Group III-Nitride semiconductors have attracted special interest for applications in several optoelectronics devices. Multi-layer epitaxial structures required for various devices present high density of dislocations, which in turn reduces the efficiency of the device. One possible solution for this problem is to substitute semiconductor nanowires for epitaxial films. Nanowires often have stress-free surfaces and better electrical and optical properties. Vapor-liquid-solid (VLS) catalytic growth is one of the most common methods used to synthesize 1-D nanostructures. Although ex-situ catalytic growth of gallium nitride (GaN) nanowires  has been achieved before, there is not a complete understanding of the role of the catalyst, the growth mechanism and the interface dynamic. This work presents a dynamic observation of the nucleation and growth mechanisms of GaN nanowires which were formed by direct reaction of ammonia (NH₃) with gold (Au) - gallium (Ga) alloy liquid particle.

An environmental scanning/transmission electron microscope (E(S)TEM), Tecnai F20, was used for in-situ observations. Au was deposited ex-situ on porous silicon membrane TEM ready grids by physical vapor deposition (sputering of a Au target). These grids were introduced into the E(S)TEM column and heted up to 400C using a GATAN heating holder. Next, 60 mTorr of Trimethylgallium (TMG) was introduced into the E(S)TEM column for 3 minutes to deposite Ga particles. The sample area and delivery lines were evacuated after closing the inlet of the TMG to the E(S)TEM column. Subsequently, the sample temperature was increased to 800C and 40-70 mTorr of NH3 was introduced into the column. Low and high magnification images and digital videos (15 frames per second) were recorded using Gatan Orious 600SC camera. JEOL 2010F TEM/STEM was used for ex-situ imaging (High Resolution TEM (HR-TEM) and STEM) and for  chemical analysis (Energy Dispersive Spectrometry (EDS)) of the samples.

GaN nanowires nucleation started at 800C after 40mTorr of NH3 was introduced.  They  grew over the whole substrate, thus growth due to electron beam effect is discarded. Ex-situ analysis confirms the presence of Ga and N, as well as the wurzitic structure for  GaN.

1. POSTER: In-situ catalytic growth of Gallium Nitride nanowires using an environmental transmission electron microscope, PDF document, version 1.5, 2.6MB

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