Volume 83, Issue 6, 15 March 1998
Index of content:
- CROSS-DISCIPLINARY PHYSICS (PACS 81-98)
83(1998); http://dx.doi.org/10.1063/1.367137View Description Hide Description
We present a study of the different mechanisms governing the growth of GaAs by atomic layer epitaxy (ALE). The gallium precursors such as trimethylgallium (TMGa), triethylgallium (TEGa), and trisneopentylgallium (TNPGa) were characterized and compared during ALE by in situ reflectance difference spectroscopy (RDS). A fundamental difference is observed in the RDS behavior after the alkyl exposure between self-limiting and non-self-limiting precursors. A transient is observed during the purge following alkyl exposure for both self-limiting sources, (TMGa and TNPGa), and is absent with TEGa. This is attributed to the presence of methyl radicals when using self-limiting precursors. Atomic force microscopymeasurements of the surface morphology show that a non-self-limiting surface prepared with TEGa has dropletsforming on it. In contrast, TMGa and TNPGa show well-defined terraces without droplets. RDS real-time measurements show that Ga incorporating on the c(4×4) surface first reacts with the As in the top layer with a process involving both desorption of As and rearrangement of the remaining top As. We used these measurements to provide a detailed structural model of the process of Ga incorporation, and thus, solve the problem of how an As-rich surface with more than 1 ML coverage can yield 1 ML of material per ALE cycle.
83(1998); http://dx.doi.org/10.1063/1.367107View Description Hide Description
This work deals with the study of boron nitride (BN)thin filmsdeposited onto silicon substrates using the ion beam-assisted pulsed laser deposition method. Influence of experimental deposition parameters on the percentage of chemical bonds (representative of the cubic BN phase) contained in the depositedfilm and on chemical composition is presented. The best percentages of bonds, up to 80%, are obtained under bombardment by a pure nitrogen ion beam, and we do not observe any significant contribution of argon ions in the bombarding ion beam to the presence of bonds in the depositedfilms.X-ray photoelectron spectroscopy and atomic force microscopy performed on various BNfilms reveal important changes with the type of chemical bonds ( and ) contained within these films.
Modification of the mechanical and optical properties of a polycarbonate by 50 keV and ion implantation83(1998); http://dx.doi.org/10.1063/1.367108View Description Hide Description
The effects of 50 keV and ions on the mechanical properties and ultraviolet-visible absorption of the polymer CR39 were investigated. It was found that the implantation produced a yellow–brown material with optical properties similar to amorphous hydrogenated carbon, whereas implantation produced a material with optical properties more like evaporated amorphous carbon. The mechanical properties of the implanted material were measured using a nanoindentation technique and increases in both the elastic modulus and hardness (maximum sustainable contact pressure) were observed following irradiation with both ion species. Compared to implantation, implantation of CR39 was found to produce a more transparent material at an equivalent maximum sustainable contact pressure and therefore ions were found to be more desirable than ions for the treatment of CR39 optical components.
Three-dimensional site dependence of single-ion-induced charge collection at a junction—role of funneling and diffusion processes under different ion energy83(1998); http://dx.doi.org/10.1063/1.367138View Description Hide Description
The amount of charges induced by high energy single ion irradiation at a junction diode has been measured and its dependence on the ion incident position has been evaluated by using single-ion microprobe technique. By irradiating single He ions with various incident energy (1.4–4.05 MeV), dependence of the profiles of collected charges on the ion incident energy has been investigated. Origins of the different profiles among the different incident energy are discussed in terms of different contribution of two mechanisms of charge collection, namely, field funneling and diffusion of carriers. In the case of the ion incidence within the junction area, dependence of the charge collection profile on the ion incident energy comes from different contribution of the funneling in the charge collection process, while difference in the collection efficiency of the diffused charges affects the profile in the case of the ion incidence at outside of the junction.
83(1998); http://dx.doi.org/10.1063/1.367109View Description Hide Description
This article presents a Monte Carlo approach to simulate the dispersive transport of holes/ ions in silicon-dioxide using simplified formalism of continuous time random walk theory given by Montroll and Scher [E. W. Montroll and H. Scher, J. Stat. Phys. 9, 101 (1973); H. Scher and E. W. Montroll, Phys. Rev. B 12, 2455 (1975)]. It has been shown that the simulated results of this approach match quite well with the theoretical predictions for a value of dispersion coefficient, α, which validates our Monte Carlo simulator. We have used this simulator to resolve the memory effect observed by Saks et al. [N. S. Saks, D. B. Brown, and R. W. Rendell, IEEE Trans. Nucl. Sci. 38, 1130 (1991)] in their simulations of switched gate bias experiments in context with the hydrogen ion transport model for the buildup of radiation-induced interface states. We have accounted for the memory effect, which is related with the dwell time of an ion at the last hopping site just before field switching, by treating the first hop after field switching differently from all other hops. We have shown that the memory effect can be incorporated by modifying the value of α only for the first hop after field switching depending on the dwell time at the last hopping site just before field switching. We have found that a logarithmic relationship between the two gives a very good match between the simulated and the experimental results of half-time (the time required to build 50% of saturated interface states) versus time of field switching, relationship.