Growth kinetics in silane gas-source molecular beam epitaxy

Growth kinetics in gas-source molecular beam epitaxy (GS-MBE) using silane have been investigated through detailed Arrhenius analysis of the growth rate. For Si(100) surfaces, the growth rate showed a break at about 600°C, separating the higher- and the lower-temperature region. The higher-temperature region is characterized by the activation energy of 3.6 kcal/mol and the reaction is second order. The activation energy of the lower-temperature region is 21 kcal/mol and the reaction is first order. A comparison with the photoemission measurement on silane-adsorbed silicon surfaces indicates that the transition from the lower- to the higher-temperature region is accompanied by a depletion of hydrogen atoms from the surface. Effects of co-irradiation of 147 nm photons on the substrate during growth were also investigated for the first time. The photons, which are known to produce silane radicals on collision with silane molecules, were found to be effective in enhancing the growth rate only in the higher temperature region. These results indicate that the higher-temperature region is rate-limited by the silane adsorption process, while the low-temperature region is rate-limited by the hydrogen desorption process. For Si(111) surfaces, the growth rate was greatly reduced compared with (100) surfaces. In addition, the activation energy obtained for the growth rate above 700°C was 13 kcal/mol, which shows a clear departure from the value of 3.6 kcal/mol for the (100) surface.