arXiv subjects

Ahmed Ibreljic

Publications and source records attributed to Ahmed Ibreljic.

13 recordsLinked to original sources

arXiv2026

Fast-Neutron Irradiation Effect in Heteroepitaxial $β$-Ga$_2$O$_3$ Schottky Diodes Fabricated on Low-Cost Sapphire Substrates

In this work, we investigate the response of Ni/$β$-Ga$_2$O$_3$ Schottky barrier diodes fabricated on c-plane sapphire to fast-neutron irradiation up to a fluence of $1\times10^{15}$ n$\cdot$cm$^{-2}$. The LPCVD-grown heteroepitaxial structure consists of an unintentionally doped buffer, an n$^{+}$ contact layer, and an n-type drift layer, with mesa isolation realized by plasma-free Ga-assisted LPCVD etching. Prior to irradiation, the devices exhibit a turn-on voltage of 1.20 V, specific on-resistance of 8.43 m$Ω\cdot$cm$^2$, ideality factor of 1.32, and Schottky barrier height of 1.29 eV. Following irradiation, the devices remain operational, although the forward current decreases, the turn-on voltage increases to 2.40 V, and the barrier height increases to 1.34 eV. Capacitance-voltage measurements reveal a $\sim$50% reduction in net donor concentration, corresponding to a carrier-removal rate of $\sim$105 cm$^{-1}$. Temperature-dependent measurements from 25 to 250 $^\circ$C confirm that thermionic emission remains the dominant transport mechanism and show significant suppression of reverse leakage current after irradiation. The breakdown voltage increases from 101 to 135 V, consistent with neutron-induced donor compensation. TCAD simulations show a more uniform electric-field distribution and reduced field crowding at the Schottky edge after irradiation. These results provide insight into neutron-induced donor compensation in heteroepitaxial $β$-Ga$_2$O$_3$ and demonstrate the ability of LPCVD-grown $β$-Ga$_2$O$_3$ Schottky diodes on sapphire to maintain stable operation under high-fluence neutron environments relevant to space and nuclear electronics.

physics.app-ph↗

arXiv2026

High-Mobility Ge-Doped $β$-Ga$_2$O$_3$ Growth on Sapphire by Low-Pressure Chemical Vapor Deposition

In this work, high-quality Ge-doped (-201) $β$-Ga$_2$O$_3$ thin films were heteroepitaxially grown on c-plane sapphire substrates with offcut angles of 0 deg, 2 deg, 6 deg, and 8 deg using low-pressure chemical vapor deposition (LPCVD). Increasing sapphire offcut promoted step-flow growth, resulting in improved terrace alignment, reduced surface roughness, and enhanced crystalline quality. Phase-pure monoclinic $β$-Ga$_2$O$_3$ with strong (-201) preferential orientation was confirmed by X-ray diffraction and Raman spectroscopy, while X-ray photoelectron spectroscopy revealed near-stoichiometric composition with an O/Ga ratio of 1.48. Electrical transport properties exhibited a strong dependence on substrate offcut angle, with room-temperature Hall mobility increasing from 15 to 117 cm$^2$/V s as the offcut angle increased from 0 deg to 6 deg, across carrier concentrations spanning $1.43 \times 10^{17}$ to $2.75 \times 10^{18}$ cm$^{-3}$. The 6 deg offcut sample achieved a room-temperature mobility of 117 cm$^2$/V s at a carrier concentration of $1.43 \times 10^{17}$ cm$^{-3}$ and a peak low-temperature mobility of 337 cm$^2$/V s at 128 K with a carrier concentration of $8.96 \times 10^{16}$ cm$^{-3}$, representing the highest reported room-temperature and low-temperature mobilities for Ge-doped $β$-Ga$_2$O$_3$ films grown on sapphire substrates. Carrier concentration and mobility data were analyzed using charge-neutrality and Boltzmann transport models incorporating donor activation together with polar optical phonon, ionized impurity, neutral impurity, acoustic deformation potential, and dislocation scattering mechanisms. The fitting revealed shallow donor activation energies of 12.5-19 meV, a deeper donor level at 80 meV, low acceptor compensation ($< 5 \times 10^{15}$ cm$^{-3}$), and threading dislocation densities on the order of $10^9$ cm$^{-2}$.

