GaN-based single-nanowire devices
Rudeesun Songmuang and Eva Monroy
The downscaling of semiconductor devices is a continuous trend in the microelectronics industry. Following this trend, semiconductor nanowires (NWs) become a powerful and diverse kind of functional nanomaterials for electronics, optoelectronics, and biotechnology. An attractive feature of these one-dimensional (1D) nanostructures is the fact that their chemical and physical characteristics (chemical composition, size, electronic or optical properties) can be rationally controlled during their synthesis in a predictable manner. Furthermore, NWs provide an opportunity to combine different materials, since their large surface- to-volume ratio allows misfit strain to be elastically released without dislocation formation, which extends the range of size and band-gap engineering beyond the limits of planar systems.
This chapter presents a summary of new device concepts incorporating GaN NWs as active media. The text is structured as follows:
- • Nanowire synthesis: We introduce the growth processes to achieve controlled-by-design GaN-based NW heterostructures and discuss the resultant structural and optical properties.
- • Energy conversion: We first present a comprehensive study of single GaN NWs operated as photoconductors—devices which are characterized by giant photocurrent gain and by a visible rejection of several orders of magnitude. The potential application of In-containing core-shell structures to photo- voltaics is also discussed. Finally, we introduce the operation of NWs as piezoelectric transducers for energy harvesting.
- • Nanoelectronics: Progress in the performance of single-NW field-effect transistors (FETs) is discussed. Then, the potential of band-gap engineering via NW heterostructures for nanoelectronic applications is demonstrated via their electrical characteristics. For instance, the two-dimensional electron gas (2DEG) formed in GaN/AlN/AlGaN NW radial heterostructures can be operated as a nanoscale high-mobility transistor. On the other hand, AlN axial-double-barriers inserted in GaN NW can show different transport regimes, opening the possibility to realize single electron transistors (SETs) or resonant tunneling diodes (RTDs), depending on the heterostructure design.
- • Sensorics: Due to their chemical robustness and its large surface-to-volume ratio, the application of GaN NWs as chemical sensors has been proposed.
Functionalization by metal or oxide nanoparticles is applied to enhance the selectivity and sensitivity of their optical/electrical properties to the environment.