“Direct Atomic-Scale Imaging and Spectroscopy of the
Interior and Exterior of III-V Nanowires”
Anders Mikkelsen, Lund University, Sweden
Free-standing III-V nanowires and nanotubes are likely to become central components in future electronics and photonics with applications in IT, life sciences and energy. A very wide variety of III-V materials can be self-assembled and doped, resulting in complex axial and radial heterostructures tailored down to the atomic scale. Importantly they can also be grown directly on silicon, allowing integration with existing Si technologies and the use of rather exotic III-V materials combinations.
We have used scanning tunneling microscopy/spectroscopy (STM/STS) and synchrotron-based X-ray photoemission spectroscopy/microscopy and low-energy electron microscopy (XPS/XPEEM/LEEM) to study nanowires and nanowire surfaces. Previously we have developed the means to directly study the interior of III-V semiconductor nanowires by STM, and now we have also developed direct methods for studying also the exterior nanowire surfaces to the atomic scale with STM. We describe several significant results on the fundamental limits to atomic scale interface precision in AlGaAs/GaAs nanowire heterostructures, STS measurements on the interior of these wires and new insights into the influence of the growth substrate. We present atomically resolved STM images of the outside surface of InAs nanowires with InP segments along with STS measurements. The imaged surfaces of InAs nanowires are quite intriguing as the wires grow in the wurtzite crystal phase, in contrast to the zincblende bulk phase. Further we present very recent STM images and STS measurements of InP nanowire pn-junctions.
Using XPEEM and XPS we have characterized surface chemistry and electronic properties of both III-V nanowires and III-V bulk crystals. We have investigated atomic layer deposition of various ultra-thin dielectrics to reduce surface band-bending effects especially on III-V materials beyond GaAs such as InAs and InSb.
Anders Mikkelsen is an associate professor of physics at Lund University, recently ranked the top university in Sweden. He earned his doctorate in physics in 2001 from Århus University. His research has dealt with understanding the growth, structure and properties of low-dimensional objects, particularly on the all important atomic scale. This has involved a very broad range of materials such as semiconductors, metal alloys, oxides, quasi crystals, water overlayers and novel magnetic materials. Common for all these materials is the observation that as a material gets confined to the nanometer range in one or more dimensions, one observes completely new atomic-scale structures, huge changes in electrical, optical and chemical properties, and growth modes very different from the bulk. To study these phenomena he has used a wide range of advanced experimental techniques based on diffraction, spectroscopy and scanning tunneling microscopy, and has performed full quantum mechanical calculations to interpret the experimental results. He has also worked on new experimental methods that address the considerable challenges in studying structures that are extremely confined in one or more dimensions.