Optical and Electrical Properties of Epitaxial and Diffused GaAs Injection Lasers

GaAs injection lasers were prepared by an epitaxial solution growth method and their properties compared with those of diffused junctions. The optical gain factor β was up to a factor of 7 higher for the epitaxial diodes at 300°K. This resulted in threshold current densities as low as 26 000 A/cm2 (3.8×10−3 cm length) at 300°K. At 77°K, gain factor and loss numbers were similar for the two laser types. The spontaneous line-width of the epitaxial lasers was unusually large (∼300 Å at 77°K) and increased with decreasing junction voltage. The internal quantum efficiency of epitaxial diodes drops from 100% at 4.2°K to 40% at 300°K. The vertical beam spread was found to be between 20°–30° half-width at 77°K as well as at 300°K. Diffused diodes frequently show a delay between the current pulse and the stimulated emission of up to 30 nsec, dependent on the current value at higher temperatures. No such delay was observed in epitaxial lasers.