Exciton Broadening and Non-Linear Absorption of Ultrathin Gallium-Arsenide Samples.

The excitonic linewidth of single GaAs wells are investigated for well widths of 500, 800, and 1500 Angstroms. The thermal components of the broadening are determined from absorptive measurements of the exciton halfwidth at half maximum for temperatures ranging from 10 K to 50 K. This dependence is found to be linear, with an identical slope of 0.14 +/- 0.01 A/K for all samples examined. The temperature independent components are extrapolated to be smaller than 0.5 Angstroms for the 500 and 1500 Angstrom wells, and 1.5 Angstroms for the 800 Angstrom well. A CW hole-burning experiment on the latter sample reveals that a major portion of its temperature independent broadening is inhomogeneous. A discussion on the limitations of this nonlinear technique in the CW time domain is included.