arXiv subjects

Vitaly Z. Zubialevich

Publications and source records attributed to Vitaly Z. Zubialevich.

6 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↗

arXiv2026

High Uniformity GaN Micro-pyramids and Platelets by Selective Area Growth

The development of uniform GaN micro-pyramids and platelets via selective area growth is a critical step toward advancing III-nitride device technologies, particularly for micro-light-emitting diode applications. This work investigates the origins of morphological non-uniformity in micro-pyramids and micro-platelets grown by metal-organic chemical vapor deposition (MOCVD). We observe that a direct one-step growth approach leads to significant growth rate inhomogeneity across arrays. To shed light on this issue, we examine the mechanisms driving non-uniformity and explore process modifications aimed at mitigating these effects. Building on these insights, we propose a controlled multi-step growth strategy that combines sequen-tial growth and thermal treatment phases. This approach is demonstrated to enhance surface morphology and structural regularity. The work contributes to the broader objective of enabling scalable, high-precision GaN microstructure fabrication for next-generation optoelectronic applications.

physics.optics↗

arXiv2025

Temperature-dependent investigation of polarisation doping in 330 nm ultraviolet light-emitting diodes

Polarisation doping of Al$_x$Ga$_{1-x}$N, through grading of $x$, has realised major improvements in $p$-type conductivity in ultraviolet (UV) light-emitting diodes (LEDs) compared to conventional impurity doping. However, the exact balance between the two doping regimes to achieve the best device performance is not clear, especially as a function of operating wavelength. In this work, 330 nm LEDs with varied $p$-doping approaches were characterised as a function of temperature: Mg doped only (reference); polarisation doped and Mg doped (co-doped); and polarisation doped only. At room temperature, the co-doped LED showed the highest electroluminescence (EL) intensity, with a similar operating voltage to the reference LED. The highest hole concentration, confirmed by Hall effect measurements, as well as improved injection efficiency revealed by simulations, are credited as the main reasons for EL improvement. A parasitic near-UV luminescence tail, analogous to the "blue luminescence" in $p$-GaN, was observed in both the reference and co-doped LEDs, but was absent in the polarisation doped LED. The reference LED demonstrated the highest increase in operating voltage with decreasing temperature, while the LED with only polarisation doping showed a temperature-independent behaviour, demonstrating the benefits of a polarisation field-induced carrier concentration. Further optimisation of the compositional grading with concurrent Mg doping can potentially produce higher performance LEDs with cleaner spectra.

physics.app-ph↗

arXiv2024

Geometrically-Controlled Microscale Patterning and Epitaxial Lateral Overgrowth of Nitrogen-Polar GaN

In this study we report on a novel two-step epitaxial growth technique that enables a significant improvement of the crystal quality of nitrogen-polar GaN. The starting material is grown on 4° vicinal sapphire substrates by metal organic vapour phase epitaxy, with an initial high-temperature sapphire nitridation to control polarity. The material is then converted into a regular array of hexagonal pyramids by wet-etch in a KOH solution, and subsequently regrown to coalesce the pyramids back into a smooth layer of improved crystal quality. The key points that enable this technique are the control of the array geometry, obtained by exploiting the anisotropic behaviour of the wet-etch step, and the use of regrowth conditions that preserve the orientation of the pyramids' sidewalls. In contrast, growth conditions that cause an excessive expansion of the residual (000-1) facets on the pyramids' tops cause the onset of a very rough surface morphology upon full coalescence. An X-ray diffraction study confirms the reduction of the threading dislocation density as the regrowth step develops. The analysis of the relative position of the 000-2 GaN peak with respect to the 0006 sapphire peak reveals a macroscopic tilt of the pyramids, probably induced by the large off-axis substrate orientation. This tilt correlates very well with an anomalous broadening of the 000-2 diffraction peaks at the beginning of the regrowth step.

cond-mat.mtrl-sci↗

arXiv2021

Pseudomagnetic fields and strain engineering: graphene on GaN nanowires

Gallium nitride nanowire and nanorod substrates with different morphology are prospective platforms allowing to control the local strain distribution in graphene films top of them, resulting in an induction of pseudomagnetic fields. Atomic force microscopy measurements performed in a HybriD mode complemented by scanning electron microscopy allow for a detailed visualization of the strain distribution on graphene surface. Graphene in direct contact with supporting regions is tensile strained, while graphene located in-between is characterized by lower strain. Characteristic tensile strained wrinkles also appear in the areas between the supporting regions. A detailed analysis of the strain distribution shows positive correlation between strain gradient and distances between borders of supporting regions. These results are confirmed by Raman spectroscopy by analysis the D' band intensity, which is affected by an enhancement of intravalley scattering. Furthermore, scanning tunneling spectroscopy shows a local modification of the density of states near the graphene wrinkle and weak localization measurements indicate the enhancement of pseudomagnetic field-induced scattering. Therefore, we show that nanowire and nanorod substrates provide strain engineering and induction of pseudomagnetic fields in graphene. The control of graphene morphology by a modification of distances between supporting regions is promising for both further fundamental research and the exploration of innovative ways to fabricate pseudomagnetic field-based devices like sensors or filters.

cond-mat.mes-hall↗

arXiv2016

Ag colloids and arrays for plasmonic non-radiative energy transfer from quantum dots to a quantum well

Ag nanoparticles in the form of colloids and ordered arrays are used to demonstrate plasmon-mediated non-radiative energy transfer from quantum dots to quantum wells with varying top barrier thicknesses. Plasmon-mediated energy transfer efficiencies of up to ~25% are observed with the Ag colloids. The distance dependence of the plasmon-mediated energy transfer is found to follow the same d^{-4} dependence as the direct quantum dot to quantum well energy transfer. There is also evidence for an increase in the characteristic distance of the interaction, thus indicating that it follows a Förster-like model with the Ag nanoparticle-quantum dot acting as an enhanced donor dipole. Ordered Ag nanoparticle arrays display plasmon-mediated energy transfer efficiencies up to ~21%. To explore the tunability of the array system, two arrays with different geometries are presented. It is demonstrated that changing the geometry of the array allows a transition from overall quenching of the acceptor quantum well emission to enhancement, as well as control of the competition between the quantum dot donor quenching and energy transfer rates.

physics.optics↗