Facet degradations in Ga1−xAlxAs/Ga1−yAlyAs double-heterostructure lasers

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Abstract
Degradation phenomena in Ga1−xAlxAs/Ga1−yAlyAs double‐heterostructure lasers with AlAs mole fractions x of 0–0.17 in the active layer have been investigated. Degradation rate was found to markedly depend upon x and is a minimum value at x = 0.08. It is shown that the degradation in the lasers with x below 0.08 is primarily caused by the dark defects formation in the vicinity of the mirror surfaces, which is suppressed with increasing x. The degradation in the region of x = 0.08–0.17 results from the facet oxidation, which is enhanced with increasing x. This degradation was found to be affected by the humidity of the operating ambient and was effectively suppressed with the Al2O3 facet coatings. In particular, the long‐term degradation in the lasers with x = 0.08 was suppressed with increasing the humidity. Auger analysis revealed that the native oxide formed at the facet was only partially oxidized and the enhanced oxidation for larger x had its origin in the initial stage of oxidation, where the faster oxidation rate of Al than that of Ga enhanced the oxidation. In addition, oxidation is diffusion controlled in the oxide after more than 102‐Å thick oxide is formed.