The synthesis and application of InGaN nanowires: A review

Abstract In the past few years, the field of indium gallium nitride (InGaN) nanowires has seen a great deal of interest, as the compositional tunability and conveniently placed band-gap of the material coincide quite well with the special physical qualities possessed by nanowire heterostructures. These nanowires can be grown with a variety of methods and in combination with other materials, producing a wide array of possible applications. Among these, light-emitting diodes remain promising as a light source, with research efforts focused on efficiency, while substantial breakthroughs have been made in the field of photoelectrochemical catalysis, primarily through water splitting. Photovoltaic cells too hold promise, though they may be years away from application. In this review, we seek to inform the reader of key developments in the field of InGaN nanowire synthesis and application.

Introduction

Humanity’s demand for energy is on a general upward trend, but traditional sources are becoming less viable as long term solutions, given that the vast majority of power generated today comes from nonrenewable sources. As such, the harvesting and efficient use of energy have become very important topics of study in scientific research, with radiant energy– the energy of the light produced by the sun, and that of the light we use to mimic it– taking a central role in this field. From solar power, which seeks convert the sun’s energy into a useful form, to more efficient sources of the lighting we find invaluable in our daily lives, the study of radiant energy and photonics has reach across fields, with numerous methods and applications. In particular, semiconducting nanowires have shown great potential, with applications in light-emitting diodes (LEDs)(Yan 2009)(Chen 2012), photovoltaic cells(Dasgupta 2013), and photoelectrochemical energy conversion(Liu 2014).

Among the many semiconducting nanowire materials, indium gallium nitride has been a material of practical interest for quite some time. As early as 1998 there had developed an extensive field of research into InGaN laser diodes(Nakamura 1998), and this research has reached fruition in the blue-violet laser diodes currently utilized in modern compact disc technology(Nakamura 2000). More recently, as InGaN has become better characterized, there has been an upsurge in interest in InGaN nanowire structures. This is due to an increase in studies in the general field of nanowires(Law 2004), which have demonstrated that nanowires possess several capacities which make them uniquely suited as structures for InGaN. A one dimensional structure minimizes the large lattice constant mismatch between InN and GaN, and the large amount of surface area present in nanowires is ideally suited to InGaN’s both traditional and emerging applications for InGaN.

The synthesis of InGaN nanowires was initially focused on the wide range of bandgaps available with InGaN, made possible by varying the stoichiometric ratio within the alloy. Any InGaN nanowire is not an equal mixture of the three constituent elements, but rather InN and GaN alloyed, giving possible formulas of the format In\(_{x}\)Ga\(_{1-x}\)N, each having a slightly different bandgap, and thus bridging a very wide emissions spectrum. Developments in the synthesis of these nanowires have naturally focused on these band gaps, as creating conditions that allow for the full spectrum of InGaN stoichiometries is critical to any major utilization of the mat