E-Beam Induced ZnO Quantum Dots Growth And Hole Carriers Modification

ZnO has direct wide bandgap and is widely used in optoelectronic applications due to its near-ultraviolet emission and transparent properties. The bandgap and light-emitting property of nanoscale ZnO are dependent on its size, shape and microstructure as a result of quantum confinement effects. In this paper, we in-situ grow ZnO quantum dots (QDs) controllably by using environmental transmission electron microscope (E-TEM). The QDs growth condition and the growth mechanism are investigated. In addition, we control the intrinsic defects of ZnO QDs and make QDs dominated by hole carriers.We first study the ZnO QDs growth in transmission electron microscope (TEM). We demonstrate 300-keV electron beam irradiation assisted growth of ZnO QDs on the (1010) side facets of wurtzite ZnO nanorods (NRs). The ZnO NRs, which acts as substrate, has a diameter of～40nm, while the as-grown ZnO QDs have a dimension of～5 nm. The QDs are terminated with (1010), (0001) and (0001) three low energy facets. The growth of ZnO QDs can be accelerated with high e-beam flux dose and high oxygen partial pressure.Electron energy loss spectrum (EELS) indicates that atomic percentage of oxygen is 55% in ZnO QDs and the QDs are dominated by hole carriers. According to the calculation of intrinsic defect energies, the extra oxygen in QDs prefers to reside in an interstitial site. Electron holography gives the potential difference between QDs and NR of～0.47 V. In-situ current-voltage curve demonstrates the rectifying behavior of a single QD-NR homojunction. The in-situ opto-electrical experiment shows an obvious visible light response, exhibiting its potential to fabricate nanoscale optoelectronic devices.