Imaging individual dopant atoms on cleavage surfaces of wurtzite-structurecompound semiconductors

We report the identification of bulk-dopant atoms in (11 (2) over bar 0) an d (10 (1) over bar 0) cleavage surfaces of wurtzite CdSe in atomically reso lved scanning tunneling microscopy images. The In dopant atoms give rise to elevations (hillocks) of up to 5 nm in diameter in the empty- and occupied -state images. This contrast is simulated and it shows that the dopant atom s are positively charged. Hillocks with different symmetries with respect t o the underlying lattice are correlated with different subsurface locations of the In-dopant atoms. Dopant atoms can be observed up to a depth below t he surface of 3 to 5 layers. A quantitative analysis of the concentration o f dopant atoms in the bulk yield the same values for both surfaces and agre es well with the In content of the crystal. Similar features in CdS(10 (1) over bar 0) surfaces are;also attributed to In-dopant atoms. [S0163-1829(99 )01404-6].