Indium incorporation in quaternary In_x Al_y Ga_1-x-y N for UVB-LEDs

Consistent studies of the quaternary composition are rare as it is impossible to fully determine the quaternary composition by X-ray diffraction or deduce it from that of ternary alloys. In this paper we determined the quaternary composition by wavelength dispersive X-ray spectroscopy of In_x Al_y layers grown by metal organic vapor phase epitaxy. Further insights explaining the peculiarities of In_x Al_y Ga_1-x-yN growth in a showerhead reactor were gained by simulations of the precursor decomposition, gas phase adduct formation and indium incorporation including desorption. The measurements and simulations agree very well showing that the indium incorporation in a range from 0% to 2% is limited by desorption which is enhanced by the compressive strain to the relaxed Al_0.5Ga_0.5N buffer layer as well as indium incorporation into AlN particles forming in the gas phase. Utilizing In_x Al_y Ga_1-x-yN layers containing 2% of indium for multiple quantum wells (MQWs), it was possible to show an almost five times higher photoluminescence intensity of InAlGaN MQWs in comparison to AlGaN MQWs.