Far-Infrared Recombination Radiation from Impact-Ionized Shallow Donors in GaAs

Radiation corresponding to transitions from excited shallow donor states and from conduction-band states to the donor ground state has been observed in impact-ionized GaAs at temperatures near 4.2°K. Spectral measurements show a main peak at a wavelength of 282 μ (4.4 meV), corresponding to a $2p\to 1s$ transition, and a broader continuum extending to higher photon energies. A total radiated power of ${10}^{-7\mathrm{}}$ W has been measured corresponding to an external quantum efficiency of about ${10}^{-6\mathrm{}}$.