Impact of gallium concentration in the gas phase on composition of InGaAsN alloys grown by AP-MOVPE correlated with their structural and optical properties

This work presents the epitaxial growth and material properties of InGaAsN epilayers obtained by atmospheric pressure metal organic vapour phase epitaxy. The main goal was to obtain InGaAsN quaternary alloys lattice-matched to GaAs in order to apply them as an intrinsic thick absorber in p-i-n solar cells. It allows improvement of their photovoltaic parameters (e.g. short circuit current, open circuit voltage) by reducing the density of misfit dislocations. To overcome the main difficulties connected with achieving InGaAsN composition with In/N ratio of ~ 3, which guarantees a lattice matching to GaAs, epitaxial processes were carried out with different concentration of gallium source in the gas phase. Diffraction curves, measured using HRXRD, indicated that the main aim of this work was achieved for the gas molar ratio Ga/(Ga + In) = 0.935. The optical quality and surface morphology of the investigated structures examined by PL, CER and AFM methods are also presented and discussed.