M. Chicoine

Microstructural evolution in H ion induced splitting of freestanding GaN

We investigated the microstructural transformations during hydrogen ion-induced splitting of GaN thin layers. Cross-sectional transmission electron microscopy and positron annihilation spectroscopy data show that the implanted region is decorated with a high density of 1 – 2 nm bubbles resulting from vacancy clustering during implantation. These nanobubbles persist up to 450 ° C. Ion channeling data show a strong dechanneling enhancement in this temperature range tentatively attributed to strain-induced lattice distortion. The dechanneling level decreases following the formation of plateletlike structures at 475 ° C. Extended internal surfaces develop around 550 ° C leading to the exfoliation of GaN thin layer.

Fabrication of high resistivity cold-implanted InGaAsP photoconductors for efficient pulsed terahertz devices

A multiple-energy, high fluence, MeV Fe ion implantation process was applied at 83 K to heavily damage a low band gap (0.79 eV) epitaxial InGaAsP layer. Optimal rapid thermal annealing conditions were found and produced a fast photoconductor with high resistivity (up to 2500 Ωcm) and Hall mobility around 400 cm2V−1s−1. Short photocarrier trapping times (0.3 ps – 3 ps) were observed via transient differential reflectivity measurements. Furthermore, photoconductive terahertz devices with coplanar electrodes were fabricated and validated. Under pulsed excitation with a 1550 nm femtosecond fiber laser source, antennas based on Fe-implanted InGaAsP are able to emit broadband radiation exceeding 2 THz. Given such specifications, this new material qualifies as a worthy candidate for an integration into optical terahertz spectrometer designs.

Terahertz emission properties of arsenic and oxygen ion-implanted GaAs based photoconductive pulsed sources

In this work we compare the characteristics of asymmetrically excited small-aperture antenna-type pulsed terahertz emitters fabricated using an ion implantation process. Our photoconductive materials consist of high resistivity GaAs substrates. Multienergy implantations of arsenic (1.2 and 2MeV) and oxygen (180, 450, and 700keV) have been used to obtain an almost uniform density of vacancies over the optical absorption depth in bulk GaAs substrates. Terahertz pulses are generated by exciting our devices with ultrashort laser pulses. Ion implantation followed by a thermal annealing process introduces nonradiative centers in our substrates which reduce the carrier lifetime and modify the shape of our terahertz pulses. Results obtained as functions of the laser excitation power and bias voltage are discussed and a comparison of the performance of these devices with conventional small-aperture antennas is given.

Organometallic vapor phase epitaxy of GaAs1−xNx alloy layers on GaAs(001): Nitrogen incorporation and lattice parameter variation

Epitaxial GaAs1−xNx alloy layers, nominally 200-nm-thick, with x up to 0.0375 were grown on GaAs(001) at temperatures Ts varying from 500 to 650 °C to investigate nitrogen incorporation and lattice parameter variations during organometallic vapor phase epitaxy from trimethylgallium, tertiarybutylarsine, and 1,1-dimethylhydrazine. Quantitative secondary ion mass spectrometry measurements (SIMS) indicate that N incorporation decreases systematically with increasing Ts to become almost negligible at 650 °C. All films are coherent with the substrate as judged by high-resolution x-ray reciprocal lattice mapping although atomic force microscopy and cross-sectional transmission electron microscopy reveal the presence of cracks in films with x>0.02. High-resolution x-ray diffraction measurements combined with SIMS analyses indicate that the lattice constant decreases linearly with increasing x following closely the predictions of Vegard’s rule for x<0.03. At higher concentrations, the lattice constant decreases m...

Bandgap and optical absorption edge of GaAs1−xBix alloys with 0 < x < 17.8%

The compositional dependence of the fundamental bandgap of pseudomorphic GaAs1−xBix layers on GaAs substrates is studied at room temperature by optical transmission and photoluminescence spectroscopies. All GaAs1−xBix films (0 ≤ x ≤ 17.8%) show direct optical bandgaps, which decrease with increasing Bi content, closely following density functional theory predictions. The smallest measured bandgap is 0.52 eV (∼2.4 μm) at 17.8% Bi. Extrapolating a fit to the data, the GaAs1−xBix bandgap is predicted to reach 0 eV at 35% Bi. Below the GaAs1−xBix bandgap, exponential absorption band tails are observed with Urbach energies 3–6 times larger than that of bulk GaAs. The Urbach parameter increases with Bi content up to 5.5% Bi, and remains constant at higher concentrations. The lattice constant and Bi content of GaAs1−xBix layers (0 < x ≤ 19.4%) are studied using high resolution x-ray diffraction and Rutherford backscattering spectroscopy. The relaxed lattice constant of hypothetical zincblende GaBi is estimated t...

