Abstract
In this paper, we report a nitrogen (N) doped zinc oxide (N:ZnO) film grown by the reactive high power impulse magnetron sputtering (HiPIMS) technique on glass substrates, where nitrogen gas (N2) is used as the N source. The proposal is to investigate the influence of process parameters on the alteration of the N:ZnO film from n- to p-type conductivity and the stability of the p-type behavior. It is obtained that the n- or p-type behavior of the as-deposited N:ZnO film is affected by the N2 flow rate, deposition temperature, and inductively coupled plasma (ICP) assistance, of which the ICP assistance had a great impact. It is noticed that, owing to the improved ionization rate of the N2 dopant by ICP, the N:ZnO film almost totally prefers to exhibit p-type behavior. Based on the measurement by temporal resolution optical emission spectroscopy, the components in plasma are obtained and the ion reaction in film growth is confirmed: a high concentration of active N+ in the ICP-assisted plasma reacts with sputtered Zn+ in vapor to form No defect in the p-type N:ZnO film. We then forecast that a stable p-type N:ZnO film can be grown using the HiPIMS technique.
Highlights
Zinc oxide (ZnO) is a semi-conductor material with hexagonal crystal structure
We report a nitrogen (N) doped zinc oxide (N:ZnO) film grown by the reactive high power impulse magnetron sputtering (HiPIMS) technique on glass substrates, where nitrogen gas (N2) is used as the N source
When Ar (30 sccm), O2 (22 sccm), and working pressure (0.5 Pa) were constant, and No 2.32 (N2) flow rates were varied from 4 sccm to 16 sccm, the carrier densities in all samples were over 1014 cm−3, even reached 1.12×1016 cm−3 at 10 sccm N2 flow rate, while the mobility was varied between 7.89 cm2/V s and 59 cm2/V s
Summary
ZnO has a direct and wide bandgap (3.37 eV at room temperature) with a high excitation energy (60 meV) These properties make ZnO widely applied in optoelectronic devices, solar cells, sensors, and so on. In the N-doped ZnO (N:ZnO) material, N substitutes O sites for No defects and forms a shallow acceptor with a hole binding energy of 200 meV.. N is considered as a promising candidate to obtain p-type ZnO, the solubility of N in ZnO is low and the hole concentration is low, and as a result, it is still impossible to form a stable N:ZnO film with N2 dopant. In order to create more No defects in the as-grown material, HiPIMS might provide enough energy to break the molecular N–N bonds and to replace O by N in the N:ZnO film with N2 as the dopant. Temporal resolution optical emission spectroscopy (OES) revealed the kinetics of the film grown in the vapor plasma, and reasonably explains the p-type N:ZnO formation in HiPIMS
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