Prior to the growth of ZnO nanowires, we first deposited a
50-nm thick Ga-doped ZnO thin film onto glass substrates by rf
magnetron sputtering. X-ray diffraction measurement showed
that the sputtered ZnO:Ga film was oriented along the (0 0 2)
direction. Using four-point resistivity measurement, we found
that the sheet resistance of the sputtered ZnO:Ga film was around
200 /sq. We then used standard photolithography to partially
etch away the ZnO:Ga film and define the comb-like pattern.
During wet etching, the template was dipped in 2% HCl for
3 min to remove the exposed ZnO:Ga. As shown in Fig. 1,
we designed our etching mask so that fingers of the comb-like