Reaction kinetics and mechanisms of inorganic hydrides on germanium surfaces

[摘要] The surface reactivity of germanium is of interest because of novel Si$sb{x}$Ge$sb{1-x}$ heterostructure applications and the insight into semiconductor surface chemistry attainable through comparative studies on silicon and germanium. The adsorption of the inorganic hydrides H$sb2$S, H$sb2$O, NH$sb3$, and HX (X = Cl, Br) on Ge(100) was investigated by temperature-programmed desorption (TPD) for the first time. The initial sticking probability $Ssb0$ for H$sb2$S exhibits at most only a minor temperature effect, remaining roughly constant at $sim$0.23 within the temperature range 173 K $le$ T $le$ 373 K. Adsorbed H$sb2$S decomposes upon heating into H$sb2$ and GeS, which desorb at 570 K and 660 K, respectively. The initial sticking probability for H$sb2$O depends strongly upon substrate temperature, dropping from 0.28 at 173 K to $sim$0.02 at 273 K. Adsorbed water decomposes to yield H$sb2$ and GeO, which desorb at peak temperatures of 570 K and 660 K, respectively. Both HCl and HBr adsorb on Ge(100), and desorb upon heating to 570 K as H$sb2$ and to 580 K as HX in roughly equal proportions. The remaining X(a) desorbs as GeX$sb2$ at 680 $sim$ 760 K. The initial sticking probability for HBr is 0.77 at 273 K, falling slightly to 0.55 at 373 K, whereas S$sb0$ for HCl falls from 0.30 at 273 K to 0.066 at 373 K. The peak shapes and independence of peak temperature with coverage for H$sb2$ and HX for all adsorbates indicate approximately first-order desorption kinetics, but GeX$sb2$ desorption follows second-order desorption kinetics. Adsorption of NH$sb3$ was not observed, implying $Ssb0$ $le$ 6 $imes$ 10$sp{-5}$. The adsorption and desorption behavior of these molecules can be understood by regarding the Ge(100) dimer atoms as being linked by a strained double bond and examining analogous addition and elimination reactions of molecular germanium compounds.

[发布机构] Rice University