Finite size effect in ZnO nanowires

Abstract

In this talk, we present electrical and optical measurements on ZnO nanowires whose sizes do not yet reach quantum confinement region. Thin ZnO nanowires were synthesized via carbon thermal chemical vapor deposition method under low growth temperature using tin as catalyst. Electron microscopy reveals that the as-grown nanowires are of high crystalline quality with an average diameter around 12 nm. Electrical transport measurements show significant increase in conductivity with a lack of gate modulation and a reduction in mobility. This phenomenon is attributed to the enrichment of surface states owing to the larger surface-to-volume ratio. This enhanced surface effect in thinner nanowires is confirmed by the temperature dependent photoluminescence measurements. In addition, the photoluminescence spectra clarify the apparent blue shift observed at room temperature with respect to the nanowires with larger diameters. These results provide a fundamental insight into nanowires of smaller diameters, and show that their surface states are extremely important and should be properly tailored or controlled for future device applications.

Exciton-related electroluminescence from ZnO nanowire light-emitting diodes

“…15 These ZnO nanowires have been shown to exhibit carrier densities of about N =10 17 cm −3 at room temperature and distinct bound exciton-related photoluminescence ͑PL͒ emission lines at liquid-helium temperatures. 16,17 Despite this, the evidence of excitonic recombination in electroluminescent ZnO devices has been indirect, and inferred from a peak emission energy smaller than what one would expect for band-to-band recombination. 12,[18][19][20][21] The main drawback of the ZnO material system is the lack of reproducible, stable, high-quality p-type doping with a reasonable concentration, which is required for most optoelectronic applications.…”

Enhancement of the photoelectrochemical properties of Cl-doped ZnO nanowires by tuning their coaxial doping profile

“…16 Such correlation pointed towards an important role of the surface in the associated radiative recombination processes. 14,[16][17][18][19] Again, there is no agreement on the origin of such a surface enhancement of the visible band in NWs. It could be related with a higher surface density of the contributing states, their surface activation by the hole accumulation at the surface depletion, or the promotion of slower recombination processes related with the charge separation occurring in the built-in electric field layer.…”

Investigation of growth parameter influence on hydrothermally grown ZnO nanowires using a research grade microwave

“…ZnO nanowires grown in this fashion possess a highly crystalline structure and can have a high aspect ratio [4,13,15], but THE high temperatures required for this growth process pose problems for thermally-restricted fabrication processes. Hydrothermal growth methods allow for low-temperature synthesis of ZnO nanowires (NWs) directly on a variety of novel substrates required for proposed flexible substrate applications such as power-harvesting fabrics [11,16].…”

“…Popular methods for growing ZnO nanowires include vapor-solid or vapor-liquidsolid (gas-phase synthesis) [2,4,9,13], and hydrothermal (solution-phase synthesis) [1,3,5,7,8,[10][11][12]14,16] 13,15,16]. ZnO nanowires grown in this fashion possess a highly crystalline structure and can have a high aspect ratio [4,13,15], but THE high temperatures required for this growth process pose problems for thermally-restricted fabrication processes.…”

“…Nanowires made out of ZnO are of particular interest due to the unique properties of ZnO such as a wide direct bandgap, a large exciton binding energy, piezoelectric properties, and chemical sensitivity. Potential applications for ZnO nanowires include optoelectronics such as photodetectors [1][2][3][4][5][6][7][8][9], piezoelectric actuators and generators [2,6,[10][11][12], UV nanolasers [3,4,6,8,12], field effect transistors [1,3,5,9,12,13], solar cell components [3,5,9,11,12,14], gas sensors [3,5,7,15], and organic filters [16].…”