Detection of Subsurface, Nanometer-Scale Crystallographic Defects by Nonlinear Light Scattering and Localization

Heteroepitaxial crystalline films underlie many electronic and optical technologies but are prone to forming defects at their heterointerfaces. 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, noninvasive, bench-top diagnosis of subsurface defects have been demonstrated by optical second-harmonic scanning probe microscope. A high-contrast pattern is observed of subwavelength 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. The results not only demonstrate a global and versatile method for diagnosing subsurface scattering sites but uniquely elucidate optical properties of disordered media. An extension to third harmonics would enable irregularities detection in non-chi((2)) materials making the technique universally applicable.

Automated summary

The article introduces a method for noninvasive, bench-top diagnosis of subsurface defects using an optical second-harmonic scanning probe microscope, which correlates the observed hotspots caused by defect scattering with the density of dislocation defects, providing insights into the optical properties of disordered media. Extending this approach to third harmonics could enable irregularities detection in non-chi((2)) materials, making the technique universally applicable.