Role of nonradiative recombination in the degradation of InGaAsP/InP-basedbulk lasers

The role of nonradiative recombination in the degradation of InGaAsP/InP bu ried-heterostructure bulk lasers with semi-insulating current-blocking has been investigated by current-voltage (I-V), output power response (I-P), an d differential carrier lifetime measurements, Changes in the I-P characteri stic show nonradiative recombination to be main cause of degradation; inter nal losses having negligible influence, This was confirmed by carrier lifet ime measurements, which showed the increase in the nonradiative recombinati on rate to be proportional to the increase in the threshold current. Other recombination processes remained unaffected. A degradation-generated increa se in forward bias current below threshold was, for the first time, interpr eted in terms of an equivalent circuit, Results show the rate of nonradiati ve recombination to increase and be proportional to results from the more l aborious carrier lifetime method. Observed changes in the reverse bias char acteristic are, for the first time, shown to be caused by field-assisted th ermal emission from weakly interacting donor-acceptor pairs created during degradation. Pair separation is 8-10 nm; One bandgap level lies 0.36 eV fro m one edge and the other close to the other edge. A decrease in the series resistance showed out-diffusion of interstitial Zn donors from the p-InP:Zn cladding layer to take place. Pairs are created by interaction of Zn inter stitials with defects in the active layer.