On the primary process in the plasma-chemical and photochemical vapor deposition from silane. III. Mechanism of the radiative species Si*(1P ) formation

Abstract

The mechanism of the radiative species Si*(1P0) formation from SiH4 was investigated with ab initio molecular orbital–configuration interaction calculations on two reaction routes: (a) the simplest one-step reaction mechanism SiH4→Si+2H2 and (b) the second simplest two-step reaction mechanism SiH4→SiH2+H2→Si+2H2. The conclusions obtained are as follows: (i) the one-step mechanism (a) operates effectively in the generation of the radiative species Si*(1P0), (ii) no effective path was found for the formation of Si*(1P0) in the two-step mechanism, (iii) the radiative species Si*(1P0) originates from the fifth lowest excited singlet state 11T1 of SiH4 at the Td structure in the one-step mechanism (a), whereas the nonradiative species Si(1D) is produced spontaneously from the fourth lowest excited singlet state 11E in both reaction mechanisms of (a) and (b), (iv) the nonradiative species SiH2(11B1) is spontaneously generated from the lowest excited singlet state 11T2 of SiH4, (v) the electronic state of the radiative Si*(1P0) has Rydberg character and the emission of Si*(1P0) at 288.2 nm is approximately expressed by 3p4s(1P0)→3p2(1D) where 4s is a Rydberg atomic orbital (AO). It was also concluded that the contributions of 3d AOs are important for making a description of the quantitative energy separations among the lower lying singlet states, 1D, 1S, and 1P0 of Si atoms.