arXiv subjects

Debaditya Bhattacharya

Publications and source records attributed to Debaditya Bhattacharya.

4 recordsLinked to original sources

arXiv2026

Second-Order Optical Nonlinearity of AlScN Films Grown By Molecular Beam Epitaxy

Alloys of AlN have rapidly emerged as a material platform for nonlinear optics. In this paper, we measure the second-order optical nonlinearity of AlScN films grown directly on nitrided c-plane sapphire by molecular beam epitaxy. This direct growth approach, which bypasses a thick AlN buffer layer, allows us to isolate the true nonlinear response of the AlScN film. Our results show a large enhancement of d31, but a suppression of d33 in AlScN films compared to AlN. We observe that d31 can be as high as 4.92 pm/V , which is 60 times larger than that of AlN. The development of AlScN-based photonic devices can enable energy-efficient nonlinear optical operations that can be epitaxially integrated with electronic and photonic devices based on Si, GaN and AlN.

cond-mat.mtrl-sci↗

arXiv2025

Edge emission from 265~nm UV-C LEDs grown by MBE on bulk AlN

UV-C LEDs pseudomorphically grown by MBE on bulk AlN substrates emitting at 265 nm are demonstrated. High current density up to 800 A/cm$^2$, 5 orders of on/off ratio, and low differential on-resistance of 2.6 m$\Omega\cdot$cm$^2$ at the highest current density is achieved. The LED heterostructure has a high refractive index waveguide core surrounded by n- and p-cladding layers similar to a laser diode designed for mode confinement at 270 nm to facilitate edge emission and collection of photons. Edge-emitting devices are made by cleaving the fabricated LEDs along the $m$-plane of the wurtzite crystal. Electrical injection results in emission of high energy 4.7 eV photons that are collected from the cleaved edge of the LEDs corresponding to the optical bandgap of the AlGaN active region. The contribution of power dissipation across the n- and p-regions of the diode is discussed. The n-contact resistance to n-AlGaN is identified as the largest contributor to the series resistance of the LED in the present generation of devices.

physics.optics↗

arXiv2025

Low Resistance Non-Alloyed Ohmic Contacts to High Al Composition n-type AlGaN

Ohmic contacts to high (>70\%) Al content n-type Al$_x$Ga$_{1-x}$N ultra-wide bandgap semiconductor layers in nitride electronic and photonic devices are typically fabricated by a lift-off process and high temperature ($>700^\circ$C) thermal alloying. These conditions often result in significant structural deformations of the fabricated structures and impose a harsh thermal budget on all other aspects of the device. Here, we report the fabrication of \textit{non-alloyed} \textit{as-deposited} ohmic contacts to 71\% n+AlGaN ($E_\text{g}\sim5.4$~eV) with a free carrier concentration of roughly $7\times 10^{19}$~cm$^{-3}$ and a resistivity of 4 - 5.5 m$\Omega$cm (among the lowest reported for Al$_{0.71}$Ga$_{0.29}$N) with linear $I-V$ characteristics and a contact resistivity of $\rho_\text{c}=(4.4\pm1.0)\times10^{-4}$~$\Omega$cm$^2$ (measured at zero voltage). Contacts with this quality are formed by two separate fabrication schemes: (i) metal-first patterning, and (ii) lift-off with an oxygen asher descum prior to metal deposition. Given the low threading dislocation density in the single-crystal AlN substrate used for epitaxy, the smooth morphology of the contacted epitaxial surface, and the non-alloyed nature of the contacts, this contact resistivity is attributed purely to thermionic field emission through the metal-semiconductor junction. Contact resistivity extraction at low current injection enables us to model these results using a thermionic field-emission model of contact resistivity, yielding a barrier height for Ti/Al$_{0.71}$Ga$_{0.29}$N of $(0.81\pm0.02)$ eV.

cond-mat.mtrl-sci↗

arXiv2025

The effect of boron incorporation on leakage and wake-up in ferroelectric Al_{1-x}Sc_xN

This study explores the influence of boron incorporation on the structural and electrical properties of ferroelectric Aluminum Scandium Nitride (Al_{1-x}Sc_xN ) thin films, focusing on leakage currents, wake-up effects, and imprint behavior. Al_{1-x}Sc_xN films were incorporated with varying boron concentrations and analyzed under different deposition conditions to determine their structural integrity and ferroelectric performance. Key findings include a reduction in leakage currents, non-trivial alterations in bandgap energy as well as an increasing coercive fields with increasing boron content. Films with 6-13 at.% boron exhibited N-polar growth, while those with 16 at.% boron showed mixed polarity after deposition, which affected their ferroelectric response during the initial switching cycles - as did the addition of boron itself compared to pure Al1-xScxN . With increasing boron content, wake-up became gradually more pronounced and was strongest for pure Al_{1-x}B_xN .

cond-mat.mtrl-sci↗