(187e) Atomically Abrupt, “Leaky” Gallium Nitride Interface to Achieve High-Efficiency Photo-Electrocatalytic Hydrogen Conversion

Group III-V semiconductors, such as InP, GaInP₂, and GaAs, has been found as excellent photoabsorbers when performing light-to-chemical conversion due to their high quantum efficiency. These semiconductors are being manufactured at scale for optoelectronic devices and solar cells. However, they are not only very easily photo-corroded, but also they will form interface recombination sites. TiO₂ coatings by Atomic Layer Deposition (ALD) can mitigate corrosion; however, so far is the stability during hydrogen evolution is still the biggiest challenge. To address these problems, we herein developed a novel GaN ALD coating that can protect and passivate III-V semiconductors using atomically abrupt interfaces. Using p-type InP as the photoabsorber, we grow GaN coating with sputtered Pt as cocatalyst and achieved a record-breaking performance for photoelectrochemistry (PEC) hydrogen evolution reaction (HER). During photo-electrocatalytic H2 evolution, the photocathode has a photovoltage of 0.8 V, photocurrent of 34 mA/cm² under 1 sun illumination, and stability of at least 150 hours in pH 0 acid, as shown in Fig (a) and (b). To understand such unprecedented performance, we carried out a variety of interface characterizations, including Transmission Electron Microscopy (TEM) and surface photovoltage (SPV) measurement. We observed an atomically abrupt boundary between GaN and InP, which indicates that the GaN passivates the surface of InP from being oxidized. The results show that this outstanding performance is contributed by the low recombination rate, the energetic matching, and the high barrier height of InP/GaN. This results in a lower recombination rate on the interface and consequently a higher photovoltage, as shown in Fig (c). In Fig (e) and (f), the SPV study shows the charge separation process and carrier behavior in GaN/InP system, and it also reveals the unconventional defect states in the GaN mid-bandgap.