Electronic stopping power in a narrow band gap semiconductor from first principles

TL;DR

This study uses first-principles calculations to analyze how electronic stopping power varies with direction, impact parameter, and velocity in a small band gap semiconductor, revealing threshold behaviors and directional dependencies.

Contribution

It provides a detailed first-principles analysis of electronic stopping in a semiconductor, including impact parameter effects and velocity thresholds, with insights into the role of band gap and density functionals.

Findings

Stopping power varies with crystal direction.

Impact parameter dependence is direction-specific.

Velocity threshold aligns with perturbation theory predictions.

Abstract

The direction and impact parameter dependence of electronic stopping power, along with its velocity threshold behavior, is investigated in a prototypical small band gap semiconductor. We calculate the electronic stopping power of H in Ge, a semiconductor with relatively low packing density, using time-evolving time-dependent density-functional theory. The calculations are carried out in channeling conditions with different impact parameters and in different crystal directions, for projectile velocities ranging from 0.05 to 0.6 atomic units. The satisfactory comparison with available experiments supports the results and conclusions beyond experimental reach. The calculated electronic stopping power is found to be different in different crystal directions; however, strong impact parameter dependence is observed only in one of these directions. The distinct velocity threshold observed in experiments is well reproduced, and its non-trivial relation with the band gap follows a perturbation theory argument surprisingly well. This simple model is also successful in explaining why different density functionals give the same threshold even with substantially different band gaps.