Blackbody radiation from hot two-dimensional electrons in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs heterojunctions

We have studied the broad-band far-infrared (FIR) radiation from hot two-dimensional (2D) electrons in selectively doped ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs heterojunctions. The combination of a composite Si bolometer and a magnetic-field-tuned InSb cyclotron resonance filter allows a spectroscopic as well as an intensity analysis of the FIR emission from hot 2D electrons. It is found that the radiation spectra are well explained by the theory of blackbody radiation and the emissivity assuming a classical Drude conductivity. The behavior of the determined effective blackbody temperatures of hot 2D electrons is quantitatively explained by a theory of acoustic- and optical-phonon emissions.