Vapor phase growth method

A method for growing crystals from the gas phase. There are two methods: sublimation and gas-phase reaction. In the gas-phase reaction method, a reactive gas mixture or a gas that decomposes easily at high temperatures is flowed onto a substrate that also serves as a catalyst or base crystal, and the mixture reacts and crystallizes there. For example, a mixture of _GeCl4 and _H2 is flowed onto a heated substrate, and a thin Ge film is epitaxially grown (epitaxy) by a reduction reaction, or _SiH4 is introduced onto a substrate heated to around 1100°C,

SiH ₄ (g) → Si(s) + 2H ₂ (g)

or silicon crystals are obtained by the reaction of (thermal decomposition method). These methods are considered to be a type of chemical transport reaction, and the transport speed of gas molecules is low and concentration differences are easily caused by turbulence, so the crystals obtained by this method are generally small particles, thin films, whiskers, or plate-like crystals. It is widely applied to oxides, arsenides, nitrides, etc., and it is common to use a volatile halide as an intermediary, with _H2O or _NH3 gas as an intermediary.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

気相から結晶を育成する方法．昇華法と気相反応法とがある．気相反応法では，反応性混合気体や高温で熱分解しやすい気体を触媒や下地結晶などを兼ねた基板上に流して，そこで反応させて結晶化させる．たとえば，GeCl₄と H₂ との混合気体を加熱した基板上に流し，還元反応によりGe薄膜をエピタキシャル成長(エピタキシー)させたり，1100 ℃ 前後に加熱された基板上にSiH₄を導いて，

SiH₄(g) → Si(s) ＋ 2H₂(g)

の反応によりSi結晶を得たりする(熱分解法)．これらの方法は，化学輸送反応の一種と考えられ，気体分子の輸送速度が小さく，また乱流が発生することによって濃度差を生じやすいので，一般にこの方法で得られる結晶は，微粒子，薄膜，ウィスカーや板状の小さな結晶が多い．酸化物，ヒ化物，窒化物などに広く応用され，蒸発性のハロゲン化物を媒介として，H₂O，NH₃ガスを介在させるのが普通である．

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