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

Quantum cascade (QC) lasers have been fabricated with Ge_0.25Se_0.75 chalcogenide lateral waveguide claddings. Aside from a strongly (up to ∼50%) 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 μm are measured for 11, 12, and 13 Å wide GaN quantum wells, respectively. We also measured the IS electron scattering time by conventional pump-probe technique. Using 1.55 μm as pump- and 1.70 μm as probe-wavelength, we obtain an electron scattering time of 370 fs.