cond-mat.mtrl-sci↗

arXiv2026

Sn-Doping in LPCVD-Grown (010) $β$-Ga$_2$O$_3$ Films

In this work, Sn-doped (010) $β$-Ga$_2$O$_3$ homoepitaxial films were grown by low-pressure chemical vapor deposition (LPCVD), and the influence of Sn incorporation on their structural, morphological, and electrical properties was systematically investigated. Controlled room-temperature carrier concentrations ranging from $1.17 \times 10^{17}$ to $3.06 \times 10^{18}$ cm$^{-3}$ were achieved, with corresponding Hall mobilities decreasing from 113 to 63 cm$^2$ V$^{-1}$ s$^{-1}$. The films exhibited the monoclinic $β$-Ga$_2$O$_3$ phase, near-stoichiometric composition, and well-defined step-flow morphology, with a minimum rocking-curve FWHM of 68.4 arcsec and an RMS roughness of 2.63 nm. Film thicknesses ranging from 1.66 to 11.3 $μ$m were obtained at growth rates of 6.4 to 16.6 $μ$m h$^{-1}$, demonstrating the ability of LPCVD to produce thick epitaxial layers. The sample with a room-temperature carrier concentration of $1.17 \times 10^{17}$ cm$^{-3}$ exhibited room-temperature and low-temperature Hall mobilities of 113 cm$^2$ V$^{-1}$ s$^{-1}$ and 380 cm$^2$ V$^{-1}$ s$^{-1}$ at 84 K, respectively. Both represent the highest reported values for LPCVD-grown Sn-doped $β$-Ga$_2$O$_3$. Transport modeling of the same sample yielded a shallow donor activation energy of 32.7 meV, a deeper donor level at 95 meV, and a low compensating acceptor concentration of $2.0 \times 10^{16}$ cm$^{-3}$, indicating efficient donor activation and a low degree of compensation. These results demonstrate that LPCVD enables controlled Sn doping while maintaining excellent structural and electrical quality, providing a viable route for realizing thick $β$-Ga$_2$O$_3$ epitaxial drift layers.

cond-mat.mtrl-sci↗

arXiv2026

High-Quality Ge-Doped (010) $β$-Ga$_2$O$_3$ Homoepitaxial Films Grown by Low-pressure CVD: Structural, Electrical, and Schottky Diode Characteristics

In this work, Ge-doped $β$-Ga$_2$O$_3$ homoepitaxial films were grown on native (010) $β$-Ga$_2$O$_3$ substrates using low-pressure chemical vapor deposition (LPCVD). Controlled $n$-type doping was achieved with room-temperature carrier concentrations ranging from $7.4\times10^{17}$ to $2.57\times10^{18}\ \mathrm{cm}^{-3}$ and corresponding electron mobilities of 105-62 cm$^2$/V$\cdot$s. The films exhibited smooth surface morphology with RMS roughness values of 2.94-3.97 nm, while X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy confirmed phase-pure $β$-Ga$_2$O$_3$ with excellent crystalline quality and near-stoichiometric composition. Temperature-dependent Hall measurements on the film with a room-temperature carrier concentration of $7.4\times10^{17}\ \mathrm{cm}^{-3}$ and mobility of 105 cm$^2$/V$\cdot$s yielded a peak electron mobility of 234 cm$^2$/V$\cdot$s at 116 K, while charge-neutrality and transport modeling revealed a dominant shallow donor level with an activation energy of 14 meV, confirming efficient electrical activation of Ge donors. Vertical Ni/$β$-Ga$_2$O$_3$ Schottky barrier diodes fabricated using the Ge-doped drift layer exhibited good rectifying behavior with a turn-on voltage of 0.74 V, an ideality factor of 1.32, a Schottky barrier height of 1.02 eV, and a specific on-resistance of 2.49 m$Ω\cdot$cm$^2$. Capacitance-voltage measurements yielded a net donor concentration of $7.7\times10^{17}\ \mathrm{cm}^{-3}$ and a Schottky barrier height of 1.13 eV, in good agreement with Hall and current-voltage measurements. These results demonstrate that LPCVD enables controllable Ge doping while maintaining high structural and electronic quality, establishing LPCVD-grown Ge-doped $β$-Ga$_2$O$_3$ as a promising platform for future high-voltage power electronic devices.

