Development of Terahertz Quantum Cascade Lasers with Novel Quantum Designs
Notice bibliographique
Résumé
Terahertz (THz) quantum cascade lasers (QCLs) are arguably the most promising THz radiation source, as they have high output power and efficiency. The main limitation of THz QCLs is the need of a cooling system due to the below-room-temperature operation. Therefore, achieving room temperature operation with good frequency-tunning ability are essential for many potential applications of THz QCLs. This thesis simulates THz QCLs’ operation, designs and demonstrates the possible THz QCLs with novel quantum designs that have potential to improve the maximum lasing temperature (Tmax) and frequency-tuning ability of THz QCLs. \nResonant-phonon (RP) and scattering-assisted (SA) schemes are two widely used THz QCLs quantum schemes that show good temperature performance at different frequency ranges. However, both schemes have limitations, such as the pre-threshold electrical instability in RP designs and thermally activated leakage to continuum in SA designs, which have prevented significant temperature improvements in the last eight years. To overcome those limitations, this thesis develops a six-level hybrid extraction/injection design (HEID) scheme in which the RP and the SA-based injection/extraction are combined within a single Al0.15Ga0.85As/GaAs based structure. By utilizing extra excited states for hybrid extraction/injection channels, this design minimizes the appearance of an intermediate negative differential resistance (NDR) before the lasing threshold. The final negative differential resistance is observed up to 260 K, and a high characteristic temperature of 259 K is measured. These observations imply very effective suppression of pre-threshold electrical instability and thermally activated leakage current. \nBroadband emission of THz QCL is usually demonstrated at low temperature. One possible way of extending THz QCLs’ frequency coverage involves activating multiple-lasing transit channels in the device active region (AR). This thesis discusses a dual-lasing channel THz QCL both theoretically and experimentally. The dual-lasing channel device combines two optical transitions at different frequencies under different device biases. The device exhibits a low threshold current density of 550 A/cm2 at 50 K and a maximum operating temperature of 144 K. It provides 0.3 THz emission frequency coverage with the lowest reported threshold current density among SA THz QCLs. The combination of a dual-lasing channel operation, low lasing threshold current density, and high-temperature performance makes such devices ideal candidates for broadband emission applications and paves the way for achieving high-temperature-performance THz QCLs with a greater frequency-tuning ability. \nThe thesis also theoretically investigates two further novel designs. One design addresses an issue observed in the first reported HEID structure for Tmax improvement. The second design is a quasi one-well (Q1W) design consisting of the fewest number of layers (three) and lowest thickness per period (~20 nm) of all the THz QCL quantum structures. The Q1W design exhibits sufficient high optical gain in the positive differential resistance (PDR) region up to a lattice temperature above 250 K.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».