R.M. Gwilliam

Ion beam synthesized silicides : Growth, characterization and devices

Semiconducting silicides promise particular advantages for the development of optoelectronic devices in silicon. In particular, the direct gap of some of these silicides and the strong optical transitions make them good candidates for efficient light sources in silicon. Our work on the fabrication of iron disilicide and diruthenium trisilicide, materials and devices, using ion beam synthesis, is described here and offers a technology closely compatible with conventional silicon processing.

Characterization of the interface region during the agglomeration of silicon nanocrystals in silicon dioxide

Si nanocrystals embedded in thermally grown SiO2 have been annealed at temperatures between 400 and 900 °C in a variety of atmospheres. Positron annihilation spectroscopy has been employed to study changes in the interface regions between nanocrystalline Si (nc-Si) and SiO2 with the support of photoluminescence measurements. We find that nitrogen and oxygen are trapped in the voids around nc-Si at low annealing temperatures. High-temperature annealing during the formation of nc-Si causes hydrogen originally residing in the SiO2/substrate region to enter the SiO2 structure. Hydrogen diffuse back to the SiO2/substrate region on annealing in vacuum at 400 °C because no other impurities block its diffusion channels. At annealing temperatures above 700 °C, both nitrogen and oxygen react with nc-Si, resulting in a volume increase. This introduces stress in the SiO2 matrix, which is relaxed by the shrinkage of its intrinsic open volume. The present data suggest that nitrogen suppresses Si diffusion in SiO2, so t...

Concentration profiles of antimony-doped shallow layers in silicon

Antimony implants at 40 keV and at a dose of 4 × 1014 cm−2 have been characterized for their potential use in n-type shallow junction formation. The electrical characterization was done using sheet resistivity and Hall effect measurements. High electrical activities (>80%) and low sheet resistance values (<200 Ω/) were obtained for annealing temperatures below 800 °C. A novel differential Hall effect technique was used to obtain doping profiles at a depth resolution down to 1 nm, with a comparison made between these and Rutherford backscattering (RBS) measurements of the atomic profile as a function of annealing temperature. The antimony shows insignificant diffusion for annealing temperatures of 800 °C and below, with junction depths of about 60 nm. Electrical activation correlates well with the substitutional fraction of antimony determined by RBS.

Diagnostic measurement of ion implantation dose and uniformity with a laboratory-based positron probe

The development of a sensitive, depth-tuneable probe, with mapping capability, for low-energy ion implantation dosimetry, is described. The technique is based on the dependence of the extent of Doppler broadening of the positron annihilation linewidth upon the concentration of open-volume defects produced by the implanted ions. By varying the incident positron energy one can ensure that most of the annihilation events occur near the damage peak. A series of diagnostic measurements have been performed which demonstrate that the positron response lies on an almost universal curve, independent of ion mass and energy. The probe is highly sensitive, with a dose threshold in the 10−9 cm−2 range for many implants, and has the potential to measure dose/dose uniformity to better than 1×1011 cm−2 in the 1011−1012 cm−2 range in run times of a few seconds. Considerations underlying the development of a practical instrument based on these findings are discussed.

Ion beam synthesized Ru2Si3

In this letter we report the synthesis of the semiconductor Ru2Si3 by ion implantation into a silicon substrate. The formation of this compound has been confirmed by x-ray measurements and electron diffraction. The absorption coefficient has been determined directly by optical transmission measurements. The band gap is found to be direct with a value in the region of 0.9 eV.

Electrical characterization of silicon nitride produced by plasma immersion ion implantation

Abstract Amorphous silicon nitride (a-SiNx) thin films have been synthesized by nitrogen plasma immersion ion implantation (PIII) into a-Si:H and crystalline silicon. The electrical properties of the a-SiNx thin films were assessed using current-voltage (I–V) measurements on thin film diode structures incorporating these synthesized layers. The I–V characteristics showed that the electrical properties of the diodes were dominated by damage defects at low doses but as the time in the plasma immersion kit increased, alloying effects and the formation of silicon nitride began to take over. After long immersion times the composition of the a-SiNx saturated at about x = 0.6. Following annealing-out with hydrogen passivation, thin film diode characteristics could be obtained that were similar to those measured on high quality PECVD films with a similar composition.

Concentration dependent interdiffusion in InGaAs∕GaAs as evidenced by high resolution x-ray diffraction and photoluminescence spectroscopy

A high resolution x-ray diffraction (HRXRD) and photoluminescence study of a 10nm InGaAs∕GaAs quantum well structure repeatedly diffused under thermally accurate and timed annealing conditions demonstrates that the Fickian model with a constant coefficient of diffusion is inadequate and that the distribution of compositions of the diffused well cannot be fitted with error functions. A simple model, with the well retaining its square shape and homogeneity while dissolving the barriers when annealed, is successful in modelling both the HRXRD and photoluminescence data.

Strain compensation by heavy boron doping in Si 1– x Ge x layers grown by solid phase epitaxy

› 0.21, 0.26, and 0.34 grown by solid phase epitaxy on (001) Si wafers has beenanalyzed using high resolution electron microscopy, high resolution x-ray diffractometry,and ion channeling. The structure of the epilayers consists of a defect-free region locatednext to the layer-substrate interface and a top region which contains strain-relievingdefects. In the undoped samples the defect-free layers are partially relaxed and theirrelaxation increases as the Ge fraction increases. Substitutional boron incorporated to theSiGe lattice to levels of 2.8 6 0.3 3 10

DAMAGE PRODUCTION DURING MEV ION-IMPLANTATION IN GAAS AND INAS

Abstract 〈100〉-GaAs and InAs were implanted with 2 or 3 MeV Se + or As + ions over a wide dose range at different target temperatures. The implanted layers were investigated with respect to the damage production by means of Rutherford backscattering spectrometry. Defect profiles were calculated using the discontinuous model of dechanneling. The defect production is described within a defect-interaction and amorphization model. Self-annealing effects during room temperature implantation indicate an influence of electronic energy deposition in the near surface region.

Direct observation of indium precipitates in silicon following high dose ion implantation

We present electron microscopy, electrical measurement and secondary ion mass spectroscopy (SIMS) characterization of silicon doped with indium to concentrations well above the assumed solid solubility. Samples have been prepared using ion implantation at an energy of 40 keV to achieve as-implanted indium concentrations up to 1 ? 1020 cm?3, with post-implantation annealing performed at temperatures between 600 and 1050??C. We provide direct evidence for nano-scale indium precipitates in the silicon matrix and on the sample surface after annealing. Precipitates having a tetragonal crystal structure and a rectangular shape were observed in all of the samples implanted at the highest dose of 1 ? 1015 cm?2, and some of the samples implanted with a lower dose. Comparing SIMS and electron microscopy data allows us to conclude a solid solubility of ?1018 cm?3, consistent with previously published work (Solmi et?al 2002 J. Appl. Phys. 92 1361?6). This paper determines the limitations of indium utility as a dopant in silicon with regard to solid solubility and dose loss. The latter is in excess of 75% for samples annealed at temperatures at and above 750??C.