ZnO Nanowire Array-Based Optoelectronic Devices

ZnO nanowire array-based optoelectronic devices are discussed in this dissertation. ZnO has a wide band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature, which make it a promising candidate for optoelectronic devices such as blue-light emitting diodes, ultraviolet laser diodes and photodiodes. Recently, there have been tremendous interests in ZnO nanowire arrays. It is well known that one of the biggest challenges toward good ZnO-based optoelectronic devices is the difficulty of reliably fabricating p-type ZnO due to the self-compensating effect from native defects(for example, oxygen vacancy Vo and zinc interstitial Zni) and/or H incorporation. There has already been a great deal of efforts on the fabrication of p-type ZnO films by doping group I (Na, Ag) and group V elements (N, P, As, Sb) as p-type dopants. In contrast, there have been only a few reports on p-type ZnO nanowires (doped with N, P and Na). Recently, researchers are interested in developing optoelectronic devices based on ZnO nanowires such as biosensors, ultraviolet detectors, ultraviolet light emitting diodes and electrically driven nanowire lasers. The growth of p-type ZnO nanowires with good stability will be an essential step for the applications of nanowires in nanoelectronics and optoelectronics. In this dissertation, firstC n-type ZnO nanowire array and its application have been discussed. ZnO has very high electronic carrier mobility and electron affinity, making it a very possible candidate as an effective dye-sensitized solar cell (DSSC) semiconductor. The great properties of vertically aligned ZnO-nanowire array, such as large surface area and fast electron-transport rate, make it a very promising option for the photoanode of DSSCs. Nanowires provide electrons injected from optically excited dye a direct effective path to collecting electrode via the semiconductor conduction band, offering the potential for much faster charge transport than nanoparticle cells. In order to make homojunctional devices based on ZnO nanowire, a great deal of efforts has been made on the growth of p-type ZnO nanowire. Ag, a group Ib element, was predicted to be an acceptor in ZnO when incorporated into substitutional Zn sites and researchers experimentally demonstrated reliable fabrication of p-type ZnO thin films doped with Ag on sapphire substrate and also demonstrated the possibility of achieving Ag-doped p-type ZnO nanowires. Also Sb as an effective dopant for reproducible p-type ZnO thin films has been shown in our group. In chapter 3 of this dissertation, the synthesis and characterization of single-crystalline Ag-doped p-type ZnO nanowires and also Sb-doped p-type ZnO nanowire arrays have been discussed. In chapter 4 of this dissertation, ZnO homojunction photodiodes based on Sb-doped p-type nanowire array have been discussed. In chapter 5 of this dissertation, LED devices based on Sb-doped p-type nanowire array have been discussed. In chapter 6 of this dissertation, electrically pumped ZnO nanowire-waveguided lasing based on Sb-doped p-type nanowire array has been discussed. In chapter 7, the gain calculation for ZnO has been made and a brief discussion about the comparison between the calculation results and the experimental results has also been made. In chapter 8, Lists of conclusions are made for this dissertation