G. Bisognin

Evolution of boron-interstitial clusters in crystalline Si studied by transmission electron microscopy

The thermal evolution of large boron-interstitials clusters (BICs) in crystalline Si has been studied by transmission electron microscopy (TEM). After ion implantation (20keV and 1×1014Si∕cm2) and annealing (815°C and 5min), large clusters (6–8nm) have been observed in correspondence of a narrow, highly doped Si:B layer (2×1020B∕cm3). Under prolonged annealing, such clusters dissolve, progressively shrinking their mean size below the TEM detection limit. The time evolution of such a BIC shrinking is fully compatible with the slow path dissolution kinetics recently published. These data suggest the identification of the slow dissolving BICs with the large observed clusters.

Modeling of boron and phosphorus implantation into (100) Germanium

Boron and phosphorus implants into germanium and silicon with energies from 20 to 320 keV and ion doses from 5/spl times/10/sup 13/ to 5/spl times/10/sup 16/ cm/sup -2/ were characterized using secondary ion mass spectrometry. The first four moments of all implants were calculated from the experimental data. Both the phosphorus and boron implants were found to be shallower in the germanium than in the silicon for the same implant parameters and high hole concentrations, as high as 2/spl times/10/sup 20/ cm/sup -3/, were detected by spreading resistance profiling immediately after boron implants without subsequent annealing. Channeling experiments using nuclear reaction analysis also indicated high substitutional fractions (/spl sim/19%) even in the highest dose case immediately after implant. A greater straggle (second moment) is, however, observed in the boron implants in the germanium than in the silicon despite having a shorter projected range in the germanium. Implant profiles predicted by Monte Carlo simulations and Lindhard-Scharff-Schiott theory were calculated to help clarify the implant behavior. Finally, the experimentally obtained moments were used to calculate Pearson distribution fits to the boron and phosphorus implants for rapid simulation of nonamorphizing doses over the entire energy range examined.

Implantation and activation of high concentrations of boron in Germanium

There is renewed interest in the development of Ge-based devices. Implantation and dopant activation are critical process steps for future Ge devices fabrication. Boron is a common p-type dopant, which remarkably is active immediately after implantation in Ge at low doses. This paper examines the effect of increasing dose (i.e., 5/spl times/10/sup 13/-5/spl times/10/sup 16/ cm/sup -2/) and subsequent annealing (400/spl deg/C-800/spl deg/C for 3 h in nitrogen) on activation and diffusion of boron in Ge. Secondary ion mass spectrometry (SIMS), spreading resistance profiling (SRP), high resolution X-ray diffraction (HRXRD), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA) are used to characterize the implants before and after annealing. It is found that very high fractions of the boron dose (/spl sim/5%-55%) can be incorporated substitutionally immediately after implantation leading to very high hole concentrations, /spl ges/2/spl times/10/sup 20/ cm/sup -3/, deduced from SRP. Small increases in activation after annealing are observed, however, 100% activation is not indicated by either SRP or NRA. Negligible diffusion after annealing at either 400/spl deg/C or 600/spl deg/C for 3 h was, furthermore, observed.

Transient enhanced diffusion of B mediated by self-interstitials in preamorphized Ge

The dissolution of interstitial-type end-of-range (EOR) damage in preamorphized Ge is shown to induce a transient enhanced diffusion of an epitaxially grown boron delta at temperatures above 350 °C that saturates above 420 °C. The B diffusion events are quantitatively correlated with the measured positive strain associated with the EOR damage as a function of the annealing temperature with an energy barrier for the EOR damage dissolution of 2.1±0.3 eV. These results unambiguously demonstrate that B diffuses in Ge through a mechanism assisted by self-interstitials, and impose considering the interstitial implantation damage for the modeling of impurity diffusion in Ge.

High-level incorporation of antimony in germanium by laser annealing

In this work we investigate pulse laser annealing as an alternative approach to reach high-level incorporation of Sb in substitutional location in crystalline germanium. Laser irradiation is demonstrated to recover also those structural defects, like honeycomb structures, that form during high-fluence heavy-ion implantations in Ge and that cannot be eliminated by conventional thermal treatments. Indeed, concentrations of substitutional Sb higher than 1×1021 at./cm3 have been obtained, well above the solid solubility of Sb in Ge. The strain induced on the Ge host lattice is also investigated, evidencing that the obtained Sb doped Ge layer is pseudomorphic to the Ge substrate while positively strained by the substitutional Sb atoms present within the Ge matrix. The kinetics of this Sb-rich Ge alloy phase is finally investigated, showing that most of Sb goes out of lattice with increasing the annealing temperature up to 488 °C, leading to a decrease in the related lattice deformation. These results are very ...

