Improved Room-Temperature Laser Performance in GaAs Diffused-Junction Diodes

Significant reduction in room-temperature laser threshold and stimulated emission delay is obtained in diodes made from zinc-diffused wafers (850°C—3 hours in Zn–As atmosphere) if the single-diffusion process is modified with multiple diffusions, or, more controllably, by the addition of a post-annealing step (∼900°C in As atmosphere) following the initial diffusion. Incremental sheet-conductivity measurements show the zinc concentration gradient is reduced and etching studies show a lowered dislocation density near the junction after annealing. Without an annealing step, diffused-junction diodes show consistently larger emission delays (observed above ∼200°K) than epitaxial-junction diodes made from the same n-type substrates. The deliberate in-diffusion of high copper concentrations causes large delays even at 77°K. However, copper is probably not the center causing delays near room temperature because a mass spectrographic analysis did not reveal higher copper concentrations in diffused-junction wafers than in epitaxial-junction wafers when there was no deliberate copper doping.