Extinction ratio improvement of an electroabsorption modulator by using Be as a p-type dopant with small diffusion coefficient

Beryllium (Be) has been applied as an acceptor in the p-type cladding layer and the contact layer of an InGaAsP-based electroabsorption modulator (EAM) fabricated by metalorganic chemical vapor deposition (MOCVD). The concentration of diffused dopants in the absorption layer of the EAM was significantly reduced by employing Be instead of zinc (Zn) which has been conventionally used as an acceptor for MOCVD-grown III–V semiconductors. Numerical simulation of the diffusion of Be and Zn in the EAM device structure showed that the diffusion of Be was dominated by interstitials with small diffusion coefficient, while the diffusion of Zn was dominated by a fast diffusion mechanism of a divacancy-related complex which was not observed in the Be-doped EAM. The measured extinction ratio of the Be-doped EAM was higher by approximately 40% than that of the Zn-doped counterpart. The improvement of the extinction ratio is due to improved uniformity of the electric field applied to the absorption layer of the EAM.