Effect of thermal carrier spreading on the temperature dependence of threshold current in InP quantum dot lasers

the magnitude of the change in threshold current with temperature in InP quantum dot lasers caused by the distribution of carriers among dot states is quantified and demonstrated. Samples with differing distributions of allowed states, as assessed using absorption spectra and achieved by varying the composition of the quantum well above each layer of quantum dots, are affected differently by this thermal broadening although the underlying mechanism is the same. This difference is shown to be a result of different optical loss and the different gain magnitude achieved at a similar inversion level in the different samples. Uncoated, cleaved facet Fabry-Perot lasers with 2 mm long cavities are demonstrated with a threshold current density of 138 Acm(-2) at 300 K that increases to 235 Acm(-2) at 350 K (77 degrees C).