T. E. Jackman

Selective amorphization of ion‐bombarded SiGe strained‐layer superlattices

Si/SixGe1−x multilayers were implanted with Si ions of 540 keV at doses between 1.0×1014 and 2.5×1015 ions/cm2. Channeling spectra were taken using 3 MeV B++ ions. These measurements showed a rapid increase of the Ge minimum yield with implantation dose. The increases were paralleled by a growth of disorder peaks in those parts of the Si backscattering spectrum corresponding to the SixGe1−x layers. After 1.2×1015 Si ions/cm2 the SiGe layers were completely amorphized. Cross‐sectional transmission electron microscope pictures confirmed the selective amorphization of the SiGe layers. Annealing of an irradiated sample resulted in recrystallization of all the amorphous layers in the 450–550 °C temperature range.

Channeling studies of implantation damage in SiGe superlattices and SiGe alloys

Abstract Recent studies have shown a large difference in damage rate between the Si and the SiGe layers of strained-layer superlattices. In order to understand this phenomenon, we have measured amorphisation rates in strained SiGe layers of different composition grown on both Ge and Si substrates and compared these with the damage rates in a pure Si and in a pure Si and in SiGe bulk (i.e. strain free) crystals. The combined data suggest that the presence of Ge, rather than the strain, causes the enhancement of the amorphisation rate.

On the electron microscope contrast of doped semiconductor layers

Abstract The origin of the electron microscope contrast of doped semiconductor layers viewed in cross-section has been investigated. It has been demonstrated that the built-in elastic displacements associated with misfitting dopant atoms is the principal source of electron scattering contrast when imaging layers of relatively low dopant concentration. In the absence of atomic misfit, any observed contrast must be associated with the difference in atomic scattering factors of the dopant and matrix atoms. Diffraction contrast experiments on substitutionally doped B–Si multilayers indicate an increase in the two-beam normal and anomalous absorption coefficients and extinction distance which are quantitatively shown to be a manifestation of the relatively large atomic misfit between B and Si atoms. Furthermore, the image contrast is a sensitive function of the configuration of the dopant atoms; a reduction in the dopant atom misfit strain via clustering or precipitation will result in lower contrast levels as...

Compositional disordering of strained InGaAs/GaAs quantum wells by Au implantation: Channeling effects

Compositional disordering of strained InGaAs quantum wells by the implantation of Au ions has been examined as a function of the incident implantation angle. Together, photoluminescence and secondary ion‐mass spectrometry demonstrate that mixing at depths significantly greater than the mean‐implantation range is due to the creation of point defects by ions which have channeled into the crystal. Compositional disordering effects due to the rapid thermal diffusion of Au ions was negligible.

Absolute calibration of the 16O(α,α)16O elastic scattering resonance at 7.30–7.65 MeV and applications to oxygen depth profiling

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.

Point-defect production in arsenic-doped silicon studied with variable-energy positrons

Silicon epilayers grown by molecular beam epitaxy and doped in-situ using low-energy implantation were examined using a variable-energy positron beam. The samples had been previously characterized using electrical measurements, ion channeling, SIMS, and electron microscopy. The positron results show that defects have been created in layers grown at 460°C and in the highly doped layers grown at 700°C. The assignment of defect structures is difficult at present, but is consistent with the formation of As clusters or Asvacancy complexes.