Monte Carlo simulation of energy loss and collection of hot charge carriers, first step towards a more realistic hot-carrier solar energy converter

The energy distribution of hot electrons generated via absorption of above band gap light in a semiconductor was calculated employing the Monte-Carlo (MC) technique with material parameters corresponding to p-InP. Spatial transport and scattering of photo-generated electrons were calculated in the range of kinetic energies up to 0.3 eV above the lower conduction band edge. In view of the large effective mass and the fast energy relaxation rates a contribution from the heavy holes was neglected. The scattering rates of hot electrons were calculated with quantum-mechanical rate expressions for ionized impurities, LO-phonons, acoustic phonons for deformation potential and piezo-electric scattering, and for scattering with heavy holes. Electron-electron scattering was neglected since it does not play a role in semiconductors like InP under solar-irradiation conditions. MC-simulations of the hot carrier dynamics showed that the energy distribution of the hot electrons reaching the contact is very different from the thermalized Fermi-Dirac distribution previously assumed in the scenarios for a hot carrier solar converter. The InP absorber material must be less than 50 nm thick for the hot electrons to reach an ideal sink contact prior to suffering energy losses. A contact with two(multi) energy levels is proposed here for the collection of hot carriers. The suggestion is based on recent experimental and theoretical results [L. Toben, L. Gundlach, R. Ernstorfer, R. Eichberger, T. Hannappel, F. Willig, A. Zeiser, J. Forstner, A. Knorr, P.H. Hahn, W.G. Schmidt, Phys. Rev. Lett. 94 (2005) 0676011 for hot electron capture in a two-dimensional surface resonance of InP(I 0 0). (c) 2006 Elsevier B.V. All rights reserved.