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Notes: We have studied the effect of erbium-impurity interactions on the 1.54 μm luminescence of Er3+ in crystalline Si. Float-zone and Czochralski-grown (100) oriented Si wafers were implanted with Er at a total dose of ∼1×1015/cm2. Some samples were also coimplanted with O, C, and F to realize uniform concentrations (up to 1020/cm3) of these impurities in the Er-doped region. Samples were analyzed by photoluminescence spectroscopy (PL) and electron paramagnetic resonance (EPR). Deep-level transient spectroscopy (DLTS) was also performed on p-n diodes implanted with Er at a dose of 6×1011/cm2 and codoped with impurities at a constant concentration of 1×1018/cm3. It was found that impurity codoping reduces the temperature quenching of the PL yield and that this reduction is more marked when the impurity concentration is increased. An EPR spectrum of sharp, anisotropic, lines is obtained for the sample codoped with 1020 O/cm3 but no clear EPR signal is observed without this codoping. The spectrum for the magnetic field B parallel to the [100] direction is similar to that expected for Er3+ in an approximately octahedral crystal field. DLTS analyses confirmed the formation of new Er3+ sites in the presence of the codoping impurities. In particular, a reduction in the density of the deepest levels has been observed and an impurity+Er-related level at ∼0.15 eV below the conduction band has been identified.This level is present in Er+O-, Er+F-, and Er+C-doped Si samples while it is not observed in samples solely doped with Er or with the codoping impurity only. We suggest that this new level causes efficient excitation of Er through the recombination of e-h pairs bound to this level. Temperature quenching is ascribed to the thermalization of bound electrons to the conduction band. We show that the attainment of well-defined impurity-related luminescent Er centers is responsible for both the luminescence enhancement at low temperatures and for the reduction of the temperature quenching of the luminescence. A quantitative model for the excitation and deexcitation processes of Er in Si is also proposed and shows good agreement with the experimental results. © 1995 American Institute of Physics.

Notes: Solid phase epitaxy of Er-implanted amorphous Si results in segregation and trapping of the Er, incorporating up to 2×1020 Er/cm3 in single-crystal Si. Segregation occurs despite an extremely low Er diffusivity in bulk amorphous Si of ≤10−17 cm2/s, and the narrow segregation spike (measured width ≈3 nm) suggests that kinetic trapping is responsible for the nonequilibrium concentrations of Er. The dependence of trapping on temperature, concentration, and impurities indicates instead that thermodynamics controls the segregation. We propose that Er, in analogy to transition metals, diffuses interstitially in amorphous Si, but is strongly bound at trapping centers. The binding enthalpy of these trapping sites causes the amorphous phase to be energetically favorable for Er, so that at low concentrations the Er is nearly completely segregated. Once the concentration of Er in the segregation spike exceeds the amorphous trap center concentration, though, more Er is trapped in the crystal. We also observe similar segregation and trapping behavior for another rare-earth element, Pr.

Notes: Segregation and trapping of Er during solid-phase crystallization of amorphous Si on crystalline Si is studied in a concentration range of 1016–5×1020 Er/cm3. Amorphous surface layers are prepared on Si(100) by 250 keV Er ion implantation, recrystallized at 600 °C, and then analyzed using high-resolution Rutherford backscattering spectrometry using 2 MeV He+ or 100 keV H+. The segregation coefficient k depends strongly on Er concentration. At Er interface areal densities below 6×1013 Er/cm2 nearly full segregation to the surface is observed, with k=0.01. At higher Er densities, segregation and trapping in the crystal are observed, with k=0.20. The results are consistent with a model in which it is assumed that defects in the a-Si near the interface act as traps for the Er. © 1997 American Institute of Physics.

Notes: Erbium is incorporated in crystalline silicon during molecular beam epitaxy on Si(100) at 600 °C, either in vacuum (6×10−11 mbar) or in an O2 ambient (4×10−10 mbar). Strong Er segregation takes place during growth in vacuum, and only 23% of the total deposited Er is incorporated in the epitaxial layer. Films grown in an O2 ambient show no Er segregation, and an Er concentration of 1.5×1019 Er/cm3 is incorporated in the crystal. The O content is 4×1019 O/cm3. Photoluminescence spectra taken at 10 K show the characteristic intra-4f luminescence of Er3+ at 1.54 μm for both samples, grown with and without O2. Differences found in the spectral shape indicate a difference in the local environment (presumably O coordination) of Er for the two cases. The O codoped film shows a 7 times higher Er luminescence peak intensity than the film grown without O. This is due to the higher incorporated Er concentration as well as an increased luminescence efficiency (lifetime without O: 0.33 ms, with O: 1.81 ms). The Er excitation efficiency is lower in the O codoped film than in the O-undoped film, which is attributed to the lower minority carrier lifetime in the O-doped material. Thermal annealing of the O codoped film at 1000 °C increases the excitation efficiency and hence the Er luminescence intensity. © 1996 American Institute of Physics.

Notes: The redistribution of Ga in amorphous silicon (a-Si) in the temperature range of 560–830 K by means of medium-energy ion scattering has been studied. During the initial 10 s of the annealing the diffusivity shows a transient behavior that is attributed to the change in the relaxation state of the amorphous matrix. From 560 to 830 K the diffusivity during relaxation is enhanced by seven to two orders of magnitude compared to the value for bulk a-Si. Possible models that show the observed transient diffusion behavior are discussed.

