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)less than or equal to4.8x10(18) cm(-3), on the growth kinetics of Si(001):As layers deposited at temperatures T-s=575-900 degreesC 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 3.8x10(18) cm(-3) (T-s=800 degreesC), 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 degreesC and exposed to atomic deuterium (D) until saturation coverage. In situ D-2 temperature-programmed desorption (TPD) spectra from both as-deposited Si(001):As and As-adsorbed Si(001) layers are composed of beta (1) and beta (2) peaks, due to D-2 desorption from Si monodeuteride and dideuteride surface phases, together with a new peak beta (3) 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 theta (As) vs C-As and T-s, we obtain an As surface segregation enthalpy DeltaH(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 As-2 desorption is also second order with a rate constant k(d,As2)=1x10(13) 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(Si2)H(6), and T-s. (C) 2000 American Institute of Physics. [S0021- 8979(00)08824-1].