Investigating the optical degradation of InAs quantum dot lasers on silicon through combined electro-optical characterization and gain measurements

We evaluate the degradation of 1.3 mu m InAs quantum-dot laser diodes epitaxially grown on silicon. For the first time, the optical degradation mechanisms are investigated by evaluating the variations in the gain spectra measured during a constant-current stress test. Remarkably, the gain spectra showed that the reduction in the peak modal gain is dominant compared to the increase in internal absorption losses. Moreover, the increase in threshold current (Ith) induced by stress was found to be correlated to the gain peak reduction. This experimental evidence was investigated by modeling the peak modal gain variation through a rate equation model. The outcome of this activity confirms that the variation of both Ith and modal gain can be explained solely by the reduction in injection efficiency, caused by the stress-induced increase in non-radiative recombination centers (NRRCs). This result supports previous findings on the optical degradation of 1.3 mu m InAs quantum dot lasers, which is ultimately ascribed to the increase in concentration of NRRCs within the active region.