M. Q. Huda

Use of ErSi2 in source/drain contacts of ultra-thin SOI MOSFETs

The prospect of Erbium silicide (ErSi 2 ) contacts for source/drain metallization in ultra-thin n-channel silicon-on-insulator (SOI) MOSFETs have been studied. Very thin layer of ErSi 2 was formed on Si(001) by Er deposition followed by in situ annealing in the range of 400-600 °C under ultra-high vacuum (UHV) condition. The silicification process was found to depend on surface conditions prior to the Er deposition. The silicide layers were found to be stable up to a temperature of 700 °C. Good ohmic nature on n-type Si and well-defined rectifying behavior on p-type Si have confirmed a low electron barrier height at the ErSi 2 /Si contact. A simplified analysis based on transmission line modeling has been used to show that parasitic source/drain resistances of the order of 100 Ω μm or less can be achieved for SOI thickness of 10 nm.

Luminescence from erbium implanted silicon–germanium quantum wells

We have investigated the luminescence emitted at 1.54 μm from erbium-implanted strained ultrahigh vacuum chemical vapor deposition-grown (UHVCVD-grown) Si1−xGex quantum wells. Germanium fractions of up to 13% were used, and all well widths were below the critical thickness for pseudomorphic growth. A preliminary study was carried out on Si1−xGex quantum wells implanted with amorphizing doses of silicon at 77 K in order to study the regrowth across the interfaces, and subsequent structural and optical recovery. After amorphization and regrowth by a two stage anneal process, transmission electron microscopy (TEM) clearly showed the presence of the quantum wells, with sharp contrast. X-ray diffraction (XRD) studies showed that good regrowth has been achieved, with line widths very similar to the original material. However, the photoluminescence (PL) was found to be dependent upon the duration of the first anneal. Increasing the anneal time resulted in PL spectra being dominated by broad signals between 0.9 a...

Explaining the luminescence profile of erbium in silicon under short excitation pulses

Abstract A mechanism for the luminescence of erbium in silicon has been developed. Erbium atoms in silicon have been considered as recombination centers with specific values of capture and emission coefficients. Electron–hole recombination through these levels has been considered to be the origin of erbium excitation. Capture and emission processes of photo generated excess carriers in the erbium related level have been equated for non-steady-state conditions. The extended rise of erbium luminescence after termination of short excitation pulses of micro/nano second durations has been explained by the model.

Technique for Large Elevation of Source/Drain Using Implantation Mediated Selective Etching

A process involving implantation mediated selective etching has been developed for source/drain elevation of metal-oxide-semiconductor devices. A 100 nm thick epitaxial silicon/polysilicon layer was formed on a patterned Si/SiO 2 structure by chemical vapor deposition (CVD) at 700°C. Samples were then implanted with 2 × 10 1 4 /cm 2 argon at 140 keV in the channeling direction, followed by I min annealing at 420°C. The polysilicon layer was then removed by wet etching with more than an order of magnitude selectivity over epitaxial silicon. The resulting structure of elevated silicon is free from faceting effects. The process is independent of sidewall/isolation materials, and not bound by thickness limits.

Incorporation and optical activation of erbium in strained silicon–germanium structures

Abstract Erbium has been incorporated in strained Si/Si 0.87 Ge 0.13 /Si multiple quantum well structures with a density of 10 18 cm −3 . The process of ion implantation was used. Samples were amorphized by silicon implantation at liquid nitrogen temperature following the erbium implant. Recrystallization and optical activation of erbium atoms were achieved simultaneously by low temperature annealings in the range of 550–650°C. Detailed study on this low temperature window for erbium activation has been done. Reduction or complete elimination of erbium luminescence was observed for recrystallized samples having an additional step of rapid thermal annealing. It was shown that the uncontrolled sharp quenching of temperature that follows the rapid thermal annealing process deteriorates the sample structure and the erbium luminescence.

Erbium luminescence through silicon nanocluster sensitizers in Silicon Rich Oxide

A model has been developed for Erbium luminescence in Silicon Rich Oxide (SRO) through sensitization of silicon nanoclusters (si-nc). Energy transfer routes to and from Er atoms in the neighbourhood of nanoclusters are analyzed. The fraction of Er atoms in excited state has been calculated by equating all possible energy transfer mechanisms. Sensitization effect of ncs is found to be efficient at lower incident photon fluxes, whereas higher excitation fluxes were found to result in saturation effects. Significance of nc density and different coefficients of energy coupling has been aanlyzed. Good agreement with published experimental results has been observed.

Inversion layer properties of 〈110〉 uniaxially strained silicon n-channel MOSFETs

This paper discusses the influence of <110> uniaxial tensile stress on some of the inversion layer properties of (100) silicon n-channel MOSFETs. Quantum mechanical calculations are performed assuming Airy function approximation holds. Uniaxial tensile strain lowers the eigen-energies and increases the occupation of the ground state. Average inversion layer penetration is also decreased. The change in the surface electric field due to strain is insignificant.

1.54 μm lasing from silicon in presence of Erbium doping

Lasing at 1.54 mum from Erbium doped silicon has been studied. A model has been developed for the mechanism of energy transfer to erbium by electron-hole recombination through erbium sites. Emission rates of erbium through intra 4f shell transitions by spontaneous and stimulated processes have been equated with the excitation rates. Detailed analysis on rate equations show the feasibility of achieving population inversion and lasing threshold for incorporation of 1019 cm-3 of optically active erbium sites. Low threshold current densities of the order of A/cm2 has been estimated for optimized lasing conditions. Linear increase of laser output with excitation current has been simulated. Modulation compatibility of the erbium doped silicon lasing system has been studied by introducing small signal components at various operating conditions. It was found that direct modulation of the 1.54 mum erbium emission with frequencies up to Gega hertz level is feasible. The 3 dB bandwidth of laser response was found to be a strong function of the power output. Rate equations of laser operation were also solved for large signal conditions. Turn-on delays of the order of tens of nanoseconds have been estimated.

Analytical Study of Erbium-Doped Silicon Lasers

Operation of erbium doped silicon laser has been analytically studied. A quasi two level system has been considered. Spontaneous and stimulated processes involving the 4I13/2 - 4I15/2 erbium transitions have been analyzed. Threshold conditions of erbium excitation and the corresponding drive currents have been calculated. Optical output from laser and its dependence on system parameters like background doping, emission linewidth, etc. have been studied. For typical values of erbium doping and laser cavity dimensions, output power in milliwatt range with turn-on delay of the order of 500 ns has been estimated.

Spontaneous and Stimulated Emission from Erbium Doped Silicon Nanocrystals

Mathematical model has been developed for erbium luminescence in silicon nanocrystals. Parameters involving the erbium excitation and de-excitation processes have been analyzed. It has been shown that, carrier injections of the order of 1019/cm3 in a nanocrystal system can produce sustained lasing action. Laser outputs of the order of milliwatts have been estimated for realistic values of erbium incorporation and excitation conditions.