A comparative study of dissociative adsorption of NH3, PH3, and AsH3 on Si(001)–(2×1)

Abstract

Effect of the cluster size in modeling the H 2 desorption and dissociative adsorption on Si(001)Using a first-principles pseudopotential method we have studied the adsorption and dissociation of NH 3 , PH 3 , and AsH 3 on the Si͑001͒-͑2ϫ1͒ surface. Apart from the existence of a barrier for the adsorption of the precursor state for arsine, we observe that the global behavior for the chemisorption of the XH 3 molecules considered in this work is as follows: the gas phase XH 3 adsorbs molecularly to the electrophilic surface Si atom and then dissociates into XH 2 and H, bonded to the electrophilic and nucleophilic surface silicon dimer atoms, respectively. The energy barrier, corresponding to a thermal activation, is much smaller than the usual growth temperature, indicating that all three molecules will be observed in their dissociated states at room temperature. All adsorbed systems are characterized by elongated Si-Si dimers that are ͑almost͒ symmetric in the dissociative case but asymmetric in the molecular case. According to our first-principles calculations, all XH 3 and XH 2 systems retain the pyramidal geometry observed for the gas molecules. Our calculated vibrational spectra further support the dissociative model for the XH 3 molecules considered here.

Methanol adsorption on silicon (001)

“…The dimer elongation is consistent with experimental [29] as well as theoretical [14,15] findings for other small hydrocarbon molecules, while the dimer tilting follows the same pattern observed for the dissociative adsorption processes of other small molecules like XH 3 (X = N, P, and As) [31]. The calculated C-H bond length of $1.10 Å for all the considered models is also in good agreement with early theoretical estimates for other small hydrocarbon molecules and is close to that observed for the free CH 3 OH molecule.…”

Diffusion pathways of phosphorus atoms on silicon (001)

“…Extensive theoretical modeling 19,[28][29][30][31][32][33] in conjunction with detailed STM images provided a consistent interpretation of the first stage of this reaction, namely the thermal dissociation of PH 3 into phosphorus and hydrogen adatoms. However, the subsequent incorporation reactions that take phosphorus adatoms into the surface remain unclear.…”

A simple two-step phosphorus doping process for shallow junctions by applying a controlled adsorption and a diffusion in an oxidising ambient

“…There are a number of publications about the interaction of phosphine with the silicon surface (see [13,14] and citations therein). It has been reported that PH 3 easily adsorbs on (1 0 0) Si; a non-dissociative adsorption of PH 3 on the dangling bonds of the (2 × 1)-reconstructed surface was found at room temperature.…”