Abstract

Quantum cascade lasers (QCLs) are unipolar semiconductor devices based on the engineering of electronic wavefunctions at the nanoscale level in multiple quantum well structures. Heat extraction from QCLs is difficult because of three main reasons: i) the high electrical power (P); ii) the large device thermal resistance due to the low heat conductivity of QCL active regions; iii) the poor thermal coupling between the active region and the heat sink related with the waveguide and mounting configurations. A common feature of such complex multiple heterostructures is the strong anisotropy of thermal conductivity, its cross-plane component being much smaller than the in-plane one. Bulk contributions to this phenomenon are negligible, whereas a dominant role is played by the presence of abrupt sub-nanometer sized interfaces. The presence of a high density of interfaces, mainly in long wavelength QCLs, causes phonon interference effects, which inherently limit the heat extraction.

© 2009 IEEE