Synthesis and electrical properties of aligned ZnO nanocolumns

Highly aligned ZnO nanocolumns were synthesized by catalyst-free metalorganic chemical vapor deposition on various substrates including Al₂O₃ (0001). The alignment of ZnO nanocolumns greatly depends on the substrates used for the growth. In particular, ZnO nanocolumns grown on GaN buffered Al₂O₃ (0001) show an excellent alignment in both the vertical and the horizontal direction. In spite of different sizes and alignments of ZnO nanocolumns depending on the substrates or other processing parameters employed, individual nanocolumns are of defect free single-crystalline nature and of high optical quality. Field effect transistors were fabricated using individual ZnO nanocolumns to characterize their electrical properties as well as to test a potential of their use in nanoscale electronic devices. Our ZnO nanocolumns show a clear n-type gate modulation with a typical electron concentration and a typical electron mobility of ∼3×10¹⁷ cm^-3 and ∼1.1 cm²/V s, respectively.