Ultra-energy-efficient photoelectrode using microstriped GaN on Si

A prototype photoelectrode with a unique design has been fabricated using GaN microstripes grown on a patterned Si substrate. The photoelectrode has demonstrated a record-high photocurrent density of 11 mA/cm2 upon one sun illumination and a H2 generation rate of up to 2.67 mL·cm–2·h–1. This performance with a step-change has been achieved due to the contribution from both the GaN and the silicon substrate, as such a combination covers a wide spectral region (from the ultraviolet region due to the GaN bandgap to the infrared region due to the silicon bandgap). Unlike conventional GaN grown on a silicon substrate, where a thick AlN layer is required to separate GaN from the silicon in order to avoid the well-known Ga melt-back issue, a GaN/silicon heterojunction in our photoelectrode can be formed as a result of a weak Ga melt-back reaction, which is due to the specially designed configuration of our photoelectrode grown using the microstripes. Two reference photoelectrodes have been fabricated for comparison in order to support our conclusion. The results presented may pave the way for the fabrication of ultra-energy-efficient GaN-on-Si-based photoelectrodes or even photovoltaics devices.