Influence of the film properties on the plasma etching dynamics of rf-sputtered indium zinc oxide layers

The etching characteristics of indium zinc oxide (IZO) films were investigated using a high-density plasma in Ar, Ar∕Cl2, and Ar∕CH4∕H2 chemistries. The IZO layers were deposited by means of rf magnetron sputtering, in which the target composition and growth temperature were varied to selectively tune the film properties. X-ray diffraction, elastic recoil detection, and Rutherford backscattering spectroscopy were used to determine the crystallization quality, atomic density, and composition of the as-deposited IZO films. As the In∕(In+Zn) composition ratio in the IZO layer increases, the etch yield in Ar and Ar∕Cl2 plasmas remains fairly constant, indicating that the etching dynamic is essentially independent of the film properties. In sharp contrast, a strong increase of the IZO etch yield with the In∕(In+Zn) fraction is observed in Ar∕CH4∕H2 plasma due to the preferential desorption of the group-III etch products. By comparing these experimental data to the predictions of a simple rate model accounting ...

Nanocavities in He implanted InP

The formation of nanocavities in InP(001) by room-temperature He implantation and subsequent thermal annealing was studied using a combination of high-resolution x-ray diffraction (HRXRD) and cross-sectional transmission electron microscopy (XTEM) analyses. The nanocavities size and depth distributions were measured as a function of He ion dose φHe (1×1016 to 9×1016 cm−2) and ion energy E (25 to 70 keV), as well as annealing temperature Ta (600 to 750 °C) and time ta (5 to 25 min). HRXRD scans from annealed samples indicate an expansion of the InP lattice, contrary to what is usually observed following heavy-ion implantation. The critical φHe and Ta values for the formation of nanocavities were found by XTEM analysis to be between 1 and 2×1016 cm−2 and between 600 and 620 °C, respectively. Cavities of diameter 4–50 nm with {110}, {101}, and {001} facets were obtained. Increasing Ta and ta resulted in larger cavities and increasing φHe produced a larger number of cavities. Furthermore we find that nanocavi...

Novel beam effect: mass transport due to the lateral component of the ion momentum

Abstract A new effect in ion beam-solid interaction is described, namely mass transport in the bombarded solid due to lateral momentum transfer from the ions. It manifests itself, after high energy (several MeV) ion implantation at low temperature through a contact mask, as a surface depression at one end, and an elevated surface at the other end of the masked region. It is only evident for off-normal implantations, and then the depressed surface is always on the windward side of the mask and the elevated surface region is always on the downwind side, and it increases superlinearly with ion energy. Electronic stopping effects play a major role not only for the momentum transfer but also for the plastic deformation of the solid.

Ion channeling effects on quantum well intermixing in phosphorus-implanted InGaAsP/ InGaAs/ InP

been used to study In 0.73 Ga 0.27 As 0.57 P 0.43 /I n 0.53 Ga 0.47 As/ InP single quantum well heterostructure after 20-keV phosphorus ion implantation followed by rapid thermal annealing. The annealing process induces intermixing in the heterostructures and results in the blueshift of the quantum well peak emission. In order to investigate ion channeling effects on this band-gap tuning process, room-temperature implantations have been performed at tilt angles of 0° and 7° with respect to the sample 001-growth axis. We show that the ion channeling increases the blueshift from 24 to 42 nm, while it reduces both the density of the nonradiative defects within the active layer and the structure disordering. These features are attributed to the nature of the damage generated by channeled ions. The band-gap increase observed in the sample implanted at 0° is consistent with the formation of a compressive strain at the barrier/quantum well interface, whose intensity is measured by Raman spectroscopy.

Characterization of GaAs1−xNx epitaxial layers by ion beam analysis

GaAs1−xNx epitaxial layers grown on (001) GaAs substrates by metal organic vapor phase epitaxy, with x ranging from 0.01 to 0.036, were characterized by ion beam analysis. The layers thickness and quality were measured by Rutherford backscattering spectrometry (RBS) in channeling mode. The channeling results confirm that GaAs1−xNx epitaxial layers are of high crystalline quality, in agreement with high resolution x-ray diffraction and transmission electron microscopy analyses. For the sample with x=0.036, the results reveal a 0.7 at. % of misplaced (or highly locally strained) Ga or As atoms. More than 80% of nitrogen atoms in this layer occupy substitutional sites, as determined by the 14N(α,p)17O nuclear reaction analysis (NRA). Furthermore, RBS analyses using a 5 MeV O3+ probe beam reveal measurable departures from III–V stoichiometry near the surface, which remains unexplained. Finally, the total content of nitrogen in the layers measured both by NRA and elastic recoil detection by time-of-flight are ...