Spatially resolved electronic structure of an isovalent nitrogen center in GaAs

TL;DR

This study uses scanning tunneling microscopy and tight binding calculations to reveal the local electronic structure and anisotropic spatial features of nitrogen dopants in GaAs, elucidating their impact on the material's conduction band.

Contribution

It provides the first detailed spatially-resolved imaging and analysis of individual nitrogen dopants in GaAs, linking atomic-scale features to electronic properties.

Findings

Nitrogen dopants cause large, nonlinear shifts in GaAs conduction band energies.

Imaged resonant states are highly anisotropic and match tight binding calculations.

Features suggest some nitrogen-related states may modify surface states.

Abstract

Small numbers of nitrogen dopants dramatically modify the electronic properties of GaAs, generating very large shifts in the conduction-band energies with nonlinear concentration dependence, and impurity-associated spatially-localized resonant states within the conduction band. Cross-sectional scanning tunneling microscopy provides the local electronic structure of single nitrogen dopants at the (110) GaAs surface, yielding highly anisotropic spatial shapes when the empty states are imaged. Measurements of the resonant states relative to the GaAs surface states and their spatial extent allow an unambiguous assignment of specific features to nitrogen atoms at different depths below the cleaved (110) surface. Multiband tight binding calculations around the resonance energy of nitrogen in the conduction band match the imaged features. The spatial anisotropy is attributed to the tetrahedral symmetry of the bulk lattice. Additionally, the voltage dependence of the electronic contrast for two features in the filled state imaging suggest these features could be related to a locally modified surface state.