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Qu, Yuan; Zhuo, Ning; Liu, Feng-Qi; Luo, Jun-Wei Source: Physical Review B, v 109, n 23, June 15, 2024; ISSN: 24699950, E-ISSN: 24699969; DOI: 10.1103/PhysRevB.109.235304; Article number: 235304; Publisher: American Physical Society

Author affiliation:

Key Laboratory of Semiconductor Photovoltaic Technology, Universities of Inner Mongolia Autonomous Region, Inner Mongolia University, Hohhot; 010021, China

Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing; 100083, China

State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing; 100083, China

Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing; 100049, China

Abstract:

Extensive efforts are being made to improve the material quality of semiconductor quantum cascade lasers (QCLs) to suppress the carrier scattering from the interface roughness (IFR), which is commonly regarded as the leading cause of the emission linewidth broadening in QCLs. Here, we uncover an intrinsic lower bound to the emission linewidth in the prevailing QCLs by performing atomistic pseudopotential calculations of the electronic and optical properties without ad hoc assumptions as made in standard effective mass approaches. We demonstrate that our atomistic simulation results could reproduce the experimental results well on both emission peaks and emission linewidths for a wide range of temperatures and applied bias voltages, even without considering the effect of the IFR. Specifically, we find that the multiple intersubband optical transitions, which are broadened each by the nonparabolicity of subband energy dispersions, render a very broad emission spectrum and could explain the experimentally measured spectra for a wide external bias. Therefore, we illustrate that the previously ignored multiple intersubband optical transitions give rise to an intrinsic lower bound to the emission linewidth in QCLs. These findings imply that the IFR may play a minor role in broadening the emission linewidth in the state-of-the-art QCLs and shed light on the design of QCLs.