Band-structure engineering of new photonic materials: high performance mid-infrared quantum cascade lasers

摘要

Quantum engineering of electronic energy levels, wavefunctions and band structure, using ultrathin semiconductor layers grown by Molecular Beam Epitaxy (MBE) allows one to design and observe quantum phenomena on a mesoscopic scale (typically 1 to 100nm), much larger than the atomic dimension (Capasso 1987, Capasso and Cho 1994). This band-structure engineering approach is the basis for modifying in unprecedented ways the electronic, transport and optical properties which has led in many cases to altogether new materials (materials by design) and useful device applications. The quantum cascade (QC) laser (Faist et al. 1994, Capasso et al. 1995) is an excellent example of how quantum engineering can be used to design new photonic materials and related optoelectronic devices based on intersubband transitions (Capasso et al. 1997a,b). A population inversion between the states of the laser transition is designed by tailoring the electron intersubband scattering times. This design of scattering rates adds an important dimension to quantum engineering. Rosencher in a preceding chapter of this volume has systematically reviewed intersubband transitions in quantum wells and their applications to mid-infrared photodetectors and to optical materials with extremely large resonant nonlinear susceptibilities.