arXiv subjects

Gregory J. Salamo

Publications and source records attributed to Gregory J. Salamo.

9 recordsLinked to original sources

arXiv2026

Atomic short-range order: a new degree of freedom for band engineering of GeSn semiconductor alloys

Chemical short-range order (SRO) in alloys denotes the statistical preference or avoidance between atomic species on neighboring lattice sites. Here, we highlight SRO as a powerful new mechanism for semiconductor alloy band engineering. Atom probe tomography reveals a significantly higher probability of Sn-Sn first nearest neighbors (1NNs) in thin-film GeSn alloys grown by molecular beam epitaxy (MBE) vs. chemical vapor deposition (CVD). Remarkably, although lower Sn concentration typically widens the bandgap, we find that the stronger presence of Sn-Sn 1NN pairs in MBE samples overrides this trend, resulting in a narrower bandgap despite having 2 at.\% lower Sn content than CVD samples. First-principles modeling corroborates this effect, attributing these SRO variations to distinctive surface terminations and growth temperatures between MBE and CVD. These findings establish SRO as a new degree of freedom for semiconductor band engineering beyond composition, strain, and quantum confinement, unlocking novel device mechanisms for the post-Moore era.

cond-mat.mtrl-sci↗

arXiv2025

Neutralizing Optical Defects in GeSn

Reports of photoluminescence from GeSn grown on Ge substrates by molecular beam epitaxy have been limited. We find that one limiting factor to observing photoluminescence is due to localized defect states marked by photoluminescence at 2400 nm and originating from the Ge substrate and buffer layer. In this study, we report on an optical study utilizing doped Ge(001) substrates to effectively suppress defect-related photoluminescence in GeSn layers by filling localized defect trap states. For this experiment, a GeSn layer with Sn content up to 10.5% was grown on a doped Ge(001) substrate. Analysis of the physics of the photoluminescence spectrum collected from the GeSn thin film shows an emission at the expected wavelength of 2300 nm for 10.5% Sn content and the absence of the typically observed defect related signal at 2400 nm. This understanding is further confirmed using short pulse optical excitation of the GeSn grown on undoped Ge substrates.

cond-mat.mtrl-sci↗

arXiv2025

Direct Bandgap Photoluminescence of GeSn grown on Si(100) substrate by Molecular Beam Epitaxy Growth

Group IV alloys of GeSn have gained significant attention for electronic and optoelectronic applications on a Si platform due to their compatibility with existing CMOS technology, tunable band structure, and potential for a direct bandgap at high Sn concentrations. However, synthesizing Sn-rich GeSn structures remains challenging due to the low solid solubility of Sn in Ge (less than 1%) and the substantial lattice mismatch ( about 14%) between Sn and Ge. In this work, we demonstrate the successful growth of high-quality, relaxed GeSn layers with Sn contents of 9.2% and 11.4% on Si(100) substrates via molecular beam epitaxy (MBE). As far as we know, this is the first report of direct bandgap photoluminescence observed from MBE-grown GeSn films without post-growth annealing. Structural characterizations including X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), and transmission electron microscopy (TEM) confirm uniform Sn incorporation with minimal defect formation. Atomic force microscopy (AFM) reveals smooth surfaces with low roughness. Temperature-dependent photoluminescence (PL) measurements further confirm direct bandgap emission, representing a new stage in the development of MBE-grown GeSn.

physics.app-ph↗

arXiv2024

Study of Group III-V Waveguides on Sapphire Platform for Photonic Integrated Circuits

Photonic integrated circuits (PICs) have been acknowledged as the promising platforms for the applications in data communication, Lidar in autonomous driving vehicles, innovative sensor technology, etc. Since the demonstration of optical components individually, integration of both electronics and photonics for functional devices on a common platform has been a key technology driver enhancing the stability and scalability of integrated photonic technologies. Recently, we proposed to use sapphire as a high-performance PIC platform, which enables a fully integrated solution to include a complete set of components with light source, modulator, light detection, passive devices, silicon on sapphire control circuit all-in-one sapphire platform to achieve high-performance low-cost mixed-signal optical links. In parallel to developing ac-tive components such as group III-V lasers on sapphire, in this work, the performance of group III-V straight waveguides on sapphire was systemically studied. The refractive indices contrast between GaAs, InP, GaSb, and sapphire are sufficiently high to achieve low loss over a broad optical wavelength. The calculated loss at wavelengths of 1330 nm, 1550 nm, and 2000 nm for the GaAs, InP, and GaSb rib waveguides are 0.32 dB/cm, 0.67 dB/cm, and 0.70 dB/cm, re-spectively. Since the fundamental element to construct all passive building blocks is the straight waveguide, results from this work would allow us to assess other basic passive building blocks.

physics.optics↗

arXiv2024

Algorithm-Based Linearly Graded Compositions of GeSn on GaAs (001) via Molecular Beam Epitaxy

