Transmission Cathodoluminescence

Diode lasers, light-emitting diodes (LEDS), and photodiodes are integral components of the current lightwave transmission systems. These devices are mainly based on the III-V materials systems, e.g., GaAs/GaAlAs and InP/InGaAsP. Both material and device development are recent, relative to the highly developed Si-based technology. Material defect analysis is required to evaluate and monitor material growth and device processing procedures, especially during the early stages of development. The performance and reliability of optoelectronic devices are determined by the quality of materials and fabrication processes. Threading dislocations have been shown to increase the leakage current of both InP and GaAs photodiodes;1" these dislocations are also sources of microplasmas in avalanche photodiodes.3"5 The quantum efficiency of GaP and GaAlAs:Si LEDS is strongly dependent on the dislocation 2187 density.6 ' Threading dislocations and inclusions are known sources of dark line and dark spot defects in degraded LEDS and solid-state lasers fabricated from the GaAs/GaAlAs and InP/InGaAsP materials systems.8-12 Finally, stresses from dielectric coatings are known to induce defects and accelerate device degradation.1213 Characterization techniques are required to assess the effects of growth and processing procedures on material or device quality. Because of the variety of defects, materials, and devices, a number of characterization techniques have been developed. These techniques are listed and compared in Table I.