cond-mat.mtrl-sci↗

arXiv2026

Vertical $β$-Ga$_2$O$_3$ Schottky Diodes with Deep-Etch Field Termination using Plasma-free Ga-assisted Etching

A deep-etch field termination strategy using a Ga-assisted plasma-free etching technique in a low-pressure chemical vapor deposition (LPCVD) system is demonstrated for $β$-Ga$_2$O$_3$ Schottky barrier diodes (SBDs). The thermally activated etching method provides a plasma-free approach for forming deep mesa terminations while maintaining excellent device integrity. The fabricated diodes exhibit excellent forward conduction characteristics with a turn-on voltage of 1.14~V, a Schottky barrier height (SBH) of 1.15~eV, an ideality factor of 1.20, and a specific on-resistance of 3.72~m$Ω\cdot$cm$^2$, all closely matching those of the unetched planar devices. Capacitance-voltage analysis further confirms a uniform carrier concentration of $2\times10^{16}$~cm$^{-3}$ and an SBH of 1.23~eV, indicating stable electrical characteristics after deep mesa formation. Temperature-dependent electrical measurements from 25 to 250$^\circ$C demonstrate stable thermionic-emission transport behavior, with a gradual increase in on-resistance at elevated temperatures due to phonon-limited carrier mobility. Over this temperature range, the SBH decreases from 1.16 to 1.12~eV, while the ideality factor increases from 1.21 to 1.33. The leakage current remains low throughout the entire temperature range, and the rectification ratio remains above $10^{5}$ even at 250$^\circ$C. Under reverse bias, the diodes exhibit an increase in breakdown voltage from 287V to 500V, confirming the effectiveness of geometric electric-field redistribution achieved by the deep-etched mesa structure. Silvaco TCAD simulations corroborate these experimental observations by showing significant suppression of electric-field crowding near the anode edge. These results establish Ga-assisted plasma-free etching as a reliable, damage-free field termination technique for high-performance $β$-Ga$_2$O$_3$ power devices.

physics.app-ph↗

arXiv2026

High-Purity Diamond Integration on $β$-Ga$_2$O$_3$ via Microwave Plasma CVD for Enhanced Thermal Management

The integration of diamond with $β$-Ga$_2$O$_3$ presents a promising pathway to enhance thermal management in high-power electronic devices, where the inherently low thermal conductivity of $β$-Ga$_2$O$_3$ can lead to localized self-heating and elevated junction temperatures. In this work, we demonstrate a scalable, low-damage approach for integrating polycrystalline diamond films on (010) $β$-Ga$_2$O$_3$ substrates via microwave plasma chemical vapor deposition (MPCVD), employing dielectric interlayers and polymer-assisted electrostatic nanodiamond seeding to systematically evaluate the impact of growth conditions on film morphology, grain evolution, phase purity, and optical characteristics. At a growth temperature of 800$^\circ$C, progressive grain coarsening is observed with extended deposition, with the lateral grain size increasing from 37.6 nm (53 nm thickness) to 192.5 nm for an 886 nm-thick film. This microstructural evolution is accompanied by narrowing of the diamond Raman peak and a monotonic increase in the sp$^3$ phase fraction from 95.9\% to as high as 98.9\%, indicating continued suppression of non-diamond carbon with prolonged growth. Comparison of SiO$_2$ and SiN$_x$ interlayers under identical growth conditions shows only marginal differences in grain size and phase purity, indicating limited interlayer influence once a high nucleation density is established. Importantly, diamond films exhibiting greater than 96\% sp$^3$ phase content were achieved at substrate temperatures as low as 480$^\circ$C, highlighting the viability of diamond-on-Ga$_2$O$_3$ integration under reduced thermal budgets. These findings establish a robust and scalable platform for integrating diamond on $β$-Ga$_2$O$_3$, supporting the development of next-generation power and RF devices with improved thermal management.

