Bibliographic record
Abstract
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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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".