CHARACTERIZATION OF N-CHANNEL SI/SIGE MODULATION-DOPED STRUCTURES GROWN BY GAS-SOURCE MOLECULAR-BEAM EPITAXY

We have grown n-channel Si/SiGe modulation doped structures by gas source molecular beam epitaxy using arsine as the n-type dopant source. The structures were characterized by transmission electron microscopy, secondary ion mass spectroscopy, electrochemical capacitance voltage analysis and x-ray diffraction. Arsenic and free electron concentrations in excess of 10(19) cm(-3) could be obtained with substantial surface segregation. Several different structures have been grown and their transport properties investigated. Low-temperature electron mobilities of up to 60 000 cm(2) V-1 s(-1) in the dark (75 800 cm(2) V-1 s(-1) after illumination) were obtained with a sheet density range (4-7) x 10(11) cm(-2). Parallel conduction is discussed in terms of the effect of illumination.