Recent results in quantum cascade lasers and intersubband transitions in GaN/AlGaN multiple quantum wells

Quantum cascade (QC) lasers have been fabricated with Ge0.25Se0.75 chalcogenide lateral waveguide claddings. Aside from a strongly (up to similar to50%) reduced waveguide loss this device lay-out also displays a significantly reduced stray capacitance and improved high-speed modulation properties. This has been exploited for the first use of QC lasers in optical wireless communications as well as for gain-switched and actively mode-locked QC-lasers. Optical devices based on intersubband (IS) transitions face a rising interest also in other wavelength ranges due to their anticipated ultrafast electron dynamics. We present initial measurements of IS-transitions in the fiber-optics wavelength range in GaN/AlGaN samples grown by molecular beam epitaxy. IS-absorption at wavelengths of 1.44, 1.41, and 1.52 mum are measured for 11, 12, and 13 Angstrom wide GaN quantum wells, respectively. We also measured the IS electron scattering time by conventional pump-probe technique. Using 1.55 mum as pump- and 1.70 mum as probe-wavelength, we obtain an electron scattering time of 370 fs. (C) 2002 Elsevier Science B.V. All rights reserved.