Energy selective optically pumped stimulated emission from InGaN/GaN multiple quantum wells

Optically pumped stimulated emission (SE) from InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition has been systematically studied as a function of excitation photon energy (E-exc) to further understand the origin of SE in these structures. Optically pumped SE was observed for excitation photon energies well below that of the absorption edge of the MQWs, indicating the states responsible for the soft absorption edge in these structures can efficiently couple carriers with the gain region. "Mobility edge"-type behavior in the SE peak was observed as E-exc was varied. The effective mobility edge measured in these SE experiments lies similar to 110 meV above the main spontaneous emission peak and similar to 62 meV above the SE peak. Tuning the excitation energy below the mobility edge was found to be accompanied by a drastic increase in the SE threshold due to a decrease in the effective absorption cross section. The experimental results indicate that the SE peak observed here has the same microscopic origin as the spontaneous emission peak, i.e., radiative recombination of localized states. (C) 1998 American Institute of Physics.