This paper reports the incorporation of erbium into MBE Si and Si/Ge alloys with substrate temperatures of 500°C and 700°C. Using a solid source MBE system, concentrations of erbium between 1018 and 1022 cm−3 have been studied by photoluminescence, electrical measurements, SIMS and TEM. We find no shallow donors or acceptors attributable to erbium but we observe a high concentration of deep states with an activation energy of ~360 meV. The photoluminescence output is of greatest magnitude when [Er] =2 × 1018 cm−3. Above this concentration the onset of erbium precipitates can just be observed using TEM and at even higher concentrations structured growths of erbium suicide are apparent. The effect on the optical activity of Si:Er that has subsequently been implanted with oxygen is also reported.

The understanding of the epitaxy of pure Ge layers on Si is an important step towards the synthesis of Si(m)Ge(n) (m, n < 10 monolayers) short-period superlattices. The possibility of a direct band-gap character makes these structures extremely attractive. We have grown thin buried Ge(n) (1 less-than-or-equal-to 12 monolayers) films on (100) Si by molecular beam epitaxy and studied their structural properties by a variety of techniques including Raman scattering spectroscopy, glancing incidence X-ray reflection, Rutherford backscattering, transmission electron microscopy, and extended X-ray absorption fine structure analysis. All these techniques allowed detection of the thin Ge layers and provided information about the thickness, morphology, strain distribution, and interface sharpness of these heterostructures. The Ge(n) films with n less-than-or-equal-to 5 had a two-dimensional nature and showed no sign of strain relaxation. Intermixing at the Si-Ge interfaces was present in all these films and estimated to be not more than two monolayers. This smearing at the interfaces may have contributed to the maintenance of that pseudomorphicity. A thicker Ge layer (n = 12) showed evidence of strain relaxation and clustering in three-dimensional islands.

Few non-destructive techniques are available which provide information regarding defect type, concentration and depth distribution in semiconductors. The variable-energy positron beam technique has recently demonstrated a sensitivity to near surface defects and impurities at low defect concentrations. In the present study, intrinsic silicon (100) epilayers of ~3000 Å thickness grown by MBE at different temperatures were examined by this method for evidence of changing defect concentration and type.

Si/Ge/Si (100) structures consisting of a thin epitaxial layer of Ge (1-64 monolayers) on Si and covered with a 5 nm overlayer of epitaxial Si were grown by MBE. The layers were analyzed by Rutherford backscattering(RBS)-channeling and transmission electron microscopy (TEM). For structures containing 4 or 8 monolayers of Ge, the channeling &lt;110&gt; angular scans showed unusual features that could be due to imperfect steering of the ion beam in the thin Si overlayer. Cross sectional TEN showed that the Ge epitaxy was good for these Ge thicknesses, but that for an average Ge coverage of 16 monolayers, Ge hillocks up to 90 monolayers thick occurred.

High-energy resolution X-ray photoelectron spectroscopy, with full width at half maximum of 0.41 eV for the Si 2p and of 0.54 eV for the Ge 3d, has been used to study the valence band offsets of different strained Ge layers grown on Si (100). The fractional volume changes in Ge epilayers have been measured by X-ray photoelectron diffraction and are used to correct the valence band maximum shifts caused by strained-induced spin-orbit splitting at the maxima. Band offset values of 0.80, 0.76, and 0.71 eV are found for Si/(Ge5Si5)/Si (100), Si/(Ge4Si4)/Si (100), and Si/(Ge0.5Si0.5)/Si (100) epilayers, respectively.

A careful comparison of K X-ray yields produced by 64 MeV 16O ions and 4 MeV protons of identical velocity has been carried out with ±2% precision, using thin (∼ 10 nm) targets of Ti, Cr and Ag. The incident oxygen charge state was varied from 6+ to 8+. Since the path length for charge exchange in the K-shell of oxygen greatly exceeds our target thickness, the effective 16O charge state is essentially equal to its incident value. For the highest-Z2 target (Ag), our O6+, 7+ and 8+ yields were identical (to ± 2%) but were only 24 times the proton yield. This ratio is considerably smaller than the Z12 prediction of 64, but agrees well with the factor of 28 predicted by the ECPSSR theory. The lack of dependence on charge state indicates that electron capture into the K-shell of oxygen is negligible when Z2 ⪡ Z2. For the lower-Z2 targets, a strong dependence on charge state is observed. Moreover, the measured O8+ enhancement factor relative to 4 MeV protons is 125 in Ti, i.e., twice the simple Z12 scaling value. Again, these observations are well reproduced by the ECPSSR calculations and the major cause of the enhanced O7+ and O8+ yields in Ti and Cr is electron capture into K-shell vacancies of the oxygen ion. Residual discrepancies between the X-ray yield data and the ECPSSR ionization calculations are attributed to enhancement of fluorescence yield when Z1Z2 is large and the emergence of molecular orbital effects when the projectile velocity is small relative to the target's K-shell electron orbital velocity.

