EXCITATION ENERGY-DEPENDENT OPTICAL CHARACTERISTICS OF INGAN GAN MULTIPLE-QUANTUM WELLS/

We have systematically studied the optical properties of InGaN/GaN mul tiple quantum wells (MQWs) at 10 K under different excitation conditio ns using photoluminescence (PL), PL excitation, and time-resolved PL s pectroscopy. We found that the PL emission consists of a strong main p eak at 2.80 eV and a much weaker and broader secondary peak at similar to 2.25 eV. We observed that the peak position blueshifts and the spe ctral width narrows for the main peak when the excitation energies are varied from 3.81 eV (above the band gap of the AlGaN capping layer) t o 2.99 eV the band (below gap of the GaN barrier layers). The intensit y ratio of the main peak to the secondary peak also varied with excita tion energy. The two observed emission peaks originate from different layers of the MQWs. Time-integrated and time-resolved PL revealed that the InGaN-related spontaneous emission processes are strongly affecte d by inhomogeneity and carrier localization in the MQWs. From these st udies under varying excitation energies, we conclude that interface-re lated defects and roughness may play an important role in the InGaN-re lated emission mechanism during the carrier transfer between different layers of the MQWs. (C) 1998 American Institute of Physics. [S0003-69 51(98)00648-2].