GROWTH-RATE DEPENDENCE ON GEH4 DURING GAS-SOURCE MBE OF SIXGE1-X ALLOYS GROWN FROM SI2H6 AND GEH4

The epitaxial growth of Si and SixGe1-x alloys from molecular beams of gaseous Si (Si2H6) and Ge (GeH4) hydrides on Si(001) substrates (Si-G SMBE) has been studied using reflection high energy electron diffracti on (RHEED). Diffraction patterns reveal that Ge deposited on Si result s in a Stranski-Krastanow growth mode with a change in surface reconst ruction in the two-dimensional (2D) regime from the two-domain Si(001) -(2 x 1) to a two-domain Si(2 X 8)-Ge, prior to the onset of three-dim ensional (3D) growth. Using the RHEED intensity oscillation technique during alloy growth it is found that at substrate temperatures below 6 00-degrees-C there is an enhancement in growth rate of the alloy above that of pure Si growth from disilane. This phenomenon has been attrib uted to the increased desorption rate of hydrogen adatoms due to the p resence of Ge, which leads to an acceleration of the heterogenous reac tion rate. Consistent with this, during growth at substrate temperatur es above the desorption rate maximum for hydrogen, 600-degrees-C no en hancement of the growth rate due to the addition of GeH4 to the beam f lux is observed and the growth rate is dependent upon disilane arrival rate. Reaction kinetics are discussed in terms of Ge concentration in the films and the ratio of GeH4 to Si2H6 in the incident beams under various growth conditions.