ZnO-based Films And Devices On Si

ZnO possesses a 3.37 eV direct bandgap and a considerably high exciton binding energy of 60 meV at temperature, thus being a promising material for ultraviolet (UV) electroluminescence (EL) devices. When ZnO is alloyed with CdO to be Cd_xZnO_1-xO, its bandgap energy can be as low as～1.8 eV. Therefore, Cd_xZnO_1-xO alloys are expected to be employed in the visible EL devices. In this thesis, EL devices based on ZnO-containing films have been fabricated on silicon substrates, being addressed with their EL performances. Moreover, Cd_xZnO_1-xO films have been prepared by reactive magnetron sputtering. The evolution of their photoluminescence (PL) with the subsequent anneals has been investigated. The primary results in this thesis are listed in the following.The Zn₂SiO₄ films containing ZnO grains (Zn₂SiO₄:ZnO films) were prepared on heavily boron-doped silicon (p⁺-Si) substrates by sol-gel method, thus forming Si-based Zn₂SiO₄:ZnO film light-emitting devices. Such devices exhibit well-defined rectifying characteristics. Under forward bias, the devices generate EL related to the defects in ZnO and, moreover, the EL intensity increases with the forward bias voltage. While, the devices do not exhibit EL under reverse bias. Based on the energy band structure of the devices, we have tentatively explained the mechanisms of the aforementioned electrical transportation and EL.Highly c-axis oriented Cd_xZnO_1-xO films have been prepared by reactive magnetron sputtering. Based on the investigation on the effect of heat treatments on the crystallinity and PL of the films, it has been shown that: (a) After the conventional furnace annealing at 500-800℃, the Cd contents in the films are notably decreased. To be worse, quite a few of voids are formed in the films due to the volatilization of Cd. In the meantime, phase segregation occurs in the films and the PL peaks change notably with the evolution of phases in the films. (b) After the rapid thermal annealing (RTA) at 500-700℃in N₂ ambient, the PL intensities of the films increase significantly. With the increase of RTA temperature, for the low-Cd-content films, they are of single hexagonal phase and the near-band-edge (NBE) emission peak is somewhat blue-shifted. While, for the high-Cd-content films, there are two NBE peaks related to Cd-containing ZnO and Zn-containing CdO respectively in their PL spectra. Moreover, the two NBE peaks are blue-shifted with the increase of RTA temperature.