Zinc oxide nanorod based photonic devices: recent progress in growth, light emitting diodesand lasers

Abstract

Zinc oxide (ZnO), with its excellent luminescent properties and the ease of growth of itsnanostructures, holds promise for the development of photonic devices. The recentadvances in growth of ZnO nanorods are discussed. Results from both low temperature andhigh temperature growth approaches are presented. The techniques which are presentedinclude metal–organic chemical vapour deposition (MOCVD), vapour phase epitaxy(VPE), pulse laser deposition (PLD), vapour–liquid–solid (VLS), aqueous chemical growth(ACG) and finally the electrodeposition technique as an example of a selective growthapproach. Results from structural as well as optical properties of a variety of ZnO nanorodsare shown and analysed using different techniques, including high resolution transmissionelectron microscopy (HR-TEM), scanning electron microscopy (SEM), photoluminescence(PL) and cathodoluminescence (CL), for both room temperature and for lowtemperature performance. These results indicate that the grown ZnO nanorods possessreproducible and interesting optical properties. Results on obtaining p-type doping inZnO micro- and nanorods are also demonstrated using PLD. Three independentindications were found for p-type conducting, phosphorus-doped ZnO nanorods: first,acceptor-related CL peaks, second, opposite transfer characteristics of back-gate field effecttransistors using undoped and phosphorus doped wire channels, and finally, rectifyingI–V characteristics of ZnO:P nanowire/ZnO:Ga p–n junctions. Then light emitting diodes(LEDs) based on n-ZnO nanorods combined with different technologies (hybridtechnologies) are suggested and the recent electrical, as well as electro-optical,characteristics of these LEDs are shown and discussed. The hybrid LEDs reviewed anddiscussed here are mainly presented for two groups: those based on n-ZnO nanorods andp-type crystalline substrates, and those based on n-ZnO nanorods and p-type amorphoussubstrates. Promising electroluminescence characteristics aimed at the development ofwhite LEDs are demonstrated. Although some of the presented LEDs show visible emissionfor applied biases in excess of 10 V, optimized structures are expected to provide the sameemission at much lower voltage. Finally, lasing from ZnO nanorods is briefly reviewed.An example of a recent whispering gallery mode (WGM) lasing from ZnO isdemonstrated as a way to enhance the stimulated emission from small size structures.