Arsenic incorporation during Si(001): As gas-source molecular-beam epitaxyfrom Si2H6 and AsH3: Effects on film-growth kinetics

The effects of As doping, at concentrations C(As)less than or equal to4.8x1 0(18) cm(-3), on the growth kinetics of Si(001):As layers deposited at temp eratures T-s=575-900 degreesC by gas-source molecular-beam epitaxy from Si2 H6 and AsH3 have been investigated. With constant AsH3 and Si2H6 fluxes, fi lm deposition rates R-Si increase while C-As decreases with increasing T-s. All incorporated As resides at substitutional electrically active sites fo r C-As up to 3.8x10(18) cm(-3) (T-s=800 degreesC), the highest value yet re ported for Si(001):As growth from hydride source gases. Immediately followi ng film growth or partial-monolayer As adsorption on clean Si(001), the sam ples were quenched to 300 degreesC and exposed to atomic deuterium (D) unti l saturation coverage. In situ D-2 temperature-programmed desorption (TPD) spectra from both as-deposited Si(001):As and As-adsorbed Si(001) layers ar e composed of beta (1) and beta (2) peaks, due to D-2 desorption from Si mo nodeuteride and dideuteride surface phases, together with a new peak beta ( 3) which we attribute to desorption from Si-As mixed dimers. Analyses of th e TPD spectra show that, because of the lone-pair electrons associated with each As surface atom, the total dangling-bond coverage, and hence R-Si, de creases with increasing incoming flux J(AsH3) at constant T-s. From measure ments of the steady-state As surface coverage theta (As) vs C-As and T-s, w e obtain an As surface segregation enthalpy DeltaH(s)=-0.92 eV. Dissociativ e AsH3 adsorption on Si(001) was found to follow second-order kinetics with a relatively T-s-independent reactive sticking probability of 0.3. Associa tive As-2 desorption is also second order with a rate constant k(d,As2)=1x1 0(13) exp(-3.0 eV/kT(s)). From the combined set of results, we develop a pr edictive model with no fitting parameters for C-As vs J(AsH3), J(Si2)H(6), and T-s. (C) 2000 American Institute of Physics. [S0021- 8979(00)08824-1].