Terahertz Emission Spectroscopy of Hot Electron Systems in Semiconductor Heterostructures

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Application of strong external electric fields to the high-mobility low dimensional electron systems in semiconductor heterostructures and quantum wire structures results in a rapid rise in electron temperature as well as a drastic reduction of electron mobility. Such "hot carrier" phenomena are one of the most important issues in practical device applications.The combination of a broadband terahertz (THz) detector and a magnetic-field tuned cyclotron resonance filter allows us a unique opportunity for a spectroscopic as well as an absolute intensity analysis of weak THz radiation from semiconductor devices. In this work, we have utilized this technique as a tool for a diagnosis of "hot carrier" phenomena in semiconductors and studied the broadband THz radiation from hot low-dimensional electrons in smiconductor nanostructures. From its spectral line shape the observed broadband THz radiation was identified as the blackbody radiation from the hot electron systems. This fact enabled us to successfully determine the effective blackbody temperature (or the thermodynamic temperature) of the hot electron systems, T_e in a wide temperature range (-5K to-100K) when the lattice temperature was kept at 4.2K.The behavior of T_e is quantitatively explained by a theory of acoustic and optical phonon emission.