Insights into Interfacial Changes and Photoelectrochemical Stability of In_xGa_1–xN (0001) Photoanode Surfaces in Liquid Environments

Abstract

The long-term stability of InGaN photoanodes in liquid environments is an essential requirement for their use in photoelectrochemistry. In this paper, we investigate the relationships between the compositional changes at the surface of n-type In(x)Ga(1-x)N (x ∼ 0.10) and its photoelectrochemical stability in phosphate buffer solutions with pH 7.4 and 11.3. Surface analyses reveal that InGaN undergoes oxidation under photoelectrochemical operation conditions (i.e., under solar light illumination and constant bias of 0.5 VRHE), forming a thin amorphous oxide layer having a pH-dependent chemical composition. We found that the formed oxide is mainly composed of Ga-O bonds at pH 7.4, whereas at pH 11.3 the In-O bonds are dominant. The photoelectrical properties of InGaN photoanodes are intimately related to the chemical composition of their surface oxides. For instance, after the formation of the oxide layer (mainly Ga-O bonds) at pH 7.4, no photocurrent flow was observed, whereas the oxide layer (mainly In-O bonds) at pH 11.3 contributes to enhance the photocurrent, possibly because of its reported high photocatalytic activity. Once a critical oxide thickness was reached, especially at pH 7.4, no significant changes in the photoelectrical properties were observed for the rest of the test duration. This study provides new insights into the oxidation processes occurring at the InGaN/liquid interface, which can be exploited to improve InGaN stability and enhance photoanode performance for biosensing and water-splitting applications.

Charge Transfer Characteristics of n-type In0.1Ga0.9N Photoanode across Semiconductor–Liquid Interface

“…The difference of valence band offset among In 0.1 Ga 0.9 N and formed oxide yields to a barrier which opposes to the photohole flow from the InGaN layer to the electrolyte at low bias voltages, as also described in detail in a previous work. 17 Despite the photocurrent reduction, the photovoltage further shifted to −417 mV at the 75th cycle. At the end of the CV test, the hole transfer occurred prevalently from the valence band (Figure 5b).…”

“…Further details of the sample growth can be found elsewhere. 17 The thickness of the In x Ga (1−x) N layers (31 ± 0.4 nm) and the indium content (x = 0.102 ± 0.003) were measured by the XRD technique with a PANalytical X'Pert system. The indium content was further confirmed by photoluminescence (PL) measurements.…”

Improved solar hydrogen production by engineered doping of InGaN/GaN axial heterojunctions

“…The current density of the two photocathodes increase for the first two hours. The plausible explanation is the interfacial changes at the InGaN surface [4,45]. Then, the current density of the u-InGaN/p-GaN and p-InGaN/p-GaN saturated at approximately -4.0 and -9.4 mA/cm 2 , respectively.…”

Modulating Surface/Interface Structure of Emerging InGaN Nanowires for Efficient Photoelectrochemical Water Splitting

“…investigated the PEC stability of InGaN photoanode in neutral and basic phosphate buffer solutions. [ 146 ] The experimental measurements reveal that the chemical composition of the formed oxide layer on InGaN is related to the pH of electrolyte. Abundant GaO bonds are formed at pH 7.4, leading to a photocurrent quenching, which is contradictory to the result reported by Tu et al.…”