A systematic study was made of the effects of Zn doping and diffusion in capped mesa buried heterostructure lasers which had been grown by means of metalorganic chemical vapor deposition. It involved varying the Zn content (7 x 1017 to 3.1 x 1018/cm3) of the p-type InP cladding layer in the base epitaxial structure, while keeping the growth conditions constant during 2 subsequent re-growth steps. Secondary ion mass spectrometry was used to make quantitative determinations of the Zn depth profiles, following re-growth, by using test sites on 50mm round wafers which contained the appropriate epitaxial layers. Clear evidence of Zn diffusion was found, such as the penetration of Zn into the active layer and the presence of inflection points (accumulation and depletion of Zn near to the p-n heterojunction) in the depth profiles. It was observed that the diffusion of Zn during the third growth step dominated the Zn profile in the base growth part of the p-type InP layer, and the final amount of Zn in this region was independent of the initial dopant level. Above a Zn threshold level of about 2.2 x 1018/cm3, the Zn diffusion increased significantly and resulted in the presence of 5 x 1018/cm3 or more of Zn in the active layer. The threshold for the onset of diffusion was found to be in accord with the substitutional-interstitial diffusion of Zn.

Zn Diffusion Behavior in InGaAsP/InP Capped Mesa Buried Heterostructures. V.Swaminathan, C.L.Reynolds, M.Geva: Applied Physics Letters, 1995, 66[20], 2685-7