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

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 toward MACE due to its drawbacks, including insufficient surface passivation, increased junction recombination, and possible metal contamination, which are especially detrimental to p-n photodiodes. Here, we aim to change this by demonstrating how to fabricate high-performance MACE p-n 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 (ALD) 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 p-n photodiodes.