Notes: Solid phase epitaxy of amorphous SnxGe1−x films on strain relieved Ge films on Si(001) substrates was investigated for alloy compositions in the range 0.02≤x≤0.26. Films with compositions x〈0.05 crystallize by solid phase epitaxy as substitutional, strain relieved, diamond cubic alloys without phase separation or surface segregation of Sn. Films with higher Sn compositions exhibit more complicated behavior in which phase separation is believed to follow solid phase epitaxy. This sequence of transformations for higher Sn compositions yields epitaxial, substitutional, strain relieved, diamond cubic SnxGe1−x films with x∼0.05, and excess Sn is segregated in ∼100 nm size domains within the epitaxial alloy film. © 1996 American Institute of Physics.

Notes: In situ wafer curvature measurements were performed to study mechanical stress in amorphous SiO2 during Xe, Ne, and Er ion irradiation at energies in the 0.27–4.0 MeV range. Three phenomena are observed: network compaction, radiation-induced viscous flow, and a nonsaturating anisotropic deformation phenomenon. The radiation-induced viscosity is shown to be inversely proportional to the energy density deposited into atomic displacements. The relation between radiation-induced flow and diffusion is discussed in the context of the Stokes–Einstein relation. Viscous flow serves to relax stress, yet a continuous nonsaturating anisotropic deformation effect causes the stress in the irradiated layer to saturate at nonzero values: Xe irradiation at an energy below 3.6 MeV results in a tensile saturation stress; for higher energies a compressive stress builds up. These effects are explained in terms of competing bulk and surface deformation processes resulting from local heating of the SiO2 around the ion tracks. The macroscopic effect of deformation phenomena is illustrated by showing the surface morphology after 4.9 MeV Er irradiation of silica through a contact implantation mask. Finally, an in situ stress study of an alkali borosilicate glass is presented. In this case a fourth radiation induced effect is observed, namely, the generation and annihilation of volume occupying point defects. These defects are shown to anneal out at room temperature, following a broad spectrum of activation energies. © 1995 American Institute of Physics.

Notes: The optical activation, excitation, and concentration limits of erbium in crystal Si are studied. Preamorphized surface layers of Czochralski-grown (Cz) Si(100), containing 1.7×1018 O/cm3, were implanted with 250 keV Er at fluences in the range 8×1011–8×1014 cm−2. After thermal solid-phase epitaxy of the Er-doped amorphous layers at 600 °C, Er is trapped in the crystal at concentrations ranging from 3×1016 to 7×1019 Er/cm3, as measured by secondary-ion-mass spectrometry. Photoluminescence spectra taken at 77 K show the characteristic Er3+ intra-4f luminescence at 1.54 μm. Photoluminescence excitation spectroscopy shows that Er is excited through a photocarrier-mediated process. Rapid thermal annealing at 1000 °C for 15 s increases the luminescence intensity, mainly due to an increase in minority-carrier lifetime, which enhances the excitation efficiency. Luminescent Er forms clusters with oxygen: the maximum Er concentration that can be optically activated is determined by the O content, and is (3±1)×1017 Er/cm3 in Cz-Si. The internal quantum efficiency for electrical excitation of Er in Cz-Si is larger than 3×10−6. © 1995 American Institute of Physics.

Notes: Room-temperature electroluminescence at 1.54 μm is demonstrated in erbium-implanted oxygen-doped silicon (27 at. % O), due to intra-4f transitions of the Er3+. The luminescence is electrically stimulated by biasing metal-(Si:O, Er)-p+ silicon diodes. The 30-nm-thick Si:O, Er films are amorphous layers deposited onto silicon substrates by chemical-vapor deposition of SiH4 and N2O, doped by ion implantation with Er to a concentration up to ≈1.5 at. %, and annealed in a rapid thermal annealing furnace. The most intense electroluminescence is obtained in samples annealed at 400 °C in reverse bias under breakdown conditions and it is attributed to impact excitation of erbium by hot carriers injected from the Si into the Si:O, Er layer. The electrical characteristics of the diode are studied in detail and related to the electroluminescence characteristics. A lower limit for the impact excitation cross section of ≈6×10−16 cm2 is obtained. © 1995 American Institute of Physics.

Notes: When pumped with a 1.48 μm laser diode, Er-implanted Al2O3 ridge waveguides emit a broad spectrum consisting of several distinct peaks having wavelengths ranging from the midinfrared (1.53 μm) to the visible (520 nm). In order to explain these observations, three different upconversion mechanisms are considered: cooperative upconversion, excited state absorption, and pair-induced quenching. It is found that for samples with a high Er concentration (1.4 at. %), cooperative upconversion completely dominates the deexcitation of the Er3+ ions. For a much lower concentration (0.12 at. %), the influence of cooperative upconversion is strongly reduced, and another upconversion effect becomes apparent: excited state absorption. These conclusions are based on measurements of the luminescence emission versus pump intensity, and also on measured luminescence decay curves. The upconversion coefficient is found to be (4±1)×10−18 cm3/s; the excited state absorption cross section is (0.9±0.3)×10−21 cm2. It is shown that in spite of these upconversion effects, a high fraction of the Er3+ can be excited at low pump powers. For pump powers between 2 and 10 mW, the optimum Er concentration is calculated. The results show that for an Er concentration of 0.5 at. %, more than 2 dB/cm net optical gain is achievable at a pump power less than 10 mW. © 1996 American Institute of Physics.