Nonrelevant quantum levels limited laser dynamic in narrow-period terahertz quantum cascade lasers. (1st October 2022)

• Record Type: Journal Article
• Authors: Wang, Li; Lin, Tsung-Tse; Wang, Ke; Hirayama, Hideki
• Is Part Of: Japanese journal of applied physics. Volume 61:Number 10(2022)
• Publication Date: 2022-10-01
• Subjects: quantum cascasde laser -- laser device -- MBE epitaxy; Physics -- Periodicals; 621.05
• DOI: 10.35848/1347-4065/ac8c0e
• Languages: English
• ISSNs: 0021-4922

Abstract

Abstract: The fundamental challenges faced by terahertz quantum cascade lasers are the operations below room temperature, and the recent improved operating temperatures are actually based on the narrow-period designs (2-well resonant-phonon scheme). In this study, we address the critical effect of nonrelevant high-confined quantum levels on the laser threshold current in such designs, i.e. at high temperatures, the resonant-tunneling channels passing through neighboring periods via those levels can dominantly increase the laser threshold current. As a result, the laser dynamics significantly shrink to zero even at 270 K. The channels cannot be easily eliminated as they are derived from the specific configuration of a two-quantum-well periodic structure, in which the width of the period is narrow, and the nonrelevant levels from the lower-well are confined down in energy. It is reasonable to suppress the current flowing across those levels by narrowing the lower-well further, but an appropriate balance of its thickness is essential.