arXiv subjects

Sourav Sarker

Publications and source records attributed to Sourav Sarker.

6 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

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↗

arXiv2024

Qwen2.5-32B: Leveraging Self-Consistent Tool-Integrated Reasoning for Bengali Mathematical Olympiad Problem Solving

We present an innovative approach for solving mathematical problems in Bengali, developed for the DL Sprint 3.0 BUET CSE Fest 2024 Competition. Our method uses advanced deep learning models, notably the Qwen 2.5 series, with improvements made through prompt engineering, model quantization, and Tool Integrated Reasoning (TIR) to handle complex calculations. Initially, we explored various model architectures, including fine-tuned Mistral and quantized Qwen models, refining them with translation techniques, Retrieval-Augmented Generation (RAG), and custom dataset curation. Manual hyperparameter tuning optimized parameters like temperature and top-p to enhance model adaptability and accuracy. Removal of RAG and parameter adjustments further improved robustness. Our approach highlights the potential of advanced NLP techniques in solving Bengali mathematical problems.

cs.AI↗