E. C. Paloura

Raman study of Mg, Si, O, and N implanted GaN

The effect of Mg, Si, N, and O ion implantation (with doses in the range 5×1013–1×1018u200acm−2), in epitaxially grown GaN samples has been studied using Raman spectroscopy. It is found that implantation increases the static disorder and activates modes that were not allowed in the as-grown material. More specifically it causes the appearance of three additional Raman peaks at 300, 420, and 670 cm−1. It is found that the position of these peaks does not depend on the type of the implant and thus they do not correspond to local vibrational modes. They are attributed to disorder activated Raman scattering (300 cm−1) and/or to implantation induced N and Ga vacancies or interstitials (420 and 670 cm−1). Finally, ion implantation causes a marginal increase of the build-in hydrostatic stress.

On the identification of N dangling bonds in SiN films using x‐ray absorption studies

Thin amorphous Si3N4 films grown on Si are studied with the near‐edge x‐ray absorption fine structure (NEXAFS) characterization technique. The N dangling bonds in N‐rich films give rise to a strong resonance line (RL) at the onset of the N 1s absorption edge, with an intensity that increases with the N/Si ratio. Further evidence on the origin of the RL is provided by the NEXAFS spectra from nitrogen‐implanted Si and Si3N4 films bombarded with Ar+ ions. The RL can be annealed out after annealing at temperatures higher than the growth temperature. We propose that the annealing of the RL is due to formation of Si—N bonds, where the Si atoms are provided by the stressed interface. The velocity of the annealing process is controlled by the diffusivity of Si interstitials in the Si3N4 and the process is characterized by an activation energy of 0.86 eV.

Modifications in α‐Si:H during thermal annealing: In situ spectroscopic ellipsometry

Device‐quality a‐Si:H thin films, grown by rf magnetron sputtering, were annealed in the temperature range up to 850u2009°C and studied by in situ ellipsometry, spectroscopic ellipsometry, and thermal evolution measurements. Annealing causes a volume reduction which can be as high as 5%, and after annealing at T≳800u2009°C the material becomes microcrystalline with an average crystallite size that depends on the annealing temperature. A detailed analysis of the peak height of the imaginary part of the pseudodielectric function 〈e(ω)〉, combined with the examination of the fundamental gap, the average gap (Penn gap), and the refractive index of a‐Si:H, provides new insight on the role of hydrogen and the structural modifications induced by thermal annealing. Based on the presented experimental findings we propose the following: (a) annealing below Ts causes reduction of the isolated microvoids; (b) the weakly bound hydrogen is correlated with regions with a high density of microvoids; and (c) the evolution of weakl...

Performance of GaxIn1−xP/GaAs heterojunctions grown by metal‐organic molecular‐beam epitaxy and metal‐organic vapor‐phase epitaxy

The electrical and structural characteristics of GaxIn1−xP/GaAs heterostructures grown by metal‐organic molecular‐beam epitaxy (MOMBE) at 480–560u2009°C and metal‐organic vapor‐phase epitaxy (MOVPE) at 700u2009°C are comparatively studied. For the lattice‐matched composition (x=0.51) transport in Schottky diodes fabricated on MOVPE material is almost thermionic and the barrier height is 0.96±0.05 eV. Deviation from the ideal thermionic behavior is observed in diodes on MOMBE material and the deviation is stronger as the growth temperature decreases. The undoped MOMBE material, grown at TG≤520u2009°C, as well as the MOVPE material, are characterized by a deep electron trap with an activation energy of 0.80±0.05 meV. The formation of this trap in the MOMBE and MOVPE material is suppressed by doping with shallow impurities, at doping levels higher than 1017 cm−3. However, doping of MOMBE Ga0.51In0.49P (hereafter called GaInP) with S and Si introduces another trap with an activation energy of about 300 meV, which has som...

NITROGEN K-EDGE NEXAFS MEASUREMENTS ON GROUP-III BINARY AND TERNARY NITRIDES

Abstract It is demonstrated that the NEXAFS spectra are a “fingerprint” of the microstructure and the composition of the ternary alloys In0.16Ga0.84N and AlyGa1−yN (y=0.25, 0.5) and the parent binary compounds GaN, AlN and InN. From the angular dependence of the N K-edge NEXAFS spectra, the hexagonal symmetry of the under study compounds is deduced and the (px, py) or pz character of the final state is identified. The energy position of the absorption edge (Eabs) of the binary compounds GaN, AlN and InN is found to red-shift linearly with the atomic number of the cation. The Eabs of the AlyGa1−yN alloys takes values in between those corresponding to the parent compounds AlN and GaN. Contrary to that, the Eabs of In0.16Ga0.84N is red-shifted relative to that of GaN and InN, probably due to ordering and/or phase separation phenomena.

