Incorporation of accelerated low-energy (50-500 eV) In + ions in Si(100) films during growth by molecular-beam epitaxy

A single-grid broad-beam ion source was used for low-energy (50-500 eV) accelerated In⁺ ion beam doping during growth of Si(100) layers by molecular-beam epitaxy. Indium incorporation behavior was studied as a function of ion energy (E⁺_In=50-500 eV), substrate temperature (T_s=500-1050 °C), ion flux (J⁺_In=1×10⁹-5×10¹² cm^-2 s^-1), and Si growth rate (R=0.1-1.3 nm s^-1). Dopant concentration profiles obtained using secondary ion mass spectroscopy showed that abrupt doping profiles were obtained at T_s<900 °C and R=0.7 μm h^-1, the incorporation probability σ⁺_In was close to unity for E⁺_In≥200 eV, while σ⁺_In was less than unity and decreased gradually with increasing T_s for E⁺_In≤100 eV. At T_s≥900 °C, σ⁺_In decreased rapidly with increasing T_s for all ion energies. The incorporation results are interpreted using a qualitative model based on different types of binding sites for In with incident energies ranging from thermal to 500 eV. A procedure, utilizing accelerated ions, for the growth of ultrathin doped layers is also suggested.