Controlled Mass Production of Nanowires

Controlled Mass Production of Nanowires
Reliable manufacturing of nanowires for large-scale, integrated devices (lab-on-a-chip, for example) requires that these structures can be grown at desired locations over a large area. Kris Bertness and colleagues at the National Institute of Standards and Technology (NIST) have grown Gallium Nitride nanowires on silicon substrates at controlled locations with essentially perfect selectivity.

The nanowires are grown by molecular beam epitaxy through a silicon nitride mask that is patterned on to a silicon wafer. The mask acts as a stencil layer through which the nanowires grow uniformly. The size and location of the openings control the position and the diameter of the nanowires grown, respectively. After optimization of growth and processing conditions, there is mostly no growth on the mask surface. Mask openings of approximately 500 nm or less produce single nanowires with a well-formed hexagonal shape and a symmetrical tip with six facets. Structures grown in openings of over 1000 nm appear to be coalesced nanowires, and medium-size openings (500 nm to 900 nm) yielded single crystalline nanowires with multifaceted tops.

The NIST researchers also derived the dependence of the vertical growth rate of various GaN features as a function of distance from the center of the silicon wafer. With this ability to influence the shape and size of semiconductor nanowires over a large area, further progress can be made towards the miniaturization of devices.
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