Homogeneous linewidth of bound excitons in high-purity GaAs measured by spectral hole burning

We measured spectral hole burning in an optical-absorption spectrum of a bound exciton (D⁰,X) in high-purity GaAs at 1.8 K. Precise temperature-controlled semiconductor lasers with a lasing wavelength accuracy of less than 0.001 nm are used as wavelength-tunable pump-and-probe light sources in the hole-burning experiments. The homogeneous linewidth of the bound exciton is determined from the burned hole spectral width. The dipole dephasing time T₂ estimated from the measured half width of the burned hole is 300 ps, which is more than an order of magnitude longer than the T₂ value reported for two-dimensional excitons in a GaAs quantum well. Such a long value of T₂ for bound excitons is due to exciton localization or, more specifically, the reduction in the optical-dipole scattering rate is due to zero-dimensional exciton confinement. {} 1996 The American Physical Society.