(574h) Investigation of Electrical and Optical Properties of Indium Oxide Thin-Films Prepared By Atomic Layer Deposition Using Trimethylindium and Ozone Precursors

Atomic layer deposition (ALD) is a chemical vapor deposition method in which precursor pulses are separated from one another by purge periods. Purging with an nonreactive gas such as argon removes residual gases and potential reaction by-products remaining inside the reaction chamber after each precursor pulse; this mode of operation inhibits gas-phase reactions between precursors, limiting reactions to those that take place only on the deposition surface. Despite ALD being a relatively simple thin-film manufacturing method, it provides very fine control over the deposited film thickness which is simply determined by fixing the number of ALD cycles under a specific set of reactor conditions (each cycle defined by the sum of precursor pulses and their subsequent purge periods) [1]. Its ability to deposit a wide range of films on different substrates makes ALD applicable to manufacturing electronics, optical and energy related devices provided there is a precursor system available which meets the criteria necessary for a successful ALD. These criteria include the precursor having significant vapor pressure, good thermal stability and sufficient reactivity towards substrate so surface reactions can nucleate and proceed [1,2].

Indium oxide (In₂O₃) has a wide and direct band gap (~3.5 eV) and is one of the most common materials used for transparent conducting oxides (TCO) for applications such as optical coatings, touch screen displays, and electrochromic devices. There are several methods to deposit films of indium oxide including sputtering, electron beam evaporation, sol-gel techniques, and ALD [3]. Additionally, it is well-known that indium oxide experiences a significant increase in film conductivity when doped with 10 wt% of element Sn producing indium tin oxide, or ITO [4].

In this work, we have studied the growth of indium oxide films on different substrates by ALD using trimethylindium (TMIn) and ozone precursors. This system provides a practical growth per cycle (gpc) at low temperatures (~0.4 A at 100^oc) making it a potential candidate for future flexible electronics or other processes with temperature-sensitive substrates. We have investigated the electrical and optical properties of the deposited films to evaluate the potential of indium oxide ultra-thin films (thickness < 20nm) as a transparent conductive coating. As-deposited films show resistivity on the order of 10^-2 Ohm cm. The presence of oxygen vacancies is considered to be responsible for the relatively high conductivity and n-type behavior of these films. We have investigated the changes in conductivity by performing a series of experiments testing the sensitivity of film conductivity to an ozone environment and will report those results in this presentation.

Furthermore, contrary to what is observed in thick and highly crystalline films, our results suggest that while in ultra-thin form and with amorphous crystalline structure, indium oxide films doped with Sn do not provide significant improvement in conductivity. Potential reasons for the ineffectiveness of Sn doping in out ultra-thin films also will be presented.

[1] Suntola, T., 1996. Appl. Surf. Sci. 100, 391.

[2] Puurunen, R.L., 2014. Chem. Vap. Depos. 20(10), 332.

[3] Mane, A.U., Allen, A.J., Kanjolia, R.K., Elam, J.W., 2016. J. Phys. Chem. C 120(18), 9874.

[4] Khusayfan, N.M., El-Nahass, M.M., 2013. Adv. Condens. Matter Phys. 2013, 408182.