Norman Hascoe Distinguished Lecture Series

Over the last decade the forefront of research in semiconductor-laser field has moved from devices involving band-to-band (BB) electron transitions to devices involving intersubband (IS) transitions in multi-quantum-well(QW) structures. Principles of operation and inherent drawbacks of the most known IS-type device: the quantum-cascade(QC) laser, will be presented. For the short term, one main problem of QC lasers : carrier leakage out of the active QWs, has been solved by us by creating devices of deep QWs and tall barriers in their active regions, which in turn led to highly temperature insensitive operation. For the long term, the inherently low radiative efficiency of QC lasers can be overcome by using 2-D arrays of quantum boxes (QBs), thus getting rid of the cascade process and achieving power-conversion efficiencies comparable to those of BB devices (i.e., ~ 50 %). Preliminary results from IQB-laser structures will be presented and discussed.