Direct Observation of Dislocation Loops in Arsenic-Doped Germanium [Letter to the Editor]

The presence of dislocation loops in germanium resulting from condensed vacancies has been assumed^1,2 to explain various deformation, diffusion, and etching phenomena. Booker and Stickler³ have recently shown that such dislocation loops can be observed in thin foils of n-type germanium by transmission electron microscopy. The loops were produced in arsenicdoped germanium containing 10¹⁶ atoms/cc by quenching bulk material from 850°C, thinning by chemical polishing to make foil approximately 1500 A thick, and annealing the foil in the high-intensity electron beam. The loops, which grew with continued annealing, eventually transformed into discs, and Booker and Stickler explained the results by suggesting the formation of clusters consisting of vacancies and impurity atoms. According to their model, the growing clusters, upon reaching a critical size, collapse to form loops. The loops can then absorb more impurity atoms and ultimately transform into platelike particles.