Abstract
High power semiconductor laser diodes are finding increasing applications in diverse areas such as the biomedical field, materials processing, cosmetics, etc. Dissimilar materials integration and thermal management are some of the primary challenges in the fabrication and packaging of reliable laser diode systems. For example, in a specific case, a high power diode must be mounted with its epitaxy-side down, so as to achieve efficient heat transfer. The device and package junction, particularly the die attach interface, is desired to be void-free (i.e., micro-defect free), stress-managed, and contamination-free for uniform optical delivery and reliable optical alignment. Soft solders used in optoelectronic applications are typically subjected to extreme service conditions that may exceed two-thirds of the melting point. As a result, it is expected that the solder microstructure will be metastable and subjected to nearly constant modification during processing and device operation. In this study, we investigated high power laser diode packages aged under various conditions. Die attach interface, device stress, and microscopic defect analyses were carried out using primarily metallography, scanning electron microscopy (SEM), scanning acoustic microscopy, and micro-Raman spectroscopy. It was observed that the intermetallic compounds and microscopic physical defects at the die attach interface are detrimental to transient heat transfer, and thus, overall package reliability. Further, accurate device modeling can be used to assist in the overall understanding of the effect of packaging-induced stress on the performance and reliability of semiconductor lasers. The purpose of this modeling work was to better understand the interplay between electrical, optical, mechanical, and thermal effects in the operation of laser diodes. Micro-Raman spectroscopy was employed to explore the degradation of high power lasers due to mechanical stresses that appear in an active region of the diode during its growth, packaging, and operation. Using micro-Raman spectroscopy, we found that, although stress increases with aging, the shape of the stress profile and the strength changes randomly from one active region of the diode to another.
A Realization of Stabilizing the Output Light Power from a Laser Diode: A Practical Approach
