Structural and optical characterization of thick InGaN layers and InGaN/GaN MQW grown by molecular beam epitaxy

Thick In-x Ga1-xN (0.20 < x < 0.27) layers and InGaN/GaN multiple quantum wells (MQWs) are grown by plasma-assisted molecular beam epitaxy on GaN/Al2O3 templates. The strain and In-content is estimated from high-resolution X-ray diffraction, showing that the bulk samples are not fully relaxed. A bowing parameter of 3.6 eV is obtained from absorption measurements of InxGa1-xN layers. Strong In-dependent excitonic localization is observed in these bulk layers, leading to an increase in the absorption band edge with the In content. Regarding the MQWs structures, high-resolution transmission electron microscopy reveals an increase in the interface roughness for high In content. The dominant PL emission of the MQWs shows a red-shift when increasing the well thickness for a given In-content, due to internal piezoelectric field. The excitonic localization is studied and compared between thick layers and MQWs structures. (C) 2002 Elsevier Science B.V. All rights reserved.