arXiv subjects

Stephen Margiotta

Publications and source records attributed to Stephen Margiotta.

9 recordsLinked to original sources

arXiv2026

Investigation of GeSn aspect ratio trapping growth up to 8% Sn

Aspect ratio trapping (ART) growth of germanium-tin (GeSn) is a promising approach to target important objectives on the quest towards commercialization of complementary metal-oxide-semiconductor (CMOS)-compatible GeSn optoelectronics devices. Its local growth on patterned substrate allows for versatile device integration into photonics integrated circuit or for stand-alone structure like focal plane array imager. Additionally, high aspect ratio from nano-sized window can terminate early threading dislocation propagation on the oxide sidewalls, leaving subsequent growth defect-free and potentially improving the device performance. Knowledge remains missing regarding GeSn ART growth kinetics, morphology and how they evolve from thin film growth, with successful growth itself yet to be demonstrated. In this work, we report GeSn ART growth up to 8% Sn. Two configurations -- self-induced Ge core/GeSn shell for Sn content between 6% and 8%, and bulk GeSn ART for Sn content below 1% -- are observed. We present a comprehensive study on GeSn ART growth kinetics through different growth rounds and designs, showing a link between pyramid shape of ART island and successful Sn incorporation, as well as the role of growth selectivity and local heating.

cond-mat.mtrl-sci↗

arXiv2026

Study of GeSn Selective Area Growth with Demonstration of SWIR Light Detection

As germanium-tin (GeSn) epitaxial growth quality continuously improves, the search for an efficient integration strategy of GeSn optoelectronics devices into complementary metal-oxide-semiconductor (CMOS) manufacturing line also accelerates. Selective area growth (SAG) on patterned substrate emerges as a promising approach for this quest, with locally controlled growth of GeSn laser/detector suitable for either co-integration with silicon-based waveguide structure or stand-alone module like focal plane array. In this work, we report successful GeSn SAG with Sn content ranging from 3.2% to 8.7% of good optical quality, with demonstration of tunable GeSn SAG photoluminescence and GeSn SAG photoconductor device, the latter with detection cutoff wavelength up to 2 um. In addition, we present a comprehensive study of GeSn SAG condition at different window sizes, from 2 um to 100 um, and shapes: circle, square, octagon, and rectangle. Presence of loading effect is revealed, where GeSn growth rate increases as pattern fill factor and window size shrink. It introduces a different growth condition compared to thin film growth, which can weaken or inhibit Sn incorporation at very small window size and induce Sn segregation in high Sn content SAG growth.

physics.app-ph↗

arXiv2026

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

In this work, Ge-doped $\beta$-Ga$_2$O$_3$ homoepitaxial films were grown on native (010) $\beta$-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 $\beta$-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/$\beta$-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$\Omega\cdot$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 $\beta$-Ga$_2$O$_3$ as a promising platform for future high-voltage power electronic devices.

cond-mat.mtrl-sci↗

arXiv2026

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

In this work, high-quality Ge-doped (-201) $\beta$-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 $\beta$-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 $\beta$-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

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

In this work, we investigate the response of Ni/$\beta$-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$\Omega\cdot$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 $\beta$-Ga$_2$O$_3$ and demonstrate the ability of LPCVD-grown $\beta$-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↗

arXiv2025

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

The integration of diamond with $\beta$-Ga$_2$O$_3$ presents a promising pathway to enhance thermal management in high-power electronic devices, where the inherently low thermal conductivity of $\beta$-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) $\beta$-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 $\beta$-Ga$_2$O$_3$, supporting the development of next-generation power and RF devices with improved thermal management.

physics.app-ph↗

arXiv2025

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

This study demonstrates a substantial enhancement of breakdown voltage in $\beta$-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

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 {\delta}-NbN (111) films exhibited a high-intensity XRD peak, high Tc of 12.82K, and an atomically flat surface. Annealing at 500 and 950 {\deg}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 {\delta}-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 {\deg}C, increasing the annealing temperature to 950 {\deg}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↗

arXiv2024

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

We systematically investigated the growth of Si-doped $\beta$-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) $\beta$-Ga$_2$O$_3$ films grown on $\beta$-Ga$_2$O$_3$ substrates and heteroepitaxial (-201) $\beta$-Ga$_2$O$_3$ films grown on off-axis c-sapphire substrates with 6{\deg} miscut, representing the highest mobilities reported for LPCVD-grown $\beta$-Ga$_2$O$_3$ materials. Carrier concentrations were precisely tuned by varying SiCl$_4$ flow rates at a growth temperature of 1000{\deg}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) $\beta$-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 $\beta$-Ga$_2$O$_3$ films with thickness ranging between ~2.3-11.7 $\mu$m and faster growth rates (~4.7-17 $\mu$m/hr), promising transport properties, controllable doping, and scalability for developing high power vertical devices.

cond-mat.mtrl-sci↗