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

The role of nonradiative recombination in the degradation of InGaAsP/InP buried-heterostructure bulk lasers with semi-insulating current-blocking has been investigated by current-voltage (I-V), output power response (I-P), and differential carrier lifetime measurements. Changes in the I-P characteristic show nonradiative recombination to be main cause of degradation; internal losses having negligible influence. This was confirmed by carrier lifetime measurements, which showed the increase in the nonradiative recombination rate to be proportional to the increase in the threshold current. Other recombination processes remained unaffected. A degradation-generated increase in forward bias current below threshold was, for the first time, interpreted in terms of an equivalent circuit. Results show the rate of nonradiative recombination to increase and be proportional to results from the more laborious carrier lifetime method. Observed changes in the reverse bias characteristic are, for the first time, shown to be caused by field-assisted thermal emission from weakly interacting donor-acceptor pairs created during degradation. Pair separation is 8-10 nm. One bandgap level lies 0.36 eV from 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 interstitials with defects in the active layer.