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 (D-0,X) in high-purity GaAs at 1.8 K. Precise tempera ture-controlled semiconductor lasers with a lasing wavelength accuracy of less than 0.001 nm are used as wavelength-tunable pump-and-probe l ight sources in the hole-burning experiments. The homogeneous linewidt h of the bound exciton is determined from the burned hole spectral wid th. The dipole dephasing time T-2 estimated from the measured half wid th of the burned hole is 300 ps, which is more than an order of magnit ude longer than the T-2 value reported for two-dimensional excitons in a GaAs quantum well. Such a long value of T-2 for bound excitons is d ue to exciton localization or, more specifically, the reduction in the optical-dipole scattering rate is due to zero-dimensional exciton con finement.