Abstract

This Tutorial teaches the essential development of nitrogen-plasma-assisted molecular-beam-epitaxy grown InGaN nanowires as an application-inspired platform for energy harvesting and conversion applications by growing dislocation- and strain-relieved axial InGaN-based nanowires. The Tutorial aims to shed light on the interfacial, surface, electrical, and photoelectrochemical characteristics of InGaN nanowires through nanoscale and ultrafast characterizations. Understanding the interrelated optical-physical properties proved critical in the development of renewable-energy harvesting and energy conversion devices. Benefiting from their unique aspect ratio and surface-to-volume ratio, semiconductor properties, and piezoelectric properties, the group-III-nitride nanowires, especially InGaN nanowires, are promising for clean energy conversion applications, including piezotronic/piezo-phototronic and solar-to-clean-fuel energy-conversion.

Highlights

  • Group-III-nitrides compound semiconductors consist of binary GaN, InN, and AlN with their ternary compounds, which can emit and absorb light across a wide solar spectrum

  • Any threading dislocations generated from the semiconductor/substrate interface are largely eliminated at the bottom of the nanowires, as threading dislocations can be terminated at the m-plane sidewall

  • The growth temperature can be used to tune the indium composition of InGaN. Adjusting these parameters allows the PA-molecular beam epitaxy (MBE) grown on an InGaN nanowire to show a continuous visible-wavelength span from blue to red, which implies that a high indium composition can be achieved.[40]

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Summary

INTRODUCTION

Group-III-nitrides compound semiconductors consist of binary GaN, InN, and AlN with their ternary compounds, which can emit and absorb light across a wide solar spectrum. Two major applications that have been reported in the literature are piezotronics/ piezo-phototronics and photoelectrochemical (PEC) hydrogen generation devices Owing to their superior absorption of solar light, electrical conductivity, and unique piezoelectric properties, the group-III-nitride materials, (In,Ga)N materials, are capable of harvesting, converting, and coupling three forms of energy: solar energy, mechanical energy, and electrical energy. In place of the planar layer platform for group-III-nitrides, nanowires grown by molecular beam epitaxy (MBE) can be used to circumvent part of the aforementioned obstacles, as single-crystal nanowires ensemble can be grown with less strain on various kinds of unconventional substrates, such as Si,[3] metal,[4,5,6,7] or even amorphous glass.[8,9] Any threading dislocations generated from the semiconductor/substrate interface are largely eliminated at the bottom of the nanowires, as threading dislocations can be terminated at the m-plane sidewall This allows the adoption of heterostructures while decoupling the need for a favorable epitaxial relationship. By optimizing the doping concentration and indium composition of InGaN nanowires, the bandgap can favorably straddle the redox potential to facilitate PEC carbon dioxide reduction reaction (CO2RR) and nitrogen reduction reaction (NRR)

PA-MBE growth of catalyst-free GaN nanowires
Gan nanowires growth window and bulk polarity
InGaN-on-GaN axial nanowires
CHARACTERIZATIONS
Photoluminescence spectroscopy
Raman spectroscopy
X-ray structural analysis and chemical bond characterizations
Interfacial structural and morphology characterizations
Analyses of electrical properties with electrochemical impedance spectroscopy
Terahertz spectroscopy
Four-dimensional scanning ultrafast electron microscopy
PIEZOTRONICS AND PIEZO-PHOTOTRONICS
Piezoelectric properties of Wurtzite materials
Piezotronic effect
Piezo-phototronic effects
Piezotronic applications
Piezo-phototronic applications
SOLAR-TO-HYDROGEN ENERGY APPLICATIONS
Improving light absorption
Enhancing carrier separation and migration
Assisting in reaction kinetics
Materials’ growth on alternate substrates
Piezo-phototronic devices and hybrid devices
PEC-based CO2RR and NRR
Findings
Summary

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