Spontaneous Terahertz Emission under Electrical Breakdown of a Shallow Acceptor in Ge

The spectra of spontaneous terahertz (THz) electroluminescence at the breakdown of shallow Ga acceptor in Ge were observed for the first time and investigated. We found and characterized the emission lines corresponding to the hole transitions between the excited states and the ground state of the impurity center as well as the transitions of the hot holes from the valence band to the impurity and within the valence band. A high quantum yield of the radiative transitions will become an important factor in designing electrically pumped THz emitters for the≈2 THz spectral range.