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TT1.05 - Nanotailoring ZnO:X (X = Al, B) Films by Atomic Layer Deposition 
April 7, 2015   9:15am - 9:30am

Transparent conductive oxides (TCOs) have become ubiquitous in many of today�s electronic devices and their importance will keep increasing with the growing role of solar energy in our society. However, TCOs will not just find more and wider applications but in many cases more precise control of their properties will also be required. In this contribution, we will focus on ZnO, which is an abundant material that can serve as a TCO when doped with group 13 elements. We will show that the method of atomic layer deposition (ALD) can be used to prepare high-quality ZnO:X (X = Al, B) films with a very precise control of their electronic properties even at the nanometer-level. ZnO:Al and ZnO:B films were prepared by ALD using the process based on diethylzinc (DEZ, Zn(C2H5)2) and H2O dosing and with either trimethylaluminum (TMA, Al(CH3)3); dimethylaluminum isoproproxide (DMAI, Al(CH3)2(OiPr)) or triisopropyl borate (TIB, B(OiPr)3) as precursors for the dopants. The doping was obtained using so-called supercycles in which the ratio of the DEZ and dopant cycles controls the dopant density in the films. By varying this ratio the dopant density can be precisely tuned and even easily graded throughout the film, which are important merits of the ALD technique in addition to its key features such as a unparalleled uniformity over large areas, an excellent conformality on 3D surface topologies and a relatively low thermal budget (typical substrate temperatures are 150 - 250 �C). From a detailed study involving Rutherford backscattering spectroscopy and transmission electron microscopy, it will be shown that by using DMAI and TIB as precursors, the lateral spacing of the dopants can be better controlled than with TMA due to fact that DMAI and TIB are larger molecules, leading to more steric hindrance at the surface. This better control correlates directly with the electronic properties of the films and it will be shown that the doping efficiency obtained for DMAI and TIB (up to 40-60%) is much higher than for TMA (5-10%). ZnO:Al and ZnO:B films with resistivities

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