Transport and stimulated THz emission in simple weak barrier superlattices

Abstract

Emissions at 2.6 - 2.8 THz are observed from liquid helium cooled disk chips with metal - superlattice - metal cavities made of two low n type doped wafers with weak barrier GaAs-GaAlAs superlattice of 1000 periods. The emissions are at 8.6 - 18.8 Volts within region of rising chip current (at positive chip differential conductivity) that guarantees absence of inhomogeneous electric field domains. At 2.6 - 2.7 THz the emission tunable by 8 - 10 Volts voltage change is higher than the Bloch oscillations frequency; while at 2.8 THz at 12 - 18 Volts it is lower than ω B, The THz frequency bands are measured with a cyclotron resonance filter; the band width is of about that of the THz quantum cascade laser. By using long voltage pulses the chip heating above 100 K is achieved without substantial change in chip THz emission power. We speculate that the emission is super luminescence (amplification) of whispering gallery modes in the chips as a result of inverted Wannier-Stark level transitions under bias. The results advocate development of THz and higher frequency sources based on such simple superlattices; the sources should well compete with the THz quantum cascade lasers in particular at elevated temperatures.