Amorphous silicon

About: Amorphous silicon is a research topic. Over the lifetime, 26777 publications have been published within this topic receiving 423234 citations.

Analytical model for the optical functions of amorphous semiconductors from the near-infrared to ultraviolet: Applications in thin film photovoltaics

Abstract: We have developed a Kramers–Kronig consistent analytical expression to fit the measured optical functions of hydrogenated amorphous silicon (a-Si:H) based alloys, i.e., the real and imaginary parts of the dielectric function (e1,e2) (or the index of refraction n and absorption coefficient α) versus photon energy E for the alloys. The alloys of interest include amorphous silicon–germanium (a-Si1−xGex:H) and silicon–carbon (a-Si1−xCx:H), with band gaps ranging continuously from ∼1.30 to 1.95 eV. The analytical expression incorporates the minimum number of physically meaningful, E independent parameters required to fit (e1,e2) versus E. The fit is performed simultaneously throughout the following three regions: (i) the below-band gap (or Urbach tail) region where α increases exponentially with E, (ii) the near-band gap region where transitions are assumed to occur between parabolic bands with constant dipole matrix element, and (iii) the above-band gap region where (e1,e2) can be simulated assuming a single ...

Stretched-exponential relaxation arising from dispersive diffusion of hydrogen in amorphous silicon.

Abstract: In this paper we find that the stretched-exponential relaxation commonly observed in disordered systems is explained by time-dependent atomic diffusion. The relaxation is observed in the electronic properties of hydrogenated amorphous silicon (a-Si:H), a ``hydrogen glass'' material, and reflects the equlibration of localized electronic states. The relaxation is attributed to the motion of bonded hydrogen which exhibits dispersive diffusion with a characteristic power-law time dependence. A quantitative relation between the relaxation and the diffusion is established.

Coaxial Nanocable: Silicon Carbide and Silicon Oxide Sheathed with Boron Nitride and Carbon

Abstract: Multielement nanotubes comprising multiple phases, with diameters of a few tens of nanometers and lengths up to 50 micrometers, were successfully synthesized by means of reactive laser ablation. The experimentally determined structure consists of a β-phase silicon carbide core, an amorphous silicon oxide intermediate layer, and graphitic outer shells made of boron nitride and carbon layers separated in the radial direction. The structure resembles a coaxial nanocable with a semiconductor-insulator-metal (or semiconductor-insulator-semiconductor) geometry and suggests applications in nanoscale electronic devices that take advantage of this self-organization mechanism for multielement nanotube formation.

Current Losses at the Front of Silicon Heterojunction Solar Cells

Abstract: The current losses due to parasitic absorption in the indium tin oxide (ITO) and amorphous silicon (a-Si:H) layers at the front of silicon heterojunction solar cells are isolated and quantified. Quantum efficiency spectra of cells in which select layers are omitted reveal that the collection efficiency of carriers generated in the ITO and doped a-Si:H layers is zero, and only 30% of light absorbed in the intrinsic a-Si:H layer contributes to the short-circuit current. Using the optical constants of each layer acquired from ellipsometry as inputs in a model, the quantum efficiency and short-wavelength current loss of a heterojunction cell with arbitrary a-Si:H layer thicknesses and arbitrary ITO doping can be correctly predicted. A 4 cm2 solar cell in which these parameters have been optimized exhibits a short-circuit current density of 38.1 mA/cm2 and an efficiency of 20.8%.