"Black Silicon" photodiodes

Title: Excellent Responsivity and Low Dark Current Obtained with Metal-Assisted Chemical Etched Si Photodiode

Author: Kexun Chen, Olli E. Setälä, Xiaolong Liu, Behrad Radfar, Toni P. Pasanen, Michael D. Serué, Juha Heinonen, Hele Savin, Ville Vähänissi

Affiliation: Aalto University, Finland

Abstract: Metal-assisted chemical etched (MACE, also known as MacEtch or MCCE) nanostructures are utilized widely in the solar cell industry due to their excellent optical properties combined with a simple and cost-efficient fabrication process. The photodetection community, on the other hand, has not shown much interest towards MACE due to its drawbacks including insufficient surface passivation, increased junction recombination, and possible metal contamination, which are especially detrimental to pn-photodiodes. Here, we aim to change this by demonstrating how to fabricate high-performance MACE pn-photodiodes with above 90% external quantum efficiency (EQE) without external bias voltage at 200–1000 nm and dark current less than 3 nA/cm2 at −5 V using industrially applicable methods. The key is to utilize an induced junction created by an atomic layer deposited highly charged Al2O3 thin film that simultaneously provides efficient field-effect passivation and full conformality over the MACE nanostructures. Achieving close to ideal performance demonstrates the vast potential of MACE nanostructures in the fabrication of high-performance low-cost pn-photodiodes.