physics.app-ph↗

arXiv2026

HVPE Growth of Si-Doped $β$-Ga$_2$O$_3$ on Sapphire: Influence of Substrate Offcut on Structural and Electrical Properties

Si-doped $β$-Ga$_2$O$_3$ films were heteroepitaxially grown on sapphire substrates using HVPE. The influence of sapphire offcut on growth kinetics, surface morphology, crystalline quality, and electrical transport properties was systematically investigated. Growth kinetics studies revealed a strong dependence of deposition rate on HCl flow, growth pressure, and source-to-substrate distance, with growth rates reaching up to 30 $μ$m/hr. Increasing sapphire offcut angle from 0$^\circ$ to 8$^\circ$ promoted a transition from multidirectional growth to highly aligned terrace-dominated surfaces, reducing the surface roughness from 14.69 to 2.74 nm. The improved surface morphology was accompanied by enhanced crystalline quality, with phase-pure (-201)-oriented $β$-Ga$_2$O$_3$ growth and a reduction in the rocking-curve full width at half maximum from 994 to 414 arcsec as the sapphire offcut increased. Electrical characterization of films grown on 6$^\circ$ offcut substrates yielded carrier concentrations ranging from $1.0\times10^{17}$ to $3.4\times10^{18}$ cm$^{-3}$. A maximum room-temperature electron mobility of 100cm$^2$/V$\cdot$s was achieved at a carrier concentration of $1.0\times10^{17}$cm$^{-3}$, representing the highest reported room-temperature mobility for HVPE-grown $β$-Ga$_2$O$_3$ on a foreign substrate. Analysis of the temperature-dependent transport characteristics yielded donor activation energies of 35 and 90 meV together with a low acceptor concentration of $3\times10^{15}$ cm$^{-3}$, consistent with the improved crystalline quality achieved on the offcut sapphire substrates. These results demonstrate that HVPE is capable of producing high-quality $β$-Ga$_2$O$_3$ heteroepitaxial layers with good crystalline quality and carrier transport characteristics, providing a promising pathway for scalable $β$-Ga$_2$O$_3$ epitaxy on low-cost foreign substrates.

physics.app-ph↗

arXiv2025

Neutron-Assisted Breakdown Enhancement in $β$-Ga$_2$O$_3$ Schottky Diodes

This study demonstrates a substantial enhancement of breakdown voltage in $β$-Ga$_2$O$_3$ Schottky diodes through an approach that combines fast neutron irradiation with controlled post-irradiation electro-thermal annealing. Devices irradiated with 1 MeV neutrons at a high fluence of 1E15 n/cm^2 exhibited substantial degradation, including a drastic reduction in on-current and an increase in on-resistance. Electrothermal testing, conducted through simultaneous current-voltage (J-V) measurements and thermal annealing, resulted in significant recovery. After four cycles of electro-thermal testing, the devices demonstrated significant improvements in performance, with a substantial recovery of on-current and a reduction in on-resistance compared to the post-radiation condition, approaching pre-radiation levels. Most recovery occurred during the first two cycles, with diminishing improvements in later cycles, indicating that most thermally recoverable traps were mitigated early. Capacitance-voltage (C-V) measurements revealed a substantial reduction in carrier concentration, decreasing from 3.2E16 cm^-3 pre-radiation to 5.5E15 cm^-3 after the first electro-thermal testing cycle, indicating an over 82% reduction. Following the third cycle, the carrier concentration partially recovered to 9.9E15 cm^-3, reflecting a carrier removal rate of ~22 cm^-1. The breakdown voltage exhibited a remarkable enhancement, increasing from approximately 300 V to 1.28 kV (a ~325% improvement) after the first electro-thermal testing, attributed to the reduction in carrier concentration by compensating radiation-induced traps. Subsequent testing reduced breakdown voltage slightly to 940 V due to partial recovery of carrier concentration, but it remained significantly higher than pre-radiation levels.

physics.app-ph↗

arXiv2025

Single-crystalline high-quality beta-Ga2O3 pseudo-substrate on sapphire through sputtering for epitaxial deposition

