Electric dipole of InN/InGaN quantum dots and holes and giant surface photovoltage directly measured by Kelvin probe force microscopy

Yinping Qian,Lujia Rao,Richard Nötzel,Changkun Song,Xingyu Wang,Guofu Zhou,Peng Wang,Hongjie Yin

doi:10.1038/s41598-020-62820-3

Yinping Qian, Lujia Rao + Show 6 more

Open Access

https://doi.org/10.1038/s41598-020-62820-3

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Abstract

We directly measure the electric dipole of InN quantum dots (QDs) grown on In-rich InGaN layers by Kelvin probe force microscopy. This significantly advances the understanding of the superior catalytic performance of InN/InGaN QDs in ion- and biosensing and in photoelectrochemical hydrogen generation by water splitting and the understanding of the important third-generation InGaN semiconductor surface in general. The positive surface photovoltage (SPV) gives an outward QD dipole with dipole potential of the order of 150 mV, in agreement with previous calculations. After HCl-etching, to complement the determination of the electric dipole, a giant negative SPV of −2.4 V, significantly larger than the InGaN bandgap energy, is discovered. This giant SPV is assigned to a large inward electric dipole, associated with the appearance of holes, matching the original QD lateral size and density. Such surprising result points towards unique photovoltaic effects and photosensitivity.

Highlights

Beyond the established applications of III-nitride semiconductors for blue lasers, solid state lighting and high-power amplifiers, the great potential of InGaN for electrochemical devices has been widely recognized recently
The number of InN MLs is determined from calibration samples which are InGaN layers with different In content deduced from X-ray diffraction (XRD) and thickness deduced from scanning electron microscopy (SEM)
High-resolution cross-sectional transmission electron microscopy (TEM) images of such quantum dots (QDs) have been reported in ref

Summary

Introduction

Beyond the established applications of III-nitride semiconductors for blue lasers, solid state lighting and high-power amplifiers, the great potential of InGaN for electrochemical devices has been widely recognized recently This is due to the intrinsic materials properties of InGaN, most relevant, the wide direct bandgap tunability upon In content from the ultraviolet to the near-infrared spectral region, the huge near bandgap absorption coefficient, one order of magnitude larger than that of GaAs, the large carrier mobility, the non toxicity and bio-compatibility. Super-Nernstian sensitivity is observed in potentiometric sensing and the efficiency of hydrogen generation by water splitting is enhanced by almost a factor of three compared to that for a bare InGaN layer This has been explained by the existence of a large electric dipole associated with the InN QDs in addition to the pure surface charge effect. Respective energy band diagrams are given at the end for full clarification

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