ANALYSIS OF STRESSES IN GAAS SINGLE-CRYSTAL WAFERS BY X-RAY-DIFFRACTION AND PHOTOELASTICITY METHODS

The stress data in GaAs wafers measured by the photoelasticity technique are compared with strain data measured by the X-ray diffraction. For a Czochralski-grown undoped single crystal both methods provide the determination of elastic strains and stresses caused by dislocations. In a strongly silicon-doped single crystal grown by horizontal Bridgman technique, X-ray measurements reveal the lattice parameter variations along the wafer due to the dopant, whereas the photoelasticity method provides the determination of elastic strains and stresses due to inhomogeneous dopant distribution. Comparing the data obtained by these two techniques, it is possible to separate the elastic lattice distortions caused by dislocations and/or inhomogeneity in the dopant distribution from the effect on the lattice parameter caused by the dopant proper. The sensitivity and the information capacities of both methods are compared.