Physico-Chemical nanomaterials science

Effect of stirring time on the light-emitting properties of ZnO nanorods/p-GaN LEDs
B. Tsykaniuk1, A. Nikolenko1, V. Strelchuk1, M. Vuychik1, B. Sadovyi2, Omer Nur3, Hatim Alnoor3 and Magnus Willander3
1 V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, 41 Prospect Nauky, 03028 Kyiv, Ukraine
E-mail: btsykaniuk@gmail.com
2 Department of Physics, Ivan Franko National University of Lviv, Dragomanova 50, Lviv 79005, Ukraine.
3 Department of Science and Technology, Linköping University, 60174 Norrköping, Sweden.

Zinc oxide with its excellent luminescent properties and the ease of growth of nanostructures holds promise for the development of photonic devices. Among the diﬀerent synthesis methods used for ZnO nanostructures, the low-temperature aqueous chemical synthesis (LT-ACS) is promising due to many advantages. One of the important parameters in this method is stirring of precursor solutions in preparation steps as required for the enhancing the chemical homogeneity.
N-type ZnO nanorods (NRs) were grown by the LT-ACS on commercial p-type GaN substrates. The time of stirring the precursors was 3, 5 and 15 hours. The electrical ohmic contacts (Ni/Au to n-GaN and Ag to p-ZnO) were deposited and wired to form LED structures. The I-V and C-V characteristics of the LEDs were analyzed. The electroluminescence (EL) measurements were performed using a stabilized voltage source to power the LED devices and the emission spectra were collected using a confocal JobinYvon T64000 triple spectrometer.
The EL at forward bias is dominated by the blue emission centered at 400 nm, which is due to the transition from the conduction band or shallow donors in n-ZnO to Mg-acceptor level in p-GaN. Application of the reverse bias led to domination of the wide emission band, that can be decomposed into four sub-bands: green emission at 570 nm attributed to oxygen and zinc vacancies (VO, VZn); yellow band at 590 nm caused by presence of OH groups and oxygen interstitials (Oi); orange-red emission at 627-648 nm and red emission at 732-747 nm attributed to the oxygen interstitials (Oi) present on the surface of the NRs. Increase of stirring time from 5 to 15 hours leads to decrease of the EL intensity because of the decreased number of defects on the surfaces of ZnO NRs.