Nathaniel Woodward

Excitation of Eu3+ in gallium nitride epitaxial layers: Majority versus trap defect center

We report studies of the excitation mechanism of Eu ions in situ doped during organometallic vapor-phase epitaxy (OMVPE) of GaN. We find that the bright red emission under above-band gap excitation originates primarily from an incorporation site that exhibits high excitation efficiency but occurs in low relative abundance ( 97%).

Laser fabrication of semiconducting ferroelectric single crystal SbSI features on chalcohalide glass

This paper demonstrates a laser direct-write method to form single crystal semiconductor ferroelectric SbSI features on chalcogenide glasses for integration into infrared devices. The method overcomes a major limitation of thin-film deposition techniques, viz. the uncontrolled stoichiometry of SbSI due to very different vapor pressure of its constituents. It promises advantages of selective single-crystal formation and control on the morphology of the crystal. Mechanism of and control parameters for laser crystallization are explored.

Crystal-field split levels of Nd3+ ions in GaN measured by luminescence spectroscopy

We present the Stark energy sublevels of Nd3+ ions in GaN grown by plasma-assisted molecular beam epitaxy as determined by luminescence spectra. We correlate the photoluminescence spectra with transitions from the F43/2 excited state to the I49/2, I411/2, and I413/2 multiplets of the Nd3+ ion for above and below bandgap excitation, with the strongest emission occurring at 1.12 eV (1106 nm). We determine a splitting of the F43/2 excited state to be 4.1 meV. From photoluminescence excitation spectra, we also identify the Stark sublevels of the upper states F45/2, H29/2, F47/2, S43/2, G27/2, and G45/2. Photoluminescence excitation spectra reveal an optimal excitation energy of 1.48 eV (836 nm). Site-selective spectroscopy studies using combined excitation-emission spectroscopy with confocal microscopy indicate enhanced substantial doping at the Ga site.

Near-infrared photoluminescence properties of neodymium in in situ doped AlN grown using plasma-assisted molecular beam epitaxy

We present luminescence spectroscopy measurements of in situ Nd doped AlN grown by plasma-assisted molecular beam epitaxy. A Nd concentration as high as 0.08 at. % is incorporated into the host material. The Nd incorporation efficiency within the AlN matrix is found to be highly sensitive to the Al flux but independent of the substrate temperature (between 800 °C to 950 °C). Photoluminescence, photoluminescence excitation, and combined excitation-emission spectroscopy (CEES) spectra are used to identify the Stark sublevels of the following manifolds: 4I9/2, 4I11/2, 4I13/2, 4F3/2, 4F5/2, 2H9/2, 4F7/2, 4S3/2, 4G5/2, and 4G7/2. A main Nd incorporation site and two minority sites are identified using CEES measurements.

Crystal-field analysis and Zeeman splittings of energy levels of Nd3+ (4f3) in GaN

The crystal-field splitting and Zeeman splitting of energy levels of Nd3+ (4f3) doped into semi-conducting GaN (3.2 eV) grown in the hexagonal (huntite) phase by plasma-assisted molecular beam epitaxy have been modeled using a parameterized Hamiltonian defined to operate within the complete 4f3 electronic configuration of Nd3+ substituted for Ga3+ in the lattice. Zeeman splittings were obtained by applying magnetic fields up to 6.6 T with the fields parallel and perpendicular to the crystallographic c-axis. The experimental energy (Stark) levels were obtained from a recent spectroscopic study on the same samples, where the combined excitation emission spectroscopy (CEES) identified the majority of Nd3+ ions as replacing Ga3+ in sites of C3v symmetry. The manifolds of Nd3+ (4f3)2S+1LJ modeled for the crystal-field splitting include the ground state, 4I9/2, and excited states 4I11/2, 4I13/2, 4F3/2, 4F5/2, 2H9/2, 4F7/2, 4S3/2, 4G5/2, and 4G7/2. The energies of 41 experimental Stark levels from these manifold...

Optical and magneto-optical properties of neodymium and erbium doped gallium nitride epilayers

Following the commercial availability of high power III-nitride light emitting diodes in the 370–540 nm range, a strong desire for efficient rare earth-doped (In)GaN epilayers has developed to produce light source and electrically pumped optical amplifiers in the visible and IR spectral region. To this end, Er-doped GaN epilayers have been grown by OVMPE with excellent crystal quality [1]. Similar success has been achieved with in-situ doped Nd:GaN samples grown by plasma-assisted MBE [2]. For each dopant, we have studied site-selective emission spectroscopy using combined excitation-emission spectroscopy (CEES) to give important insight for the optimization of the growth conditions. Aside from application in novel light sources, there has been an increasing interest in the magnetic properties of the dilute RE-dopants, which are found to introduce ferromagnetism to the GaN host [3] enabling the realization of spin-memory based on this class of material [4].

Site Selective Spectroscopy on Erbium Ions in Stoichiometric Lithium Tantalate

Ferroelectric materials such as lithium niobate (LiNbO3) and the isostructural lithium tantalate (LiTaO3) play an important role in integrated optics since they allow the possibility to combine their favourable electro-optical, acousto-optical, and nonlinear properties with the ability to add additional functional groups by doping. Examples are rare earth ions that act as active centres for laser and optical amplifier applications. We present our sites-selective spectroscopic studies on Er3+ doped nearly stoichiometric LiTaO3 that include results about the assignment of excitation and emission peaks to different sites, symmetry properties of these sites, energy transfer among major sites, and up-conversion efficiencies. We compare the results in LiTiO3 with the corresponding ones in the much better studied LiNbO3 host and find that the type of centres and their spectral feature are very similar.