Ultraviolet electroluminescence of LED devices based on n-ZnO nanorods grown by various methods and p-GaN films

Abstract

Light emitting diodes (LEDs) structures based on p-GaN lm/n-ZnO nanorods quasiarray heterojunction were fabricated. ZnO nanostructures were grown on the p-type GaN templates using two dierent methods. The turn-on voltages of ZnO/GaN heterojunctions based on ZnO nanorods grown using the gas-transport reaction and hydrothermal methods were equal to 3.2 V and 6.5 V, respectively. The diode-ideality factors were estimated to be of around 45 and 36 for the samples with ZnO nanorods grown using the method of the gas-transport reaction and the hydrothermal method, respectively. The large values of the ideality factors can be explained by a high density of trap states and quality of the contacts with the p − n junctions. The electroluminescence (EL) spectra of LEDs with ZnO nanorods grown by the gas-transport reaction and hydrothermal methods were approximated by four and three Gaussians, respectively. On the basis of the X-ray diraction (XRD), electrical and optical studies data, one can conclude that the emission peaks at 389391, 410412, 436438 and 502 nm correspond to the near-band-edge (NBE) recombination in ZnO, interface carriers recombination in ZnO/GaN junction, the electrons transition from GaN conduction band to Mg 2+ doping level, and to the emission from the defect levels in ZnO, respectively. The LED based on ZnO nanorods synthesized using the hydrothermal method emitted a more pure ultraviolet (UV) light.

Photovoltaic Cell Based on n-ZnO Microrods and p-GaN Film

“…ZnO hexagonal microrods (Fig. 1) were grown by the method of gas-transport reactions on a p-GaN epitaxial film [7]. For seed-supported growth of ZnO nanorods, nanocrystalline ZnO seed particles were prepared in a solution of 0.005 mol/l zinc acetate [Zn(CH 3 CO 2 ) 2 ] dissolved in ethanol at 90 • C for 15 min.…”

“…The contacts on the p-GaN template were deposited using thermal evaporation of Ni (30 nm) followed by Au (35 nm) [6,7]. A quartz-crystal microbalance was used as a thin film deposition monitor.…”

“…The In contact was deposited through the shadow mask. The liquid photo-positive resist "Cramolin Positiv Resist" was used as a photoresist-insulator [7,13]. A schematic image of the photovoltaic cell is shown in Fig.…”

“…ZnO/GaN heterostructure-based light-emitting devices, photodetectors and lasers have already been demonstrated [3,6,7], but there are few reports on the photovoltaic cells based on such structures [3,8]. The reported photovoltaic cells [3,8] were made on the basis of p-GaN epitaxial films and ZnO films grown by the molecular beam epitaxy [3] or obtained by the radio-frequency magnetron sputtering [8].…”

“…Owing to the fundamental principles of thermodynamics, in particular the detailed balance between light absorption and emission, the performance of the photovoltaic cells and electroluminescent diodes is linked by reciprocity relations [10,11]. Recently, we created LED devices based on n-ZnO nanostructures deposited on p-GaN films with a photopositive resist as an insulator that emits light in the near-UV spectral region [7]. The corresponding technology possesses some advantages, such as ease of manufacture and does not require expensive instrumentation.…”