Near band-edge field-dependent absorption coefficient and refractive indexdetermined by photocurrent and transmittance measurements

A technique is proposed for the extraction of precise values of field-depen dent absorption coefficient alpha and refractive index n from photocurrent and transmittance measurements of optical modulator structures. The techniq ue uses approximate results of alpha and n extracted from a simplified devi ce as the initial input into an iterative procedure that utilizes the consi stency between alpha and n to obtain successively better estimates of these parameters. The technique was applied to results that were measured experi mentally, and we verified the accuracy by using synthetic data. Errors caus ed by measurement inaccuracy are also investigated. It is shown that the ab sorption coefficient has a modest sensitivity whereas the refractive index is insensitive to these errors. (C) 1999 Optical Society of America. OCIS c odes: 120.4530, 230.5590, 230.2090, 230.4110, 190.5970, 310.6860.