STRUCTURE OF SI(111) SURFACES ETCHED IN 40-PERCENT NH4F - INFLUENCE OF THE DOPING

The morphology of precisely oriented n and p(+) type Si(111) hydrogenated surfaces has been studied by UHV-STM and AFM at ambient after ''chemical'' etching in 40% NH4F. Whereas atomically flat surfaces are obtained with the n-type samples, the surface of p(+) substrates is rough. It is shown that these observations stem from a variation of the partition between the chemical (anisotropic) and the electrochemical (isotropic) components of the etching reaction. This is the uptake of the latter reaction path at the p(+)-type specimen which explains the surface roughening in this case.