Abstract
Measurements are presented of the temperature dependence of the differential quantum efficiency ηd and threshold current density Jth of 1.6 µm In1-xGaxAsyP1-y lasers. The observed sharp decrease in ηd near room temperature is interpreted as due to absorption associated with transitions of electrons from the split-off valence band into holes injected into and thermally generated within the heavy hole valence band. Preliminary calculations using conventional laser theory predict a temperature variation corresponding to T0≃145 K. This together with the influence of ηd, appears to be sufficient to explain most of the observed temperature variation of Jth.