Ultrahigh B-doped Ge(001) layers, with concentrations CB up to 8 × 1021 cm-3, were grown by gas-source molecular beam epitaxy from Ge2H6 and B2H6 at temperatures Ts = 325°C (in the surface-reaction-limited regime) and 600°C (in the flux-limited regime). The samples were quenched, D site exchanged for H, and D2 temperature-programed desorption (TPD) used to determine B coverages θB as a function of CB and Ts by comparison with B-adsorbed Ge(001) reference samples with known θB values. During Ge(001):B film growth, strong surface B segregation to the second layer was observed with surface-to-bulk B concentration ratios ranging up to 6000. The TPD spectra exhibited α2 and α1 peaks associated with dideuteride and monodeuteride desorption as well as lower-temperature B-induced α*2 and α*1 peaks associated with deuterium desorption from Ge* surface atoms with B backbonds. Increasing θB expanded the area under α*2 and α*1 at the expense of α2 and α1 and decreased the total D coverage θD. The TPD results were used to determine the B segregation enthalpy, -0.64 eV, and to explain and model the effects of high B coverages on Ge(001) growth kinetics. At Ts = 325°C, where B segregation is kinetically hindered, film deposition rates RGe are not a strong function of CB, exhibiting only a small decrease at CB≳5×1018 cm-3 However, at Ts = 600°C, RGe decreases by up to 40% with increasing CB≳1×1018 cm-3. This is due primarily to the combination of B-induced Ge dimer vacancies and the deactivation of surface dangling bonds caused by charge transfer to Ge-B backbonds. Calculated RGe(CB,Ts) curves, based upon equilibrium segregation, exhibit very good agreement with deposition rate data at Ts = 600°C and overestimate the effect of B on RGe at 325°C.
|Number of pages||9|
|Journal||Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films|
|Publication status||Published - 1999 Jan 1|
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films