| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Tuesday Sessions |
| Session TF+EM+MI-TuM |
| Session: | Thin Films for Microelectronics, Photonics, and Optoelectronic Applications |
| Presenter: | Willem-Jan Berghuis, Department of Applied Physics, Eindhoven University of Technology, Postbus 513, 5600 MB Eindhoven, The Netherlands |
| Authors: | W.J.H. Berghuis, Department of Applied Physics, Eindhoven University of Technology, Postbus 513, 5600 MB Eindhoven, The Netherlands W.M.M. Kessels, Eindhoven University of Technology, The Netherlands J.E.M. Haverkort, Eindhoven University of Technology, The Netherlands E.P.A.M. Bakkers, Eindhoven University of Technology, The Netherlands A. Dijkstra, Eindhoven University of Technology, The Netherlands E.M.T. Fadaly, Eindhoven University of Technology, The Netherlands M.A. Verheijen, Eindhoven University of Technology, The Netherlands |
| Correspondent: | Click to Email |
Semiconductor nanowires (NWs) are nanoscale rods with a typical length of a few microns. They are made of materials such as Ge, Si, InP, GaAs. Due to their high aspect ratio, nanowires have a very high surface-to-volume-ratio, which leads to a large influence of the surface on their electronic and optical properties. Surface states facilitate recombination of electron-hole pairs, which reduces the photovoltaic conversion efficiency of NW solar cells [1] or which decreases the output of NW based LEDs or lasers. The surface can also induce space charge regions in the nanowires, which greatly affects their conductivity and which can be critical in for example sensing applications [2]. To reach the desired performance of nanowires in their applications, it is important to control the surface effects.
Atomic layer deposition (ALD) is a deposition technique that allows for preparation of ultrathin films with sub-nanometer thickness control and with an excellent conformality on high aspect ratio structures such as nanowire arrays. For these reasons ALD is a suitable technique to cover nanowires with thin films to control the surface properties.
Recently, nanowires have enabled the growth of Ge and SiGe in the hexagonal diamond crystal phase [3]. In contrast to the cubic crystal phase of these materials, the hexagonal crystal phase leads to a direct bandgap. The latter makes this material an interesting candidate to realize solid-state lasers that are compatible with the current silicon-based electronics. One of the important steps to accomplish this is to reduce the surface recombination losses; i.e. to passivate the surface.
The aim of this work is to explore the surface passivation of these hexagonal Ge and SiGe nanowires. We do so by covering the nanowires with ultrathin films of Al2O3 prepared by thermal and plasma-assisted ALD (PE-ALD). Secondly, we cover the wires with a stack of POx/Al2O3. The latter is a relatively new passivation scheme that has proven very successful for the surface passivation of InP nanowires [4] and Si wafers [5]. The change in photoluminescence (PL) of the nanowires as a function of the ALD films has been studied to assess the surface passivation and the influence of various pre- and post-treatments. Conformal coating of hexagonal Ge nanowires has been realized and we have observed an improvement of the photoluminescence for NWs covered with PE-ALD Al2O3 and POx/Al2O3.