| The physics and engineering issues associated with laser cooling of bulk semiconductors are experimentally investigated. This research addresses the key concepts of internal and external quantum efficiency in a semiconductor laser cooler. The former describes how optical excitations at the semiconductor band-edge recombine radiatively and the latter is a measure of how well recombination radiation is removed from the cooling device. The quantum efficiency of a GaAs device is affected by optical absorption, device processing and geometry, and background temperature. The technique of differential luminescence thermometry (DLT) was developed to provide a real-time, non-contact temperature measurement of semiconductors with an unprecedented accuracy of < 10mu° K. Using DLT, a record external quantum efficiency of 99% has been obtained with a GaAs laser cooler held at 100°K. The knowledge gained in the research described here is essential for the realization of net laser cooling in semiconductors. |
