High performance interminiband quantum cascade lasers with graded superlattices

A new class of quantum cascade lasers is presented. They are based on interminiband transitions in chirped superlattices (SL), where the applied electric field is compensated by the quasielectric field resulting from a gradually varying SL period length and average composition. In this way “flat” minibands can be obtained without the need for dopants. At room temperature record high peak (0.5 W) and average (14 mW) powers are obtained for a laser of 7.6 μm wavelength, with the lowest threshold current densities (5 kA/${\mathrm{cm}}^2)$ reported so far for quantum cascade lasers. The maximum temperature for continuous wave operation is an unprecedented 160 K.