Abstract
Band edge optical spectra of all direct-gap semiconductors show evidence of electron–hole pair correlation. In sufficiently pure crystals and for low pair densities, n • aB << 1 (where aB is the exciton Bohr radius), one finds discrete individually bound pair states below the fundamental gap energy Eg—the excitons—and a strongly enhanced continuum spectrum above Eg. We discuss the characteristic changes in this spectrum induced by the excitation of e–h pairs in the crystal. We concentrate on (1) empirical absorption spectra in the model III–V semiconductor GaAs in the 1013–1016 cm−3 density range at 2 K in conditions of resonant excitation and (2) the concept of dielectric vs metallic screening in nonequilibrium e–h pair distributions. Thin platelets (0.5–4 μm) of high-purity LPE GaAs were excited with tunable picosecond light pulses, the nonlinear absorption was probed with a second independently tunable pulse with ≤6 ps temporal jitter.
© 1987 Optical Society of America
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