B.J. Sealy

Characteristics of rare-earth element erbium implanted in silicon

Rare‐earth element erbium implanted into silicon was studied by photoluminescence and Rutherford backscattering analysis. Two sets of luminescent bands related to the weakly crystal field split spin‐orbit levels 4I13/2→4I15/2 of Er 3+ (4f 11) at different lattice sites having different symmetries were observed.

Interdiffusion in InGaAs/GaAs quantum well structures as a function of depth

Interdiffusion in InGaAs/GaAs quantum wells has been studied using photoluminescence to follow the development of the diffusion with time in a single sample. Two distinct regimes are seen; a fast initial diffusion and a second steady‐state diffusion. The steady‐state diffusion was found to be dependent on the depth of the quantum well from the surface and to correlate with published data on the indiffusion of gallium vacancies into gallium arsenide.

Visible photoluminescence at room temperature from microcrystalline silicon precipitates in SiO2 formed by ion implantation

We have investigated the photoluminescence of microcrystalline silicon formed in SiO2 layers by ion beam synthesis. 28Si+ ions over the dose range 1 × 1017 to 6 × 1017 cm−2 at energies of 150 keV and 200 keV were implanted into thermal oxide. Samples were annealed in a halogen lamp furnace at temperatures of 900°C, 1100°C and 1300°C for times between 15 and 120 min. The implanted layers were analysed by Rutherford Backscattering Spectroscopy (RBS), Cross-Sectional Transmission Electron Microscope (XTEM) and Photoluminescence (PL) (80 K to 300 K) using an Ar laser of 488 nm wavelength. Room temperature (300 K) visible photoluminescence has been observed from all the samples. XTEM confirms the existence of Si microcrystals (within the SiO2 layers), which typically have a diameter within the range of 2–15 nm. The luminescence peak wavelength was about 600 nm or 800 nm, depending upon processing. Changes in the peak wavelength and intensity from these samples and other samples in which the crystallites were reduced in size by thermal oxidation, show trends which are generally consistent with quantum confinement, however, other mechanisms cannot be ruled out.

The thermal stability of AlN

The thermal stability of AlN powders and thin films has been investigated using reflection high-energy electron diffraction (RHEED) and X-ray diffraction. AlN powder was treated thermally and chemically to assess the oxidation resistance of this compound and to identify the phases formed. The results show that AlN is stable up to 1000° C in air and remains stable up to 1400° Cin vacuo. γ-AIOOH is formed when AlN is treated with water at 100° C but AlN does not react readily with atmospheric moisture at room temperature. The thermal stability of thin films of AlN on GaAs has been evaluated at temperatures between 900 and 1100° C in a nitrogen atomosphere. It was found that AlN did not oxidize under these conditions. Pure AlN is a suitable encapsulant for GaAs at high annealing temperatures in an inert atmosphere.

Electrical, Rutherford backscattering and transmission electron microscopy studies of furnace annealed zinc implanted GaAs

Abstract Electrical, Rutherford backscattering and transmission electron microscopy measurements have been carried out on GaAs samples implanted with 150 keV, 1.10 15 zinc ions/cm 2 and furnace annealed in the temperature range from room temperature to 900°C. A correlation between three types of measurement technique was established and four distinct annealing stages have been identified. For perfect recrystallization and maximum electrical activation an annealing temperature of 900°C is required. The maximum peak hole concentration was in the range 1–2.10 19 holes/cm 3 .

