Nonlinear compositional and morphological evolution of ion irradiated GaSb prior to nanostructure formation

Michael A Lively,Jean Paul Allain,Stefan Facsko,Michael Toriyama,Brandon Holybee

doi:10.1038/s41598-020-64971-9

Abstract

Low-energy ion irradiation of III-V semiconductor surfaces can lead to the formation of regular hexagonal dot patterns at the surface. We present experimental and computational results for ion irradiation of GaSb surfaces which elucidate the nature of the coupled compositional and morphological pattern-formation mechanisms. We demonstrate by in-situ grazing-incidence small-angle x-ray scattering (GISAXS) and angle-resolved Auger electron spectroscopy (ARAES) that the emergence of an altered compositional depth profile is essential to induce morphological changes at the surface. This morphological evolution of the surface follows nucleation-and-growth kinetics. Furthermore, we show from massive-scale molecular dynamics (MD) simulations that the compositional depth profile evolution leads to thermodynamic phase separation, providing a lateral compositional instability that drives pattern formation. Additionally, high-fluence simulations elucidate the irradiation-induced mechanisms of compositional depth profile formation. Prompt ion effects drive formation of single-element “protoclusters”, predominantly of Sb. Structural and energetic characterization of the simulation results indicate that Sb may be more mobile than Ga, providing a diffusional pathway for long-temporal-scale compositional evolution of the irradiated surface. Our findings motivate the development of new, comprehensive models which consider the total spatial and temporal complexity of multicomponent systems evolving under ion irradiation.

Highlights

Low-energy ion irradiation of III-V semiconductor surfaces can lead to the formation of regular hexagonal dot patterns at the surface
Since the discovery of regular and ordered nanoscale dot pattern formation induced on GaSb by Ar+ irradiation[1], ion-induced pattern formation at the surfaces of III-V semiconductors has garnered significant experimental and theoretical attention
More recent experiments have shown that the surface instability is “likely driven by chemical instability based on phase separation”[3], but have not demonstrated a concrete mechanism which drives pattern formation

Summary

Introduction

Low-energy ion irradiation of III-V semiconductor surfaces can lead to the formation of regular hexagonal dot patterns at the surface. Atomistic computational models are not limited to a particular set of assumptions as continuum models are and are able to consider all possible mechanisms without bias These simulations can provide critical information about the prompt ion effects in ion-irradiated III-V materials, including preferential sputtering[15], surface mass redistribution[16], ion-induced defect production[17] and accumulation[18], and structural transformations[19]. The second set of simulations considered 500 eV Kr+ irradiation of initially pristine 50/50 GaSb to an experimentally relevant fluence (Φ = 7.5 × 1015 cm−2) These experimental and computational approaches elucidate the connection between ion-induced compositional depth profile disruption and the resulting long-scale lateral instability leading to pattern formation, which no approach far has been capable of demonstrating

Methods

Results

Conclusion