A Photoelectrochemical Study of In[sub x]Ga[sub 1−x]N Films

Abstract

The III-nitride semiconductor n-In x Ga 1Ϫx N was investigated by optical absorbance and luminescence measurements and by various photoelectrochemical methods. Evidence is found for the presence of localized states and compositional fluctuations. Upon illumination with the appropriate wavelength and positive polarization in an indifferent electrolyte, i.e., aqueous 1 mol L Ϫ1 HCl, photocurrent flow is observed, resulting in the photoanodic etching of the solid. Measurements of the quantum efficiency Q and the transient photocurrent show that recombination of photogenerated charge carriers competes effectively with photoanodic dissolution.In the last decade, III-nitride materials such as GaN and In x Ga 1Ϫx N have been the subject of a considerable amount of research. Although the layers grown by metallorganic vapor-phase epitaxy ͑MOVPE͒ generally contain a large quantity of defects, highbrightness light-emitting diodes ͑LEDs͒ with excellent operating lifetimes as well as blue and violet laserdiodes, based upon these materials, are commercially available. 1,2 In the specific case of MOVPE-grown In x Ga 1Ϫx N layers, it has been demonstrated that indium is incorporated in the In x Ga 1Ϫx N lattice in an inhomogeneous way. 3-7 These fluctuations in composition may lead to substantial fluctuations in the bandgap energy E g of the alloy. Moreover, both extended and point defects are generally present in the alloy. 1,8 The aim of this study is to gain insight into the defect structure of this material. The use of ͑photo͒electrical characterization techniques such as photocurrent spectroscopy would require the formation of a high-quality rectifying semiconductor/metal contact. 9 However, to date little work has been done on the formation of good Schottky contacts on In x Ga 1Ϫx N. 10 In the present case, a semiconductor/electrolyte contact may constitute an elegant alternative to a semiconductor/metal contact for such studies.Despite the large amount of research done on III-N compoundbased optoelectronic devices, no suitable wet etchant has been found yet for In x Ga 1Ϫx N. 11 A photoelectrochemical study of the III-nitride/ electrolyte junction can also provide valuable information on the wet-etching behavior of this material. For GaN, such a study has already been conducted, both the photoanodic dissolution reaction and the open-circuit photoetching of GaN being investigated. 12 As in the case of In x Ga 1Ϫx N, no such study has to our knowledge been reported, so we have also performed this type of measurement in the present case. ExperimentalThe In x Ga 1Ϫx N films were grown by MOVPE at the Department of Information Technology at Ghent University. The In x Ga 1Ϫx N epi layers ͑x ϭ 0.21, to be discussed further, average thickness 1 m, unintentionally doped n-type͒ were grown on top of a structure consisting of a GaN epi layer, a 60 nm thick undoped GaN buffer layer, and a 350 m thick ͑0001͒ sapphire substrate.For details on the electrochemical measuring equipment and the electrode fabrication, see Ref. 12. Illuminati...

Photoelectrochemical studies of InGaN/GaN MQW photoanodes

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Si/InGaN Core/Shell Hierarchical Nanowire Arrays and their Photoelectrochemical Properties

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Stable response to visible light of InGaN photoelectrodes

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