Abstract
Semiconductor nanostructure heterojunctions are expected to be efficient structures for next-generation photovoltaic solar cells, radiation detectors, and light-emitting diodes. In this letter we report heterojunctions made of vertically aligned ZnO/ZnTe nanocones synthesized using a combination of thermal vapor deposition and pulsed-laser deposition (PLD). The ZnO nanocones and nanorods were synthesized as cores by utilizing the growth rate difference between central and boundary sites of precursor domains during thermal vapor deposition. The p-n heterojunctions were subsequently formed by growing ZnTe as shells on the nanocone surface using PLD. The ZnTe shells were polycrystalline structures, while ZnO cores were wurzite structures. The p-n junction of the nanocone core-shell structure exhibited I-V characteristics consistent with a p-n diode, but the nanorod junction did not. These structural and electric characteristics indicate that the ZnO nanocones are more feasible than ZnO nanorods as heterojunctions because the sloping facets of the nanocones facilitate deposition of ZnTe by PLD without the deleterious effects of shadowing. Furthermore, based on theoretical modeling of nanostructure heterojunctions, the nanocone-based junction exhibits an electrostatic potential profile that is much more effective for carrier transport than the electrostatic potential for the nanorod-based junction.
