A (Photo‐)Electrochemical Study on n‐GaN in Aqueous Solutions

Huygens, Inge; Theuwis, Antoon; Gomes, W. P.; Strubbe, Katrien

doi:10.1002/pssc.200390085

Cited by 5 publications

(5 citation statements)

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“…Although its wide bandgap of 3.4 eV severely limits its maximum efficiency under solar illumination, this material provides a model system for the study of semiconductor–electrolyte interfaces. More recently, the GaN:ZnO solid solution has been reported as a powerful photocatalytic material for electrolysis. − In separate but related work, the electrochemical etching of GaN has been investigated for device processing applications, with a focus on photoanodic decomposition, oxidation, and etching in acidic and basic solutions. , In this context, it was reported that Cl – ions in solution stabilize n-type GaN surfaces against photodecomposition and a mechanism for interfacial charge transfer of photogenerated holes via intrinsic surface states was proposed. , Chakrapani et al provided further spectroscopic evidence of the charge transfer between the oxygen redox couple in an adsorbed water film and GaN via midgap states . However, a thorough understanding of both charge transfer energetics and kinetics at the n-type GaN–electrolyte interface, which is required for applications in biosensing and photocatalysis, remains incomplete.…”

Section: Introductionmentioning

confidence: 99%

“…18,19 In this context, it was reported that Cl − ions in solution stabilize n-type GaN surfaces against photodecomposition and a mechanism for interfacial charge transfer of photogenerated holes via intrinsic surface states was proposed. 20,21 Chakrapani et al provided further spectroscopic evidence of the charge transfer between the oxygen redox couple in an adsorbed water film and GaN via midgap states. 22 However, a thorough understanding of both charge transfer energetics and kinetics at the n-type GaN−electrolyte interface, which is required for applications in biosensing and photocatalysis, remains incomplete.…”

Section: ■ Introductionmentioning

confidence: 99%

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Charge Transfer across the n-Type GaN–Electrolyte Interface

et al. 2012

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The interfacial charge transfer characteristics of n-type GaN are investigated in pure phosphate buffered saline, as well as in solutions containing I − / I 3 − or hydroquinone/benzoquinone redox couples. Cyclic voltammetry and transient photoresponse measurements in the presence of above-bandgap illumination reveal that hole transfer to the solution is mediated by surface states in all cases. For measurements in pure PBS, a modification of the surface during cyclic potential sweeps is observed. In contrast, the presence of the redox species used in this work efficiently suppresses the oxygen evolution reaction and the associated surface modification. Furthermore, charge transfer to the redox couple is fully reversible using GaN as a dark cathode and photoanode, respectively. The presented study is of significant importance for applications of GaN in photocatalysis and biosensing, where the stability of (bio)functionalized surfaces is an essential requirement.

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Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Charge Transfer across the n-Type GaN–Electrolyte Interface

et al. 2012

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“…GaN nanowires exhibit better photocatalytic activity because of the large surface area which enhanced photocatalytic activity in the acid pH region [ 38 ]. Because of the surface states at the bandgap, the electrons will fill in the gap state and the Fermi level is pinned over there [ 34 , 43 , 48 ]. The band bending is shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Stable and Reversible Photoluminescence from GaN Nanowires in Solution Tuning by Ionic Concentration

Nguyen

et al. 2021

Nanoscale Res Lett

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We report response of photoluminescence (PL) from GaN nanowires without protection in solutions. The distinct response is not only toward pH but toward ionic concentration under same pH. The nanowires appear to be highly stable under aqueous solution with high ionic concentration and low pH value down to 1. We show that the PL has a reversible interaction with various types of acidic and salt solutions. The quantum states of nanowires are exposed to the external environment and have a direct physical interaction which depends on the anions of the acids. As the ionic concentration increases, the PL intensity goes up or down depending on the chemical species. The response results from a competition of change in surface band bending and charge transfer to redox level in solution. That of GaN films is reported for comparison as the effect of surface band bending can be neglected so that there are only slight variations in PL intensity for GaN films. Additionally, such physical interaction does not impact on the PL peaks in acids and salts, whereas there is a red shift on PL when the nanowires are in basic solution, say NH4OH, due to chemical etching occurred on the nanowires.

