Electrically resolving 1 nanometer semiconductor quantum wells and superlattices in photodiodes by conductive scanning probe microscopy

As semiconductor architectures advance into the nanoscale regime, spatially resolving local electrical properties presents a critical challenge. In this paper, we report a high-resolution method based on contact-mode conductive scanning probe microscopy to characterize quantum structures. By exploiting the barrier sensitivity of the localized tip-sample Schottky contact, this technique achieves a nanoscale resolution that surpasses the limitation of the tip radius. We validate this capability by successfully resolving low-dimensional semiconductor heterostructures, enabling the electrical imaging of 1-5 nm quantum wells. Additionally, the system is sensitive enough to detect photogenerated carriers under optical injection. Leveraging these superior characterization capabilities, we further investigated the superlattice (SL) structure within extended wavelength InAlAs/InGaAs p-i-n photodetectors. The measurements indicate the effectiveness of the SL layers at the interfaces in suppressing dislocation propagation. Simultaneously, it was observed that the SL layers have a blocking effect on Zn diffusion under different conditions, providing valuable insights for optimizing diffusion parameters. Both effects of SLs have a key impact on the performance improvement of extended-wavelength devices, which can significantly affect dark current and noise. These results demonstrate that this electrical characterization method is an indispensable tool for nanostructure analysis, providing crucial feedback for the interface engineering and practical optimization of next-generation optoelectronic devices.