A. Kozanecki

Lattice location and optical activity of Yb in III-V semiconducting compounds

The location of Yb atoms in indium (InP, Ga0.51In0.49P) and gallium (GaAs, Al0.35Ga0.65As, GaAs0.6P0.4) III–V semiconducting compounds was investigated. It has been shown that Yb atoms occupy substitutional lattice positions only in indium compounds. Solid solubility of Yb in InP is of the order of 1020 cm−3, as estimated from Rutherford backscattering spectroscopy (RBS) measurements and is high by a factor of 2.5 than in 50% GaInP alloy. In gallium compounds the substitutional fraction of Yb is much below the detection limit of the RBS method, even in the case of elevated temperature (250 °C) implantation. It is suggested that optical activity of Yb is related to its substitutional location in the lattices and/or to the character of the YbP bond. The reasons for the material dependent behavior of Yb atoms in III–V crystal hosts are discussed.

Defect-mediated and resonant optical excitation of Er3+ ions in silicon-rich silicon oxide

Sensitization of the 4I13/2–4I15/2 Er3+ luminescence at 1.54 μm in silicon-rich silicon oxide (SRSO) is studied in the blue-green range. We show that defects due to excess Si in silica act as luminescence sensitizers. We also suggest that there exist two types of Er centers—isolated ones and others—strongly coupled to defects. In SRSO competition of direct, resonant excitation of Er3+ and indirect processes via defects is observed. Enhancement of the Er emission for off-resonant excitation does not seem to compensate losses in the direct channel of excitation to the 2H11/2 state of Er3+. We suggest that the emission efficiency of Er3+ is limited by distance-dependent transfer rate and little spectral overlap of the interacting states.

Evidence of interstitial location of Er atoms implanted into silicon

Silicon implanted with 2 MeV Er ions at 350 °C is studied by Rutherford backscattering and channeling spectroscopy. Angular scans through the 〈100〉, 〈111〉, and 〈110〉 axial channels were measured. The angular scan profiles of erbium, in particular flux peak in the 〈110〉 scan profile suggest that the implanted Er atoms are predominantly located in the middle of the 〈110〉 channel (the hexagonal interstitial site). Monte Carlo simulations have been performed for the assumed hexagonal interstitial location of Er atoms. They well reproduce the experimental data, giving additional evidence for the location of Er atoms in the middle of the 〈110〉 channel.

On the location of ytterbium in GaP and GaAs lattices

Yb‐implanted layers in GaP and GaAs were analyzed by Rutherford backscattering and channeling of 1.7‐MeV 4He+ ions. It is shown that Yb diffused to the surface and formed precipitates in both crystals, and the nonsubstitutional fraction of Yb in furnace annealed samples exceeded 95%. Pronounced segregation of Yb to the surface in laser annealed GaAs was also observed. Nonsubstitutional location of rare earth ions and their out‐diffusion from the crystals seem to be the main difficulties in obtaining III–V semiconductors doped with rare‐earth elements.

Excitation of Er3+ ions in silicon dioxide films thermally grown on silicon

We investigate photoluminescence (PL) and photoluminescence excitation spectroscopy of Er3+ ions implanted into SiO2 films thermally grown on silicon wafers. We show that at 10 K the Er3+ PL excited with the 514.5 nm line of an Ar laser is limited by the total number of Er ions, whereas at resonant excitation within the 960–1000 nm range the PL efficiency is rather concentration limited. Some samples were codoped with Yb3+ ions to study sensitization of the 4f–4f PL of Er3+ ions. At resonant excitation the presence of Yb leads to an enhancement of the Er3+ PL only at dilute Er concentrations.

Ytterbium as a probe of the local lattice environment in GaxIn(1−x)P crystals

Environmental effects in the intraimpurity emission of Yb3+(2F5/2‐2F7/2 intracenter transition) in GaxIn1−xP (0<x<0.3) bulk crystals are reported. Cationic disorder manifests itself in the appearance of line splittings and substantial broadening of all the emission lines with increasing Ga contents. Spectra of the crystals with small Ga contents are dominated by emission from two types of centers. One, typical of InP:Yb, corresponds to Td symmetry, while the second is most likely due to a Yb center perturbed by the presence of a single Ga atom in the next‐nearest‐neighbor position (Yb‐P4‐In11‐Ga).

Electron beam induced current profiling of the p-ZnO:N/n-GaN heterojunction

The high quality p-n structures studied consist of nitrogen doped ZnO:N films grown by plasma assisted molecular beam epitaxy on n-type GaN templates. The nitrogen concentration, determined by secondary ion mass spectroscopy, is about 1 × 1020 cm−3. Temperature dependent photoluminescence studies confirm the presence of acceptor centers with an energy level lying approximately 130 meV above the valence band. The maximum forward-to-reverse current ratio IF/IR in the obtained p-n diodes is about 107 at ±5 V, which is 2–5 orders of magnitude higher than previously reported for this type of heterojunctions. Electron-beam-induced current measurements confirm the presence of a p–n junction, located at the p-ZnO/n-GaN interface. The calculated diffusion length and activation energy of minority carriers are presented. The heterostructures exhibit strong absorption in the UV range with a four orders of magnitude high bright-to-dark current ratio.

Site selective studies of Er3+ emission centers in Er-implanted 6H-SiC

In this work the high resolution site selective photoluminescence (PL) using Fourier transform spectrometer and PL excitation spectra near 1.54μm in Er-implanted 6H-SiC were investigated. Direct evidence for the existence of three different Er3+ emitting centers which dominate luminescence at 1.54μm has been presented. The Stark splitting of the I9∕24 excited states and I15∕24 ground states for all three centers were determined. All centers reveal low local symmetry, probably due to complexes with impurities and defects.

ION BEAM ANALYSIS OF 6H SIC IMPLANTED WITH ERBIUM AND YTTERBIUM IONS

Abstract Recrystallization of 6H SiC implanted at room temperature with 800 keV Er+ and Yb+ ions was analysed using Rutherford backscattering and channeling of 1.5 MeV He+ ions. Erbium doses were 1013, 1014 and 2 × 1015cm−2. Ytterbium ions were implanted with doses of 2 × 1014and 2 × 1015cm−2 into SiC samples which had been preimplanted with a 20 times lower fluence of Er ions. It has been found that annealing within the 1000–1300°C range results in partial damage removal depending on the initial defect concentration. Perfect recrystallization is achieved at 1350°C, however it is accompanied by the segregation of rare earth impurities to the surface.

Lattice location of erbium atoms implanted into silicon

Abstract Silicon implanted at a temperature of 350°C with Er ions at energies of 0.55–2 MeV is studied by Rutherford backscattering and channeling spectroscopy. Angular scan profiles through the 〈110〉 and 〈100〉 channels taken in the (100) plane were measured. The angular scan profiles of erbium, in particular flux peaking in the 〈110〉 channel, show that the Er atoms locate predominantly in the middle of the 〈110〉 channel, corresponding to the hexagonal interstitial positions. Monte Carlo simulations have been performed for the assumed hexagonal interstitial location of the implanted Er atoms. They well reproduce the experimental backscattering spectra and angular scan profiles. It has also been shown that annealing at 600°C results in an increase of the hexagonal interstitial fraction. Additional short time annealing at 900°C leads to precipitation of an ErSi phase, which is reflected by the remarkable increase in the backscattering yield from the erbium doped layer.