Effects of mixing germane in silane gas-source molecular beam epitaxy

Growth of SiGe gas-source molecular beam epitaxy (GSMBE) using silane/germane mixture has been investigated for the germane content of 0%, 0.8%, and 2.6%. From detailed measurements on the growth rate, a separation into high- and low-temperature regions of the growth rate, as in silane-GSMBE system, has been found to exist in this silane/germane system. A simultaneous measurement on the surface hydrogen coverage has revealed that the growth in the low-temperature region is rate limited by the surface hydrogen desorption process, reasoning the enhanced growth rate with germane in terms of the reduced coverage of the surface hydrogen. All the growth rates followed a same fourth power dependence on the free-adsorption site, which suggests a validity of the four-site adsorption model, established for silane-GSMBE, in silane/germane GSMBE.