Results and discussion Figure 1 represents the morphological study of both the ZnO nanorods and the nanotubes. The SEM image in Figure 1a has shown the uniform and well-aligned growth of nanorods. Also, almost all the nanorods are chemically etched as shown in Figure 1b. The X-ray Cilengitide ic50 diffraction study has shown good selleck inhibitor crystal quality with preferred c-axis orientation of the as-grown ZnO nanostructures. It can be seen that (002) crystal plane of ZnO seems more intense due to the similar X-ray diffraction pattern of GaN at (002) crystal plane as shown in Figure 1c. Figure 1 SEM images and XRD pattern of ZnO. (a,b) SEM images of as-grown ZnO nanorods and nanotubes on GaN. (c) XRD pattern of ZnO grown on GaN substrate.

The schematic diagram of the fabricated light-emitting diode based on the n-type ZnO/NiO/p-type GaN heterojunction is shown in Figure 2a. Figure 2b shows

the I-V measurement of heterojunction diodes based on ZnO nanorods in the absence and presence of the NiO buffer layer. The I-V behaviour shown by both diodes is highly nonlinear and rectifying. It is also observed that GSK1120212 solubility dmso the presence of the NiO buffer layer decreased the leakage current and showed higher series resistance compared to the device based on only n-ZnO/p-GaN heterojunction. Using the Au/Ni on p-type GaN and Al on n-type ZnO contacts has demonstrated acceptable Ohmic response, and it has also indicated that the rectifying response is solely coming from the n-type ZnO and p-type GaN heterojunction. With the help of Anderson’s model, energy band diagram for the proposed devices is described using the band gap FER and the electron affinities of semiconducting materials. The band gaps of ZnO, NiO and GaN which have been taken from the reported work are 3.37, 3.86 [24] and 3.4 eV, respectively,

while the electron affinities for ZnO, NiO and GaN are 4.35 [25], 1.46 [26] and 4.2 eV [27], respectively. Energy barrier for holes and electrons at the interfaces of the ZnO/NiO and the NiO/GaN are found to be 2.89 and 2.28 eV, respectively; the calculated values of electron and hole barriers for the n-ZnO/p-GaN are 0.15 and 0.12 eV, respectively as shown in Figure 2c,d. The difference of the energy band offsets in the presence of the NiO buffer layer is slightly higher than that without the NiO buffer layer. This indicates that the presence of the NiO buffer layer might block the transport of electrons from the ZnO to the GaN and also work as the hole injection source in the device. Also, the emission is more probably coming from the ZnO. Figure 2 Schematic diagram, I-V characteristic curves of proposed devices and band diagrams of p-n junctions. (a) Schematic diagram of fabricated LED. (b) I-V characteristic curves of proposed devices based on ZnO nanorods with and without buffer layer of NiO. (c,d) Band diagrams of ZnO/GaN and ZnO/NiO/GaN p-n junctions, respectively.