Cavity-enhanced thermal emission from semiconductor lasers

The thermal emission properties of GaAs-based semiconductor diode lasers are studied with a calibrated setup for quantitative measurements of spectrally resolved emittances. Emission spectra are measured for a stack of high-power diode-laser bars and for n-doped bulk GaAs reference samples and are compared to a calibrated blackbody radiator. The thermal radiation measurements are analyzed with a formalism providing the directional spectral emittance, transmittance, and reflectance under normal incidence. The thermal emission properties are related to the underlying materials properties such as absorption coefficients and carrier concentrations. The thermal emission from the semiconductor lasers displays a pronounced enhancement compared to the bulk reference samples. The metallic contacts and the heavily p-doped layers of the diodes are identified as the origin of this cavity enhancement. The semitransparent nature of the semiconductor materials influences the results of thermal infrared imaging substantially. We derive guidelines for extracting reliable information on device temperatures and discuss limitations of the technique. (C) 2008 American Institute of Physics.