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On-chip integration of micro-optoelectronic devices through advanced fabrication processes imposes an urgent need for optical means of visualizing hidden structural defects noninvasively. Here, based on a physical scheme, we develop an optical second harmonic generation (SHG) imaging technique to directly visualize structural defects at hidden interfaces. Interfacial optical scatterings caused by structural defects weakening both fundamental fields confined in the microdevice and reflected SHG fields from the microdevice lead to a high contrast of SHG image. We apply our technique to floating gallium nitride (GaN)/aluminum nitride (AlN) microdisks fabricated by the micromanufacturing process, revealing the spatial distribution of hidden debris formed by incomplete wet-etching process, which are beneath the surfaces of microdisks. Through comparison measurements, we show that such debris tends to further degrade wet-etching quality and cause residual strain, which will markedly reduce luminescence performances. Our results provide substantial insights into hidden interfacial defect visualization of on-chip integrated micro-optoelectronic devices.
Xia et al. (Sat,) studied this question.