M. L. Swanson

Regrowth of radiation-damaged layers in natural diamond

Abstract The regrowth of radiation-damaged layers created by carbon ion implantation in natural diamond was investigated by the Rutherford backscattering/channeling technique and by optical absorption. We present the first results of rapid thermal annealing of the implanted samples directly from the 77 K implantation temperature to 1100° C as well as data for isochronal annealing. We found that isochronal annealing up to 900° C was more effective than rapid thermal annealing for amorphized samples. The critical dose for amorphization of diamond was between 1.65 × 1015 and 3 × 1015 cm−2 for 200 keV carbon ion implantation at 77 K.

Transition between Ge segregation and trapping during high‐pressure oxidation of GexSi1−x/Si

A transition from Ge segregation to trapping during high‐pressure oxidation of GexSi1−x alloys has been observed. The atomic fraction x of Ge was varied from 0.4% to 26%, and oxidations were performed at 740u2009°C under 102 atm of dry O2. It was observed that the effect of oxidation on the Ge distribution could be divided into three stages. In the initial stage of the oxidation, Ge was segregated from the growing oxide and accumulated in a Ge‐rich layer at the oxide/alloy interface. For alloys with high Ge content this initial stage was very short. In the second stage of oxidation, after a critical quantity of Ge had accumulated at the interface, there was a transition from segregation to trapping of Ge in the oxide. In the third stage, the critical amount of Ge remained segregated at the interface, and the final oxide layer was Ge free. A kinetic model based on a steady‐state equilibrium between the diffusive flux of Si across the Ge‐rich layer and the rate of Si consumption by the oxidation reaction predic...

Depth profiling of light elements using elastic recoil coincidence spectroscopy (ERCS)

Abstract We have developed elastic recoil coincidence spectroscopy (ERCS), a technique with high sensitivity to profile light elements, ranging from H up to O, in thin polymer foils or in thin samples containing heavier elements. In this technique, MeV He + ions are incident on a thin target, typically 2 μm thick, and the energies of both the forward-scattered He ions and the elastically recoiled light atoms are detected in coincidence. Concentration-versus-depth profiles can be derived from the measured number of coincidence events for a depth range of up to l μm and for all recoiled light elements. This is done by relating each pair of energies of scattered and recoiled atoms to a depth where scattering has occurred and to the mass of the recoiled elements. To analyze the coincidence spectra and to derive concentration-versus-depth profiles, computer programs have been developed. To demonstrate the capabilities of ERCS we have chosen polycarbonate films (48 at.% C, 9 at.% O) and have derived the expected uniform concentration-depth profiles from the coincidence spectra for a depth range of 1 μm. In a second experiments, ERCS was applied to profile B and O in a thin boron-diffused Si window.

Elastic recoil coincidence spectroscopy (ERCS)

Elastic recoil coincidence spectroscopy (ERCS) is a scattering-recoil coincidence technique with a high sensitivity for profiling light elements ranging from H up to O in thin film samples. In this technique He+ ions with energies of at least 2 MeV are incident on a thin target, typically 2 μm thick, and the energies of both forward scattered He ions and elastically recoiled light atoms are detected in coincidence using detectors subtending large solid angles. From each pair of energies the depth where scattering has taken place as well as the mass of recoiled atoms can be derived. ERCS is preferably applied to profile light elements in a heavier matrix and in cases where a low beam current (< 1 nA) or a low total ion dose is required to reduce damage, e.g. to study polymer samples, or for microbeam analysis. A gain in counting rates of 2–3 orders of magnitude compared to conventional elastic recoil detection analysis (ERDA) and a depth resolution of 20 nm can be achieved. In a first experiment, we applied ERCS to profile simultaneously C and O in thin polycarbonate foils and in a second experiment we have analyzed O and B in thin B-diffused Si crystals. In this paper we discuss the basic principles of ERCS and describe in detail the derivation of concentration-versus-depth profiles from coincidence spectra measured for polycarbonate and Si samples.

In situ doping by As ion implantation of silicon grown by molecular‐beam epitaxy

The incorporation and electrical activation of As, implanted in situ during molecular‐beam epitaxial growth of epilayers on Si(100), is reported. Parameters varied included growth temperature (460–700u2009°C), implantation energy (500–1000 eV), and concentration (1017→>1020/cm3 ). In general, the material was excellent with 100% activation and bulk mobilities for concentrations up to the equilibrium solid solubility limit and carrier densities in excess of five times this limit in highly doped samples.

