Quantum cascade lasers: coupled quantum well optoelectronics in the 4-100 µm wavelength region

Abstract

A new semiconductor injection laser, which differs in a fundamental way from diode lasers, has been demonstrated using quantum structures grown by MBE and designed by band-structure engineering.1 Called the quantum cascade laser (QCL), this device relies on only one type of carrier (it is a unipolar semiconductor laser), and on electronic transitions between conduction band states arising in quantum wells. This is to be contrasted with diode lasers (including quantum well lasers) where the lasing transition occurs between electron and hole states across the semiconductor bandgap. Such pure quantum confinement unipolar lasers were originally proposed 25 years ago, but despite considerable effort this is the first structure to achieve laser action.