arXiv subjects

Alexander B. Kotlyar

Publications and source records attributed to Alexander B. Kotlyar.

4 recordsLinked to original sources

arXiv2026

Broadband Photo- and Electroluminescence from Bulk Silicon via Strong Photonic Confinement

Silicon indirect bandgap fundamentally limits its ability to emit light, hindering the development of silicon-based light sources. Here, we explore a conceptually new solution to this long-standing challenge. We demonstrate ultrabroadband photo- and electroluminescence from bulk silicon, enabled by a radiative pathway mediated by momentum-expanded photonic states that bypass phonon-assisted transitions. This mechanism, previously demonstrated using metallic nanoparticles as photon confiners, is here realized in an all-silicon system using embedded sub-1.5 nm silicon nanoparticles. Since such ultrasmall particles possess negligible intrinsic emission efficiency, we instead demonstrate that they act as photonic confiners, enabling radiative recombination in the surrounding bulk material. The agreement with prior metal-based systems confirms that confinement size, rather than material composition, governs the activation of radiative transitions in a momentum-forbidden system. The emission spans the visible to near-infrared spectral range, with electroluminescence in an undoped semiconductor device visible under ambient conditions and a quantum efficiency estimated as ~0.2%. These findings establish a new route to efficient light emission in silicon and reveal a hybrid light-matter regime in which extreme photonic confinement reshapes the electronic transition landscape.

physics.optics↗

arXiv2025

Overcoming the indirect bandgap: efficient silicon emission via momentum-expanded photonic states

Silicon's inherently indirect bandgap severely limits its radiative efficiency, posing a fundamental challenge to the development of practical silicon-based light sources. While strategies such as nanoscale confinement of electrons and holes (quantum dots), Mie resonators, and hybrid plasmonic structures have improved emission, they typically require complex fabrication workflows. Here, we demonstrate a conceptually distinct and scalable approach to enable light emission from a bulk silicon wafer by decorating its surface with gold or copper nanoparticles. Remarkably, the effect is nearly identical for Au and Cu, with particle size emerging as the dominant factor. We show that strong luminescence from the bulk wafer emerges only when the nanoparticle diameter is below 2 nm. We attribute this effect to the formation of spatially confined photonic states with broadened momentum distributions, which must enable diagonal, phonon-independent optical transitions that bypass the limitations imposed by silicon's indirect bandgap. This mechanism yields broadband emission across the visible and near-infrared spectrum, with quantum efficiencies comparable to direct bandgap semiconductors, representing a 10^5-fold increase in integrated spectral intensity. This discovery challenges the conventional understanding of silicon's optical constraints and opens a practical pathway toward high-performance silicon-based optical and optoelectronic components.

physics.optics↗

arXiv2024

Photon momentum enabled light absorption in bulk silicon

Photons do not carry sufficient momentum to induce indirect optical transitions in semiconducting materials such as silicon, necessitating the assistance of lattice phonons to conserve momentum. Compared to direct bandgap semiconductors, this renders silicon a less attractive material for a wide variety of optoelectronic applications. In this work, we introduce an alternative strategy to fulfill the momentum-matching requirement in indirect optical transitions. We demonstrate that when confined to scales below ~3 nm, photons acquire sufficient momentum to allow electronic transitions at the band edge of Si without the assistance of a phonon. Confined photons allow simultaneous energy and momentum conservation in two-body photon-electron scattering; in effect, converting silicon into a direct bandgap semiconductor. We show that this less-explored concept of light-matter interaction leads to a marked increase in the absorptivity of Si from the UV to the near-IR. The strategy provides opportunities for more efficient use of indirect semiconductors in photovoltaics, energy conversion, light detection and emission.

physics.optics↗

arXiv2014

Comparative Electrostatic Force Microscopy of Tetra- and Intra-Molecular G4-DNA

Two forms of G4-DNA, with parallel and pairwise anti-parallel strands, are studied using atomic force microscopy. The directionality of the strands affects the molecules' structural properties (different height and length) and their electrical polarizability. Parallel G4-DNA is twice as polarizable as anti-parallel G4-DNA, suggesting it is a better electrical wire for bio-nanoelectronics.

physics.bio-ph↗