High-resolution imaging of the EL2 distribution in thin semi-insulating GaAs wafers: A comparison with x-ray topography

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Abstract
A detailed comparison of two-dimensional near-infrared absorption maps and x-ray topographs of commercial semi-insulating (100) GaAs wafers grown by the liquid-encapsulated Czochralski technique is reported. The absorption measurements with a spatial resolution up to 100×100 μm2 were performed using a highly sensitive silicon diode array as the detector element. Fluctuations of the EL2 concentration up to 60% are found in conventional undoped wafers. In preannealed wafers, these fluctuations are reduced by a factor of 2, approximately. The spatial one-to-one correlation of the EL2 distribution with grown-in dislocation networks, which is observed in both cases, is discussed. In indium-doped wafers of low dislocation density, the homogeneity of EL2 is better than 5% in the central area of about 40 mm in diameter. By investigating the EL2 distribution near peripheral slip lines, it is definitely established that gettering is a relevant process leading to nonuniformities.