Depth-Dependent EBIC Microscopy of Radial-Junction Si Micropillar Arrays

TL;DR

This study uses depth-dependent EBIC microscopy to analyze the quality of radial PN junctions in silicon micropillar arrays, revealing uniform junctions and efficiency variations related to fabrication processes.

Contribution

It introduces a depth-dependent EBIC method to evaluate 3D PN junctions in microstructured semiconductors, providing insights into junction quality and fabrication effects.

Findings

EBIC efficiency increases with electron beam energy.

Pillar array EBIC efficiency is about 70%, slightly lower than planar devices.

Surface passivation and fabrication-induced defects affect junction performance.

Abstract

Recent advances in fabrication have enabled radial-junction architectures for cost-effective and high-performance optoelectronic devices. Unlike a planar PN junction, a radial-junction geometry maximizes the optical interaction in the three-dimensional (3D) structures, while effectively extracting the generated carriers via the conformal PN junction. In this paper, we report characterizations of radial PN junctions that consist of p-type Si micropillars created by deep reactive-ion etching (DRIE) and an n-type layer formed by phosphorus gas diffusion. We use electron-beam induced current (EBIC) microscopy to access the 3D junction profile from the sidewall of the pillars. Our EBIC images reveal uniform PN junctions conformally constructed on the 3D pillar array. Based on Monte-Carlo simulations and EBIC modeling, we estimate local carrier separation/collection efficiency that reflects the quality of the PN junction. We find the EBIC efficiency of the pillar array increases with the incident electron beam energy, consistent with the EBIC behaviors observed in a high-quality planar PN junction. The magnitude of the EBIC efficiency of our pillar array is about 70 % at 10 kV, slightly lower than that of the planar device (about 81 %). We suggest that this reduction could be attributed to the unpassivated pillar surface and the unintended recombination centers in the pillar cores introduced during the DRIE processes. Our results support that the depth-dependent EBIC approach is ideally suitable for evaluating PN junctions formed on micro/nanostructured semiconductors with various geometry.