Quantum Optoelectronics

Abstract:

The polarization dependence of biexcitonic signals and quantum beats between A-excitons (X-A) and A-biexcitons (XAXA) in a high-quality GaN epilayer is measured by spectrally-resolved and time-integrated four-wave mixing. With cross-linear polarised light, mixed beats with two periods are observed: the first beating period corresponds to the energy splitting between X-A and XAXA, and agrees well with the calculated XAXA binding energy, while the second beating period corresponds to that between X-A and donor bound excitons ((DX)-X-0). The temperature-dependent homogeneous linewidth shows that the (DX)-X-0 has a larger acoustic phonon coupling coefficient than the XAXA. We also measured the polarization dependent B-biexciton (XBXB) signal. The effective masses for the A- and B-hole were deduced from the binding energy.

Abstract:

We present spectrally resolved and time-integrated four-wave mixing measurements at coherent dynamics of bound excitons in a high-quality GaN epilayer. Coherent excitation, with co-circular polarized light, of the neutral donor-bound excitons (D ⁰X) and A excitons (XA) results in quantum beats, corresponding to the energy splitting between D ⁰X and XA. The temperature-dependent dephasing rate is used to deduce the strength of the D ⁰X-acoustic-phonon interaction via the homogeneous linewidth. © 2001 American Institute of Physics.

Abstract:

Hot carrier relaxation has been studied in GaN using femtosecond time-resolved optical transmission and reflection. A non-thermal electron distribution with a pronounced `cut-off' at ELO is observed for up to approximately 3 ps after photoexcitation. Monte Carlo simulations show that this behaviour is due to a remarkably strong electron-LO phonon interaction. Excitonic effects are also pronounced, and strongly influence the dynamics.