Jul 26, 2012
Surface oxide mask directs InP nanowire growth
Catalyst-assisted selective-area growth of InP nanowires on InP(111) B wafers has been performed using the native oxide layer of the substrate as the growth mask in an MOMBE (metal organic molecular beam epitaxy) growth system. Nanowire growth was found to be surface diffusion mediated with a large characteristic length – a surprising result for selective-area growth in MOMBE systems, according to the team from Technion – Israel Institute of Technology.
The researchers used a catalyst layout of evenly spaced (120 nm) gold-catalyst columns, arranged in rows that were 0.5, 1, 2, 4, 8 and 16 µm apart, to extract the growth precursor migration length on the oxidized surface. The value was found to be about 4 µm, which is about an order of magnitude larger than the migration length on a bare III-V surface.
This large precursor migration length affects growth conditions. Due to the large collection area, the precursor flow needed for growth is around 20 times smaller than the amount required for growth on oxide-free surfaces, which may affect the resulting nanowire properties.
In addition, pre-growth heating treatment at 450 °C (prior to growth at 400 °C) was found to increase nanowire nucleation yield. Untreated samples exhibited island growth and contained off-axis nanowires, grown from poorly nucleated catalysts. This finding is linked to catalyst-substrate interaction, and is the subject of subsequent work regarding this growth regime.
In future work, the group plans to fabricate vertical nanowire-based electronic devices; exploring their properties, and relating this information to the structural properties of the nanowires such as diameter, surface detail and crystalline structure and quality.
Full details can be found in the journal Nanotechnology.
About the author
The research was performed by members of the Electronic Materials and Devices Group of the Electrical Engineering Department at the Technion – Israel Institute of Technology. Yonatan Calahorra is a PhD student in the group and his research interests are III-V semiconductor nanowire growth, properties and devices. Yaakov Greenberg is also a PhD student in the group and focuses on nanowire growth and characterization. Shimon Cohen is responsible for the group's MOMBE growth, including nanowires and high-quality thin films. Prof. Dan Ritter is head of the Electronic Materials and Devices Group. In addition to nanowire technology, his current research interests include planar semiconductor devices such as fast heterojunction bipolar transistors and high-k dielectrics MOS capacitors, as well as resistive switching in metal-oxides.