Temperature-modulated Si(001):As gas-source molecular beam epitaxy: Growth kinetics and As incorporation

Arsenic doping at concentrations C_As ≳ 10¹⁸ cm^-3 during Si(001) growth from hydride precursors gives rise to strong As surface segregation, low film growth rates R_Si, poor electrical activation, and surface roughening. Based upon the results of temperature-programmed desorption studies of Si(001):As surface processes during film deposition, we have investigated the use of temperature-modulated growth including periodic arsenic desorption (10 s at 1000 °C) from the surface segregated layer. Both constant-temperature and temperature-modulated Si(001):As layers were grown at T_s=750 °C, selected as a compromise between maximizing C_As and providing a usable deposition rate, by gas-source molecular beam epitaxy from Si₂H₆/AsH₃ mixtures. For constant-temperature growth, R_Si is only 0.08 μmh^-1, the fraction of electrically active dopant is 55%, and film surfaces are very rough (rms roughness 〈w〉 = 110 A°). In sharp contrast, T_s-inodulated layers exhibit increases in R_Si by 2.5× to 0.20 μm h^-1, 100% electrical activity, and atomically smooth surfaces with 〈w〉 = 2 Å. The results are explained based upon the competition among As surface segregation, desorption, and incorporation rates.