Lifetimes of Photoinduced Hot Charge Carriers Influenced by Momentum Dispersion in Silicon Nanowires
Fatima1 , Yulun Han1 , Dayton J. Vogel1 , Talgat M. Inerbaev2,3, Nuri Oncel4 , Erik K. Hobbie5 , and Dmitri S. Kilin1
1Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108, USA
2 L.N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan
3National University of Science and Technology MISIS, 4 Leninskiy pr., Moscow 119049, Russian Federation
4Department of Physics & Astrophysics, University of North Dakota, Grand Forks, North Dakota 58202, USA
5Department of Physics, North Dakota State University, Fargo, North Dakota 58102, USA
Silicon nanowires (SiNWs) are promising candidates for optoelectronic and light emitting devices due to their unique properties such as band gap, radiative/nonradiative lifetimes of carriers and photoluminescence (PL). All of these properties are affected by quantum confinement effect and are influenced by momentum dispersion along the growth directions. Here, motivated by our previous studies1-2, we report the effect of momentum dispersion on (1) photo-excited relaxation, (2) nonradiative lifetimes and (3) PL quantum yield (QY) of photo- induced electrons and holes in SiNWs grown in <100> and <111> orientations. In laser and solar cell applications, transitions among the valence band and conduction band states are crucial as optical transition matrix elements are anisotropic. We calculated nonradiative lifetimes considering nonradiative transitions among both conduction and valence band states including such transitions for which momentum is not conserved. Changes in energy and momentum for electronic degrees of freedom are achieved via interaction with a thermal bath of nuclear degrees of freedom. Description of photo-excited dynamics processes is enabled by computing “on–the– fly” nonadiabatic couplings (NAC) between electronic and nuclear degrees of freedom using density functional theory (DFT) with explicit treatment of periodic boundary conditions. The dynamics of electronic degrees of freedom is propagated by the reduced density matrix with Redfield equation of motion3. Oscillator strengths are used to compute radiative relaxation and to generate time resolved PL4 . The results of this study would contribute to the material choice for photovoltaic (PV) and light emitting applications.
1. Fatima; Vogel, D. J.; Han, Y.; Inerbaev, T. M.; Oncel, N.; Kilin, D. S., First-Principles Study of Electron Dynamics with Explicit Treatment of Momentum Dispersion on Si Nanowires Along Different Directions. Molecular Physics 2018, 1-10.
2. Fatima; Vogel, J.; Inerbaev, T.; Oncel, N.; Kilin, D., First-Principles Study of Charge Carrier Dynamics with Explicit Treatment of Momentum Dispersion on Si Nanowires Along< 211> Crystallographic Directions. MRS Advances 2018, 3, 3477-3482.
3. Kilin, D. S.; Micha, D. A., Relaxation of Photoexcited Electrons at a Nanostructured Si (111) Surface. The Journal of Physical Chemistry Letters 2010, 1, 1073-1077.
4. Vogel, D. J.; Kilin, D. S., First-Principles Treatment of Photoluminescence in Semiconductors. The Journal of Physical Chemistry C 2015, 119, 27954-27964.