and the so-called V-shaped defects at the front facet [6]. The main degradation mechanisms identified by the spectral analysis of the CL are the plastic deformation associated with thermal stresses induced by local heating due to non radiative recombination and self absorption at defects in the front facet, and stress relaxation, and quant
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