122 research outputs found
An analytical model for the mechanical deformation of locally graphitized diamond
We propose an analytical model to describe the mechanical deformation of
single-crystal diamond following the local sub-superficial graphitization
obtained by laser beams or MeV ion microbeam implantation. In this case, a
local mass-density variation is generated at specific depths within the
irradiated micrometric regions, which in turn leads to swelling effects and the
development of corresponding mechanical stresses. Our model describes the
constrained expansion of the locally damaged material and correctly predicts
the surface deformation, as verified by comparing analytical results with
experimental profilometry data and Finite Element simulations. The model can be
adopted to easily evaluate the stress and strain fields in locally graphitized
diamond in the design of microfabrication processes involving the use of
focused ion/laser beams, for example to predict the potential formation of
cracks, or to evaluate the influence of stress on the properties of opto
mechanical devices.Comment: 29 pages, 7 figure
Localization landscape theory of disorder in semiconductors. III. Application to carrier transport and recombination in light emitting diodes
This paper introduces a novel method to account for quantum disorder effects
into the classical drift-diffusion model of semiconductor transport through the
localization landscape theory. Quantum confinement and quantum tunneling in the
disordered system change dramatically the energy barriers acting on the
perpendicular transport of heterostructures. In addition they lead to
percolative transport through paths of minimal energy in the 2D landscape of
disordered energies of multiple 2D quantum wells. This model solves the carrier
dynamics with quantum effects self-consistently and provides a computationally
much faster solver when compared with the Schr\"odinger equation resolution.
The theory also provides a good approximation to the density of states for the
disordered system over the full range of energies required to account for
transport at room-temperature. The current-voltage characteristics modeled by
3-D simulation of a full nitride-based light-emitting diode (LED) structure
with compositional material fluctuations closely match the experimental
behavior of high quality blue LEDs. The model allows also a fine analysis of
the quantum effects involved in carrier transport through such complex
heterostructures. Finally, details of carrier population and recombination in
the different quantum wells are given.Comment: 14 pages, 16 figures, 6 table
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