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We have reported high internal quantum efficiency (IQE) (~60%) of photoluminescence(PL) at 470 nm wavelength from oxygenated amorphous silicon nitride (a-SiNx:O) films. In this work, we explored the dynamics of high PL IQE from luminescent N-Si-O bonding states in a-SiNx:O films by using a combination of time resolved PL(TRPL) and temperature dependent PL (TDPL) measurements. The TRPL measurements include time integrated PL, microsecond range PL, and nanosecond range PL measurement modes. The a-SiNx:O films exhibit ns PL decay dynamics that is independent of pumping fluence (WPF) and uniform across the PL spectrum, which is different from the PL decay behavior in a-SiNx films. Particularly, we precisely monitored the temporal evolution of the PL spectra profile to verify that the luminescent N-Si-O bonding states are responsible for the observed blue PL with a radiative recombination rate of ~108 s-1. Such very fast radiative recombination rate can be compared with that in direct band gap CdSe nanocrystals and can also help us to understand the high PL IQE in a-SiNx:O films. Moreover, by combining the TD-PL lifetimes with the PL IQE values, the temperature dependence of radiative and nonradiative lifetime can be determined. [ABSTRACT FROM AUTHOR]

Last year, we have reported that the internal quantum efficiency of photoluminescence (PL) from amorphous silicon oxynitride (a-SiNxOy) films has been achieved as high as 60%. The present work intensively investigated the mechanisms for tunable PL in the 2.05-2.95eV range from our a-SiNx:O films, by using a combination of optical characterizations, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) measurements. The results of XPS, EPR, and photoluminescence excited measurements indicated that the incorporation of oxygen atoms into silicon nitride (a-SiNx) networks not only reduced the band tail structure disorder (Urbach tail width EU) but also created N-Si-O (Nx) defect states in the band gap. We have discovered the distinctive PL characteristics from a-SiNx:O films with various NH3/SiH4 ratios. The PL peak energy (EPL) is independent of the excitation energy (Eexc) and the PL intensity (IPL) is regardless of the optical band gap (Eopt) but is proportional to the Nx defects concentration, both of which are completely different from the PL characteristics by band tail states recombination mechanism, in which the EPL is proportional to Eexc (when Eexc ≤ Eopt) and the IPL is dependent on the relative position of Eexc and Eopt. Based on the N-Si-O bonding configurations and the distinctive PL characteristics, the radiative recombination mechanism through the N-Si-O defect states has been proposed, by which the performance of stimulated emission may be realized in this kind of a-SiNx:O films. [ABSTRACT FROM AUTHOR]

Phase changes in chalcogenides such as Ge2Sb2Te5 can be exploited in non-volatile random-access memory, with fast crystallization crucial for device operation. Ultra-fast differential scanning calorimetry, heating at rates up to 40 000 K s-1, has been used to study the crystallization of amorphous Ge2Sb2Te5 with and without sandwich layers of ZnS-SiO2. At heating rates up to 1000 K s-1, the sandwich layers retard crystallization, an effect attributed to crystallization-induced stress. At greater heating rates (≥5000 K s-1), and consequently higher crystallization temperatures, the stress is relaxed, and sandwich layers catalyze crystallization. Implications for memory-device performance are discussed. [ABSTRACT FROM AUTHOR]

We investigated optical, structural, and chemical properties of SiOxNy layers irradiated by CW IR laser during a time lapse of few milliseconds. We observed tunable photoluminescence signal at room temperature in the range 750-950 nm, without Si/SiO2 phase separation, depending on the IR laser power irradiation. Furthermore, no photoluminescence signal was recorded when the IR laser power density was high enough to promote phase separation forming Si quantum dots. By chemical analysis the source of the luminescence signal has been identified in a change of silicon chemical environment induced by IR laser annealing inside the amorphous matrix. [ABSTRACT FROM AUTHOR]

