Twin generation in zinc-blende type III–V compound semiconductors: New insights from an InP case study
The type of twinning in zincblende-or sphalerite-type III-V compound semiconductors is well known. However, its detailed formation mechanism, although intensively studied in the eighties and nineties, is not entirely understood. In addition to a lot of empirical observations, there is a theoretical approach, published in 1995 [1] and improved in 1998 [2]. The latter predicts a correlation between crystal slope angle a and twin generation frequency. However, a critical overview of our own experimental results on GaAs and InP, grown by LEC (Liquid Encapsulated Czochralski) and VCz (Vapour Pressure controlled Czochralski) techniques, leads to no unambiguous relation between twin formation and crystal slope angle. This paper gives a comparison between experimental results and the above mentioned theory, revealing that twinning is more correlated to dynamical effects like oscillations of growth rate, i.e. noise of the system.
The mechanism of growth-twin formation in zincblende crystals: new insights from a study of magnetic liquid encapsulated Czochralski-grown InP single crystals
Abstract Synchrotron white beam X-ray topography (SWBXT) [1, 2] [M. Dudley, in: Mater Res. Soc. Symp. Proc., vol. 307, 1993, p. 213; Encyclopedia of Applied Physics, vol. 21, 1997, p. 533] combined with chemical etching and Nomarski optical microscopy have been employed to investigate the phenomenon of twinning in sulfur-doped, MLEC-grown 〈1 0 0〉 InP single crystals. Results confirm the prediction of Hurle [3, 4] [Sir Charles Frank, OBE, FRS; on 80th Birthday tribute, 1991, p. 188; J. Crystal Growth 147 (1995) 239] that twins nucleate in regions where {1 1 1} edge facets are anchored to the three-phase boundary (TPB), and that twinning produces a {1 1 1} external facet on the shoulder region of crystal. The critical factor controlling the point at which the twin nucleates is observed to be the appearance of a {1 1 5} external shoulder facet which is then converted to the {1 1 1} external shoulder facet upon twinning. Based on the observation of both anchored edge facets and twinning at shoulder angles of approximately 74°, ν max , the maximum in the range of angles, ν (where ν is the angle between the edge facet and the extension of the crystal surface, or shoulder), over which edge facets can be expected to be trapped at the TPB, as presented by Hurle, has been increased, from ∼86.5° to ∼112°, by modifying approximations made concerning the relevant physical parameters for the particular case of S-doped InP. A correction is made to an error in Hurle: the most dangerous grow-out angle for the occurrence of twinning in 〈1 0 0〉 oriented crystals, is 74.2° and not 35.5°. Also Hurle predicted that, in crystals with diamond cubic or zincblende structures, the range of ν angles for edge facet pinning should encompass 70.5(3)° for twinning to be possible. This is here extended to the statement that it should encompass either 70.5(3)° and/or 109.47°. Incidences of twinning were also observed to occur by a similar mechanism but one which involved the conversion of a {1 1 4} external shoulder facet to a {1 1 0} one.
Growth of twin-free InP single cystals by the liquid encapsulated vertical Bridgman technique
Abstract We have successfully grown twin-free InP crystals with 50 mm diameter by the liquid encapsulated vertical Bridgman technique. In order to avoid twin formation in the crystals, a flat-bottom crucible was used instead of conventional crucibles with a conical part.