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2 March 2020 A Monte Carlo solution to hole transport processes in avalanche selenium semiconductors
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Amorphous selenium is a unique wide-bandgap disordered material, that shows a deterministic single-carrier hole impact ionization process which results in a very low excess noise factor. A key feature of the avalanche phenomenon in amorphous selenium is that transport at high electric fields shifts to non-activated extended states and this necessitates the need to obtain microscopic access into the relaxation dynamics of non-equilibrium 'hot' holes in extended states. Another interesting aspect of elemental selenium is the similarity in short range order that exists across all allotropic forms. Thus, we employ an in-house ensemble Monte Carlo algorithm, in which we take into consideration scattering from acoustic and non-polar optical phonons to describe the general details of the extended-state hole-phonon interaction. The delocalized extended state transport in the amorphous phase is modeled using the band-transport lattice theory of its crystalline counterpart, trigonal selenium. The energy and phonon band structure along with the density of states and acoustic/optical deformation potentials for the crystalline phase was calculated using density functional theory and a parabolic approximation to the density of states function was used in the simulation. We validate our calculated drift mobility with experimental results in the perpendicular and parallel directions to the c-axis, in the unit cell for trigonal selenium. Moreover, in the direction perpendicular to the c-axis we show that acoustic and non-polar optical phonons are able to maintain a stable hole-energy distribution as long as the electric field is lower than the critical value of 650 kV/cm. Beyond a certain critical electric field, holes in selenium can get 'hot' and gain energy at a faster rate than they loose to the lattice.
Conference Presentation
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Atreyo Mukherjee, Richard Akis, Dragica Vasileska, and A. H. Goldan "A Monte Carlo solution to hole transport processes in avalanche selenium semiconductors", Proc. SPIE 11274, Physics and Simulation of Optoelectronic Devices XXVIII, 112740U (2 March 2020);

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