Differential carrier lifetime as a function of subthreshold bias current in 1.3 m bulk active lasers is obtained by measurement of small‐signal modulation of amplified spontaneous emission together with careful characterization of frequency‐ and current‐dependent device impedance. The strong influence of rapidly varying device impedance upon these measurements is illustrated. In contrast to other studies, neither saturation of differential lifetime at low currents nor linear dependence of spontaneous emission on carrier density is observed. Recombination parameters, fit from current versus carrier density, along with consistent fits of spontaneous emission versus carrier density, are presented. ©1995 American Institute of Physics.