Abstract
We report on high-power terahertz quantum cascade lasers based on low effective electron mass InGaAs/InAlAs semiconductor heterostructures with excellent reproducibility. Growth-related asymmetries in the form of interface roughness and dopant migration play a crucial role in this material system. These bias polarity dependent phenomena are studied using a nominally symmetric active region resulting in a preferential electron transport in the growth direction. A structure based on a three-well optical phonon depletion scheme was optimized for this bias direction. Depending on the sheet doping density, the performance of this structure shows a trade-off between high maximum operating temperature and high output power. While the highest operating temperature of 155 K is observed for a moderate sheet doping density of 2 × 1010 cm–2, the highest peak output power of 151 mW is found for 7.3 × 1010 cm–2. Furthermore, by abutting a hyperhemispherical GaAs lens to a device with the highest doping level a record output power of 587 mW is achieved for double-metal waveguide structures.
Highlights
Quantum cascade lasers (QCLs)[1] are based on periodic semiconductor heterostructures and can be designed for a wide range of emission frequencies
We report on high-power terahertz quantum cascade lasers based on low effective electron mass InGaAs/ InAlAs semiconductor heterostructures with excellent reproducibility
The optical gain that can be achieved in the active region is apart from the quantum design fundamentally related to the material parameters associated with the semiconductor heterostructure
Summary
AThe sheet doping density ns is given in units of 1010 cm−2. In addition, the deviation of the period length ΔL from its nominal value. They were fabricated from the active region samples B and C and processed using the same processing parameters. The highest peak output power of 151 mW was achieved from a device with a sheet doping density of 7.3 × 1010 cm−2 (sample E) These results indicate that at low temperatures (5 K) the increase in optical gain, due to a larger number of free carriers, outbalances the increase in scattering resulting from the larger number of impurities. The best temperature performance was observed for a sheet doping density of 2 × 1010 cm−2 with a maximum operating temperature of 155 K for sample B
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