Impact of the sequence of precursor introduction on the growth and properties of atomic layer deposited Al-doped ZnO films

Abstract

Atomic layer deposition relies on surface chemical reactions which implies that the order of the precursor pulses (so-called “sequence”) impacts the growth, especially for multinary compounds. In the case of Al-doped zinc oxide (AZO) thin films, the sequence of introduction of precursors tri-methyl aluminum (TMA)/diethylzinc (DEZ)/H2O has been reported to impact their growth and some of their properties. Here, five different Al sequences for doping the AZO films in Al have been tested at a constant deposition temperature of 160 °C and a TMA:DEZ ratio of 1:10, and the film growth and properties are investigated by in situ quartz crystal microbalance (QCM) measurements and ex situ characterizations. This paper provides evidence of the impact of the Al sequence on AZO material and proposes an explanation of the macroscopic properties based on the nature of chemical surface reactions evidenced by QCM. The growth rate, composition, electrical and optical properties, and, to a lesser extent, structural properties are affected by the TMA/DEZ/H2O pulse sequence. In particular, better electrical properties are obtained by reducing the Al content incorporated per cycle when the TMA pulse follows a DEZ pulse and, second, the optical band gap size is increased when the TMA pulse is between two DEZ pulses. Mass variations during surface reactions of TMA on hydroxyl and zinc-alkyl surface groups have also been proven to be temperature dependent when comparing growth mechanisms at 160 and 200 °C. It is also observed that the increase in temperature has a similar impact on the mass variations as the increase in the TMA:DEZ ratio. This is probably because of an improved intermixing between Al species and ZnO layers.

Effective module level encapsulation of CIGS solar cells with Al2O3 thin film grown by atomic layer deposition

“…Al:ZnO (AZO) films of ~ 350 nm were deposited on borosilicate glass substrates by radiofrequency sputtering according to procedures described elsewhere [26]. The top Al2O3 barrier layers were prepared by atomic layer deposition (ALD) in a BENEQ TFS-200 reactor at deposition temperature Tdep = 160 °C, from trimethyl aluminum (Al(CH3)3, TMA, Optograde, Rohm & Haas) and deionized water [27]. ALD-Al2O3 of different nominal thicknesses, namely 2, 5, 10, 25, and 80 nm, were tested as barrier layer on AZO/glass.…”

Chemical Passivation with Phosphonic Acid Derivatives of ZnO Deposited by Atomic Layer Deposition and Its Influence on the Halide Perovskite Interface

“…The substrates were transferred into a BENEQ TFS-200 ALD reactor for the deposition of 10 or 50 nm of zinc oxide. The deposition was performed according to a process described elsewhere 79 .…”

ALD of ZnO:Ti: Growth Mechanism and Application as an Efficient Transparent Conductive Oxide in Silicon Nanowire Solar Cells

“…A similar behavior has been reported for ALD-AZO thin films. 11,13,19,20,40 In summary, different Ti insertion mechanisms following two different precursor sequences are clearly evidenced from the QCM studies, which eventually affects the TZO thin film properties as is discussed in the following section.…”

“…{ZnO}, was performed according to reported procedure. 13 Two precursor sequences were investigated and referred to as sequence A (H2O pulse / N2 purge / DEZ pulse / N2 purge) where the first pulse is a H2O pulse; and sequence B (DEZ pulse / N2 purge / H2O pulse / N2 purge), where the first pulse is a DEZ pulse. A titanium oxide growth cycle, i.e.…”

“…The Al-doping level can be varied by tuning the cycle ratio of {Al2O3} with respect to {ZnO}. Other parameters reported to affect the doping include the order of precursor introduction, [11][12][13] the deposition temperature, 14 and the pulse or purge duration times. [15][16][17] The doping level can also be modified by co-injecting the Zn and Al precursors, 18 by using alternative Al precursors 19,20 or inhibitors.…”