arXiv subjects

David A. J. Moran

Publications and source records attributed to David A. J. Moran.

3 recordsLinked to original sources

arXiv2026

Barrier-channel intermixing and 2-dimensional electron gas degradation in Al-rich Al(Ga)N/AlGaN high electron mobility transistor heterostructures

In this work, we report on recent results in understanding and addressing the issue of interface smearing in high-aluminium content AlGaN/AlGaN heterostructures. On the one hand, the growth of high-crystal quality AlGaN by metal-organic vapour phase epitaxy (MOVPE) requires the use of high temperatures, but on the other hand this may lead to alloy intermixing between barrier and channel layers, which smoothens out the polarization contrast and severely degrades or even completely destroys the 2-dimensional electron gas (2DEG). We show that X-Ray Diffraction (XRD) analysis can be used as a non-destructive way to assess the sharpness of the interface, and that improved growth schemes can be successfully used to achieve high-quality 2DEG, as confirmed by contactless resistivity measurements. In particular, sheet resistivities around 2,500 $Ω/\Box$ were demonstrated for AlN/Al$_{0.75}$Ga$_{0.25}$N, consistent with the best-reported values in the literature.

cond-mat.mtrl-sci↗

arXiv2024

Extreme Enhancement-Mode Operation Accumulation Channel Hydrogen-Terminated Diamond FETs with $V_{th} < -6V$ and High On-Current

In this work we demonstrate a new Field Effect Transistor device concept based on hydrogen-terminated diamond (H-diamond) that operates in an Accumulation Channel rather than Transfer Doping regime. Our FET devices demonstrate both extreme enhancement-mode operation and high on-current with improved channel charge mobility compared to Transfer-Doped equivalents. Electron-beam evaporated $Al_2O_3$ is used on H-diamond to suppress the Transfer Doping mechanism and produce an extremely high ungated channel resistance. A high-quality H-diamond surface with an unpinned Fermi level is crucially achieved, allowing for formation of a high-density hole accumulation layer by gating the entire device channel which is encapsulated in dual-stacks of $Al_2O_3$. Completed devices with gate/channel length of $1 μm$ demonstrate record threshold voltage $< -6 V$ with on-current $> 80 mA/mm$. Carrier density and mobility figures extracted by CV analysis indicate high 2D charge density of $~ 2 \times 10^{12} cm^{-2}$ and increased hole mobility of $110 cm^2 /V \cdot s$ in comparison with more traditional Transfer-Doped H-diamond FETs. These results demonstrate the most negative threshold voltage yet reported for H-diamond FETs and highlight a new strategy for the development of high-performance power devices that better exploit diamond's intrinsic dielectric properties and high hole mobility.

cond-mat.mes-hall↗

arXiv2017

High resolution structural characterisation of laser-induced defect clusters inside diamond

Laser writing with ultrashort pulses provides a potential route for the manufacture of three-dimensional wires, waveguides and defects within diamond. We present a transmission electron microscopy (TEM) study of the intrinsic structure of the laser modifications and reveal a complex distribution of defects. Electron energy loss spectroscopy (EELS) indicates that the majority of the irradiated region remains as $sp^3$ bonded diamond. Electrically-conductive paths are attributed to the formation of multiple nano-scale, $sp^2$-bonded graphitic wires and a network of strain-relieving micro-cracks.

physics.app-ph↗