Na. Bert et al., TOPOGRAPHY DEVELOPMENT ON THE SURFACE OF A SEMICONDUCTOR HETEROSTRUCTURE UNDER AR-BEAM MILLING( ION), Applied surface science, 72(4), 1993, pp. 381-392
The topography development on the cross-section surface of a single he
terostructure bombarded by 5 keV Ar+ ions was studied. From calculatio
ns based on the angular dependence of the sputtering rate, it was esta
blished that by inclination of its surface from the original flat posi
tion the epitaxial layer is able to compensate for a sputtering rate d
ifference with the substrate. This inclination for a non-rotating spec
imen depends on bombardment angle in such a way that the topographical
relief abruptly becomes rather smooth when the bombardment angle reac
hes a certain value THETA(cr). A further increase beyond THETA(cr), i.
e. more grazing incidence, invokes a further, but much slower, suppres
sion of the topography build-up. The data of experiments on ion millin
g of AlGaAs/GaAs heterostructures with various Al concentrations in th
e epitaxial layer are in good agreement with the calculations. The exp
eriments have shown the THETA(cr), for AlxGa1-xAs with x = 0.12, 0.27
and 0.60 to be 57-degrees, 60-degrees and 63-degrees, respectively. Th
e results obtained enable one to improve the conditions for ion millin
g in specimen preparation for TEM as well as in some other analytical
and technological applications.