Quantum cascade lasers: from band structure engineering to applications

Quantum cascade (QC) lasers are fundamentally new semiconductor light sources in that: (1) their wavelength can be tailored over a wide range (from 3.4 /spl mu/m to 17 /spl mu/m) using the same combination of materials by a suitable choice of the active layer thicknesses (a few nanometers), (2) their optical power is greatly enhanced by the cascade effect (one injected electron creates 25-30 photons in traversing the active region). They are a textbook case of band structure engineering since all key microscopic properties (energy levels, radiative and non radiative matrix elements and their corresponding lifetimes, etc.) are designed "bottom-up" to optimize material and device performance.