我們使用密度泛函數(DFT)法研究SiH4, GeH4, Si2H6, and Ge2H6分解吸附與氫遷移和脫附於SiGe(100)-2x1表面。由於鍺加入於Si(100)-2x1表面內影響了dimer的傾斜和表面的反應性，SiH4, GeH4, Si2H6, and Ge2H6與Si*-Si, Ge*-Si, Ge*-Ge, and Si*-Ge（*代表上位原子）此四種不同dimer反應，經系統化分析於反應能量上之影響。於半氫覆蓋表面，SiH4, GeH4, Si2H6, and Ge2H6吸附能障是高於各反應物於潔淨表面之能障，而SiH4 之吸附能障是高於GeH4的，Si2H6之吸附能障亦是高於Ge2H6。由計算結果顯示Si2H6/Ge2H6分解路徑為經由Si-H/Ge-H鍵之斷裂比經由Si-Si/Ge-Ge鍵之斷裂來得容易。我們基於兩個理由認為吸附反應下SiGe表面的反應性和鍺存在於表面有關。有鍺存在時氫脫附是較容易進行的，且於Ge*-Si dimer存在時，更易使SiH4, GeH4, Si2H6, and Ge2H6進行分解吸附反應。研究中亦使用過渡狀態理論以計算速率常數，於650℃下計算所得GeH4於Si*-Si和Ge*-Ge dimer上之速率常數比為2.1，此值和文獻中GeH4吸附於Si(100)表面和具一單層鍺覆蓋之Si(100)之反應機率比相吻合，經超音速分子束實驗所得之實驗比值為1.7。雖然計算結果顯示Ge*-Si是表面上最具反應性之dimer，然實驗結果為於Si(100)-2x1上對鍺甲烷和二鍺烷反應機率是單調下降，此意味著使用鍺烷和二鍺烷於初期磊晶時僅伴隨著Si*-Si和Ge*-Ge此二dimer。
對氫遷移和脫附而言，由於氫遷移之能障通常是低於氫脫附步驟之能障，我們認為氫分子再結合脫附為速率決定步驟。因氫由鍺位遷移至矽位之能障低於其相反方向之能障，使得氫傾向於留滯於矽位上。由於較弱之Ge-H鍵，使得於化學氣相反應下之SiGe-2x1表面是比Si(100)-2x1更具有反應性並提供了較多的懸鍵。

Dissociative adsorptions of SiH4, GeH4, Si2H6, and Ge2H6 along with hydrogen migration and desorption on the buckled SiGe(100)-2x1 surface have been studied by using density functional theory (DFT) at the B3LYP level. The Ge alloying in the Si(100)-2x1 surface affects the dimer buckling and its surface reactivity. Systematic Ge influences on the reaction energetics are found in SiH4, GeH4, Si2H6, and Ge2H6 reactions with four dimers of Si*-Si, Ge*-Si, Ge*-Ge, and Si*-Ge (* denotes the protruded atom). On a half H-covered surface, the energy barriers for silane, germane, disilane, and digermane adsorption are higher than those on the pristine surface. The energy barrier for silane adsorption is higher than the corresponding barrier for germane adsorption. The energy barrier for disilane adsorption is higher than the corresponding barrier for digermane adsorption. The calculation results suggest that disilane/digermane dissociation path on SiGe(100) surface via Si-H/Ge-H bond scission is more favorable than via Si-Si/Ge-Ge bond scission. We conclude that the SiGe surface reactivity in adsorption reaction depends on the Ge presence on surface for two-fold reasons. The hydrogen desorption is easier on Ge, and the presence of Ge*-Si dimer facilitates the dissociative adsorption of SiH4, Si2H6, GeH4, Ge2H6. Rate constants are also calculated using the transition-state theory.
The calculated rate constant ratio of GeH4 adsorption on Si*-Si over Ge*-Ge at 650℃ is 2.1, which agrees with the experimental ratio of GeH4 adsorption probability on Si(100) surface over that on one monolayer Ge covered Si(100) surface. The experimental ratio is 1.7 measured by supersonic molecular beam techniques. Although the calculation results indicate Ge*-Si is the most active dimer on surface, the experimental results of a monotonic decrease in germane and digermane reaction probability on Si(100)-2x1 indicate only two dimers of Si*-Si and Ge*-Ge are involved in the initial epitaxial growth using GeH4 and Ge2H6.
As for hydrogen migration and desorption, the H2 recombinative desorption is the rate-determining step on SiGe(100) surface, since the energy barriers of H-atom migration steps are generally lower than those of H2 desorption. The chemisorbed H trends to stay on the Si-site, since the barrier for H-migration from the Ge-site to the Si-site is lower that in the opposite dirction. The SiGe(100)-2x1 surface in chemical vapor deposition is more reactive and provides more dangling bonds than the Si(100)-2x1 because of weaker Ge-H bond.

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