Gallium K-edge EXAFS measurements on cubic and hexagonal GaN

The microstructure of undoped cubic and hexagonal GaN films is studied using temperature dependent Ga K-edge EXAFS measurements (10K-290K). The microstructure around the Ga atom is distorted due to a splitting of the second nearest neighbor shell, which consists of Ga atoms. This splitting results in an additional Ga path at a distance longer than expected by 0.8±0.05 A and is attributed to local lattice relaxation around nitrogen vacancies. From the temperature dependence of the DW factors for the 2 nd nearest neighbor shell of Ga, the Einstein temperature is equal to 318±25K.

Nitrogen K-edge X-ray absorption measurements on N- and O-implanted GaN

Abstract Nitrogen K-edge X-ray absorption measurements are used to study the effect of N+ and O+ implantation in the microstructure of GaN. In the as-grown sample, the central N atom is four-fold coordinated with 3.35 Ga atoms at the expected distance of 1.93 A, and 0.65 displaced to a distance longer by about 0.33 A. This distortion in the nearest neighbor distances is attributed to thermal strain and/or to the presence of N vacancies. Implantation with either N or O ions enhances the distortion in the microstructure and the number of the displaced Ga atoms increases from 0.65 to 1. In addition to that, implantation causes a reduction in the nearest neighbor distances by about 2% and an increase in the Debye–Waller factors. Finally, implantation induces states in the gap that are detectable in the near edge X-ray absorption fine structure (NEXAFS) spectra, where they introduce a characteristic transition at about 1.4 eV below the absorption edge.

Characterization of SiN thin films with spectroscopic ellipsometry

In this work we present spectroscopic ellipsometry (SE) measurements on a variety of SiN thin films grown with different techniques. In conjunction with the tetrahedron model for amorphous semiconductors and dielectrics and Rutherford backscattering spectroscopy results we propose that the dielectric function can be indicative of the nitrogen content in the material. In addition, we estimate major optical parameters characterizing the materials, such as the fundamental and Penn gaps and the thickness. Furthermore, we analyze and discuss the effect of annealing under vacuum conditions and in N2 atmosphere on the thin-film stoichiometry and the modification of the bonds by both SE and elastic recoil detection techniques.

On the effect of bonded hydrogen in the local microstructure of PECVD SiNx:H films

Abstract The effect of bonded hydrogen in the atomic microstructure of nitrogen-rich SiN x :H films is investigated using EXAFS. It is shown that when the hydrogen concentration is of the order of 30 at%, the measured Nue5f8Si bond length is shorter than that in the reference nitride by 2–3% and the coordination number in the 1st neighbor shell is significantly lower than the expected value of 3. Furthermore, evidence is provided on the coexistence of an a-Si:N phase, the concentration of which depends on the deposition conditions.

Characterization of ex-situ hydrogenated amorphous SiC thin films by X-ray photoelectron spectroscopy

Abstract The X-ray photoelectron spectroscopy (XPS) characterization of an ex-situ hydrogenated amorphous SiC film shows the following main features for the as-received specimen: (1) carbidic Si2p and C1s states with binding energies (BE) 100.4 ± 0.1 and 282.9 ± 0.1 eV respectively, (2) oxidic Si2p and O1s states with BE 103.2 ± 0.1 and 531.9 ± 0.1 eV respectively, (3) a strong C1s state at BE 286.8 ± 0.1 eV, (4) an O1s state with BE 533.0 ± 0.1 eV, and (5) a small adventitious carbon signal. These results, combined with the corresponding data on the as-grown film before hydrogenation and with the changes accompanying controlled Ar + sputtering, lead to the following model for the film surface: About two monolayers of adventitious carbon cover a 15 A thick, oxygen-containing carbon layer which in turn overlays a 25 A thick SiO 2 layer in contact with the bulk SiC. A good part of the oxidic layer and the oxygen in the carbon layer appear to have been inadvertently produced during the hydrogenation process.