D. De Salvador

Lattice parameter in Si1-yCy epilayers: deviation from Vegard's rule

The precise C content of a series of Si1−yCy epilayer samples (0<y<0.012) was determined by resonant backscattering experiments using a 4He+ ion beam at 5.72 MeV. This beam energy is more suitable for the determination of the C content than the previously used 4.265 MeV. From the correlation of these investigations with x-ray diffraction experiments, a significant deviation of the lattice parameter variation in Si1−yCy from Vegard’s rule between Si and diamond or β-SiC was observed, which amounts up to 30% or 13%, respectively, for y<0.012. This negative deviation is in agreement with recent theoretical predictions by Kelires.

Mechanisms of boron diffusion in silicon and germanium

B migration in Si and Ge matrices raised a vast attention because of its influence on the production of confined, highly p-doped regions, as required by the miniaturization trend. In this scenario, the diffusion of B atoms can take place under severe conditions, often concomitant, such as very large concentration gradients, non-equilibrium point defect density, amorphous-crystalline transition, extrinsic doping level, co-doping, B clusters formation and dissolution, ultra-short high-temperature annealing. In this paper, we review a large amount of experimental work and present our current understanding of the B diffusion mechanism, disentangling concomitant effects and describing the underlying physics. Whatever the matrix, B migration in amorphous (α-) or crystalline (c-) Si, or c-Ge is revealed to be an indirect process, activated by point defects of the hosting medium. In α-Si in the 450-650 °C range, B diffusivity is 5 orders of magnitude higher than in c-Si, with a transient longer than the typical a...

Complete suppression of the transient enhanced diffusion of B implanted in preamorphized Si by interstitial trapping in a spatially separated C-rich layer

A method for completely suppressing the transient enhanced diffusion (TED) of boron implanted in preamorphized silicon is demonstrated. Boron is implanted in a molecular beam epitaxy (MBE) grown silicon sample that has been previously amorphized by silicon implantation. The sample is then annealed in order to epitaxially regrow the amorphous layer and electrically activate the dopant. The backflow of silicon interstitials released by the preamorphization end-of-range (EOR) damage is completely trapped by a carbon-rich silicon layer interposed by MBE between the damage and the implanted boron. No appreciable TED is observed in the samples up to complete dissolution of the EOR damage, and complete electrical activation is obtained. The method might be considered for the realization of ultrashallow junctions for the far future complementary metal–oxide–semiconductor technology nodes.

Optimal crystal surface for efficient channeling in the new generation of hadron machines

The new generation of hadron machines may profitably take advantage of channeling for steering and collimation of high-energy particle beams. In that case, the requirements on the quality of the crystal surface are rather stringent in terms of both lattice perfection and roughness. Here, the authors show the structural and morphological characterizations of crystals fabricated through a method to achieve a surface that fulfills all needed specifications for application in hadron machines.

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.

N-type doping of Ge by As implantation and excimer laser annealing

The diffusion and activation of arsenic implanted into germanium at 40 keV with maximum concentrations below and above the solid solubility (8 × 1019 cm−3) have been studied, both experimentally and theoretically, after excimer laser annealing (λ = 308 nm) in the melting regime with different laser energy densities and single or multiple pulses. Arsenic is observed to diffuse similarly for different fluences with no out-diffusion and no formation of pile-up at the maximum melt depth. The diffusion profiles have been satisfactorily simulated by assuming two diffusivity states of As in the molten Ge and a non-equilibrium segregation at the maximum melt depth. The electrical activation is partial and decreases with increasing the chemical concentration with a saturation of the active concentration at 1 × 1020 cm−3, which represents a new record for the As-doped Ge system.

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.

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.

Silicon interstitial injection during dry oxidation of SiGe∕Si layers

The injection of Si self-interstitial atoms during dry oxidation at 815°C of very shallow SiGe layers grown on Si (001) by molecular-beam epitaxy (MBE) has been investigated. We first quantified the oxidation enhanced diffusion (OED) of two boron deltas buried into the Si underlying the oxidized SiGe layers. Then, by simulating the interstitial diffusion in the MBE material with a code developed on purpose, we estimated the interstitial supersaturation (S) at the SiGe∕Si interface. We found that S (a) is lower than that observed in pure Si, (b) is Ge-concentration dependent, and (c) has a very fast transient behavior. After such a short transient, the OED is completely suppressed, and the suppression lasts for long annealing times even after the complete oxidation of the SiGe layer. The above results have been related to the mechanism of oxidation of SiGe in which the Ge piles up at the SiO2∕SiGe interface by producing a thin and defect-free layer with a very high concentration of Ge.