We investigated the homogenous nucleation of crystalline grains in amorphous Si during transient temperature pulse of few milliseconds IR laser irradiation. The crystallized volume fraction is ∼80%. Significant crystallization occurs in nonsteady regime because of the rapid temperature variation (106 °C/s). Our model combines the time evolution of the crystal grain population with the consumption of the amorphous volume due to the growth of grains. Thanks to the experimental approach based on a laser source to heat α-Si and the theoretical model we extended the description of the spontaneous crystallization up to 1323 K or 250 K above the temperature investigated by conventional annealing. [ABSTRACT FROM AUTHOR]

The microstructures of once melt-quenched Ge2Sb2Te5 (GST) phase change contact dimensions are directly investigated with high resolution transmission electron microscopy (HR-TEM) by applying reset pulse of 7–13 V. The ovonic threshold switching voltage is decreased from 4.1 to 2.8 V when the as-deposited GST cells are once melt quenched by 10 V. HR-TEM reveals that there are hexagonal nuclei in the once melt-quenched GST and the GST can be partially left in not the amorphous but the crystalline state when the molten GST is not swiftly quenched, which is an origin of the switching failure. [ABSTRACT FROM AUTHOR]

Laser-induced Ni(Pt) germanosilicide formation on Si1-xGex/Si substrate has resulted in the formation of smooth Ni(Pt) germanosilicide/Si interface with minimum interface roughness which is preferred as a contact material. A confined (self-limiting) melting phenomenon occurred during the laser-induced silicidation process at laser fluence of 0.4 J cm-2 (just at the melting threshold of the sample). This phenomenon is caused by significant differences in material properties of Si1-xGex alloy and Si substrates. Formation of highly textured [Ni1-v(Pt)v](Si1-yGey) phase was detected in the sample after 20-pulsed laser thermal annealing at 0.4 J cm-2. The formation mechanism of the Ni(Pt) monogermanosilicide is discussed. [ABSTRACT FROM AUTHOR]

In this letter, the authors study the dopant activation and dopant distribution in a Si+ subamorphized Si (SAI-Si) when subjected to laser annealing (LA). The results show an enhanced boron activation in the SAI-Si in the nonmelt regime as compared to a crystalline Si (c-Si). The enhancement is caused by a vacancy-rich surface generated by the Si+ preimplantation that promotes the incorporation of boron atoms into the substitutional sites. On the other hand, shallow-melt LA produces a similar boron activation in both SAI-Si and c-Si samples due to a melting that consumes the entire as-implanted profile and the vacancy-rich region. [ABSTRACT FROM AUTHOR]

Surface energy and the equilibrium shape of hexagonal structured grain in Ge2Sb2Te5 were investigated by a transmission electron microscopy (TEM) study. As a result, we have found that the equilibrium shape of hexagonal structured Ge2Sb2Te5 is a lengthened shape with (0001) plane at the major axis, which was experimentally revealed by TEM images. The hexagonal structured Ge2Sb2Te5 grain has low surface energy in {0001}, {1103}, and {1106} planes which have no additional broken bonds from the atoms on the steps. Therefore, it is strongly facetted by the plane having low surface energy, thus, becoming an equilibrium shape. [ABSTRACT FROM AUTHOR]

Femtosecond laser annealing (FLA) was employed for activation of phosphorus (P)- and boron (B)-implanted silicons with negligible dopant diffusion. Preamorphizing implantation is not required. We found that the dopant profiles in FLA-activated samples essentially duplicate those of as-implanted ones even for junctions as deep as 100 nm below the surface. The measured sheet resistances and activation efficiencies of P- and B-implanted samples were in the range of 100–400 Ω/□ and 28%–35%, respectively. Moreover, thermal-energy-assisted dopant diffusion by heating was observed for substrate temperature as low as 100 °C. The shallow activated-depth feature associated with FLA reduces the separation between end-of-range defects and high-concentration portion of dopants. This generates a steep interstitial gradient responsible for observed B and P uphill diffusions at a depth of about 60 nm below the surface. [ABSTRACT FROM AUTHOR]

