Determination of the refractive index of InGaAsP epitaxial layers by mode line luminescence spectroscopy

A new method of detecting optical waveguide modes of semiconductor epitaxial layers is presented. The modes are excited by photoluminescence and coupled out of the semiconductor wafer by a grating etched on the surface of the guiding layer. As a consequence of this coupling, the spectrum of optical emission from the sample at fixed angles has "mode lines" superimposed on the spontaneous emission spectrum. This method is used to measure the refractive indexes of eight InGaAsP layers of different compositions. These data together with published data for the refractive index of InP were fit with a two-oscillator model to yield an algebraic description of the refractive index of the InGaAsP/InP system. The method was also used to measure the change in mode index of a laser in going from low current up to threshold. The observed change was measured to be -0.023 ± 0.006.