Thermal stability of plasma deposited thin films of hydrogenated carbon–nitrogen alloys

The need to grow high quality semiconducting hydrogenated amorphous carbon (a-C:H) thin films to allow n-type electronic doping by nitrogenation has lead us to deposit films with low paramagnetic defect density (1017 cm−3). The films were grown on the earthed electrode of a radio frequency driven plasma enhanced chemical vapor deposition system using methane, helium and a range of nitrogen concentrations as the precursor gases. The deposited films are shown to be polymer like. Changes in the chemical structure and relative bond fractions as a function of the nitrogen flow rate into the plasma chamber and ex situ annealing are reported. Particular attention is paid to changes in the film structure after annealing at 100 °C, since an increase in the E04 optical band gap is observed as a function of nitrogen flow after the anneal. This suggests a decrease in the defect density of the film.The need to grow high quality semiconducting hydrogenated amorphous carbon (a-C:H) thin films to allow n-type electronic doping by nitrogenation has lead us to deposit films with low paramagnetic defect density (1017 cm−3). The films were grown on the earthed electrode of a radio frequency driven plasma enhanced chemical vapor deposition system using methane, helium and a range of nitrogen concentrations as the precursor gases. The deposited films are shown to be polymer like. Changes in the chemical structure and relative bond fractions as a function of the nitrogen flow rate into the plasma chamber and ex situ annealing are reported. Particular attention is paid to changes in the film structure after annealing at 100 °C, since an increase in the E04 optical band gap is observed as a function of nitrogen flow after the anneal. This suggests a decrease in the defect density of the film.

Optical properties and phase transformations in α and β iron disilicide layers

Abstract Ion beam synthesis (IBS) has been used to fabricate semiconducting β-FeSi2 and metallic α-Fe0.82Si2. For all of the doses studied a photoluminescence (PL) signal is observed at 1.54 μm. This signal is first seen after annealing at 800°C and increases in intensity with a commensurate decrease in full width half maximum (FWHM) as the anneal temperature is increased up to 920°C. Likewise the intensity increases and FWHM decreases as the anneal time at 920°C is increased up to 18 h. Optical absorption measurements reveal a linear relationship between the square of the absorption coefficient and the incident photon energy, indicating a direct allowed transition from a semiconductor (β-FeSi2) with a band gap of about 0.87 eV. After annealing at 1000°C no PL or absorption is observed in this spectral region; this is because a thicker, conducting layer of α-Fe0.82Si2, containing ~ 18% Fe vacancies has then been formed. If an α-Fe0.82Si2 layer is subsequently annealed below the phase transition temperature (~ 950°C) then the PL signal reappears as the layer is largely reconverted back to the s-phase.

Investigation of the luminescence properties of Si/βFeSi2/Si heterojunction structures fabricated by ion beam synthesis

Abstract Photoluminescence at 1.54 μm has been observed from discontinuous βFeSi 2 layers fabricated by ion beam synthesis in silicon wafers. A minimum full width half maximum (FWHM) value of 3 me V, measured at 5 K, was obtained from a sample implanted to a dose of 2 × 10 17 Fe ions cm −2 at an energy of 200 ke V, after an 18h anneal at 920°C. When the incident energy was increased the FWHM value also increased reflecting the increased residual damage in the sample after annealing. Room-temperature optical absorption measurements indicate a direct band gap of about 0.86–0.88 e V.

Rapid thermal annealing of Mg++As+ dual implants in GaAs

Mg+ and As+ ions were implanted into GaAs to study the effects of dual implantation on the electrical properties. Increased electrical activity and significantly less redistribution of the magnesium were observed for the dual implants compared with the single implants. A maximum activity of 40% with a sheet resistivity as low as 185 Ω/⧠ was obtained for the dual implant compared to an activity of 27% with a resistivity of 250 Ω/⧠ for the single implant at a dose of 1015 cm−2. A peak hole concentration approaching 4×1019 cm−3 was recorded for the dual implant annealed at 900 °C for 30 s.

Review of Rapid Thermal Annealing of Ion Implanted GaAs

Results of rapid thermal annealing (RTA) of ion implanted for times of 1–100s are reviewed. Comparison between silicon, selenium, and other donor ions is presented and the highest doping levels achieved are highlighted. P‐type dopants such as zinc, magnesium, and beryllium are also discussed, as well as the use of dual implants to enhance activation. N‐type doping levels up to have been demonstrated, whereas for p‐type doping levels approaching 1020cm−3 with little diffusion have been achieved. The less stringent requirements imposed on both the encapsulant and substrate material when RTA is used are also discussed.