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

Abstract

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 bandgap 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 (X-STM) 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 donor up to two layers below the surface.

Influence of sample momentum space features on scanning tunnelling microscope measurements

“…This implies that the lattice incommensurate valley oscillations in the x and y directions, which contribute to the rich structure of the STM images of deep donors, contribute significantly less to the wave functions of shallow donors, supporting our understanding that indeed the presence of valley related interferences enhance the role of tip electronic state in the calculation of STM images. This is also in agreement with a recent report on AlAs:Si system [33], where the valley impact was found to be weak for impurities closer to the surface.…”