Solution-processed n-ZnO nanorod/p-Co3O4 nanoplate heterojunction light-emitting diode

Abstract A heterojunction light-emitting diode (LED) based on p-type cobalt oxide (Co 3 O 4 ) nanoplates (NPs)/n-type zinc oxide (ZnO) nanorods (NRs) is demonstrated. Using a low-temperature aqueous solution process, the n-type ZnO NRs were epitaxially grown on Co 3 O 4 NPs which were two-dimensionally assembled by a modified Langmuir-Blodgett process. The heterojunction LEDs exhibited a typical rectifying behavior with a turn-on voltage of about 2 V and emitted not only reddish-orange light at 610 nm but also violet light at about 400 nm. From the comparative analyses of electroluminescence and photoluminescence, it was determined that the reddish-orange light emission was related to the electronic transitions from zinc interstitials (Zn i ) to oxygen interstitials (O i ) or conduction-band minimum (CBM) to oxygen vacancies (V O ), and the violet light emission was attribute to the transition from CBM to valence-band maximum (VBM) or Zn i to zinc vacancies (V Zn ).