Electronic Characterization of Dislocations in Rtcvd Germanium-Silicon/Silicon Grown by Graded Layer Epitaxy

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Abstract
Carrier trapping and recombination activity have been studied with DLTS and EBIC in RTCVD grown compositionally graded Ge0.3Si0.7/Si heterostructures. DLTS peak height is found to vary with applied bias, and the bias conditions used indicate that at least one peak is present in the homoepitaxial Si buffer layer and perhaps the substrate as well. Variations in EBIC contrast as a function of reverse bias, and DLTS fill pulse experiments both indicate that the DLTS peaks observed are dislocation related. Moreover, the bias dependent decrease in DLTS peak height is observed to occur at different rates for different peaks, indicating a possible connection between certain DLTS peaks and dislocation orientation or type. Activation energies of one electron trapping center and one hole trapping center add up to roughly the expected bandgap in a relaxed GexSi1−x, alloy with x ≦ 0.3, indicating that the electron and hole trapping centers observed with DLTS may, in fact, be associated with the R-G center observed by EBIC.