Bibliographic record
Abstract
Experiments and analysis in this thesis advance the understanding of critical issues in the carrier transport properties of InAs and InAs/GaAs core/shell heterostructure nanowires (diameter 30-60 nm) grown by molecular beam epitaxy. Effects of robust sub-band quantization structure on the gate-voltage dependence of conductance are observed up to 77 K in a single InAs nanowire with diameter 34\\pm2 nm. Electronic field effect mobility at 300 K and 30 K are typically 2000-4000 cm^2V^-1s^-1 and 10000-20000 cm^2V^-1s^-1. \n\nStrain induced by lattice mismatch in epitaxial core/shell InAs/GaAs heterostructure nanowires is found to relax by formation of dislocations, correlated with nearly one order of magnitude suppression of room temperature field effect mobility compared with bare InAs nanowires. The carrier transport properties of Mn-doped ZnO nanowires were also investigated, where despite the large bandgap, conductivity is not thermally activated, and carrier mobility is consistent with strong degeneracy of the electron gas at 10 K. \n\nA novel method was developed providing the first experimental characterization of the quasi-equilibrium gate-voltage dependent surface potential in nanowire field-effect transistors, based on statistics of charging/discharging of a single Coulomb impurity evident in a random telegraph signal, which succeeds in nanostructures with tiny (attofarad) gate capacitance, where similar capacitance-voltage methods are challenging or impossible. We find that the evolution of channel potential with gate voltage is suppressed in the transistor's accumulation regime due to the screening effects of surface states with D_ss=1-2\\times10^{12} cm^-2eV^-1. \n\nThe gate voltage dependence of the random telegraph signals were used as a novel probe to spectroscopically study strong carrier reflection by single Coulomb impurities in nanowires. Reflection probabilities R=0.98-0.999 approach unity for an electron gas with density n=30-10 /micron in 30 nm diameter, 1 micron long InAs nanowires at 30 K. Results were compared with microscopic theory of electron scattering by Coulomb impurities in nanowires with dielectric confinement, i.e low dielectric constant surroundings. The latter, which is known to enhance the bare Coulomb interaction and excitonic binding energy, is an essential ingredient for the strong scattering in this regime, and in small diameter nanowires causes a breakdown in linear screening. \n\nExtending this, we show that InAs nanowires can operate is extremely sensitive charge sensors with sensitivity 60 micro eHz^-1/2 at high temperatures (200 K), a combination of characteristics that is not achieved by existing technology. Strong electrostatic coupling of a single charge to the conducting electron gas in the nanowire is enabled by miniaturization of nanowire diameter, operation in a regime of carrier density where the electronic screening length exceeds the nanowire diameter, and dielectric confinement. \n\nFinally, single ZnSe nanowire photodetectors are fabricated and studied. Peak responsivity at 2.0 V bias is 20 A/W at room temperature, similar to that of the best epitaxial ZnSe photodetectors. The high responsivity is due to a photoconductive gain g=500, the ratio of carrier lifetime to carrier transit time. The former is enhanced at room temperature due to rapid selective trapping of one species of excited carriers by surface states.
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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".