Abstract
We investigated the threshold current, Ith, and its temperature dependence, To(Ith), for 1.3μm and 1.5μm InGaAsP) based lasers for 77K<T<400K and considered the temperature variation of the radiative current, To(lRad). Below a ‘breakpoint’ temperature, TB, both Ith and To(Ith) are dominated by radiative-recombination where Ithcn2 (n is the carrier density) and To(Ith)=To(lRad)=T. Above TB, To(Ith) decreases strongly and by room temperature To(Ith)=50-60K while To(IRad) remains ~T (2/3T for bulk devices). Furthermore, Ithn3 consistent with a dominant non-radiative Auger-recombination process, amounting to 80%Ith in 1.5 μm devices and up to 50%Ith in 1.3μm devices. These results are consistent with the pressure dependence of Ith which decreases with increasing pressure due to the reduction of Auger-recombination with increasing band gap. 1.5μm devices show a stronger decrease than 1.3μm devices. We conclude that a direct Auger-recombination process producing ‘hot-holes’ (d-CHSH) is chiefly responsible for the high temperature sensitivity of these devices. Above room temperature, we observe a further decrease in To(Ith) which, from measurements of the temperature variation of the differential quantum efficiency, we attribute to an increase in optical loss, ai. For the 1.3μm devices, we also find that the n dependence of Ith increases above 3. This, we suggest, is due to spill-over of holes resulting in both non-radiative mono-molecular recombination and inter-valence band absorption in the barrier/SCH regions. This explains why ai is relatively high in the 1.3μm devices. AlGalnAs-based 1.3μm lasers show a lower temperature dependence than InGaAsP-based devices. At room temperature To(Ith)~100K where non-radiative current accounts for only -25% Ith. We additionally observe a high TB=220K and for the first time, measure an increase in Ith with pressure for a 1.3μm laser. These results are consistent with a dominant radiative current at room temperature and explain the reduced temperature sensitivity of AlGalnAs-based 1.3μm devices compared to conventional InGaAsP-based devices.