Solid-phase epitaxy (SPE) of beta-Ga2O3 thin films by radio-frequency (RF) sputtering and then crystallized through high-temperature post-deposition annealing is employed on sapphire substrates, yielding a high-quality pseudo-substrate for subsequent buffer growth via MOCVD and LPCVD. Low roughness (<0.5 nm) and sharp single-crystalline diffraction peaks corresponding to the (-201), (-402), and (-603) reflections of beta-Ga2O3 were observed in the SPE beta-Ga2O3 film and the subsequent epitaxial buffer layer. N-doped Ga2O3 film on SPE Ga2O3 film grown by LPCVD showed step-assisted growth mode with reasonable electronic behavior with 45 cm^2/V-s mobility at a bulk carrier concentration of 1.3e17 cm^-3. These results suggest that SPE Ga2O3 is a promising pathway to advance the development of beta-Ga2O3 on foreign substrates.

cond-mat.mtrl-sci↗

arXiv2025

Quasi-Vertical $β$-Ga$_2$O$_3$ Schottky Diodes on Sapphire Using All-LPCVD Growth and Plasma-Free Ga-Assisted Etching

This work demonstrates quasi-vertical beta-Ga2O3 Schottky barrier diodes (SBDs) fabricated on c-plane sapphire using an all-LPCVD, plasma-free process integrating epitaxial growth of high-quality beta-Ga2O3 and in-situ Ga-assisted etching. A 6.3 micron-thick (-201)-oriented beta-Ga2O3 layer was grown on c-sapphire with a 6-degree miscut, comprising a 3.15 micron moderately doped (2.1e17 cm^-3) drift layer and a heavily doped (1e19 cm^-3) contact layer on a UID buffer. Mesa isolation used Ga-assisted LPCVD etching, producing a 60° inclined mesa sidewalls with an etch depth of 3.6 micron. SBDs showed excellent forward J-V behavior: 1.22 V turn-on, 1.29 ideality factor, and 0.83 eV barrier height. Minimum differential specific on-resistance was 8.6 mOhm*cm^2 with high current density (252 A/cm^2 at 5 V). C-V profiling revealed uniform doping at 2.1e17 cm^-3. J-V-T from 25 C to 250 C confirmed thermionic emission. Barrier height increased from 0.80 to 1.16 eV, and ideality factor from 1.31 to 1.42. Reverse leakage current remained low, increasing from ~5e-6 A/cm^2 to ~1e-4 A/cm^2; Ion/Ioff decreased from ~1e7 to 5e5. Breakdown voltages with moderately doped (2.1e17 cm^-3) drift layer ranged between 73 and 100 V, with corresponding fields of 1.66 to 1.94 MV/cm. These results highlight the potential of LPCVD-grown and etched beta-Ga2O3 devices for high-performance power electronic applications.

physics.app-ph↗

arXiv2025

LPCVD based Plasma Damage Free in situ etching of $β$-Ga$_2$O$_3$ using Solid Source Gallium

This work demonstrates a novel in situ etching technique for $β$-Ga$_2$O$_3$ using solid-source metallic Ga in a LPCVD system, enabling clean, anisotropic, plasma damage-free etching. Etching behavior was systematically studied on (-201) $β$-Ga$_2$O$_3$ films and patterned (010) $β$-Ga$_2$O$_3$ substrates as a function of temperature, Ar carrier gas flow, and Ga source-to-substrate distance. The process exhibits vapor transport- and surface-reaction-limited behavior, with etch rates reaching a maximum of $\sim$2.25~$μ$m/hr on (010) substrates at 1050~$^\circ$C and 2 cm spacing. Etch rates decrease sharply with increasing source-to-substrate distance due to reduced Ga vapor availability, while elevated temperatures enhance surface reaction kinetics through increased Ga reactivity and suboxide formation, leading to enhanced etch rates. In-plane anisotropy studies using radial trench patterns reveal that the (100) orientation produces the most stable etch front, characterized by smooth, vertical sidewalls and minimal lateral etching, consistent with its lowest surface free energy. In contrast, orientations such as (101), which possess higher surface energy, exhibit pronounced lateral etching and micro-faceting. As the trench orientation progressively deviates from (100), lateral etching increases. Facet evolution is observed between (100) and (-102), where stepped sidewalls composed of alternating (100) and (-102) segments progressively transition into a single inclined facet, which stabilizes along (100) or (-102) depending on the trench orientation. The (100)-aligned fins exhibit minimal bottom curvature, while (201)-aligned structures display increased under-etching and trench rounding.

