III-V semiconductor nanowire/graphene hybrid structures and devices
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Heterostructured III-V semiconductor nanowires have attracted considerable attention in recent years due to their potential in future nano-electronic and nano-photonic device applications. The III-V nanowire project at NTNU today involves the epitaxial growth (MBE), structural (HRTEM), nano-optoelectrical characterization, as well as processing (NanoLab) of devices. In this talk, I will give some highlights of our work since the first GaAs nanowires were grown in our lab in 2006.
I will then focus on our most recent work on epitaxial growth of GaAs nanowires on graphene [1-2]. We have recently developed a generic atomic model, which describes the epitaxial growth of semiconductor nanostructures on graphene that is applicable to all conventional semiconductor materials. The model was first verified by cross-sectional transmission electron microscopy studies of GaAs nanowires that grow epitaxially and dislocation-free on graphene. Recently we have also shown the vertical growth of dislocation-free GaN nanowires on graphene . The epitaxial growth of semiconductor nanostructures on graphene is very appealing for device applications since graphene can function not only as a replacement of the semiconductor substrate but in addition as a transparent and flexible electrode for e.g. solar cells and LEDs.
For deep ultraviolet AlGaN based LEDs, in need for various disinfection and sterilization purposes, the concept offers a real advantage over present thin film based technology. Such UV LEDs are today very expensive and inefficient due to the lack of a good transparent electrode (ITO is absorbing in deep UV), the high dislocation density in the active thin film layers, low light extraction efficiency, and the use of very expensive semiconductor substrates or buffer layers of AlN. Both NTNU (using MBE) and our spin-off CrayoNano (using MOCVD) are now developing UV LEDs based on the growth of AlGaN nanostructures on graphene as will be further discussed in my talk.