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A parabolic potential that confines charge carriers along the growth direction of quantum wells semiconductor systems is characterized by a single resonance frequency, associated to intersubband transitions. Motivated by fascinating quantum optics applications leveraging on this property, we use the technologically relevant SiGe material system to design, grow, and characterize n-type doped parabolic quantum wells realized by continuously grading Ge-rich Si1−x Gex alloys, deposited on silicon wafers. An extensive structural analysis highlights the capability of the ultra-high-vacuum chemical vapor deposition technique here used to precisely control the quadratic confining potential and the target doping profile. The absorption spectrum, measured by means of Fourier transform infrared spectroscopy, revealed a single peak with a full width at half maximum at low and room temperature of about 2 and 5 meV, respectively, associated to degenerate intersubband transitions. The energy of the absorption resonance scales with the inverse of the well width, covering the 2.5–5 THz spectral range, and is almost independent of temperature and doping, as predicted for a parabolic confining potential. On the basis of these results, we discuss the perspective observation of THz strong light–matter coupling in this silicon compatible material system, leveraging on intersubband transitions embedded in all-semiconductor microcavities.

This study explores defect engineering in 2D materials using ion beam irradiation to modify the electrical and optical properties with potential in advancing quantum electronics and photonics. Helium and neon ions ranging from 5 to 7.5 keV are employed to manipulate charge transport in monolayer molybdenum disulfide (MoS2). In situ electrical characterization occurs without vacuum breakage post‐irradiation. Raman and photoluminescence spectroscopy quantify ion irradiation's impact on MoS2. Small doses of helium ion irradiation enhance monolayer MoS2 conductivity in field‐effect transistor geometry by inducing doping and substrate charging. Findings reveal a strong correlation between the electrical properties of MoS2 and the primary ion used, as well as the substrate on which the irradiation occurred. Using hexagonal boron nitride (h‐BN) as a buffer layer between MoS2 flake and SiO2 substrate yields distinct alterations in electrical behavior subsequent to ion irradiation compared to the MoS2 layer directly interfacing with SiO2. Molecular dynamics simulations and density functional theory provide insight into experimental results, emphasizing substrate influence on measured electrical properties post‐ion irradiation. [ABSTRACT FROM AUTHOR]

Disorder parameters of gas‐molecule decorated monolayer MoSe2 are quantitatively investigated. This material system is interesting because disorder may be introduced and removed at will by regulating the number of adsorbed gas molecules through laser annealing. These molecules electrostatically trap excitons leading to localized defect states, which are exponentially distributed in energy. Herein, experiments are described by kinetic Monte‐Carlo simulations, in summary enabling richer studies than within crystalline materials with a fixed degree of disorder. It is found that the surface coverage of the MoSe2 may reach up to one molecule per 2 nm2 and that the density of adsorbed molecules depends on the laser power by a power law. [ABSTRACT FROM AUTHOR]

Lattice defects and dielectric environment play a crucial role for 2D materials. Gas molecules can get physisorbed easily on the surface through van der Waals forces and can modify dramatically their electronic and optical properties. In this work, we investigate the impact of the physisorbed gas molecules on the optical properties of MoSe2 monolayers by means of low-temperature photoluminescence (PL). More specifically, we focus on the physics of excitons localized by gas molecules. The associated PL peak is observed to show a systematic and large red-shift with temperature and a blue-shift with laser irradiation. Both energy shifts are explained in terms of thermal instability of the localization in combination with hopping effects. Finally, a model is presented, which can reproduce the experimental data with excellent agreement. [ABSTRACT FROM AUTHOR]

We study plasmonic nanoantennas for molecular sensing in the mid-infrared made of heavily doped germanium, epitaxially grown with a bottom-up doping process and featuring free carrier density in excess of 1020 cm-3. The dielectric function of the 250 nm thick germanium film is determined, and bow-tie antennas are designed, fabricated, and embedded in a polymer. By using a near-field photoexpansion mapping technique at λ = 5.8 µm, we demonstrate the existence in the antenna gap of an electromagnetic energy density hotspot of diameter below 100nm and confinement volume 105 times smaller than λ³. [ABSTRACT FROM AUTHOR]

Disorder parameters of gas‐molecule decorated monolayer MoSe2 are quantitatively investigated. This material system is interesting because disorder may be introduced and removed at will by regulating the number of adsorbed gas molecules through laser annealing. These molecules electrostatically trap excitons leading to localized defect states, which are exponentially distributed in energy. Herein, experiments are described by kinetic Monte‐Carlo simulations, in summary enabling richer studies than within crystalline materials with a fixed degree of disorder. It is found that the surface coverage of the MoSe2 may reach up to one molecule per 2 nm2 and that the density of adsorbed molecules depends on the laser power by a power law. [ABSTRACT FROM AUTHOR]