Atomic-Scale Defect Detection by Nonlinear Light Scattering and Localization

TL;DR

This paper introduces a noninvasive optical method to detect atomic-scale subsurface defects in hetero-epitaxial films by observing localized hot spots caused by defect scattering, offering a faster alternative to traditional microscopy.

Contribution

It demonstrates a novel, noninvasive optical scanning technique using second-harmonic generation to identify and analyze subsurface defects in crystalline films.

Findings

Hot spots correlate with dislocation defect density

Method provides high-contrast, sub-wavelength defect imaging

Potential extension to third harmonic detection for broader applicability

Abstract

Hetero-epitaxial crystalline films underlie many electronic and optical technologies but are prone to forming defects at their hetero-interfaces. Atomic-scale defects such as threading dislocations that propagate into a film impede the flow of charge carriers and light degrading electrical-optical performance of devices. Diagnosis of subsurface defects traditionally requires time consuming invasive techniques such as cross sectional transmission electron microscopy. Using III-V films grown on Si, we have demonstrated noninvasive, bench-top diagnosis of sub-surface defects by optical second-harmonic scanning probe microscope. We observed a high-contrast pattern of sub-wavelength hot spots caused by scattering and localization of fundamental light by defect scattering sites. Size of these observed hotspots are strongly correlated to the density of dislocation defects. Our results not only demonstrate a global and versatile method for diagnosing sub-surface scattering sites but uniquely elucidate optical properties of disordered media. An extension to third harmonics would enable irregularities detection in non-X(2) materials making the technique universally applicable.