Resonant light delay in GaN with ballistic and diffusive propagation

TL;DR

This paper investigates resonant light delay in bulk GaN, revealing a significant delay near the neutral-donor bound exciton energy, explained by optical dispersion and scattering effects, with implications for light propagation control.

Contribution

It provides a quantitative explanation of resonant light delay in GaN involving both ballistic and diffusive propagation components.

Findings

Delay increases resonantly near BX energy

Light velocity as low as 2100 km/s observed

Both ballistic and diffusive components detected

Abstract

We report on a strong delay in light propagation through bulk GaN, detected by time-of-flight spectroscopy. The delay increases resonantly as the photon energy approaches the energy of a neutral-donor bound exciton (BX), resulting in a velocity of light as low as 2100 km/s. In the close vicinity of the BX resonance, the transmitted light contains both ballistic and diffusive components. This phenomenon is quantitatively explained in terms of optical dispersion in a medium where resonant light scattering by the BX resonance takes place in addition to the polariton propagation.