Zn diffusion behavior in InGaAsP/InP capped mesa buried heterostructures

Abstract

A systematic study of the effects of Zn doping and diffusion in InGaAsP/InP capped mesa buried heterostructure lasers grown by metalorganic chemical vapor deposition was carried out. It consisted of varying the Zn doping of the p-InP cladding layer in the base epitaxial structure over the range (0.7–3.1)×1018 cm−3 and keeping the growth conditions in two subsequent regrowth steps the same. Secondary ion mass spectrometry was employed for a quantitative determination of the Zn depth profiles following regrowth using test sites on the 50 mm round wafers that contained the appropriate epitaxial layers. Clear evidence of Zn diffusion such as the penetration of Zn into the active layer and the presence of inflection points (accumulation and depletion of Zn near the p-n heterojunction) was illustrated in the depth profiles. It was observed that the diffusion of Zn during the third growth dominated the Zn profile in the base growth part of the p-InP layer and the final amount of Zn in this region was independent of the initial doping level. Above a Zn threshold level of ≊2.2×1018 cm−3, Zn diffusion increased significantly resulting in 5×1018/cm−3 or greater Zn in the active layer. The threshold for the onset of diffusion was found to be in accordance with the substitutional-interstitial diffusion of Zn.