Catalyst-free GaAs Nanoneedles Grown on GaAs and Si Substrates with Twin-Free Single-Crystal Wurtzite Phase

Michael Moewe, Linus C. Chuang, Shanna Crankshaw, Chris Chase

SEM image: GaAs nanoneedle grown on Si substrate: 30° tilt SEM image, top-down SEM
TEM image: GaAs nanoneedle grown on GaAs substrate: [1-100] zone axis.

The nanoneedles are grown on crystal substrates through a Metal-Organic Chemical Vapor Deposition process. The deposition is quite similar to MOCVD growth with the exception of substantially lower (150C lower) temperature and spontaneous growth on lattice-mismatched substrates. We are the first to report these particular structures and this type of growth. Normally gallium arsenide atoms stack in a specific "zincblende" arrangement. Sometimes, such as in nanowire growth, the stacking can flip between zincblende and "wurtzite" arrangements, another stacking order. We are the first to observe a pure "wurtzite" arrangement for gallium arsenide. This could be very interesting as a new engineering tool to alter the electrical and optical properties of a material.

Growing decent quality thin-film gallium arsenide on silicon has previously been unattainable due to the crystal lattice mismatch between gallium arsenide and silicon (4%). GaAs Nanowires can avoid this strain limitation due to their ability to relax in 2 dimensions and relieve strain, but their diameter is limited to around < 100 nm. The nanoneedles however can be grown up to micron size in diameter and grow in a single crystal phase, free of twin defects (the switching between zincblende and wurtzite phases which often obeserved for NWs).

Since the nanoneedles are made from direct-bandgap material, we foresee that they could be used to integrate any traditional optoelectronic semiconductor devices directly with silicon circuits. Our goal is to demonstrate diode lasers on silicon. In addition, the structures could be used for efficient light detection on silicon, allowing for a chip-scale optical communication system which could improve signal bandwidth and avoid limitations of electrical signals at high bandwidths.

We also foresee that the sharp tips of the nanoneedles could be used utilized for other applications like atomic force microscopy (AFM) and Raman spectroscopy. Sharp tips in AFM could enhance imaging resolution or allow for simultaneous parallel scanning from many tips, since they can be grown on a substrate and don't have to be etched or processed to generate the sharp tips.

Tip Enhanced Raman spectroscopy works by bringing a sharp tip close to a molecule or surface of a material and measuring the frequency shift the optical electric field in the tip interacting with the molecule or surface. This signal is dependent on the square of the electric field generated at the probe tip, so our sharp tips could potentially provide exponential increases in the ability to detect single molecules using this Raman technique.

References:

Michael Moewe, Linus C. Chuang, Shanna Crankshaw, Chris Chase, and Connie Chang-Hasnain. "Bright Photoluminescence from GaAs and InGaAs Nanoneedles Grown on Si Substrates", Conference on Lasers and Electrooptics, CTuCC1 May 6th, 2008.