A general model of ultrashallow doping by excimer laser annealing is derived from only one diffusion-segregation equation. In our model, the relative dopant profile after some laser shots reaches a stationary distribution, which only depends on the segregation and liquid-phase diffusion coefficients of the dopant but not on the laser-process parameters. From this result, a one-point method is proposed to experimentally determine the out-of-equilibrium segregation coefficient k. Only the relative dopant concentration at the material surface has to be measured prior to determine the k value. Experimental dopant profiles are compared to simulations generated with experimental k values. [ABSTRACT FROM AUTHOR]

The amorphous-to-crystal transition has been studied through in situ resistance measurements in Ge2Sb2Te5 thin films doped by ion implantation with nitrogen or oxygen. The dependence of the electrical resistivity and structure on the annealing temperature and time has been investigated in samples with different dopant concentrations. Enhancement of the thermal stability and increase of the mobility gap for conduction have been observed in O- and N-doped amorphous Ge2Sb2Te5. Larger effects have been found in the case of nitrogen doping. [ABSTRACT FROM AUTHOR]

Ex situ atomic force microscopy in combination with a high-precision furnace has been employed for a systematic study of crystallization kinetics of sputtered amorphous Ag0.055In0.065Sb0.59Te0.29, Ge4Sb1Te5, and Ge2Sb2Te5 thin films used for optical data storage. Direct observation of crystals enabled us to establish the temperature dependence of the crystal nucleation rate and crystal growth velocity around 150 °C. While these alloys exhibited similar crystal growth characteristics, the crystal nucleation behavior of Ag0.055In0.065Sb0.59Te0.29 differed significantly from that of Ge4Sb1Te5 and Ge2Sb2Te5. These observations provide an explanation for the different recrystallization mechanisms observed upon laser heating of amorphous marks. [ABSTRACT FROM AUTHOR]

Examines the effects of titanium (Ti) deposition temperature on the resistivity of as-deposited films. Investigation on the microstructure of as-deposited Ti films and electrical property effect; Effects of film deposition temperature during thermal anneals; Consideration of the microstructure as a formation controlling factor.

The mechanical properties of phase-change materials including Ge2Sb2Te5 (GST) are strongly influenced by the complex interaction of phase and imperfection distributions, especially at film thicknesses relevant for phase-change memory devices. This work uses a micromechanical resonator as a substrate to study the phase dependent modulus of GST films with thicknesses from 25 nm to 350 nm. The moduli of amorphous GST and crystalline GST films increase with decreasing thickness to 10 GPa and up to 60 GPa, respectively. The phase purity is studied using X-ray diffraction and energy dissipation data, which provide qualitative information about inelastic absorption. [ABSTRACT FROM AUTHOR]

Junctions shallower than 100 nm, obtained by ion implantation and excimer laser annealing, have been characterized in two dimensions by transmission electron microscopy (TEM) on chemically treated samples. The chemical treatment selectively removes silicon as a function of the B concentration, making thinner the regions where B is present in the cross section of the sample, with respect to the n-type substrate. Both secondary ion mass spectrometry and spreading resistance profiling measurements have been performed, in order to quantify the contour line obtained by TEM in terms of B concentration. The results achieved by the two-dimensional technique show interesting features, related to the particular redistribution of B occurring when silicon is melted by excimer laser annealing irradiation. In particular, a rectangular shape of the doped region obtained by laser annealing could be evidenced, caused by the fast diffusion in the melted material, completely different from the typical half-moon-shaped, thermally annealed, two-dimensional B profile. The feasibility of ultrashallow junctions by laser annealing, with depths below 100 nm and high electrical activation, is demonstrated. However, a huge lateral diffusion in the melted silicon is also to be taken into account when considering excimer laser treatments as an alternative to standard rapid thermal annealing. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]