Temperature dependent near-band-edge photoluminescence of catalyst-free ZnO thin nanowires epitaxially grown on a-plane sapphire

Catalyst-free ZnO thin nanowires were epitaxially grown on a-plane sapphire using a seed layer. X-ray diffraction and temperature dependent temperature photoluminescence (PL) measurements confirm the desired epitaxial relationship and very high crystalline and optical quality. The luminescent peak at 3.37737 eV was assigned to be free exciton luminescence by temperature dependent PL, Vashni model fitted well of the peak shift of the free exciton while from 60 K to 150 K Vina model fitted better. Through the donor-accepter pair peak at 3.29 eV, the net donor carrier concentration was calculated to be 1.8×10¹⁸ cm^-3, which fairly comparable to other electrical measurement.