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]
Summary
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)
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