Electrical and optical properties of ZnO:Al films with different hydrogen contents in sputtering gas

Aluminum-doped zinc oxide (ZnO:Al) films were deposited by direct current magnetron sputtering in incorporating hydrogen in sputtering gas at room temperature. The influences of hydrogen content in sputtering gas on the structural, optical, and electrical properties of ZnO:Al films were systematically investigated. It is found that hydrogen incorporated into ZnO lattice forms shallow donors in ZnO:Al films and plays an important role in the properties of ZnO:Al films. The electrical conductivity and infrared (IR) reflectance are improved due to the increase of electron carrier concentration, and the average transmittance decreases, which is ascribed to the strong scattering from the hydrogen incorporated and oxygen vacancies in ZnO:Al films. In this study, the resistivity of 5.5 x 10(-4) Omega center dot cm is obtained, the average transmittance of the wavelength in the range of 400-900 nm is almost 86 %, and the IR reflectance reaches 75 % at 2,500 nm, which is higher than that of reported TCO films. The band gap determined by optical absorption is a result of competition between Burstein-Moss effect and many-body perturbation effect. However, the hydrogen content in sputtering gas is above 10 %, and the optical band gap shift is independent of hydrogen content in sputtering gas.