InGaAs/GaAs/AlGaAs and InGaAs/InGaAsP/InP laser structures, with InGaAs quantum wells approximately 1.85 μm beneath the surface, were implanted with ions having energies up to 8.6 MeV. Intermixing of the quantum wells, after rapid thermal annealing, was monitored through changes in the energy, linewidth, and intensity of the photoluminescence peak from the quantum wells. Where the defects had to diffuse primarily through Al0.71Ga0.29As, these quantities correlate strongly, for short anneal times, with calculated vacancy generation and ion deposition at the depth of the quantum well prior to annealing. This suggests that the defect diffusion length in the AlGaAs and/or GaAs is quite low. For diffusion primarily through InP, the photoluminescence data correlated well with the calculated total number of vacancies created in the sample, suggesting that defect diffusion is very efficient in InP.

The dependence of the mean penetration depth 〈z〉 on the incident positron energy E is described by the empirical power law formula used originally for electrons and adopted by Mills & Wilson [1]. Doppler broadening as a function of incident positron energy is used to study amorphous Ge overlayers grown by thermal evaporation on GaAs substrates. It is shown that experimental data can be fitted using the power law dependence of 〈z〉 on E, with parameters that are in acceptable agreement with MC simulations for Ge.

Variable-energy positrons (VEP) were used to study the depth distribution of defects in SiN(x)/Si structures fabricated using ditertiary butyl silane (CONSI 4000) as the silicon precursor in an electron cyclotron resonance plasma chemical vapor deposition system. Films were grown to thickness ranging from 500 to 3500 angstrom at substrate temperatures between room temperature and 400-degrees-C and under various plasma conditions. The VEP results give evidence for differing concentrations of very large open-volume defects at several of the SiN(x)/Si interfaces, confirmed by transmission and scanning electron microscopy. Their presence was correlated with non-reactive organosilicon adsorption on the substrates prior to the thin film deposition.

We have determined the threshold dose for 8 MeV Bi+ ions to induce intermixing of GaAs quantum wells in AlGaAs and InGaAs quantum wells in GaAs after rapid thermal annealing at 850 °C. Our measured threshold for the GaAs/AlGaAs system agrees well with previous work. The threshold for the InGaAs/GaAs system is much lower and explains, at least in part, earlier difficulties in the lateral patterning of nanostructures by focused-ion-beam lithography.

Extremely strong (alpha, alpha) elastic scattering resonances - more than 100 times the Rutherford value - occur in O-16 at 7.35-7.65 keV and in C-12 at 5.50-5.80 MeV, thus allowing the normal RBS technique to be extended to low-Z components, such as oxygen and carbon. Both resonances have been calibrated over the appropriate 300 keV energy regime with an overall accuracy of +/- 4%. Some recent examples of their use in profiling oxygen and carbon in various substrates are given.

The Si 1s (K-shell) x-ray absorption spectra of several [(Si)m(Ge)n]p atomic layer superlattices (ALS) and a range of SixGe1−x alloy thin films grown epitaxially on both Si(100) and Ge(100) have been investigated using plane-polarized synchrotron radiation. The near-edge spectral features of ALS and alloy samples with similar (average) chemical composition are remarkably similar. The spectra of both the strained ALS and alloy samples contain features at the Si 1s threshold which exhibit a small but characteristic polarization dependence. The polarization dependence is reduced or absent in strain-relaxed materials such as annealed ALS, annealed alloys, or thick alloy films. The polarization-dependent components of the signal are attributed to anisotropic states associated with strain-induced tetragonal distortions. The sense of the polarization is inverted between samples grown on Si and those grown on Ge, consistent with the expected inversion in the spatial orientation of the strain field. An explanation is proposed for the dependence of the magnitudes of the Si 1s polarization effect on the composition of alloys and ALS.

Procedures for constrained simultaneous non-linear least squares curve fits of multiple EXAFS spectra are described and their advantages discussed. The techniques are illustrated by polarisation-dependent Ge(k) EXAFS studies of buried Ge-Si interfaces in strained layer [(Si)m(Ge)n]p/Si(100) superlattices grown by molecular beam epitaxy (MBE).

