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

The effects of As doping, at concentrations C_As≤4.8 × 10¹⁸ cm^-3, on the growth kinetics of Si(001):As layers deposited at temperatures T_s = 575-900°C by gas-source molecular-beam epitaxy from Si₂H₆ and AsH₃ have been investigated. With constant AsH₃ and Si₂H₆ fluxes, film deposition rates R_Si increase while C_As decreases with increasing T_s. All incorporated As resides at substitutional electrically active sites for C_As up to 3.8 × 10¹⁸ cm^-3 (T_s = 800°C), the highest value yet reported for Si(001):As growth from hydride source gases. Immediately following film growth or partial-monolayer As adsorption on clean Si(001), the samples were quenched to 300°C and exposed to atomic deuterium (D) until saturation coverage. In situ D₂ temperature-programmed desorption (TPD) spectra from both as-deposited Si(001):As and As-adsorbed Si(001) layers are composed of β₁ and β₂ peaks, due to D₂ desorption from Si monodeuteride and dideuteride surface phases, together with a new peak β₃, which we attribute to desorption from Si-As mixed dimers. Analyses of the 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, decreases with increasing incoming flux J_AsH3 at constant T_s. From measurements of the steady-state As surface coverage θ_As vs C_As and T_s, we obtain an As surface segregation enthalpy ΔH_s = -0.92 eV. Dissociative AsH₃ adsorption on Si(001) was found to follow second-order kinetics with a relatively T_s-independent reactive sticking probability of 0.3. Associative As₂ desorption is also second order with a rate constant k_d,As2 = 1 × 10¹³ exp(-3.0 eV/kT_s). From the combined set of results, we develop a predictive model with no fitting parameters for C_As vs J_AsH3, J_Si2H6, and T_s.