Lattice bending in LEC-grown semi-insulating GaAs crystal wafers was investigated by X-ray diffraction. Various distributions in the lattice bending were observed in wafers from different boules. Prominent bends, with radii of curvature of about 20 m, were observed at places where the relevant topographs showed the presence of fine cellular dislocation networks. The apparent wafer bending was also examined optically and was found to be caused mainly by back surface damage.
Source:IOPscience
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.
Source:IOPscience