Charge transport in superlattices with low-strength barriers and the problem of a terahertz bloch oscillator

Charge-transport properties of superlattices with low-strength barriers and the possibility of designing a Bloch oscillator based on these superlattices are discussed. A terahertz Bloch oscillator based on n-GaAs-GaAlAs structures with low-strength barriers is suggested. Because of interminiband tunneling, the current is an increasing function of electric-field strength, so that domains cannot be formed. At the same time, tunneling and Bloch oscillations give rise to dynamic negative electrical conductivity in the terahertz region. Monte Carlo simulations show that dynamic negative conductivity exists in the frequency range of 1–7 THz for superlattices with moderate charge-carrier mobility at 77 K. A Bloch oscillator should include a superlattice with 350–700 periods of 150-Å, with this superlattice being sandwiched between contact regions, which are in fact strip-line sections (the oscillator cavity). Presumably, such an oscillator can operate at 77 K in the continuous-wave mode.