Manufacturing process development of high performance NiO films
Date Issued
2014
Date
2014
Author(s)
Kuo, Tsung-Yen
Abstract
Most oxide semiconductors such as indium tin oxide, zinc oxide, etc. show n-type conduction. Hence, in p–n junction devices, synthesizing a p-type oxide-based semiconductor is an important issue. Nickel oxide (NiO) is a candidate for p-type transparent conducting oxide (TCO) materials because hole transport originates from nickel vacancies. Generally, the stoichiometric NiO is an insulator with a high electrical resistivity of 1013 Ω‧cm. However, its conductivity can be enhanced significantly by adjusting certain process parameters and adding monovalent atoms.
In the first part, the conventional magnetron sputtering technique was employed to deposit the NiO thin films onto Corning 1737F glass substrates. The optoelectronic properties of NiO films can be enhanced by doping metal elements such as Ag, Cu and In in the films. The results show that the NiO–Ag composite film with Ag content of 4.2 at.% shows p-type conduction. However, it becomes n-type when the Ag content increases to 9.3 at.%, which results from the Ag atoms segregating at grain boundaries in the presence of excess Ag atoms in NiO films. Furthermore, all NiO–Cu films show p-type conduction when the Cu content increases to above 9.18 at.%. Large amounts of Ni2+ ions in a NiO crystallite are replaced by the Cu+ ions, leading to p-type conduction and the degradation of crystallinity in NiO–Cu composite films that have a higher Cu content. On the other hand, semi-transparent conductive NiO-In films with n-type conduction can be achieved by the addition of indium of more than 15.6 at.%. The thermal stability of NiO films can be improved by adding higher indium content in the films. Finally, it is found that the electrical properties of p-type NiO-Ag films are further improved by Ar ion bombardment in an oxygen atmosphere.
In the second part, the NiO films were deposited onto Corning 1737F glass substrates using high power impulse magnetron sputtering (HIPIMS) in 50 % Ar + 50 % O2 atmospheres with various duty cycles. The XRD patterns show that the NiO films with fine grains and (200) texture are obtained when the films are deposited at lower duty cycles (higher peak power densities). In addition, the ionization rate of Ni atoms in the sputtering process increases upon decreasing the duty cycle, resulting in the formation of more vacancies at Ni2+ sites and an increase of hole concentrations in the NiO films. However, both the carrier mobility and transmittance of the films drop.
Subjects
傳統磁控濺鍍
NiO薄膜
NiO-Ag薄膜
NiO-Cu薄膜
NiO-In薄膜
Ar離子轟擊
新穎高功率脈衝磁控濺鍍
光電性質
Type
thesis
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