Long Wavelength Laser Diode Reliability and Lattice Imperfections

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Abstract
Reliable long wavelength laser diodes emitting in the 1.30−1.55 μm regime with an expected operating life greater than 25 years for optical fiber communication applications are now fabricated using a combined heavy screening and accelerated aging process. For a given laser structure, the reliability of the devices depends intricately on both the crystalline perfection of the complex buried-heteroepitaxial semiconductor structures as well as the qualities of structures external to the semiconductor, such as electrical contact, dielectric coating, bonding, and packaging structures external to the semiconductor. The former (crystalline perfection) determines the intrinsic property of the laser, while the latter qualities (electrical contact, etc.) determine the contact resistance, parasitic capacitance, heating, and mechanical and thermal stresses to which a packaged laser device is subjected during operation. Since device heating and external stresses both degrade laser performance and accelerate permanent damage—through processes such as crystalline defect formation, current leakage path development, and doping profile redistribution—a reliable laser device, therefore, requires both a perfect semiconductor structure and also a high-quality external structure. Realistically, however, this may not be easily achievable, especially when a development program is limited in resource and time. Proper choice of the critical material issues in a development process becomes crucial to the success of the program.