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“…n-GaN was stabilized against photodecomposition in Cl − -containing solutions as a result of the competing oxidation of Cl − to Cl 2 via intrinsic surface states. 11 Using NaCl as the electrolyte, the photocurrent density did not decay as fast as the one using KOH or HCl as the electrolyte. 12 Moreover, NaCl is one of the main contents of seawater, which is safe and available, so we used 1 mol/L NaCl as the electrolyte.…”

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confidence: 88%

Improved Hydrogen Gas Generation Rate of n-GaN Photoelectrode with SiO[sub 2] Protection Layer on the Ohmic Contacts from the Electrolyte

Liu

Sheu

Tseng

et al. 2010

J. Electrochem. Soc.

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Direct photoelectrolysis of water to generate hydrogen was performed using n-type GaN films with Cr/Au ohmic contacts to serve as working electrodes. To enhance the efficiency of electron collection in the GaN working electrode, meshed Cr/Au contacts with a SiO 2 protection layer were immersed in the NaCl electrolyte. With an external bias of 1 V, the typical photocurrent densities ͑gas generation rate͒ of the n-GaN working electrodes with and without the immersed ohmic contact layer were approximately 19.6 ͑9.4͒ and 9.9 A/cm 2 ͑3.6 mL/h͒, respectively, which corresponded to an enhancement in the photocurrent density ͑gas generation rate͒ of around 98% ͑160%͒. The marked enhancement in the gas generation rate could be attributed to the fact that the distance between the neighbor Cr/Au ohmic contacts is small enough to reduce the recombination probability of photogenerated electrons with holes or charged defects in the GaN layer before the electrons reach the ohmic contacts. In other words, the photogenerated electrons can be effectively collected by the Cr/Au ohmic contacts and thereby reach the Pt counter electrode to lead the generation of hydrogen.Using solar power to direct photoelectrolysis is a promising method of generating hydrogen from aqueous water. 1,2 There are many kinds of oxides serving as the photoelectrodes ͑working electrodes͒ that drive electrochemical reactions. 3-5 However, using these oxides as the working electrodes for water splitting has an insufficient solar-to-hydrogen conversion efficiency for practical application because of the limitation of the usable solar spectrum. 1 There are also many kinds of lower bandgap semiconductor materials that can absorb solar light more effectively, such as InP, GaAs, and CdSe. It has been reported, however, that these materials were easily corroded in acidic or alkaline solution. 6,7 Besides, to split aqueous water by using a photoelectrochemical cell, which is made of semiconductor materials, the conduction bandedge potential of the semiconductor material must be lower than that of the cathode-reduction half-reaction; furthermore, its valence band-edge potential must be higher than that of the anode-oxidation half-reaction. 1 Therefore, InGaN-based materials are promising candidates for direct photoelectrolysis of water not only because its band-edge potential could satisfy the condition to split water 8,9 but also because it is potentially resistant to the aqueous solutions. 10 Furthermore, the bandgap can vary from 3.4 to 0.7 eV by changing the content of In, making it possible for us to produce a photoelectrochemical cell that could fit the solar spectrum to enhance the light absorption. 10 Waki et al. reported that the patterned n-GaN epitaxial layer formed by the selective area regrowth with metal stripes was used to achieve the direct photoelectrolysis of water. 8 The metal stripes functioned to eliminate current crowding, thereby improving the photocurrent. However, the metal stripes they used were directly immersed in the electrolyte. The met...

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A (Photo‐)Electrochemical Study on n‐GaN in Aqueous Solutions

Cited by 5 publications

References 6 publications

Charge Transfer across the n-Type GaN–Electrolyte Interface

Charge Transfer across the n-Type GaN–Electrolyte Interface

Stable and Reversible Photoluminescence from GaN Nanowires in Solution Tuning by Ionic Concentration

Improved Hydrogen Gas Generation Rate of n-GaN Photoelectrode with SiO[sub 2] Protection Layer on the Ohmic Contacts from the Electrolyte

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