Macroporous p-GaP Photocathodes Prepared by Anodic Etching and Atomic Layer Deposition Doping

Abstract

P-type macroporous gallium phosphide (GaP) photoelectrodes have been prepared by anodic etching of an undoped, intrinsically n-type GaP(100) wafer and followed by drive-in doping with Zn from conformal ZnO films prepared by atomic layer deposition (ALD). Specifically, 30 nm ALD ZnO films were coated on GaP macroporous films and then annealed at T = 650 °C for various times to diffuse Zn in GaP. Under 100 mW cm(-2) white light illumination, the resulting Zn-doped macroporous GaP consistently exhibit strong cathodic photocurrent when measured in aqueous electrolyte containing methyl viologen. Wavelength-dependent photoresponse measurements of the Zn-doped macroporous GaP revealed enhanced collection efficiency at wavelengths longer than 460 nm, indicating that the ALD doping step rendered the entire material p-type and imparted the ability to sustain a strong internal electric field that preferentially drove photogenerated electrons to the GaP/electrolyte interface. Collectively, this work presents a doping strategy with a potentially high degree of controllability for high-aspect ratio III-V materials, where the ZnO ALD film is a practical dopant source for Zn.

Methods for Electrochemical Synthesis and Photoelectrochemical Characterization for Photoelectrodes

“…In addition to sulfite, H 2 O 2 , whose rate constant for oxidation was reported to be 10–100 times greater than that of water, has been used as a hole acceptor, especially in basic solution with photoanodes that are oxidatively stable in an H 2 O 2 environment, such as α-Fe 2 O 3 . − Electron acceptors that have been used to investigate photocathodes include methylviologen, H 2 O 2 , and O 2 . − It should be noted that even if the oxidation or reduction kinetics of these species are faster than those of water and their photocurrent onset potentials shift toward the E FB of the photoelectrode, unless ϕ inj is close to 1 very near the E FB , their photocurrent onset potentials may still deviate from the true E FB .…”

Tailored energy level alignment at MoOX/GaP interface for solar-driven redox flow battery application

“…The resultant porous structure displayed a morphology that is similar to the one that was observed previously for GaP-based nanowire structure. 41,42 As illustrated in Fig. 7b and c, the porous films produced due to the corrosion process of the n-GaP (100) here are known to have a high aspect ratio that pores are formed perpendicular to the surface plane in the direction of the current flow.…”

“…7b and c, the porous films produced due to the corrosion process of the n-GaP (100) here are known to have a high aspect ratio that pores are formed perpendicular to the surface plane in the direction of the current flow. 41 The high aspect ratio architecture that provides a shortened lateral carrier pathway can decouple the physical constraints from the limited minority carrier diffusion length seen in GaP semiconductors (e.g., ≤ 5 μm for high-quality GaP wafer). 43 The energy-diagrams ( Fig.…”

“…Albeit the improvement of the chemical stability of the GaP substrate is technologically not easy, it is likely that one could avoid the chemical damage via applying a protective layer which screens completely the substrate from the electrolyte as demonstrated elsewhere. 2,39,41,44 Actually, the Pt conducting layer formed onto the n-GaP surface is designed to isolate the substrate from the electrolyte, and at the same time, provide a facile charge transfer. Optimization of Pt coverage over the entire surface is beyond the scope of this paper; however, it must be addressed in further development.…”

Evolution of Atomistic Topology at H2O/GaSb(100) Interface under Ambient Conditions and GaSb Surface Passivation

“…Gallium antimonide (GaSb) has attracted substantial interest in recent years because of its superb electrical properties, including much higher electron and hole mobilities compared with classic semiconductors such as Si, GaAs, and InP. − GaSb has also emerged as a promising candidate for high-speed and low-power optoelectronics, infrared detectors, and thermophotovoltaic and solar cells. ,,− In the semiconductor industry, GaSb has been frequently used as a substrate for the growth of other mid-infrared III–V materials because it can provide a lattice-matched template. ,− During the growth of passivation oxides by atomic layer deposition, the chemical identity of the substrate surface exposed to alternating cycles of trimethyl aluminum and H 2 O has significant influences on the final quality of the film grown on the substrate . Furthermore, because GaSb has been incorporated into high-performance tandem photoelectrochemical (PEC) solar cells − and used for photocatalytic CO 2 reduction, a detailed understanding of the interfacial chemistry between small environmental molecules such as H 2 O and GaSb becomes practically meaningful.…”