Enhancement of the Si p-n diode NIR photoresponse by embedding ß-FeSi2 nanocrystallites.

By using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, a p(+)-Si/p-Si/ß-FeSi2 nanocrystallites/n-Si(111) diode structure was fabricated. Transmission electron microscopy data confirmed a well-defined multilayered structure with embedded nanocrystallites of two typical sizes: 3-4 and 15-20 nm, and almost coherent epitaxy of the nanocrystallites with the Si matrix. The diode at zero bias conditions exhibited a current responsivity of 1.7 mA/W, an external quantum efficiency of about 0.2%, and a specific detectivity of 1.2 × 10(9) cm × Hz(1/2)/W at a wavelength of 1300 nm at room temperature. In the avalanche mode, the responsivity reached up to 20 mA/W (2% in terms of efficiency) with a value of avalanche gain equal to 5. The data obtained indicate that embedding of ß-FeSi2 nanocrystallites into the depletion region of the Si p-n junction results in expansion of the spectral sensitivity up to 1600 nm and an increase of the photoresponse by more than two orders of magnitude in comparison with a conventional Si p-n junction. Thereby, fabricated structure combines advantage of the silicon photodiode functionality and simplicity with near infrared light detection capability of ß-FeSi2.

An investigation of the electrical and optical properties of thin iron layers grown on the epitaxial Si(111)-(2 × 2)-Fe phase and on an Si(111)7 × 7 surface.

Electrical and optical properties of thin iron layers grown at room temperature on the epitaxial silicide Si(111)-(2 × 2)-Fe phase and on an Si(111)7 × 7 surface were investigated using in situ Hall effect registration, atomic force microscopy, and optical spectroscopy. It was established that Si(111)-(2 × 2)-Fe phase has semiconducting properties with a 0.99 eV effective band gap and acts as a diffusion barrier for the deposited iron atoms, preventing intermixing with the substrate at room temperature. Peculiarities in the optical spectra of a sample with a 2 nm iron film grown on the Si(111)-(2 × 2)-Fe phase typical for both metal and semiconducting natures prove a conservation of the phase under the iron layer. The process of iron growth on the Si(111)-(2 × 2)-Fe phase is accompanied by the development of high stress in the subsurface area resulting in band dispersion changes. Apparently the tension reaches a maximum at an iron layer thickness of 1.35 nm, and a high effective hole mobility equal to 820  cm(2) V(-1) s(-1) was registered.

Investigation of multilayer silicon structures with buried iron silicide nanocrystallites: growth, structure, and properties.

The growth of nanosize islands of iron silicides on Si(100) substrates and epitaxial silicon overgrowth atop them have been studied by low energy electron diffraction and reflectance high energy electron diffraction methods. The near optimal formation conditions of iron silicide islands with high density and minimal sizes have been determined by using of atomic force microscopy. Multilayer (8-10) monolithic structures with buried iron silicide nanocrystallites have been grown after the definition of monocrystalline burying conditions of iron silicides nanocrystallites in silicon lattice. The structure of buried nanocrystallites has been studied in multilayer monolithic heterostructures by high resolution transmission electron microscopy. It was established that in multilayer samples the majority of nanocrystallites have beta-FeSi2 structure, but some of them have gamma-FeSi2 structure. It was observed an influence of additional annealing at 850 degrees C on the morphology and structure of nanocrystallites. By means of deep level transient spectroscopy data one and two trap levels have been observed in multilayer structures (without and with additional annealing, respectively). Photoluminescence spectra have been studied at 4.2 K and the causes of its absence from buried beta-FeSi, NC have been analyzed.