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First-principles simulations of vibrational decay and lifetimes in a -Si:H and a-Si:D

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Atta-Fynn, R 
Drabold, DA 
Elliott, SR 
Biswas, P 


Phonon lifetime in materials is an important observable that conveys basic information about structure, dynamics, and anharmonicity. Recent vibrational transient-grating measurements, using picosecond infrared pulses from free-electron lasers, have demonstrated that the vibrational-population decay rates of localized high-frequency stretching modes (HSMs) in hydrogenated and deuterated amorphous silicon (a-Si:H/D) increase with temperature and the vibrational energy redistributes among the bending modes of Si in a-Si:H/D. Motivated by this observation, we address the problem from first-principles density-functional calculations and study the time evolution of the vibrational-population decay in a-Si:H/D, the average decay times, and the possible decay channels for the redistribution of vibrational energy. The average lifetimes of the localized HSMs in a-Si:H and a-Si:D are found to be approximately 51-92 ps and 50-78 ps, respectively, in the temperature range of 25-200 K, which are consistent with experimental data. A weak temperature dependence of the vibrational-population decay rates has been observed via a slight increase of the decay rates with temperature, which can be attributed to stimulated emission and increased anharmonic coupling between the normal modes at high temperature.



51 Physical Sciences, 34 Chemical Sciences, 3406 Physical Chemistry, 3407 Theoretical and Computational Chemistry

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Physical Review B - Condensed Matter and Materials Physics

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American Physical Society
The work is partially supported by the U.S. National Science Foundation under Grants No. DMR 1570166, No. DMR 1570118, and No. DMR 1506836. We acknowledge the use of computing resources at the Texas Advanced Computing Center and Ohio Supercomputer Center.