Multiple peak spectra from InGaN/GaN multiple quantum wells

Optical properties of In0.12Ga0.88N/GaN multiple quantum well (MQW) structures grown by metalorganic vapor phase epitaxy at 820 degrees C are reported. The transmission electron microscopy measurements show a roughness of the sample surfaces containing small pit like defects of a size 100 to 200 Angstrom with a density far exceeding the dislocation density. The photoluminescence (PL) spectra in this set of samples are dominated by strong multiple peak emissions associated both with the MQW exciton recombination and with strongly localized states of energies much lower than the QW bandgap. We suggest that the low energy PL peaks are due to (i) photocarriers localized in quantum islands closely related to the threading dislocations, and possibly associated with V-defect induced side-wall QWs; (ii) strongly localized excitons in OD quantum dots in the disordered surface region, formed by uncontrolled surface etching processes.