A scanning-PICTS system for imaging two-dimensional distributions of deep-traps in a semi-insulating GaAs wafer is presented. The utility of this system is demonstrated using a LEC-grown undoped semi-insulating GaAs wafer which exhibits a W-shaped dislocation-density variation along the wafer diameter. It has been found that the density of 0.14 eV electron-trap in the wafer exhibits a distinct inverse-W-shaped variation along the diameter and that this trap is closely correlated with the dislocation. The densities of 0.31 eV and 0.55 eV electron-traps have been found to exhibit a very "in-distinct" inverse-W-shaped variation along the diameter, and that the traps are correlated slightly with the dislocations. Thus the scanning-PICTS technique is a very powerful tool for observing one- and two-dimensional distributions of traps in a wafer of semi-insulating material.
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