摘要:

We describe calculations of the annihilating positron distribution necessary for the depth profiling of defects in layered systems. These calculations combine a Monte Carlo calculation of the stopping profile for variable energy positrons in a layered medium with a solution of the one‐dimensional diffusion equation in the presence of defects, electric fields and variable diffusion coefficients. The stopping profile for arbitrary energies is obtained by interpolation of a conveniently parameterized fit to the Monte Carlo results at selected energies. The method will be illustrated for the case of a heavily defected gold layer on an aluminum substrate.

ISSN:0094-243X    

DOI:10.1063/1.45486

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The diffusion‐annihilation equations for positrons implanted both thermally and epithermally are presented. The epithermal case has been solved numerically assuming a two group model in which the epithermal distribution acts as a time varying source for the thermal positrons. Using experimental data from the metals Al, Ag, and Au the model has been used to extract values for the positron diffusion and surface penetration coefficients. The two group model is shown to be inadequate in describing the transport of epithermal positrons as thermalization must be treated as a continuous process. For deeper implantation, a single diffusion equation can be applied.

ISSN:0094-243X    

DOI:10.1063/1.45494

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Variable energy positron defect profiling has revealed the sub‐surface vacancy profile in Cz Si(100) implanted to a dose of 2×1014cm−2with 120 keV fluorine ions. We demonstrate the presence of vacancies at ppm concentrations at depths exceeding 1.5 &mgr;m, many times the depth at which implantation damage is expected to occur. The vacancy profile deduced was verified by removing layers of known thickness from the surface of the sample by chemical etching and repeating the defect profiling process. In the fitting procedure, the use of a Monte Carlo deduced positron implantation profile isrequired. The annealing behavior of the defects shows that the vacancies caused by the implantation process consist of two components. The deep vacancies are found to be relatively easily removed by a moderate temperature anneal, in contrast to those vacancies nearer to the surface. The former component is suggested to be the more mobile and thus may diffuse to the depths at which it is observed.

ISSN:0094-243X    

DOI:10.1063/1.45502

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Boron ion implantation‐induced defects in SiO2were investigated using slow positron annihilation spectroscopy and electron spin resonance (ESR). The defects caused by ion implantation are manifest as a particularly low S‐parameter in the region of the SiO2layer in which B implantation damage occurs. The annealing behavior of the defect responsible for positron trapping was studied. The defect to which the positron is sensitive is found to be unobservable in ESR measurements. The defect is suggested to be dissolved O2or a charged Frenkel defect, such as the negative non bridging‐oxygen hole center (≡S−O−).

ISSN:0094-243X    

DOI:10.1063/1.45514

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have used a Monte Carlo computer code developed at Brookhaven to study the implantation profiles of 1‐10 keV positrons incident on a wide range of semi‐infinite metals and multilayer systems. Our Monte Carlo program accounts for elastic scattering as well as inelastic scattering from core and valence electrons, and includes the excitation of plasmons. The implantation profiles of positrons in many metals as well as Pd/Al, and Al/Co/Si multilayers are presented. Scaling relations and closed‐form expressions representing the implantation profiles are also discussed.

ISSN:0094-243X    

DOI:10.1063/1.45518

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

S‐parameter positron beam measurements have been done on several kinds ofa‐Si: Kr‐sputtereda‐Si, PECVDa‐Si, MeV ion beam amorphized Si anda‐Si grown in an MBE‐system at a low deposition temperature. Kr sputtereda‐Si becomes denser for higher Kr concentration. PECVDa‐Si:H contains micro‐cavities with a size depending on growth temperature. MeV ion beam amorphized Si contains 1.2 at. % small vacancies, which decreases upon annealing (relaxation) to 0.4 at. %. This effect can be mimicked by H‐implantation and subsequent annealing, showing that at least some of the dangling bonds ina‐Si are located at these vacancy‐type defects. Finally positron measurements show that MBE‐system growna‐Si contains large open‐volume defects. The positron annihilation data are supplemented by data from some other techniques.

ISSN:0094-243X    

DOI:10.1063/1.45528

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The dependence of the mean penetration depth ⟨z⟩ on the incident positron energyEis described by the empirical power law formula used originally for electrons and adopted by Mills & Wilson [1]. Doppler broadening as a function of incident positron energy is used to study amorphous Ge overlayers grown by thermal evaporation on GaAs substrates. It is shown that experimental data can be fitted using the power law dependence of ⟨z⟩ onE, with parameters that are in acceptable agreement with MC simulations for Ge.

ISSN:0094-243X    

DOI:10.1063/1.45535

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Variable energy positron beam spectroscopy is employed to study defects and arsenic precipitates in GaAs epilayers grown at low temperatures by Molecular Beam Epitaxy (MBE). We have measured the S‐parameter as a function of positron implantation energy. We have obtained results for the depth profiles of the Ga monovacancy defects in unannealed LT‐GaAs and Ga monovacancies and arsenic clusters related defects in annealed LT‐GaAs.

ISSN:0094-243X    

DOI:10.1063/1.45545

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Existing Monte‐Carlo models are capable of simulating the behavior of positrons incident at keV energies, then following the energy loss process to arbitrary final kinetic energies of from 20 eV to 100 eV. In the present work we describe a Monte‐Carlo simulation of the final stages of positron thermalization in Al, from 25 eV to thermal energies, via the mechanisms of conduction‐electron and longitudinal acoustic phonon scattering. We show that the later stages of thermalization can have important effects on the stopping profiles and mean depth. We describe a novel way to obtain information about positron energy loss by considering the time‐evolution of a point‐concentration (delta‐function distribution) of positrons. We examine, for the first time in the context of a positron Monte‐Carlo calculation, the effects of a positive positron work function. Finally, we discuss some issues relating to the agreement of Monte‐Carlo calculations with experimental data.

ISSN:0094-243X    

DOI:10.1063/1.45554

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The positron annihilation Doppler broadening technique has been used to study the effect of annealing of poly‐crystalline tungsten foils irradiated with 110 keV85Rb+ions with doses up to 1012, 1014, 1015, and 101685Rb+/cm2, and 101783Rb+/cm2. The defect depth distribution after irradiation and subsequent annealing for 15 minutes at temperatures from 300 to 1600 K in steps of 100 K has been monitored by measuring the S‐parameter as a function of the positron incident energy. The shape of the S‐curves of the as‐irradiated samples is explained by trapping of positrons in the near surface region (10 nm) containing Rb‐defect clusters and positron trapping in simple defects created at larger depths due to channeling of Rb. Annealing of the ‘‘deep’’ defects in the tail of the distribution is observed as an increase of S at 15 keV in the 400–600 K temperature interval followed by a decrease of S between 1000 and 1300 K. Above these temperatures S rises again. These observations are assigned to trapping of vacancies at the small Rb‐vacancy complexes causing their growth followed by the release of trapped vacancies. When at still higher temperatures the damage in the tail is recovered positrons diffuse back to the near surface region where large Rb‐vacancy clusters or bubbles with correspondingly high S‐parameter value have been formed.

ISSN:0094-243X    

DOI:10.1063/1.45547

出版商:AIP    

年代:1994

数据来源: AIP