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

TL;DR

This study combines cross-sectional scanning tunneling microscopy and density functional theory to analyze silicon donors in AlAs at the atomic level, revealing their distribution, local electronic structure, and imaging characteristics.

Contribution

It provides the first detailed atomic-scale characterization of Si donors in AlAs using combined experimental and theoretical methods, highlighting similarities with Si in GaAs.

Findings

Si donors identified up to four layers below the surface

LDOS of Si donors similar to those in GaAs

Excellent agreement between experimental and simulated STM images for donors up to two layers deep

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.