OPTICAL-ABSORPTION SPECTROSCOPY OF SINGLE DEFECTS IN GAAS ALXGA1-X ASTUNNEL STRUCTURES/

We measure the optical absorption spectra of single defects in GaAs/Al 0.35Ga0.65As tunnel structures. The optically induced change in charge state of individual defects produces a measurable discrete change in resistance in sufficiently small-area structures. Measuring the rate o f optical excitation as a function of wavelength yields the optical ab sorption spectrum of an individual defect or impurity. These experimen ts demonstrate the feasibility of single-defect optical spectroscopy f or a general class of defects or impurities in solids.