Abstract
A novel supercycled atomic layer deposition (ALD) process which combines thermal ALD process with in situ O2 plasma treatment is presented in this work to deposit ZnO thin films with highly tunable electrical properties. Both O2 plasma time and the number of thermal ALD cycles in a supercycle can be adjusted to achieve fine tuning of film resistivity and carrier concentration up to six orders of magnitude without extrinsic doping. The concentration of hydrogen defects are believed to play a major role in adjusting the electrical properties of ZnO films. Kelvin probe force microscopy results evidently show the shift of Fermi level in different ZnO films and are well associated with the changing of carrier concentration. This reliable and robust technique reported here clearly points towards the capability of using this method to produce ZnO films with controlled properties in different applications.
Highlights
Once defined as the future material, zinc oxide (ZnO) has attracted the interest of science community for over half a century due to its superior optical and electrical properties [1]
We recently reported the capability of tuning ZnO using a single plasma-enhanced Atomic layer deposition (ALD) process which allows the tuning of its resistivity
The proposed supercycled ALD process is illustrated in Fig. 1a with one supercycle consisting of m cycles of thermal ALD processes (DEZ and H2O) and one O2 plasma step (O2 plasma)
Summary
Once defined as the future material, zinc oxide (ZnO) has attracted the interest of science community for over half a century due to its superior optical and electrical properties [1]. ZnO has found numerous applications in electronic devices including light-emitting diodes, photo detectors, and power devices [4, 5] These different types of applications require ZnO films to have various electrical parameters, and some applications even demand multi-layer of ZnO films with different electrical properties [6]. The dominant way of tuning undoped ZnO film properties in the thermal ALD process is by changing the growth temperature [17, 18]. This enables the deposition of highly conductive films, high-quality ZnO films are difficult to obtain with low carrier concentration. We recently reported the capability of tuning ZnO using a single plasma-enhanced ALD process which allows the tuning of its resistivity
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