The fine structure constant determines spontaneous emission rates from semiconductors

The probability of spontaneous emission from a semiconductor, per oscillation of the optical field, is proportional to the cube of the fine structure constant alpha and the ratio of the semiconductor dipole parameter E(p) to hydrogen's Rydberg energy. Expressions for radiative recombination rates in quantum wells and bulk semiconductors are given, including the bimolecular radiative recombination coefficient B. We show that alpha sets the natural scale for spectral density of spontaneous emission per square wavelength area of a quantum well. The fine structure constant also sets a physical limit to the Purcell enhancement factor for spontaneous emission. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3591171]