Analysis of twin formation in sphalerite-type compound semiconductors: A model study on bulk InP using statistical methods

The type of twinning in sphalerite-type Ill-V compound semiconductors is well known. However, the detailed formation mechanism, although intensively studied in the last two decades, is not entirely understood. It is still widely accepted that twin formation is a rather fortuitous issue. In addition to many empirical observations and phenomenological explanations, there was a first theoretical approach by Hurle [Speculation Concerning the Causes of Twinning during Czochralski growth of Crystals having Diamond Cubic or Zinc-blende Structure, 1991], later refined. The theory predicts a correlation between crystal slope angle alpha and twin generation frequency, where alpha is defined as the angle between the tangent to the crystal surface and the growth axis. Angles of 70.53 degrees and 74.21 degrees should promote twinning, while that of 35.26 degrees should reduce twin frequency. However, a critical review of experimental results on InP, grown by LEC (liquid encapsulated Czochralski) and VCz (vapor pressure controlled Czochralski) techniques, does not yield such a clear correlation. To shed some more light on the possible factors already discussed in literature, a systematic study based on statistical methods is performed. It can be shown that, at least for the Czochralski technique, twin formation is closely connected to the crystal growth rate and its fluctuations, i.e. instabilities of the growth system. This confirms some of the literature suggestions. (C) 2008 Elsevier B.V. All rights reserved.