The growth of high-composition GeSn films of the future will likely be guided via algorithms. In this study we show how a logarithmic-based algorithm can be used to obtain high-quality GeSn compositions up to 16 % on GaAs (001) substrates via molecular beam epitaxy. Within we demonstrate composition targeting and logarithmic gradients to achieve linearly graded pseudomorph Ge1-xSnx compositions up to 10 % before partial relaxation of the structure and a continued gradient up to 16 % GeSn. In this report, we use X-ray diffraction, simulation, SIMS and atomic force microscopy to analyze and demonstrate some of the possible growths that can be produced with the enclosed algorithm. This methodology of growth is a major step forward in the field of GeSn development and the first demonstration of algorithmically driven, linearly graded GeSn films.

cond-mat.mtrl-sci↗

arXiv2018

Exfoliation energy, quasi-particle bandstructure, and excitonic properties of selenium and tellurium atomic chains

Effects that are not captured by the generalized-gradient density-functional theory play a prominent effect on the structural binding, and on the electronic and optical properties of reduced-dimensional and weakly-bound materials. Here, we report the exfoliation energy of selenium and tellurium atomic chains with non-empirical van der Waals corrections, and their electronic and optical properties with the GW and Bethe-Salpeter formalisms. The exfoliation energy is found to be within 0.547 to 0.719 eV/u.c. for the selenium atomic chain, and 0.737 to 0.926 eV/u.c. for the tellurium atomic chain (u.c. stands for unit cell), depending on the approximation for the van der Waals interaction and the numerical tool chosen. The GW electronic bandgap turned out to be 5.22--5.47 (4.44--4.59) eV for the Se (Te) atomic chains, with the lowest bound obtained with the Godby-Needs (GB), and the upper bound to the Hybertsen-Louie (HL) plasmon-pole models (PPMs). The binding energy of the ground-state excitonic state ranges between 2.69 to 2.72 eV for selenium chains within the HL and GB PPM, respectively, and turned out to be 2.35 eV for tellurium chains with both approximations. The ground state excitonic wave function is localized within 50 Å along the axis for both types of atomic chains, and its energy lies within the visible spectrum: blue [2.50(GN)--2.78(HL) eV] for selenium, and yellow--green [2.09(GN)--2.28(HL) eV] for tellurium, which could be useful for LED applications in the visible spectrum.

cond-mat.mes-hall↗

arXiv2015

Probing InAs quantum dot states with surface plasmon polaritons

When placed near a thin metallic film, excitons in a quantum dot (QD) decay into surface plasmon polaritons (SPPs), guided modes of light confined at the interface of the metal/dielectric. It was reported that the interaction of SPPs with excitons in a QD may give rise to a modification in the photoluminescence (PL) spectra of the exciton energy levels, however the mechanism that explains this modification remains unclear. We propose a new methodology to excite many energy levels in an exciton by placing the QDs near a metallic array of slits fabricated onto a thin metallic gold (Au) film. By changing the position under the array where the QDs are excited we can resolve between the many energy levels. The unique features of the PL spectra obtained are the result of the strong electromagnetic field (EMF), the increase in the local density of states (LDOS) and the mesoscopic effects attributed to the gradient of the SPP field near the QDs.

cond-mat.mes-hall↗

arXiv2013

Molecular Beam Epitaxial Growth of Bi2Te3 and Sb2Te3 Topological Insulators on GaAs (111) Substrates: A Potential Route to Fabricate Topological Insulator p-n Junction

High quality Bi2Te3 and Sb2Te3 topological insulators films were epitaxially grown on GaAs (111) substrate using solid source molecular beam epitaxy. Their growth and behavior on both vicinal and non-vicinal GaAs (111) substrates were investigated by reflection high-energy electron diffraction, atomic force microscopy, x-ray diffraction, and high resolution transmission electron microscopy. It is found that non-vicinal GaAs (111) substrate is better than a vicinal substrate to provide high quality Bi2Te3 and Sb2Te3 films. Hall and magnetoresistance measurements indicate that p type Sb2Te3 and n type Bi2Te3 topological insulator films can be directly grown on a GaAs (111) substrate, which may pave a way to fabricate topological insulator p-n junction on the same substrate, compatible with the fabrication process of present semiconductor optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2007

Resonance fluorescence from a coherently driven semiconductor quantum dot in a cavity

We show that resonance fluorescence, i.e. the resonant emission of a coherently driven two-level system, can be realized with a semiconductor quantum dot. The dot is embedded in a planar optical micro-cavity and excited in a wave-guide mode so as to discriminate its emission from residual laser scattering. The transition from the weak to the strong excitation regime is characterized by the emergence of oscillations in the first-order correlation function of the fluorescence, g(t), as measured by interferometry. The measurements correspond to a Mollow triplet with a Rabi splitting of up to 13.3 micro eV. Second-order-correlation measurements further confirm non-classical light emission.

cond-mat.mtrl-sci↗