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.
Etch features in Czochralski-grown single crystal indium phosphide
Two etchants for InP have been used to categorize etch features in both horizontal and vertical sections of InP single crystals grown by the Czochralski liquid encapsulation technique; these are the AB etchant, used extensively for defect analysis in GaAs and another etchant based on a phosphoric acid/hydrobromic acid mixture. The behaviour of these etchants is different but a cross correlation has been made between the types of etch feature produced. Transmission X-ray topography has been used to correlate etch features with dislocations. Nominally undoped crystals and material doped with specific impurities, e.g. Fe, Ge, Zn, have been examined. The principal features produced by etching are pits, ridges and striations. It is shown that the density and distribution of pits and ridges is consistent with these features being dislocation structures and the mechanisms by which they are revealed are discussed in terms of etching rates. The results allow comment to be made upon interface shape and the source of dislocations in InP crystals grown by the Czochralski technique.
Effects of the mineral phase and valence of vanadium on vanadium extraction from stone coal
The influence of roasting on the leaching rate and valence of vanadium was evaluated during vanadium extraction from stone coal. Vanadium in stone coal is hard to be leached and the leaching rate is less than 10% when the raw ore is leached by 4 mol/L H2SO4 at 90°C for 2 h. After the sample is roasted at 900°C for 2 h, the leaching rate of vanadium reaches the maximum, and more than 70% of vanadium can be leached. The crystal of vanadium-bearing mica minerals decomposes and the content of V(V) increases with the rise of roasting temperature from 600 to 900°C, therefore the leaching rate of vanadium increases significantly with the decomposition of the mica minerals. Some new phases, anorthite for example, form when the roasting temperature reaches 1000°C. A part of vanadium may be enwrapped in the sintered materials and newly formed phases, which may impede the oxidation of low valent vanadium and make the leaching rate of vanadium drop dramatically. The leaching rate of vanadium is not only determined by the valence state of vanadium but also controlled by the decomposition of vanadium-bearing minerals and the existence state of vanadium to a large extent.