Terahertz emission induced by self-oscillations of current in semiconductor resonant tunneling structures
Based on the simultaneous measurements of radio-frequency intrinsic self-oscillations of current and terahertz (THz) light emission from a 30-period GaAs/AlGaAs weakly-coupled superlattice, it was concluded that self-oscillations of current arise due to the cyclic process of the electric-field domain boundary spatial expansion and shrinkage. The domain boundary expands over several SL periods due to the energy dissipation of tunneling electrons, resulting in the carrier trapping in several SL periods behind the leading edge of the domain boundary. In this region, the charge accumulation gives rise to the resonant detuning of subbands in adjacent quantum wells (QWs), creating the population inversion between the two subbands, which ensure the resonant tunneling along the SL axis. The electrons injected from the cathode restore the resonant coupling of subbands, the lower subband is emptied, and the intersubband radiative transitions allowed. The electroluminescence (EL) spectra of the SL demonstrate the main peak with the left and the right sidebands. The main peak is related to the intersubband electron transition energy, while the sidebands are associated with the resonant detuning energy of subbands in adjacent QWs (~ 4 meV). The two-photon pulsed THz emission (~ 4 meV) from a double-barrier GaAs/AlAs resonant tunneling diode biased into self-oscillation regime confirms the last assertion. There is the same cyclic mechanism of relaxation self-oscillations of current (accumulation and drain type), where the first THz pulse is triggered due to the carrier trapping by miniband states, resulting in the miniband energy shift up to higher energies. After the trap release time, the electrons lost their energy via the second THz pulse emission, and the miniband gets back to its steady state.