Six-level hybrid extraction/injection scheme terahertz quantum cascade laser with suppressed thermally activated carrier leakage

Wen, Boyu; Deimert, Chris; Wang, Siyi; Xu, Chao; Rassel, SM Shazzad; Wasilewski, Z. R.; Ban, Dayan

doi:10.1364/oe.400246

Cited by 4 publications

(3 citation statements)

References 37 publications

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“…Second, since the coupling between injection level and upper laser level (ull) should not be too strong for THz QCL, [20] resonant tunneling injection is inefficient for populating the ull according to theoretical analysis, especially at elevated temperature, leading to a reduction of PI. [21,22] Moreover, thermally activated carrier leakage to the continuum level and the weak coupling between ull and extraction level have also been suggested to reduce the electron population at ull, [5,19] and therefore spoils the PI.…”

Section: Introductionmentioning

confidence: 99%

Extraction‐Dominated Temperature Degradation of Population Inversion in Terahertz Quantum Cascade Lasers

Zhang

Zhao

et al. 2022

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be exploited during the THz QCL operation due to its rapid performance degradation at elevated temperature, [7] which has impeded its practical application in many areas, such as security, astrophysics, and medical treatment. To this date, while the most progressive THz QCL based on phonon-tunneling design could be operated at the maximum temperature of 250 K in pulse mode, [5] there exists a certain distance from room-temperature operation, and its luminous efficiency deteriorates rapidly at elevated temperatures. [1,8] Indeed, we are still far away from achieving high-output THz QCL at room temperature.Regarding this major challenge, numerous researches have been directed to investigating the temperature degradation phenomenon in THz QCL and several limiting factors have been identified accordingly, including degraded population inversion (PI), [9][10][11] reabsorption of broadened states, [12][13][14] and increased parasitic current density at elevated temperature. [3,15,16] Among these factors, the reduction of PI is the most concern, as the peak gain of a laser device is proportional to the degree of PI between its upper laser state and lower level state. In view of this, clarifying the mechanism of the degraded PI is an essential precondition to optimize the elevated temperature Degraded population inversion (PI) at elevated temperature, regarded as an important temperature degradation factor in terahertz quantum cascade lasers (THz QCL), has hindered the widespread use of these devices. Herein, the mechanism of the temperature degradation of PI is investigated microscopically. It is demonstrated that the limited extraction efficiency of the extraction system dominates the decrease of PI at elevated temperatures. To be specific, the increased temperature brings about intense thermally activated longitudinal optical phonon scattering, leading to large amounts of electrons scattering to lower level state. In this case, the resonant-phonon extraction system is incapable of depleting all the electrons from lower level states. So even though the resonant-tunneling injection seems efficient enough to compensate the electron runoff at the upper state, the electron density at lower level state increases and the overall PI turns out lower. In addition, it is found that strong electron-ionized donor separation at high temperature can induce level misalignment, which can stagger the optimal conditions of injection and extraction. Also, the extraction efficiency gets lower as the extraction system requires accurate coupling between several energy levels.

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Section: Introductionmentioning

confidence: 99%

Extraction‐Dominated Temperature Degradation of Population Inversion in Terahertz Quantum Cascade Lasers

Zhang

Zhao

et al. 2022

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“…Researchers have found that THz QCL quantum structure designs are critical for the temperature performance of the devices [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and have made great efforts to explore different THz QCL quantum structure designs. Multiple quantum designs, such as the bound-to-continuum (BTC) design [6,11,17,18], resonantphonon (RP) design [19][20][21], scattering-assisted (SA) design [4,22], phonon-photon-phonon (3p) design [23][24][25], direct-phonon design [26,27], split-well direct-phonon design [28,29], extraction-controlled design [30,31], and hybrid extraction/injection design [32], have been experimentally demonstrated and exhibited good temperature performance at different frequencies of ~1. 3-5.4 THz [33].…”

Section: Introductionmentioning

confidence: 99%

“…Without a suitable radiative barrier and injection barrier in the quantum cascade period, sufficiently high positive optical gain and population inversion, which are prerequisites for lasing operation, can typically be achieved only in the so-called negative differential resistance (NDR) region [36]. When the design bias is in the NDR region, the inhomogeneous and oscillating electric field domains emerge in the AR, and the lasing operation is generally disrupted [32,37,38]. In previous theoretical research attempts, superlattice designs were employed, and simulation results show that the design bias may be attainable in a positive differential resistance (PDR) region, but the extremely diagonal transition in the design failed to achieve sufficient optical gain [38].…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of Quasi One-Well Terahertz Quantum Cascade Laser

Wen

Ban

2022

Photonics

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Developing a high-temperature terahertz (THz) quantum cascade laser (QCL) has been one of the major challenges in the THz QCL field over recent decades. The maximum lasing temperature of THz QCLs has gradually been increased, arguably by shortening the length of repeating periods of the quantum structure in the device’s active region from 7 wells/14 layers to 2 wells/4 layers per period. The current highest operating temperature of 250 K was achieved in a two-well direct-phonon design. In this paper, we propose a potential and promising novel quantum design scheme named the quasi one-well (Q1W) design, in which each quantum cascade period consists of only three semiconductor layers. This design is the narrowest of all existing THz QCL structures to date. We explore a series of the Q1W designs using the non-equilibrium green function (NEGF) and rate-equation (RE) models. Both models show that the Q1W designs exhibit the potential to achieve sufficient optical gain with low-temperature sensitivity. Our simulation results suggest that this novel Q1W scheme may potentially lead to relatively less temperature-sensitive THz QCLs. The thickness of the Q1W scheme is less than 20 nm per period, which is the narrowest of the reported THz QCL schemes.

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High-temperature terahertz quantum cascade lasers

Wen

Ban

2021

Progress in Quantum Electronics

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Six-level hybrid extraction/injection scheme terahertz quantum cascade laser with suppressed thermally activated carrier leakage

Cited by 4 publications

References 37 publications

Extraction‐Dominated Temperature Degradation of Population Inversion in Terahertz Quantum Cascade Lasers

Extraction‐Dominated Temperature Degradation of Population Inversion in Terahertz Quantum Cascade Lasers

Theoretical Study of Quasi One-Well Terahertz Quantum Cascade Laser

High-temperature terahertz quantum cascade lasers

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