The influence of the Al-content on the optical gain in AlGaN heterostructures

In the present contribution we report on the investigation of the optical gain properties of AlGaN epilayers with aluminum contents varied between 0 and 0.23. The samples were grown by MBE on (0 0 0 1)sapphire with a thickness of about 1 mu m. We performed photoluminescence and gain measurements at various excitation densities up to 5 MW-cm(2) using nanosecond excimer-laser pulses. Band filling processes and electron-hole plasma are the dominating gain mechanisms accompanied by phonon-assisted recombinations. With increasing Al content we observe that for a given excitation density the role of band filling processes increases in comparison with the electron-hole plasma. Also the threshold intensity for gain due to electron-hole plasma increases. These observations will be discussed with respect to the defect content of the samples. (C) 1998 Elsevier Science B.V. All rights reserved.