The incorporation of erbium from a solid source into molecular beam epitaxy (MBE) Si and Si/Ge alloys grown at substrate temperatures of 500 degrees C and 700 degrees C has been studied by photoluminescence, electrical measurements, secondary-ion mass spectrometry (SIMS), Rutherford backscattering (RBS) and transmission electron microscopy (TEM). Erbium concentrations between 1018 and 1022 cm-3 were obtained but the maximum photoluminescence intensity was from samples with an erbium concentration of 2*1018 cm-3. Above this concentration the onset of erbium precipitation could just be observed by TEM. The authors found no shallow donors or acceptors attributable to erbium but they observed a high concentration of deep acceptors with an activation energy of 360 meV; these may be due to impurities in the erbium source rather than being directly related to the rare earth. Implantation with oxygen is found to enhance the Er3+-related photoluminescence signal when measured at temperatures greater than 77 K but to have little effect on the low-temperature luminescence. A detailed study of the temperature dependence of the luminescence reveals tree quenching mechanisms with average activation energies of approximately 5, 20 and 130 meV. The authors attribute the first two to de-excitation effects in the matrix, and the last to processes competing with the internal 4f transition.

The differential cross-section of the 16O(α,α)16O elastic scattering resonance at 7.30–7.65 MeV has been calibrated with an overall accuracy of 4% at 170° scattering angle (laboratory frame of reference) using anodized Ta2O5 films of pre-calibrated thickness as standards. This extremely strong (about 170 times the Rutherford cross-section) and broad (about 300 keV wide) resonance varies slowly with energy in the range 7.34–7.64 MeV, has a maximum value of 837 mb/sr at 7.61 MeV, and falls off abruptly above 7.64 MeV and below 7.34 MeV. The angular dependence of the resonance was measured in the range 140–172° at incident energy 7.62 MeV and was found to increase monotonically toward 180°. This strong resonance allowed us to measure the oxygen content in the very heavy element target ThO2 pellets and in oxidized InP substrates with detection sensitivity in the atomic monolayer range. The large width of this resonance allowed oxygen depth profiling to several microns with depth resolution a few tens of nm. Measurements combined with RUMP computer simulations using TRIM stopping cross-sections and our measured values of the elastic resonance scattering cross-section have been used to depth profile SiO2 surface and buried layers in SIMOX structures.

The extension of Rutherford backscattering spectrometry (RBS) to heavier mass projectiles has several advantages over conventional RBS. To understand the interaction of heavy ions with solids properly, a systematic study of the energy straggling of MeV heavy ions has led to an empirical formula for this term. This formula, along with the stopping power, lateral spread and multiple scattering, predicts the energy width for a wide range of energies, projectiles and targets, allowing the development of realistic computer simulation for the energy spectra. This model has been verified by measurements of the depth resolution of 4 and 6 MeV C projectiles using Si/Si1−xGex/Si strained layer superlattices (SLSs) samples.

The polarization dependence of the Si K-edge X-ray absorption spectra of several [(Si)m(Ge)n]p atomic layer superlattice (ALS) materials grown on both Si(100) and Ge(100) have been investigated using plane polarized synchrotron radiation. These spectra exhibit sharp, polarization dependent, Si ls → conduction band (CB) resonance features which are absent in the spectrum of amorphous Si (a-Si). Subtraction of the spectrum of a-Si from that of the crystalline ALS materials is used to isolate the conduction band structure. A constrained curve fit analysis of up to eight data files simultaneously has been used to quantitatively analyze the signal. The CB structure is composed of a number of polarization independent components and several polarization dependent components. In [(Si)2(Ge)6]40/Ge(100) the lowest energy transition at 1839.1 eV is polarized along the surface normal (the growth direction) while a doublet structure centred at 1841 eV is polarized in the surface plane (perpendicular to the growth direction). A similar spectral pattern is found in [(Si)6(Ge)2]48/Si(100) but the polarization effect is weaker and the sense of the polarization effect is reversed. The polarization dependent signal is attributed to anisotropic states associated with strain-induced tetragonal distortions in the strained-ALS materials.

Germanium buried layers in (001) oriented silicon with thicknesses of 2–12 monolayers have been studied with synchrotron x-ray diffraction, x-ray reflectivity, and Raman scattering spectroscopy of visible light. Relaxation, strain, and intermixing have been observed via diffraction and intermixing is inferred from vibrational frequency shifts.