Atomic layer deposition of ZnO thin films: from understanding the growth toward piezoelectric applications
Julian Pilz
Institute of Solid State Physics
14:30 - 15:10 Friday 10 May 2019 KFU HS 05.12

ZnO is a direct band gap semiconductor with attractive piezoelectrical, optical, and electrical properties, particularly appealing for a variety of functional devices (e.g., gas, bio, and UV sensors, piezoelectric nanogenerators and actuators). Among other techniques to deposit ZnO thin films, atomic layer deposition (ALD) is the method of choice for the growth of high-quality conformal films with Å-level thickness control. In ALD, the substrate is sequentially exposed to two reactants, separated by an inert gas purge, defining one cycle in the deposition. The self-limiting nature of the surface reactions offers the possibility to control the film thickness by adjusting the number of cycles rather than the process time as in conventional chemical vapor deposition processes. A typical growth per cycle (GPC) for ALD is in the Å/cycle range.
In this seminar, the basics of atomic layer deposition and the process optimization to achieve self-limiting growth will be explained. [1] Furthermore, the influence of the substrate temperature on material properties will be discussed, with a focus on the optimum temperature for applications in piezoelectric devices. [2] The initial cycles of the process show interesting behavior regarding the growth per cycle and start of the crystallization. This has important consequences for the growth of ultrathin films below 5 nm. [3] At last, the techniques to investigate the ZnO piezoresponse and the steps toward device integration will be discussed.
[1] J. Pilz, A. Perrotta, P. Christian, M. Tazreiter, R. Resel, G. Leising, T. Griesser, and A. M. Coclite, "Tuning of material properties of ZnO thin films grown by plasma-enhanced atomic layer deposition at room temperature." J. Vac. Sci. Technol. A 36.1 (2018): 01A109.
[2] J. Pilz, A. Perrotta, G. Leising, A. M. Coclite, “ZnO thin films grown by plasma-enhanced atomic layer deposition: material properties within and outside the “ALD window””, submitted
[3] A. Perrotta, J. Pilz, R. Resel, A. M. Coclite, „Initial growth and crystallite formation of plasma enhanced atomic layer deposited ZnO“, in preparation