physics.app-ph↗

arXiv2025

Thermal Annealing and Radiation Effects on Structural and Electrical Properties of NbN/GaN Superconductor/Semiconductor Junction

In the rapidly evolving field of quantum computing, niobium nitride (NbN) superconductors have emerged as integral components due to their unique structural properties, including a high superconducting transition temperature (Tc), exceptional electrical conductivity, and compatibility with advanced device architectures. This study investigates the impact of high-temperature annealing and high-dose gamma irradiation on the structural and superconducting properties of NbN films grown on GaN via reactive DC magnetron sputtering. The as-deposited cubic δ-NbN (111) films exhibited a high-intensity XRD peak, high Tc of 12.82K, and an atomically flat surface. Annealing at 500 and 950 °C for varying durations revealed notable structural and surface changes. High-resolution STEM indicated improved local ordering, while AFM showed reduced surface roughness after annealing. XPS revealed a gradual increase in the Nb/N ratio with higher annealing temperatures and durations. High-resolution XRD and STEM analyses showed lattice constant modifications in δ-NbN films, attributed to residual stress changes following annealing. Additionally, XRD phi-scans revealed sixfold symmetry in NbN films due to rotational domains relative to GaN. While Tc remained stable after annealing at 500 °C, increasing the annealing temperature to 950 °C degraded Tc to ~8K and reduced the residual resistivity ratio from 0.85 in as-deposited films to 0.29 after 30 minutes. The effects of gamma radiation (5 Mrad (Si)) were also studied, demonstrating minimal changes to crystallinity and superconducting performance, indicating excellent radiation resilience. These findings highlight the potential of NbN superconductors for integration into advanced quantum devices and their suitability for applications in radiation-intensive environments such as space, satellites, and nuclear power plants.

cond-mat.supr-con↗

arXiv2025

LPCVD Grown Si-Doped $β$-Ga$_2$O$_3$ Films with Promising Electron Mobilities

We systematically investigated the growth of Si-doped $β$-Ga$_2$O$_3$ films using LPCVD system, achieving high electron mobilities of 162 cm$^2$/V.s and 149 cm$^2$/V.s at carrier concentrations of $1.51 \times 10^{17}$ cm$^{-3}$ and $1.15 \times 10^{17}$ cm$^{-3}$, respectively, for homoepitaxial (010) $β$-Ga$_2$O$_3$ films grown on $β$-Ga$_2$O$_3$ substrates and heteroepitaxial (-201) $β$-Ga$_2$O$_3$ films grown on off-axis c-sapphire substrates with 6° miscut, representing the highest mobilities reported for LPCVD-grown $β$-Ga$_2$O$_3$ materials. Carrier concentrations were precisely tuned by varying SiCl$_4$ flow rates at a growth temperature of 1000°C, resulting in concentrations ranging from $1.15 \times 10^{17}$ to $1.19 \times 10^{19}$ cm$^{-3}$, as confirmed by both Hall and C-V measurements. The films exhibited high crystalline quality, confirmed by high-resolution XRD and Raman spectroscopy, indicating phase purity and structural integrity. Surface morphologies characterized by FESEM and AFM imaging showed a strong correlation between carrier concentrations and surface smoothness, with lower concentrations resulting in reduced RMS roughness. SIMS analysis revealed uniform Si incorporation, with low carbon, hydrogen, and chlorine impurities below detection limits, indicating high purity of the films. A high low-temperature peak mobility exceeding 843 cm$^2$/V$\cdot$s was achieved for (-201) $β$-Ga$_2$O$_3$ films at 80 K, highlighting the high purity and low compensation of these films. These findings emphasize the potential of LPCVD growth system for producing high-purity $β$-Ga$_2$O$_3$ films with thickness ranging between ~2.3-11.7 $μ$m and faster growth rates (~4.7-17 $μ$m/hr), promising transport properties, controllable doping, and scalability for developing high power vertical devices.

cond-mat.mtrl-sci↗