Effects of B doping on hydrogen desorption from Si(001) during gas-source molecular-beam epitaxy from Si2H6 and B2H6

Boron doping concentrations greater than or similar to 6X10(19) cm(-3) were found to increase Si(001) growth rates R(Si) at low temperatures while decreasing R(Si) at higher temperatures during gas-source molecular beam epitaxy (GS-MBE) from Si2H6 and B(2)H6. In order to probe the mechanisms governing these effects, Si(001) samples with B coverages theta(B) ranging from <0.05 to similar or equal to 0.5 ML were prepared by exposing clean Si(001)2X1 wafers to B2H6 doses between 2X10(17) and 4X10(20) cm(-2) at 200-400 degrees C. The samples were then heated to 700 degrees C to desorb the hydrogen, cooled to 200 degrees C, and exposed to atomic deuterium until saturation coverage. D-2 temperature programmed desorption spectra exhibit beta(2) and beta(1) peaks due to dideuteride and monodeuteride desorption at 405 and 515 degrees C as well as new B-induced peaks, beta(2)* and beta(1)*, at 330 and 470 degrees C. Increasing theta(B) increases the area under beta(2)* and beta(1)* at the expense of beta(2) and beta(1). Moreover, the total D coverage continuously decreases from similar or equal to 1.23 ML in the absence of B to similar or equal to 0.74 ML at theta(B) = 0.5 ML. We propose that the observed B-induced decrease in the Si*-D bond strength, where Si* represents surface Si atoms bonded to second-layer B atoms, is due to charge transfer and increased Si* dimer strain. The Si* to B charge transfer also deactivates Si surface dangling bonds causing the decrease in theta(D). These results are used to explain the GS-MBE growth kinetics. (C) 1996 American Institute of Physics.