Roger James Elliott calculated how excitons alter optical absorption near a semiconductor band gap. Treating the electron-hole attraction with an effective mass model produces bound-state absorption lines as well as a modified continuum. The 1957 theory distinguishes direct and phonon-assisted indirect transitions, and shows how optical selection rules change the edge's shape and strength. It connects microscopic bound states with features visible in a measured absorption spectrum.[ref]
Intensity of Optical Absorption by Excitons by Roger James Elliott. Physical Review 108, 1384 (1957), abstract: direct/indirect and allowed/forbidden edge transitions
Portrait of Roger James Elliott
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