Experimental evidences for two paths in the dissolution process of B clusters in crystalline Si

We show that B clusters, produced by self-interstitial interaction with substitutional B in crystalline Si, dissolve under annealing according to two distinct paths with very different characteristic times. The two regimes generally coexist, but while the faster dissolution path is predominant for clusters formed at low B concentration (1×1019B∕cm3), the slower one is characteristic of clusters formed above the solubility limit and dominates the dissolution process at high B concentration (2×1020B∕cm3). The activation energies of both processes are characterized and discussed. It is showed that the faster path can be connected to mobile B direct emission from small clusters, while the slower path is demonstrated not to be self-interstitial limited and it is probably related to a more complex cluster dissolution process.

Hydrogen-nitrogen complexes in dilute nitride alloys: Origin of the compressive lattice strain

Hydrogenation of GaAs1−xNx and GaP1−xNx epilayers grown on GaAs(001) and GaP(001) surfaces, respectively, is known to passivate the electronic activity of nitrogen through the formation of specific nitrogen-hydrogen complexes. The same epilayers also undergo a strain reversal from tensile (as grown) to compressive (fully hydrogenated). The authors show that the extent of strain reversal is determined exclusively by the nitrogen concentration. By performing in situ high resolution x-ray diffraction measurements during annealing and photoluminescence studies, the authors demonstrate that the lattice properties of fully hydrogenated GaAs1−xNx are ruled by a H complex, which is different and less stable than that responsible for electronic passivation of nitrogen in GaAs1−xNx.

Experimental evidence of B clustering in amorphous Si during ultrashallow junction formation

The authors have investigated ultrashallow p+∕n-junction formation by solid-phase epitaxy, by using x-ray absorption near-edge spectroscopy measurements on the B K edge. A clear fingerprint of B–B clusters is detected in the spectra. The authors demonstrate that B clustering occurs during the very early stages of annealing-induced Si recrystallization, i.e., when B is still in an amorphous matrix. After complete regrowth the local structure around B remains the same as in the amorphous phase, implying that B clusters are transferred to the crystalline structure.

Determination of lattice parameter and of N lattice location in InxGa1−xNyAs1−y/GaAs and GaNyAs1−y/GaAs epilayers

We have used an experimental strategy that, combining nuclear reaction analysis and Rutherford backscattering spectrometry both in random and channeling geometry, allowed an accurate quantification of the total amount of N in InxGa1−xNyAs1−y/GaAs and GaNyAs1−y/GaAs epitaxial systems (0.038<x<0.044, 0.015<y<0.045), and a precise localization of nitrogen atoms into the lattice. All N atoms were found on substitutional positions. This information was then exploited to correlate the relaxed lattice parameter of the epilayers obtained by high-resolution x-ray diffraction to the N concentration, by taking into account the elasticity theory, allowing a verification of the validity of Vegard’s rule in the whole range of investigated N concentrations for both alloys. The effect of N incorporation on the lattice parameter has been found to be the same both for ternary and quaternary alloys.

Substitutional and clustered B in ion implanted Ge: Strain determination

The lattice strain induced both by substitutional and clustered B in B-implanted Ge samples has been investigated by means of high resolution x-ray diffraction (HRXRD). The main results can be summarized as follows: while substitutional (i.e., electrically active) B exhibits a negative strain, clustered (i.e., electrically inactive) B reverses the lattice strain from negative to positive values, the latter being much higher with respect to those found for clustered B in Si. In particular, the lattice volume modification for each B atom (ΔV) induced by substitutional (ΔVSub) and clustered (ΔVCl) B is ΔVSub=−12.4 A3 and ΔVCl=+14.8 A3, respectively. These unexpected results demonstrate the ability of HRXRD to quantitatively detect the amount of electrically inactive (and active) B.