Fabrication and Physics-Based Modeling of Polar AlGaN/GaN and AlInGaN/GaN HFETs
Bibliographic record
Abstract
Since their advent, polar AlGaN/GaN hetero-junction field effect transistors (HFETs) have drawn a great deal of attention especially in high frequency/high power applications. However, the superb prospects of these transistors are affected by a few drawbacks such as aging/crack formation under strain, presence of high gate-leakage, and challenging realization of enhancement-mode (normally-off) devices. \nQuite recently, study of quaternary AlInGaN barriers has been presented as a promising avenue for fulfilling various design demands including: lattice matching, polarization matching, and positive shifting the inherently negative threshold voltage of AlGaN/GaN HFETs. However, thus far only a limited scope of theoretical studies on AlInGaN/GaN hetero-structure characteristics has been reported. As part of this thesis, the two dimensional electron gas (2DEG) characteristics of gated metal-face wurtzite AlInGaN/GaN hetero-junctions as function of physical and compositional properties of the hetero-junction are theoretically evaluated using the variational method. According to this study, a considerable shift in the positive direction for the threshold voltage of AlInGaN/GaN HFETs can be achieved by engineering both the spontaneous and the piezoelectric polarization (using a quaternary AlInGaN barrier-layer of appropriate mole-fractions). Succeeding this study, a novel quaternary lattice-match layer structure based on employing a bilayer barrier for improving the carrier confinement in the channel of enhancement-mode AlInGaN/GaN HFETs is for the first time proposed. It is shown that while the proposed layer structure substantially improves the carrier confinement in the GaN channel layer, it also upholds the merits of employing a lattice-match barrier towards achieving an enhancement-mode operation. \nOne of the most important device characteristics of AlGaN/GaN HFETs which is often poorly understood is the gate-leakage current. As part of this thesis, reverse gate-leakage of AlGaN/GaN HFETs is studied over a wide range of lattice-temperatures. While unveiling an obscure path for gate leakage through the mesa sidewall, a model considering different leakage paths, including the identified sidewall leakage, is presented. It is illustrated that the sidewall path to the 2DEG is associated with the Poole-Frenkel electron emission. The novel contribution of the present analysis is that it postulates that in absence of absolute uniformity, Fowler-Nordheim (FN) tunneling takes place through only a small portion of the surface of the barrier, which boasts the highest electric field or the smallest Schottky barrier height. This consideration, allows the model to avoid unrealistic values for quantities such as effective electron mass (that has plagued many of the existing models). \nAlso as part of this thesis work, process recipe for microfabrication of submicron gate AlGaN/GaN HFETs using electron beam lithography was developed at McGill’s nano-tools micro-fabrication facilities. The results of DC characterization of the fabricated transistors along with the results of the DC stress test are presented.
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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) | 0.000 | 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".