Intersubband quantum-box semiconductor lasers:: High-power, efficient CW sources for the 3-10-μm wavelength range

Intersubband quantum-box (IQB) lasers, that is, devices consisting of 2D arrays of single-stage intersubband QB emitters, are proposed as an alternative to the 30-40-stage (conventional) quantum-cascade (QC) devices as sources for efficient room-temperature (RT) emission in the mid- and far-IR (3-5 mu m and 8-12 mu m) wavelength ranges. The devices rely on the much larger electron relaxation times in unipolar QBs than in quantum-well structures (i.e., the phonon bottleneck effect) to achieve low RT threshold-current densities (< 0.5 kA/cm(2)) and high RT CW wallplug efficiencies of 20-25%. Preliminary experimental results include the following: (i) The realization of the first mid-IR (lambda = 4.7 mu m) single-stage emitters operating at room temperature. These involve GaAs-based deep-well devices that, due to tight carrier confinement to the active QWs, do not need Bragg mirror/transmitter regions; (ii) etching and regrowth at the nanoscale level by employing in situ gas etching and regrowth in an MOCVD crystal-growth system; (iii) a pattern employing a high-resolution e-beam resist of 30-nm-diameter dots on 80-nm centers, and the transfer of the pattern into SiO2, thus forming a mask for the fabrication of IQBs via in situ etching and regrowth.