J. Cardenas

Er/O and Er/F doping during molecular beam epitaxial growth of Si layers for efficient 1.54 μm light emission

Er, together with oxygen or fluorine as co-dopants, has been incorporated into Si during molecular beam epitaxial growth using co-evaporation of Si and Er containing compounds. The Er doping concentration using both Er2O3 and ErF3 can reach a level of ∼5×1019 cm−3 without precipitation, which is at least one order of magnitude higher than a previously reported solid solubility limit for Er in Si. Growth, structural, and luminescence characterization of these Er/O and Er/F doped Si samples are reported. In particular, 1.54 μm electroluminescence has been observed from Er/O doped Si layers at room temperature through hot electron impact excitation.

On the formation of epitaxial CoSi2 from the reaction of Si with a Co/Ti bilayer

In spite of much work, the formation of epitaxial CoSi2 from Ti/Co on (100) Si remains something of a mystery. It has been proposed that epitaxy occurs via the formation of an intermediate phase of CoSi with a (311) preferred orientation. In the absence of sufficient information it is impossible to validate or to invalidate the specific original claim. However, one shows that the formation of preferably oriented CoSi is not a necessary condition for the subsequent growth of epitaxial CoSi2. Careful measurements of diffraction intensities reveal the probable, temporary formation of a metastable form of CoSi2, based on a diamond cubic rather than the usual CaF2 structure.

Solid solubility and diffusion of boron in single‐crystalline cobalt disilicide

The temperature dependence of the solid solubility [CsCoSi2(B)] and the lattice diffusion coefficient [DCoSi2(B)] of boron in single‐crystalline cobalt disilicide (CoSi2) has been investigated between 450 and 1000 °C. Both CsMCoSi2(B) and DCoSi2(B) are found to be considerably higher than the corresponding quantities in silicon. Using a thermodynamical interpretation, the experimental data show that boron‐doped CoSi2 can be described as a regular solution in the dilute limit with an enthalpy of solution of ∼−0.4 eV. The experimental data and theoretical estimates of the excess enthalpy of solution indicate a weak interaction of boron with the silicon and cobalt atoms in CoSi2 suggesting that the boron atoms occupy sites in the CoSi2 lattice with a small contribution to the Gibbs energy of the solution phase. The diffusion data yield a high mobility of the boron atoms with an activation energy of ∼2.0 eV for the lattice diffusion coefficient which is ∼1.0 eV lower than that reported for the self‐diffusion ...

On the formation of inhomogeneities in epitaxial CoSi2 layers grown from the interaction of Co/Ti bilayers with Si 〈100〉 substrates

The redistribution of titanium during the formation of epitaxial CoSi2, grown from the reaction of Co(20 nm)/Ti(10 nm) bilayers with Si 〈100〉, has been investigated. Annealing of Co/Ti/Si structures, at temperatures between 850 and 1050 °C, is shown to be associated with the growth of an inhomogeneous CoSi2 layer having Ti‐rich surface layer(s) on top. The formation of inhomogeneities in the CoSi2 layer is conclusively attributed to the presence of Ti‐rich surface layer(s). It is shown that smooth and morphologically stable CoSi2 layers can be grown by removing these surface layers followed by a high‐temperature treatment in nitrogen atmosphere. We propose that the underlying mechanism for the inhomogeneity formation within the CoSi2 layer is a nucleation‐controlled process, induced by an anticipated reaction between the CoSi2 layer and Ti‐rich phases near the surface.

Role of strain in dopant surface segregation during Si and SiGe growth by molecular beam epitaxy

Dopant surface segregation during molecular beam epitaxy (MBE) growth is a serious problem for controlling the doping profiles. To understand the segregation mechanism is essential. In this study, we report the B segregation ratio values, determined using concentration transient analysis based on secondary ion mass spectrometry (SIMS) measurements, for Si and SiGe, respectively. For a comparison, segregation ratio calculations based on a simplified two-site exchange model were performed. It is found that the surface segregation effects of B and Ge during MBE Si growth are interconnected, where the lattice strain likely plays an important role.

Solid solubility of As in CoSi2 and redistribution at the CoSi2/Si interface

The solid solubility of As in CoSi2 and the redistribution of As at the CoSi2/Si interface at temperatures between 650 and 950 °C have been investigated. As was implanted in the cap Si layer of mesotaxy samples (epitaxial CoSi2 layers buried in a Si substrate). The As profiles after annealing were measured by secondary ion mass spectrometry. The solubility of As is lower in the cobalt disilicide than in silicon. A detailed description of thermodynamic equilibrium between the solution of As in CoSi2 and the solution of As in Si shows that the distribution coefficient is dependent on the concentration. Within the experimental accuracy, the enthalpy of solution, deduced from the distribution coefficient, is constant in the temperature range and equal to 0.28 eV. The solution of As in CoSi2 can thus be described by Henry’s law, which is valid for dilute solutions. Accumulation of As at both interfaces of the buried CoSi2 layer has been observed and is discussed in terms of segregation and precipitation. A tra...

Injection of self-interstitials during sputter depth profiling of Si at room temperature

Samples consisting of multi B delta layers and a single Sb delta layer, grown using molecular beam epitaxy, have been sputter depth profiled using O2+ ions with incidence energy of 8.2 or 3.2 keV. The leading and the trailing edge of the B distributions show an anomalous broadening induced by the sputtering, which apparently increases with ion energy. Similar feature is not observed for the Sb distribution. Incorporation of substitutional C to concentrations ∼1019 cm−3 suppresses the broadening feature almost completely. This anomalous broadening is interpreted as a consequence of injection of Si self-interstitials from the region damaged by the ion bombardment. These interstitials may migrate far beyond the mixing depth and interact with the B dopants, which yields a mixing of the B atoms before the distribution is within the “ordinary” mixing depth.

Diffusion of Arsenic in Single Crystalline CoSi 2

The lattice diffusion of arsenic in CoSi 2 has been studied in the temperature range from 750°C to 950°C. Two types of bulk samples were used: single crystals prepared by a modified Czochralski pulling technique from a radio frequency levitated melt and polycrystals synthesised by quenching from the melt. The latter samples were subsequently annealed in vacuum at 900°C and displayed grain sizes in the millimetre range. Starting from an ion implanted arsenic profile with two different doses (5·10 14 and 5·10 15 cm −2 ) the concentration versus depth profiles after annealing at different temperatures and different times were measured using secondary ion mass spectrometry (SIMS). Contrary to previous studies by other authors substantial diffusion has been observed with an activation energy of 3.3 eV and a pre-exponential factor of 7.37 cm 2 /s for the diffusion coefficient. These values are very close to the self diffusion coefficient of Si in CoSi 2 suggesting that the As atoms migrate via thermal vacancies on nearest neighbour lattice sites by a similar type of mechanism as the Si (and Co) atoms. In the high dose implanted polycrystalline samples arsenic precipitation occurred which gives an estimate for the solid solubility in the 10 19 atoms/cm 3 range at 800 °C.

Formation of Epitaxial CoSi 2 Layers Grown from the Interaction of Co/Ti Bilayers with Si Substrates

The redistribution of titanium during the growth of epitaxial CoSi 2 from the reaction of Co(20nm)/Ti(lOnm)/Si structures has been investigated. The concentration of Ti in the CoSi 2 layers versus annealing temperature has been determined. Emphasis is placed on the formation of inhomogeneities in the epitaxial CoSi 2 layers, and the role of Ti with respect to the thermal stability of the layers. The fundamental mechanism for the development of inhomogeneities in the epitaxial CoSi 2 layers will be discussed.