Scripta METALLURGICA Vol. 23, pp. 401-406, 1989 Pergamon Press plc Printed in the U.S.A. All rights reserved ON %~aTINNINGAND POLYMORPHIC TRANSFORMATIONS IN COMPODI~D SEMICONDUCTORS P. Pirouz Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106, U.S.A. (Received December 7, 1988) (Revised January 4, 1989) Introduction A recently proposed dislocation mechanism for twinning in silicon is based on the different mobility of the Shockley partials of a screw dislocation in this material and their associated variation with temperature [i]. As noted in [i], this is similar to a mechanism originally proposed by Venables [2] and discarded by him on the grounds that the required stresses are too large. Venables assumed that the mobility of partial dislocations are the same. In silicon, however, it has been shown that, at lower temperatures, there is a substantial difference between the mobility of the leading and trailing partial dislocations [3]. In addition, the required high stresses can be achieved in mechanical tests at low temperatures. The mechanism proposed in [i] is also applicable to germanium where there is experimental evidence for the different mobilities of partial dislocations [4], and presumably diamond which is isostructural with Ge and Si and has very similar dislocation configurations [5]. The extension of this model to a compound semiconductor with the zincblende structure, mostly of the III-V or the II-VI type, is straightforward. Since this structure is also based on an fcc lattice, the slip plane is {iii} and the dislocations have a total Burgers vector of b=i/2 <II0>. The dislocations are dissociated into two Shoekley partial dislocations of the 1/6 <112> type and the stacking fault energy has been measured for a number of compound semi- conductors with these structures [6,7]. In a diamond cubic or a zincblende material, the layer structures contain {iii) planes in the sequence ...A~B~Cy... where the ~B (or ~C or yA) sepa- ration is three times as large as the A~ (or B~ or Cy) separation. Because of this double- layer arrangement, there are two inherently different types of slip planes. In one case, the slip plane may be envisaged to be in between the widely spaced As (or B~ or Cy) layers while another case may be envisaged in which the slip plane is in between the narrowly spaced ~B (or 8C or yA) layers. Mirth and Lothe [8] termed the dislocations which glide on the narrow slip planes as the "glide set" and those which glide on the widely spaced planes as the "shuffle set" of dislocations. In the zineblende structure, such as GaA, there is the additional difference that the A (or B or C) layers contain all the same type of atoms (e.g. Ga) while the (or ~ or y) layers consist of all the other type of atoms (e.g. As). Hence the core of the dislocations can also be different. In the dislocations which have an edge component, the core may be all Ga, or it may be all As atoms [9]. This applies to both perfect or partial dislocations and different notations are used to distinguish between them. A commonly used terminology is to call the two different cases ~-dislocations and 8-dislocations which refer to shuffle set dislocations whose cores are made entirely of group III (or group II) and group V (or group VI) atoms, respectively, (the converse would be true for the glide set dislocations). Thus, assuming the shuffle set, ~-dislocation in GaAs refers to a dislocation whose core is all Ga atoms, and ~-dislocation refers to the case where the core is all AS atoms. In the notation suggested by by Alexander et al. [i0], a dislocation is distinguished by specifying its slip plane (i.e. glide, g, or shuffle, s) and also the atomic species at its core (e.g. Ga or As). Thus an o~-dislocation in GaAs would be the Ga(s) or As(g) in the latter notation and the ~-dislocation would be the As(s) or Ga(g). It has been known for a long time that the velocities of e and ~ dislocations are different in semiconductors with the zincblende structure and they have different temperature dependen- cies (for a recent review see [ii]). In fact, the activation energy for the motion of ~- and 8-dislocations in a number of III-V compounds, GaP, GaA, etc., have been determined; they depend sensitively on the type and concentration of dopants in the semiconductor [12]. With the more recent observations that dislocations in such structures are dissociated [6,7], it follows that it is the different mobility of the partial components that determines the 401 0036-9748/89 $3.00 + .00 Copyright (c) 1989 Pergamon Press plc