Effects ofin-situmolecular oxygen exposure on the modulation of electrical properties of zinc oxide thin films grown by atomic layer deposition

Abstract

The possibility of employing molecular oxygen (O2) for reducing the carrier concentration of zinc oxide (ZnO) thin films grown by atomic layer deposition was investigated. The exposure of O2 after the oxygen‐source pulse (deionised water) was eventually highly effective for decreasing the carrier concentration over 3–4 orders of magnitude. In contrast, the O2 pulse, when following the zinc source pulse (diethylzinc), had a minimal effect on the electrical property. Detailed structural, chemical and electrical analyses of the oxygen‐modulated ZnO thin films were conducted. Successful electrical modulation of the ZnO thin films was further demonstrated by fabricating back‐gated thin film transistors. The improvement in the on‐to‐off current ratio of the transistors was achieved by the proper exposure of O2.

Influence of post-deposition annealing on the electrical properties of zinc oxide thin films

“…The ZnO-A film grown at 120°C exhibits a (100)-preferred orientation, while the other three films exhibit a (002)-preferred orientation. Note that the ZnO-D film, for which O 2 was additionally pulsed after the H 2 O pulse, has the most (002)-oriented structure among all the samples considered in this study [27]. When ZnO-B and ZnO-C are compared, ZnO-B is more (002)-oriented than ZnO-C.…”

“…For convenience, these films grown at 120°C, 170°C, and 300°C will be called "ZnO-A", "ZnO-B", and "ZnO-C", respectively. The last sample, "ZnO-D", was deposited at 300°C with a modified pulse sequence: exposure of molecular oxygen (O 2 ) for 7 s was carried out prior to the last N 2 purge step, i.e., DEZ/N 2 /H 2 O/O 2 /N 2 represents one growth cycle for ZnO-D. As discussed later in X-ray diffraction (XRD) analysis, this O 2 pulse changes the preferred orientation of the grown ZnO film to be highly (002)-oriented [27]. The total film thickness was set to bẽ 80 nm based on the observed growth-per-cycle (GPC).…”

Review of tailoring ZnO for optoelectronics through atomic layer deposition experimental variables

“…3 d ). 27,86–103 Key operating parameters, including turn-on voltage, carrier mobility, on/off current ratio and stability are important for optimisation, 104 and transparency can be necessary for lighting applications which has led to transparent TFTs being produced entirely by ALD and print patterning. 105 These and other devices, such as diodes, 106,107 photoelectrodes 108–110 and inorganic LEDs, 23,111 will be included in the discussion.…”

“…N 2 O, 101 O 2 . 102 Precursors such as O 2 plasmas can be used at a range of temperatures including low temperatures, and the higher reactivity produces more stoichiometric films resulting in a lower carrier concentration than the DEZ/H 2 O combination. 155 Plasmas can also aid initiation of ZnO growth on polymer surfaces, 156 which has been used in a study of ZnO growth on and in a hybrid solar cell active layer.…”