Composition, grading and doping of In1-x-yAlxGayP LED structures grown on the GaP substrate by step-wise graded InxGa1-xP buffer were investigated by employing SIMS and SEM methods. Different amount of Al precursor has been used during MOCVD growth, resulting different Al content and correspondingly different wavelength of the emitted light. The buffer comprised of eight intentionally 300 nm thick InxGa1-xP layers with step increase of In Delta x(In) approximate to 3 % toward In1-x-yAlxGayP LED layers were grown to accommodate relatively high lattice mismatch between In1-x-yAlxGayP and GaP. Vertical structure of the samples has been visualised using backscattered electron method of the SEM. From the cleaved edge of samples the layers of different composition were revealed and the thickness of In1-x-yAlxGayP and InxGa1-x-yP layers has been determined. In contrary p-n junction position was determined from SIMS depth profiling of the dopants and estimated only from secondary electron images. The compositional changes in the structures were examined using SIMS depth profiling, from which all the eight different In content steps in InxGa1-xP buffer layers were detected. Composition of the LED layers has been determined from EDS measurements and compared with SIMS depth profiles. From SIMS and EDS measurements quaternary composition of the components Al, In, P and Ga were evaluated and optimized for the growth process. (c) 2006 Elsevier B.V. All rights reserved.