| AVS 62nd International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF-TuA |
| Session: | ALD for Emerging Applications |
| Presenter: | Lachlan Black, Eindhoven University of Technology, Netherlands |
| Authors: | L.E. Black, Eindhoven University of Technology, Netherlands M.A. Verheijen, Eindhoven University of Technology A.J. Standing, Eindhoven University of Technology E.P.A.M. Bakkers, Eindhoven University of Technology W.M.M. Kessels, Eindhoven University of Technology, Netherlands |
| Correspondent: | Click to Email |
Semiconductor nanowires represent a novel class of materials structure with a number of interesting properties that give them potential applications in optoelectronic devices, including light-emitting diodes (LEDs), photoelectrochemical systems, and solar cells. Because of the unusually high surface-to-volume ratio of nanowires, the electrical performance of nanowire devices is especially sensitive to the condition of the semiconductor surface. It is well known that the application of thin-film dielectric and conductive layers to semiconductor surfaces can be an effective means of controlling surface properties. Such layers can provide chemical and electrical passivation, functionalisation, and contacting of semiconductor device surfaces. However, most conventional thin-film deposition techniques face severe challenges when confronted by the high-aspect-ratio features represented by nanowire geometry.
Atomic layer deposition (ALD), on the other hand, is ideally suited to thin film deposition on small-dimensioned, high-aspect-ratio structures due to its uniquely self-limiting nature, which results in outstanding uniformity and conformality, and thickness control on the sub-nm level. The application of thin films deposited by ALD to nanowire devices, in order to improve device properties, has previously been reported by a number of authors. However, there has been relatively little effort to systematically study the ALD process on nanowire surfaces in its own right. Nanowires represent an interesting test platform with which to study ALD processes and thin film properties because of the relative ease with which they can be characterised by transmission electron microscopy (TEM).
In this paper we present a fundamental experimental study of ALD on semiconductor nanowires. ALD thin films of various dielectric and conductive materials, including Al2O3, TiO2, ZnO, and HfO2, are deposited on Si and III-V semiconductor (GaP and InP) nanowire arrays grown by the vapour-liquid-solid (VLS) mechanism, and characterised by high-resolution TEM. Film thickness measured as a function of the number of deposition cycles is used to determine the linearity of the deposition rate and the growth-per-cycle, and these values are compared to those measured on co-deposited planar samples using in-situ and ex-situ ellipsometry. It is shown that both thermal and plasma-assisted ALD processes are capable of depositing films with excellent conformality and thickness uniformity along the length of the nanowires, although differences are observed for different materials. Moreover, TEM images reveal the presence of clearly defined interfacial layers in some samples.