Atomic-scale study of Si-doped AlAs by cross-sectional scanning tunneling microscopy and density functional theory

Silicon (Si) donors in GaAs have been the topic of extensive studies since Si is the most common and

well understood n-type dopant in III-V semiconductor devices and substrates. The indirect band gap of AlAs

compared to the direct one of GaAs leads to interesting effects when introducing Si dopants. Here we present

a study of cross-sectional scanning tunneling microscopy and density functional theory (DFT) calculations to

study Si donors in AlAs at the atomic scale. Based on their crystal symmetry and contrast strengths, we identify

Si donors up to four layers below the (110) surface of AlAs. Interestingly, their short-range local density of states

(LDOS) is very similar to Si atoms in the (110) surface of GaAs. Additionally, we show high-resolution images

of Si donors in all these layers. For empty state imaging, the experimental and simulated STM images based on

DFT show excellent agreement for Si donors up to two layers below the surface.