Identifying and quantifying point defects in semiconductors using x-ray-absorption spectroscopy: Si-doped GaAs

Both the type and concentration of point defects responsible for the observed poor electrical activity of highly Si-doped GaAs have been determined using near-edge and extended x-ray-absorption fine structure (NEXAFS and EXAFS). The measurements were made possible using a combination of synchrotron beamline features, fluorescence detection, and GaAs(311) A samples. Because Si can occupy both n-type Ga and p-type As sites, the electrical deactivation has generally been attributed to acceptor-Si atoms trapping free-electron carriers. However, the present NEXAFS data directly measure upper limts on the concentration of Si atoms occupying such p-type As sites, showing that only about half of the observed electrical inactivity is due to this autocompensation mechanism. Identification of the dominant defects responsible for the additionally missing carriers is provided by the EXAFS data, which reveal a comparatively large number of neutral SiGa-SiAs dimers and small Sin clusters. Implications of these findings and a comparison with local vibrational mode spectroscopy and scanning tunneling microscopy methods are discussed.