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Effect of annealing on electrical properties of low temperature ZnO films

Iwona A. Kowalik ¹, Elżbieta Guziewicz ¹, Krzysztof Kopalko ¹, Marek Godlewski ^1,2, Aleksandra Wójcik ¹, Victor Osinniy ¹, Tomasz A. Krajewski ¹, Tomasz Story ¹, Marek Guziewicz ³

1. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
2. Cardinal Stefan Wyszynski University, College of Science, Warszawa, Poland
3. Instytut Technologii Elektronowej (ITE), al. Lotników 32/46, Warszawa 02-668, Poland

Abstract

Last years zinc oxide is extensively studied as prospective materials for electronics (sensors) and optoelectronics. Most of electronic applications like sensors require suitable and controllable electric parameters of ZnO films, like high mobility and low doping concentration. We present results of Hall measurements on zinc oxide thin films grown at low temperature (LT) by Atomic Layer Deposition (ALD) method. In this method reagents (precursors) are introduced sequentially into the growth chamber and cycles when precursors reach the substrate are interspersed by cycles of purging with nitrogen. Because precursors meet only at a surface of the substrate we may use very reactive precursors and may apply different type of chemical reactions (synthesis, single or double exchange).

In the recent study we used double exchange reaction between metal organic diethylzinc and water vapor precursors and applied very low deposition temperature of 100-200⁰C. Hall coefficient measurements were done on ZnO thin films grown in this way show carrier mobility between 10 and 50 depending on deposition temperature and growth parameters (precursor’s time and purging time). Carrier concentration was at the level of 10¹⁹cm^-3, which is about two orders of magnitude higher than expected for good quality Schottky contacts. We show that post-grown annealing can considerably improve electrical parameters of LT ZnO films. By low temperature post-growth annealing we managed to reduce free carrier concentration to below 10¹⁷cm^-3.

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