Optical and electrical properties of epitaxial and diffused GaAs injection lasers

GaAs injection lasers were prepared by an epitaxial solution growth method. Their electrical and optical properties are compared with those of diffused junctions. At high temperatures the laser properties of the two types of junctions were quite different. The optical gain factor β was as much as 6.7 times higher for the epitaxial diodes at 300°K. This resulted in a reduction of the threshold current density jt relative to the values for diffused diodes. Threshold current densities as low as 26,000 amp/cm²were measured for epitaxial lasers ( cm length) at 300°K. At low temperatures (77°K) gain factor and loss numbers had similar values for the two laser types. The spontaneous linewidth of the epitaxial lasers was unusually large (∼ 300 Å at 77°K) and increased with decreasing junction voltage. The variation of spontaneous light intensity and diode current with voltage will be discussed in view of tunneling and thermal excitation across the junction barrier. The vertical beam spread was found to be between 20-30 degrees half width at 77°K and at 300°K. At higher temperatures diffused diodes frequently show as much as a 35 ns delay between the current pulse and the stimulated emission dependent on the current value. No such delay was observed in epitaxial lasers, and their emission spectra did not show any low energy emission lines.