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Proceedings Paper

Toward bound-to-continuum photon absorption with quantum tunneling in type-II nanostructures: a source-radiation scheme using perfectly-matched layers
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Paper Abstract

Electrons and holes in type-II nanostructures are spatially separated. Therefore, both the radiative and nonradiative recombination rates are reduced. Although the photon conversion efficiency is hence decreased, the lowered nonradiative recombination such as Auger process benefits photovoltaic applications. Furthermore, if generated carriers can be rapidly removed from nanostructures through quasi-bound states, the photon absorption may be designed and enhanced regardless of the concern on nonradiative mechanisms. Here, we model the bound-tocontinuum absorption of type-II nanostructures in the presence of tunneling using the density-matrix formalism and convert it into a radiation problem in the multiband space with band mixing. An effective source is derived from the eight-band momentum operator, and the corresponding field is expressed in terms of the source and retarded Green’s function of the eight-band Luttinger-Kohn Hamiltonian. On the other hand, the response is actually calculated without the Green’s function. Perfectly-matched layers in the multiband space are introduced to model the effect of quasi-bound states in open regions. In this way, the interplay between photon absorption and tunneling is fully taken into account. We present both the transverse-electric and transverse-magnetic absorption spectra of type-II GaAs 0:65Sb0:35/GaAs coupled quantum wells. The corresponding lineshape broadening near the resonant energy can be divided into two parts. One comes from various incoherent relaxation mechanisms, and another well-fitted by the Fano resonance originates from the coherent tunneling. For a 2-nm potential barrier, the tunneling times of metastable states in nanostructures are around 20 fs, and their degrees of mixing to the continuum are high.

Paper Details

Date Published: 7 March 2014
PDF: 15 pages
Proc. SPIE 8980, Physics and Simulation of Optoelectronic Devices XXII, 89801Q (7 March 2014); doi: 10.1117/12.2036699
Show Author Affiliations
Chi-Ti Hsieh, Academia Sinica (Taiwan)
Shu-Wei Chang, Academia Sinica (Taiwan)
National Chiao Tung Univ. (Taiwan)

Published in SPIE Proceedings Vol. 8980:
Physics and Simulation of Optoelectronic Devices XXII
Bernd Witzigmann; Marek Osiński; Fritz Henneberger; Yasuhiko Arakawa, Editor(s)

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