Y. Le Guillou

Bio: Y. Le Guillou is an academic researcher from CNET. The author has contributed to research in topics: Semiconductor & Photoplethysmogram. The author has an hindex of 1, co-authored 1 publications receiving 404 citations.

Luminescence of erbium implanted in various semiconductors: IV, III-V and II-VI materials

Abstract: Luminescence of erbium implanted in various semiconductors such as Si, InP, GaAs, AlGaAs, GaInAsP, ZnTe and CdS is presented. The Er/sup 3+/ emission wavelength is the same for all these semiconductors with a bandgap energy greater than the intrashell transition energy of Er 4f electrons (0.805 eV). The Er/sup 3+/ emission intensity depends strongly on both the bandgap energy of the host semiconductor and the material temperature. To obtain an intense room temperature emission, a wide-gap semiconductor must be used.

Validity of Ultra-Short-Term HRV Analysis Using PPG—A Preliminary Study

Abstract: Continuous measurement of heart rate variability (HRV) in the short and ultra-short-term using wearable devices allows monitoring of physiological status and prevention of diseases. This study aims to evaluate the agreement of HRV features between a commercial device (Bora Band, Biosency) measuring photoplethysmography (PPG) and reference electrocardiography (ECG) and to assess the validity of ultra-short-term HRV as a surrogate for short-term HRV features. PPG and ECG recordings were acquired from 5 healthy subjects over 18 nights in total. HRV features include time-domain, frequency-domain, nonlinear, and visibility graph features and are extracted from 5 min 30 s and 1 min 30 s duration PPG recordings. The extracted features are compared with reference features of 5 min 30 s duration ECG recordings using repeated-measures correlation, Bland–Altman plots with 95% limits of agreements, Cliff’s delta, and an equivalence test. Results showed agreement between PPG recordings and ECG reference recordings for 37 out of 48 HRV features in short-term durations. Sixteen of the forty-eight HRV features were valid and retained very strong correlations, negligible to small bias, with statistical equivalence in the ultra-short recordings (1 min 30 s). The current study concludes that the Bora Band provides valid and reliable measurement of HRV features in short and ultra-short duration recordings.

Rare-earth-doped GaN: growth, properties, and fabrication of electroluminescent devices

Abstract: A review is presented of the fabrication, operation, and applications of rare-earth-doped GaN electroluminescent devices (ELDs). GaN:RE ELDs emit light due to impact excitation of the rare earth (RE) ions by hot carriers followed by radiative RE relaxation. By appropriately choosing the RE dopant, narrow linewidth emission can be obtained at selected wavelengths from the ultraviolet to the infrared. The deposition of GaN:RE layers is carried out by solid-source molecular beam epitaxy, and a plasma N/sub 2/ source. Growth mechanisms and optimization of the GaN layers for RE emission are discussed based on RE concentration, growth temperature, and V/III ratio. The fabrication processes and electrical models for both dc- and ac-biased devices are discussed, along with techniques for multicolor integration. Visible emission at red, green, and blue wavelengths from GaN doped with Eu, Er, and Tm has led to the development of flat-panel display (FPD) devices. The brightness characteristics of thick dielectric EL (TDEL) display devices are reviewed as a function of bias, frequency, and time. High contrast TDEL devices using a black dielectric are presented. The fabrication and operation of FPD prototypes are described. Infrared emission at 1.5 /spl mu/m from GaN:Er ELDs has been applied to optical telecommunications devices. The fabrication of GaN channel waveguides by inductively coupled plasma etching is also reviewed, along with waveguide optical characterization.

Optoelectronic Properties and Applications of Rare-Earth-Doped GaN

Abstract: As discussed in the accompanying articles in this issue of MRS Bulletin, the optical properties of rare-earth (RE) elements have led to many important photonic applications, including solid-state lasers, components for telecommunications (optical-fiber amplifiers, fiber lasers), optical storage devices, and displays. In most of these applications, the host materials for the RE elements are various forms of oxide and nonoxide glasses. The emission can occur at visible or infrared (IR) wavelengths, depending on the electronic transitions of the selected RE element and the excitation mechanism. Until recently, the study of semiconductors doped with RE elements such as Pr and Er has concentrated primarily on the lowest excited state as an optically active transition. The presence of transitions at IR wavelengths (1.3 and 1.54 μm) that are coincident with minima in the optical dispersion and the loss of silica-based glass fibers utilized in telecommunications, combined with the prospect of integration with semiconductor device technology, has sparked considerable interest.The status and prospects of obtaining stimulated emission in Si:Er are reviewed by Gregorkiewicz and Langer in this issue and by Coffa et al. in a previous MRS Bulletin issue. While great progress is being made in enhancing the emission intensity of Er-doped Si, it still experiences significant loss in luminescence efficiency at room temperature, as compared with low temperatures. This thermal quenching was shown by Favennec et al. to de crease with the bandgap energy of the semiconductor. Hence wide-bandgap semiconductors (WBGSs) are attractive candidates for investigation as hosts for RE doping.

Visible emission from Er-doped GaN grown by solid source molecular beam epitaxy

Abstract: Visible light emission has been obtained from Er-doped GaN thin films. The GaN was grown by molecular beam epitaxy on sapphire substrates using solid sources (for Ga, Al, and Er) and a plasma gas source for N2. Above GaN band-gap photoexcitation resulted in strong green emission. The emission spectrum consists of two narrow green lines at 537 and 558 nm and a broad peak at light blue wavelengths (480–510 nm). The narrow lines have been identified as Er transitions from the 2H11/2 and 4S3/2 levels to the 4I15/2 ground state. The intensity of the 558 nm emission decreases with increasing temperature, while the intensity of the 537 nm line actually peaks at ∼300 K. This effect is explained based on the thermalization of electrons between the two closely spaced energy levels.

1.54‐μm photoluminescence from Er‐implanted GaN and AlN

Abstract: We report the observation of the 1.54‐μm luminescence of optically excited Er3+ in ion‐implanted epitaxially grown GaN and AlN films using below band‐gap excitation. The Er‐implanted layers were co‐implanted with oxygen. At room temperature, this luminescence for GaN grown on sapphire is nearly as intense as it is at 6 or 77 K and exhibits many resolved transitions between crystal‐field levels of the 4I13/2 first excited multiplet and the 4I15/2 ground multiplet.