Abstract
We investigate the phase and terahertz (THz) gain of Bloch oscillations in GaAs-based superlattices at various temperatures of T = 80–298 K by using THz emission spectroscopy under bias electric fields. The transient current is found to start from its maximum nearly as damped cos ωBt (ωB/2π: Bloch frequency) throughout this temperature range, having only a small initial phase even for kT > ħωB (k: Boltzmann constant) and dephasing time shortening with increasing temperature. A spectral analysis indicates inversionless THz gain that originates from the capacitive nature of a Wannier–Stark ladder system with broadened energy levels at room temperature.
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