High-temperature operation of broadband bidirectional terahertz quantum-cascade lasers

Abstract

Terahertz quantum cascade lasers (QCLs) with a broadband gain medium could play an important role for sensing and spectroscopy since then distributed-feedback schemes could be utilized to produce laser arrays on a single semiconductor chip with wide spectral coverage. QCLs can be designed to emit at two different frequencies when biased with opposing electrical polarities. Here, terahertz QCLs with bidirectional operation are developed to achieve broadband lasing from the same semiconductor chip. A three-well design scheme with shallow-well GaAs/Al0.10Ga0.90As superlattices is developed to achieve high-temperature operation for bidirectional QCLs. It is shown that shallow-well heterostructures lead to optimal quantum-transport in the superlattice for bidirectional operation compared to the prevalent GaAs/Al0.15Ga0.85As material system. Broadband lasing in the frequency range of 3.1–3.7 THz is demonstrated for one QCL design, which achieves maximum operating temperatures of 147 K and 128 K respectively in opposing polarities. Dual-color lasing with large frequency separation is demonstrated for a second QCL, that emits at ~3.7 THz and operates up to 121 K in one polarity, and at ~2.7 THz up to 105 K in the opposing polarity. These are the highest operating temperatures achieved for broadband terahertz QCLs at the respective emission frequencies, and could lead to commercial development of broadband terahertz laser arrays.

Short Barriers for Lowering Current-Density in Terahertz Quantum Cascade Lasers

“…The threshold current-densities in opposing polarities are 167 A/cm 2 and 217 A/cm 2 respectively at 53 K, which is lower than the values in Ref. [28] owing to lower waveguide losses and also possibly due to growth including possibly doping variations. Note that the maximum lasing temperatures of BIDR3W198 are lower than that in Ref.…”

“…Note that the maximum lasing temperatures of BIDR3W198 are lower than that in Ref. [28] in both polarities. We note the I-Vs near peak bias of BIDR3W198 in both polarities are very rough which may indicate slight growth problems.…”

“…There have been very few reports of bidirectional terahertz QCLs. We reported one bidirectional QCL design which showed broadband lasing in the frequency range of 3.1−3.7 THz with maximum operating temperature of 147 K and 128 K respectively in opposing polarities [28]. That QCL was grown with a thinner (∼8 µm) active region, which has higher waveguide losses for metallic cavities.…”

“…Here, we present a regrowth of the same design, when grown to a 10 µm thickness that is typical for terahertz QCLs based on metallic cavities. The design, named BIDR3W198, has same design parameters as [28]. Figure 3a shows the conduction band diagram of BIDR3W198 in forward-bias, and Figure 3b in reverse-bias respectively for the same superlattice structures.…”