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Photon energy upconversion, i.e. the conversion of several low-energy photons to a photon of higher energy, offers significant potential for nano-optoelectronics and nanophotonics applications. The primary challenge is to achieve high upconversion efficiency and a broad device performance range, enabling effective upconversion even at low excitation power. This study demonstrates that core/shell semiconductor nanowire heterostructures can exhibit upconversion efficiencies exceeding what was previously reported for semiconductor nanostructures even at a low excitation power of 100 mW/cm2, by a two-photon absorption process through conduction band states of the narrow-bandgap nanowire shell region. By engineering the electric-field distribution of the excitation light inside the NWs, upconversion efficiency can be further improved by eight times. This work showcases the effectiveness of the proposed approach in achieving efficient photon upconversion using core/shell NW heterostructures, resulting in some of the highest upconversion efficiencies reported in semiconductor nanostructures. Additionally, it offers design guidelines for enhancing energy upconversion efficiency.

This study revealed the crystalline quality of the dilute bismide alloy GaAs1âˆ' x Bi x grown on a GaAs(001) substrate below 250 °C using molecular beam epitaxy. The substrate temperature and As flux played a dominant role in tuning the crystal structure between amorphous and single crystalline GaAs1âˆ' x Bi x , as well as in the Bi introduction in GaAs below 250 °C. Sample characterization demonstrated a substrate temperature of 250 °C produced single crystalline ∼200 nm thick GaAs0.982Bi0.018 with clear X-ray diffraction fringes, while the lower substrate temperature of 180 °C yielded an amorphous film. Rutherford backscattering spectrometry showed sufficient As supply at the growing surface provides uniform Bi distribution. [ABSTRACT FROM AUTHOR]

We propose native oxide AlGaOx outer protective layer for GaAs/AlGaAs core-multishell nanowires to provide yearly stable stronger optical and electrical confinement within the nanowire core. We prepared core-multishell NWs consisting of GaAs core, Al0.2Ga0.8As multi-layered barrier layer, and amorphous Al0.9Ga0.1Ox outer shell, which was obtained simply by growing Al-rich AlGaAs and exposing the NWs to the ambient air. Photoluminescence from the NWs reveals that the Al0.9Ga0.1Ox outer shell provides efficient optical confinement and creates a compressive strain in the interior of the NW that enhances and blueshifts the photoluminescence of the GaAs core. [ABSTRACT FROM AUTHOR]

Deep-ultraviolet continuous-wave photoluminescence spectroscopy is performed for nano-polycrystalline diamond (NPD) synthesized by a high pressure high-temperature technique. NPD exhibits clear deep-ultraviolet emissions, which originate from intrinsic excitonic transitions assisted by a momentum-conserving phonon with a photon. Surprisingly, the peak emission energy is about 30 meV higher than that of the single-crystalline diamond. Raman scattering spectroscopy indicates that the energy difference should originate from the excitonic properties of the NPD and not the phonon. Hence, NPD has a large bandgap compared to single-crystalline diamond. [ABSTRACT FROM AUTHOR]

We study energy-band engineering with nitrogen delta (δ)-doping in GaAs-related quantum structures. A tight-binding calculation indicates that the band structure can be engineered by introducing the one-dimensional doping profile of nitrogen into GaAs. Using molecular beam epitaxy, we prepare δ-doped samples of AlGaAs/GaAs quantum wells and GaAs/δ-doped nitrogen superlattice structures at the growth temperature 560 °C. Photoluminescence obtained from the samples shows a clear redshift of the spectral peak positions dependent on the nitrogen coverage. The transition energies of the superlattice structures agree well with those obtained from photoreflectance, indicating the feasibility of band modification with a single or a multiple nitrogen δ-doped layer. [ABSTRACT FROM AUTHOR]

The optical gain and radiative current density of GaInNAs/GaAs/AlGaAs separate confinement heterostructure quantum well (QW) lasers with an emission wavelength of 1.3 μm have been theoretically investigated. The effect of carrier leakage from the GaInNAs QW to the GaAs waveguide layer is studied, and its influence on the optical gain and radiative current density is identified. The hole filling caused by an injected carrier has a strong impact on the optical gain and radiative current density, while the effect of electron filling is negligible, reflecting the smaller band-gap discontinuity in the valence band than in the conduction band. Hole occupation in the waveguide layer decreases the optical gain, and increases the radiative and threshold current densities of the laser. Our calculated threshold current density (659.6 A/cm2) at T=300 K is in good agreement with the experimental value (650.9 A/cm2) reported in literature [R. Fehse et al., IEEE J. Sel. Top. Quantum Electron. 8, 801 (2002)]. [ABSTRACT FROM AUTHOR]

Using photoluminescence (PL) spectroscopy, we carry out a comparative study of the optical properties of (Ga,In)(N,As) and (Ga,In)(N,As,Sb) quantum wells. The incorporation of Sb into (Ga,In)(N,As) results in a reduced quantum efficiency at low temperatures but an improved one at room temperature (RT). A PL line shape analysis as well as the temperature dependence of the PL peak energy reveals the existence of band-tail localized states in both material systems. The carrier localization energy is larger for (Ga,In)(N,As,Sb) than for (Ga,In)(N,As), leading to a longer radiative lifetime and thus a reduced quantum efficiency at low temperatures for the former material. The thermal quenching of the quantum efficiency is analyzed by a rate equation model, which shows that the density of nonradiative centers is reduced in (Ga,In)(N,As,Sb) resulting in an enhanced quantum efficiency at RT. [ABSTRACT FROM AUTHOR]