Dopant layer abruptness in strained Si1−xGex heterostructures

Abstract

Low-temperature photoluminescence (PL) has been used to evaluate dopant concentration and vertical location in heterostructures consisting of strained Si0.85Ge0.15 layers on Si (001). The boron dopant profile was established to be abrupt within 1 nm on samples grown by reduced pressure chemical vapor deposition. The structure had a 20 nm thick Si0.85Ge0.15 layer which was either uniformly doped or had a 10 nm thick dopant in the adjoining Si. The PL variation with dopant displacement was described using simple geometric considerations for exciton penetration from the SiGe into the adjacent Si. Screening by dopant atoms in the sheet caused exciton quenching which depended on dopant displacement and concentration. The best fit between the calculated and observed dependence was obtained for an exciton radius of 6 nm. For small dopant displacement with high boron concentration, dopant diffusion was observed from the Si to the SiGe.