Leakages suppression by isolating the desired quantum levels for high-temperature terahertz quantum cascade lasers

Abstract

The key challenge for terahertz quantum cascade lasers (THz-QCLs) is to make it operating at room-temperature. The suppression of thermally activated leakages via high lying quantum levels is emphasized recently. In this study, we employ the advanced self-consistent method of non-equilibrium Green’s function, aiming to reveal those kinds of leakages in the commonly used THz-QCL designs based on 2-, 3- and 4-quantum well. At the high temperature of 300 K, if all the confined high lying quantum levels and also the continuums are included within three neighboring periods, leakages indeed possess high fraction of the total current (21%, 30%, 50% for 2-, 3- and 4-quantum well designs, respectively). Ministep concept is introduced to weaken those leakage channels by isolating the desired levels from high lying ones, thus the leakages are well suppressed, with corresponding fractions less than 5% for all three designs.

Interdiffusion limiting on self-consistent optical gain in terahertz quantum cascade lasers

“…The GaAs-AlGaAs semiconductor system is predominantly utilized in THz-QCLs, with a larger conduction band offset (CBO) typically employed in designs for high-temperature operation. The high aluminum composition in the AlGaAs barrier is often set at percentages (Al%) of 25%, 15,16) 30%, 17,18) or 35% 19) to effectively suppress both the thermally induced leakages over the barrier and the downstream aligning leakages from the upper-lasing levels. 16,20) However, higher Al% of AlGaAs barriers are more susceptible to interdiffusion issues.…”

“…The high aluminum composition in the AlGaAs barrier is often set at percentages (Al%) of 25%, 15,16) 30%, 17,18) or 35% 19) to effectively suppress both the thermally induced leakages over the barrier and the downstream aligning leakages from the upper-lasing levels. 16,20) However, higher Al% of AlGaAs barriers are more susceptible to interdiffusion issues. Moreover, in THz-QCLs, these tall barriers need to be kept thin, for example, the thickness of lasing barrier is even less than 2 nm.…”