Accelerated facet degradation of InGaAsP/InP double-heterostructure lasers in water

Abstract

Facet degradation of InGaAsP/InP double-heterostructure (DH) lasers in accelerating environment of water was studied from the standpoint of quantitative comparison with GaAlAs DH lasers. Facet degradation of InGaAsP/InP DH lasers proceeds by oxidation mechanism and its degradation rate is 2–3 orders below that of GaAlAs DH lasers. The difference of oxidation behavior between InGaAsP/InP and GaAlAs DH lasers was examined by using large wafers having the same composition as lasers. The following results were obtained: the oxidation proceeds with the inward diffusion of molecule water through the oxide film, the oxidation rate of n-InP is more than two orders of magnitude lower than that of n-GaAs, In oxide and P oxide were uniformly distributed in the depth profile of the oxide for InP and InGaAsP, and As oxide has the abnormally depleted distribution in the front layer of the oxide for GaAs and GaAlAs. The facet degradation rate is influenced by some experimental factors, i.e., the optical output power, the injection current in dc-biased experiment, and the water temperature in unbiased experiment. To explain the degradation behavior caused in dc-biased and unbiased experiment under identical mechanism, we attempted to evaluate the degradation rate as a function of the facet temperature; the optical output power and the injection current in dc-biased experiment were assumed to contribute to the supplying source of carriers, which rapidly recombine nonradiatively, raise the facet temperature, and finally promote the diffusion of molecule water through oxides and the reaction rate at oxide-facet interface. Combining these results with the fact that the oxidation rate varies in proportion to the partial pressure of a molecule water in the operation environment, we estimated the degradation rate of InGaAsP/InP DH lasers operated under 6.7 mW/μm2 at 70 °C in a nearly dry nitrogen environment (relative humidity of 1–10%).