Neutron depth profiling by coincidence spectrometry

Abstract The coincidence spectrometry technique developed by Chu and Wu [1,2] was applied to find the depth profile of 25 keV 6 Li ions implanted into an Al foil, using the 6 Li(n, α) 3 H reaction. The energies of the emitted α and 3 H particles were measured in coincidence by two particle detectors mounted on opposite sides of the Al foil. The Li concentration-depth profile was derived by mapping the 4 Heue5f8 3 coincidence counts in energy space. Because of the increase in solid angle subtended by the detectors, an improvement of two orders of magnitude in counting statistics could be achieved with no loss of depth resolution. Some suggestions for further improvement are also discussed.

Ion channeling and perturbed angular correlation (pac) studies of In-As atom Pairs in silicon

Abstract Ion channeling and PAC measurements were used to show that Inue5f8As atom pairs were formed during epitaxial regrowth of In-implanted Si(As). The pairs had an electric field gradient characterized by a frequency νq = 229 MHz and a 〈111〉 axial symmetry which implied either substitutional or tetrahedral interstitial sites of In atoms. The binding energy of the pairs was strong, as determined by measurement of their thermal equilibrium concentration. Ion channeling data showed that this binding caused an enhanced In solubility in As-doped Si, and that the In atoms in the pairs occupied substitutional lattice sites, rather than tetrahedral interstitial sites. At high As concentration, Inue5f8-As 2 atom clusters were also observed, and these In atoms were also substitutional.

Ion-channeling investigations of nitrogen in zirconium

In this study, ion-channeling techniques were used to determine the lattice sites of N in the a-Zr hexagonal close-packed (hep) structure and the effect of trapping irradiation-produced defects at the N atoms. A Zr single crystal was implanted along 〈1120〉 at 293 K with 300 keV 15N2 ions to a fluence of 2.2 × 1015 ionscm−2. The position of 15N atoms in the Zr lattice was studied using measurements of yields of 1H ions (incident energy 800 keV) backscattered from the Zr atoms and the alpha-particle yields from the nuclear reaction 19N(p, α)12C. Dechanneling of the protons in the Zr crystal provided information on changes in the overall defect concentration during the irradiation and annealing stages. n nInformation was obtained for the 〈1120〉 and 〈1010〉 channels. The 15N ion implantation resulted in an appreciably larger yield of a particles when the 1H ion beam was incident along 〈1120〉 compared to that found for incidence along 〈1010〉. Angular scans through 〈1120〉 also indicated an appreciable peaking in the α-particle yield at the aligned 〈1120〉 position. These observations indicated that the N atoms occupied the octahedral interstitial positions in the α-Zr hep lattice. Subsequent to the 15N implantation, the Zr crystal was irradiated at 35 K with 800 keV 4He ions to fluences of 1.8 × 1016 and 9.1 × 1016 ionscm−2, followed by post-irradiation annealing in both instances. No appreciable displacement of the N atoms from their lattice sites was detected after these irradiations, or during annealing up to 423 K. Hence N atoms in octahedral sites are very stable and their position remains essentially unaltered during subsequent defect formation and migration, at least up to 423 K.

Characterization Of Diamond-Like Films

Thin diamond-like and diamond films, grown by remote plasma-enhanced CVD (RPECVD) and by plasma CVD, were characterized using optical microscopy, elastic recoil detection spectroscopy (ERD), and Raman scattering. The H concentration of the films was measured by ERD and was related to the growth parameters and to the quality of the films as determined by Raman scattering. The H content of samples grown by RPECVD at the Research Triangle Institute (RTI) increased with decreasing growth temperature, varying from 6 at% H at growth temperatures from 500-720°C, to 25 at% H at a growth temperature of 20°C. The characteristic Raman frequency of natural diamond, 1332 cm-1, was observed for samples grown by Crystallume Corp. and by General Electric Corp. The samples obtained from Crystallume showed circular bulls-eye features by optical microscopy, and the width of the 1332 cm-1 peak was broad, indicating highly strained crystallites. For a sample from G.E., most of the film was good quality diamond, as indicated by a sharp 1332 cm-1 diamond frequency; the bottom (substrate) part of the film contained more H than the top part.

Doping of Diamond by Co-Implantation with Dopant Atoms and Carbon

We have investigated the challenging problem of doping diamonds, by co-implanting boron, nitrogen or phosphorus together with carbon into natural insulating type -a1 diamonds. All the implantations were done at liquid nitrogen temperature and then the samples were rapidly heated to 1100 °C. Unlike the previous attempts to dope diamond by room temperature or high temperature ion implantations, this method is expected to yield a higher doping efficiency for the implanted atoms. We have characterized the implanted diamonds with electrical and electron spin resonance (EPR) measurements. Boron doped samples showed low electrical resistivities and the EPR signal showed a strong dependence on the boron fluence, indicating a high substitutional fraction of boron atoms. The samples in which nitrogen and phosphorus were co-implanted with carbon showed lower resistivities compared with samples implanted with carbon only. Preliminary thermo-emf measurements indicated n-type conduction in these samples.