Photoluminescence characteristics and pit formation of InGaN/GaN quantum-well structures grown on sapphire substrates by low-pressure metalorganic vapor phase epitaxy

We have examined how a growth interruption, caused by closing group-III sou rces, affects the crystalline quality of InGaN/GaN quantum-well (QW) struct ures grown by metalorganic vapor phase epitaxy. The QW samples were charact erized by their photoluminescence (PL), and by atomic force microscopy (AFM ), transmission electron microscopy (TEM), and energy dispersive x-ray (EDX ) microanalysis. The PL peak wavelength was strongly dependent-on the durat ion of the growth interruption and on the number of QW layers. AFM measurem ents revealed that the size of the open hexagonally shaped pits in the QW s tructures increased dramatically as the interruption duration was lengthene d. Through TEM and EDX microanalysis, we found that the formation of these hexahedronal pits, formed due to the growth interruption, causes a large fl uctuation in the In composition, especially around the pits, and the presen ce of such pits in an underlying QW layer strongly affects the In incorpora tion into the upper QW layers, leading to significant growth-rate variation in an InGaN QW layer and red-shifting of the PL spectra when a multiple-QW structure is grown.