ELLIPSOMETRIC DETERMINATION OF THICKNESS AND REFRACTIVE-INDEX AT 1.3-MU, 1.55-MU, AND 1.7-MU-M FOR IN(1-X)GAXASYP(1-Y) FILMS ON INP

There is a definite need for accurate, but simple techniques for evaluation of refractive index and thickness of epitaxial In(1-x)GaxAsyP(1-y) films on InP. By ellipsometry, one can obtain these quantities for a transparent film on a substrate by a single measurement. We have calculated the ellipsometric angles PSI and DELTA for an In(1-x)GaxAsyP(1-y) film on InP at lambda = 1.3, 1.55, and 1.7 mum to determine the best experimental conditions. A 1 nm thick oxide layer on the top of the quaternary was found not to affect the PSI and DELTA at these wavelengths in a significant way. Futhermore, by studying the relative error in the refractive index and the thickness versus the error in the angle of incidence, we could deduce that at the optimum experimental conditions one can obtain the refractive index and the thickness with a 5% precision or better using ellipsometry. We have also measured the refractive index and the thickness by null ellipsometry for several In(1-x)GaxAsyP(1-y) films with different composition grown by metal organic vapor phase epitaxy on InP substrates. The refractive index data agree well with those obtained by other techniques as reported in literature and the thicknesses agree within the experimental precision with the nominal thickness obtained by the growth conditions.