The formation and elimination of helical dislocations in semiconductors

Abstract

Arrays of straight dislocations are transformed into helical dislocations by annealing. Upon prolonged annealing, the helices can be made to annihilate. The density of dislocations has been reduced in this way by five to six orders of magnitude. The process has been observed to operate in Zn-doped epitaxial GaAs grown from both the liquid and the vapour phases, and in Se and Zn-doped GaAs0·6P0·4 grown from the vapour phase. A model is proposed in which self-annihilation of the helices occurs when they form return-loops and pinch-off dislocation loops which exit from the crystal, leaving it 'dislocation-free'.