Nonrelevant quantum levels effecting on the current in 2-well terahertz quantum cascade lasers

Area of Science:

• Semiconductor device physics
• Quantum electronics
• Laser technology

Background:

• Terahertz quantum cascade lasers (TQCLs) require precise quantum level engineering for efficient operation.
• High operating temperatures in TQCLs necessitate strategies to mitigate performance degradation due to thermal effects.
• Resonant-phonon designs are crucial for achieving clean quantum level structures in TQCLs.

Purpose of the Study:

• To systematically investigate the impact of engineered depopulation energies on current leakage in a 2-well TQCL design.
• To analyze the influence of high-lying nonrelevant energy levels on device currents.
• To explore methods for suppressing leakage currents and improving thermal stability in TQCLs.

Main Methods:

• Utilizing the non-equilibrium Green's function (NEGF) method for theoretical analysis.
• Engineering various depopulation energy levels (small and large) within a 2-well structure.
• Simulating device performance under different design parameters to study current transport.

Main Results:

• Leakage channels, activated by sequential tunneling across multiple periods, are unavoidable regardless of depopulation energy.
• A large depopulation energy effectively suppresses thermal backfilling, significantly reducing net leakage currents at high temperatures.
• Pre-alignment of quantum levels becomes a critical design consideration when employing large depopulation energies.

Conclusions:

• Engineering large depopulation energies is a viable strategy to enhance the high-temperature performance of TQCLs by minimizing leakage.
• Addressing pre-alignment issues through improved barrier engineering is essential for optimizing laser dynamics with large depopulation energies.
• The study provides insights into the complex interplay between quantum level design, leakage currents, and thermal effects in TQCLs.