Studies of Interface Demarcation and Structural Defects in Ga Doped Ge Single Crystals Using Synchrotron White Beam X-Ray Topography

Synchrotron White Beam X-ray Topography (SWBXT) has been applied to the characterization of marked growth interfaces in Ga doped Ge single crystals. The techniques employed in interface demarcation include modifications of the cold zone temperature, mechanical pulsing and Peltier pulsing. As revealed by our observations, the visibility of growth interfaces is a sensitive function of diffraction conditions. A combination of the correct orientation of the active reciprocal lattice vector with respect to the interface plane and the necessary strain sensitivity controlled by the rocking curve width of the reflection are proved to be important for interface visibility. This can easily be achieved by using synchrotron radiation since the tunability of the synchrotron source provides great flexibility in the choice of proper diffraction conditions. Structural defects such as small-angle tilt boundaries and dislocation cell structures were also observed. The formation mechanism of these defects will be discussed. Direct evidence of dislocations present in the seed crystal propagating into the as-grown crystal through the melt-back interface during crystal growth was also obtained.