Development of Zinc Nitride Materials for Semiconductor Applications

Zinc Nitride has recently attracted research interest as a candidate for use in earth-abundant semiconductor devices. However, zinc nitride is in a group of semiconductor materials that have not been studied extensively in past literature. As a result, this study is focused on the fundamental properties of zinc nitride from a materials science point of view, with an emphasis on properties relevant to semiconductor applications. The samples presented throughout this work were deposited by means of Reactive Sputtering and Molecular Beam Epitaxy. Samples with a wide range of material quality were obtained between these two techniques. The samples examined were polycrystalline in structure and highly doped due to intrinsic defects. The absorption onset for zinc nitride samples varied in the range of 1.15-1.50 eV. Photoluminescence measurements on optimised samples further indicated that the bandgap of the films was in the energy region of 1.40 eV. Variations in the measured optical bandgap were attributed to the Burstein-Moss effect for highly doped samples. A parabolic approximation of the conduction band suggested an intrinsic bandgap of ~ 1.10 eV. Furthermore, tuning of the optical properties of zinc nitride was demonstrated in the form of a II-III-V AlZnN alloy. By increasing the Al content in the ternary films, an increase of the bandgap of AlZnN up to 2.76 eV was demonstrated. Finally, a method for improving the ambient stability of zinc nitride thin films is discussed. It was found that ex-situ thermal annealing improved the stability of the zinc nitride films dramatically. The mechanism suggested to explain these observations is an improvement in the structural quality of the native oxide caused by the annealing process. The improvement in stability was gradual for annealing temperatures up to 400 °C examined here. This is a promising method as it improves the stability of zinc nitride layers significantly by utilising the native oxide and does not require the growth of any capping layers.