Metallodielectric antenna for spontaneous emission enhancement

Semiconductors have an intrinsically slow spontaneous emission rate, on the order of 1ns. Consequently, light emitting diodes (LEDs) can be directly modulated at a maximum rate of 250 MHz (in contrast to lasers, which can be directly modulated at a maximum rate of about 50 GHz). The slow spontaneous emission rate can fundamentally be attributed to the mismatch between the wavelength of light emission and a characteristic dipole length, which is approximately given by the lattice period. In other words, bare LEDs serve as poor antennas for their own radiation.