A broad band of radiation near 5 µ has been observed from free carriers in both n- and p-type germanium. The mechanism involves the modulation of the emissivity due to the pulsed injection of excess carriers. This produces the measured periodic increase of the spontaneous emission. A calculation based on the interaction of the germanium with the background radiation gives good agreement with the experimental results. The exitance increases with increasing pulse current and sample temperature, and the spectrum contains structure due to transitions between the branches of the valence band.
EDWARD A. ULMER JR. and DANIEL R. FRANKL, "Infrared Emission from Free Carriers in Germanium," J. Opt. Soc. Am. 59, 1233-1239 (1969)