Al doping in ZnO nanowires enhances ultraviolet emission and suppresses broad defect emission

The effect of Al doping on the nature of ultraviolet (UV) near band edge emission and broadband "green" visible emission from deep defects in ZnO nanowires is explored by temperature- and excitation intensity-dependent photoluminescence (PL) spectroscopy. Unlike comparably fabricated undoped ZnO nanowires, whose PL spectra is dominated by green emission from oxygen vacancies and whose UV emission broadens and redshifts with increasing excitation intensity, Al-doped ZnO nanowires grown by chemical vapor deposition are smaller and have PL spectra dominated by UV emission that neither broadens nor redshifts significantly with increasing excitation intensity. The excitation intensity-dependent manner in which Al doping enhances UV emission at the expense of green emission indicates that the doping process creates many new donor sites that prevent excitons localized there from activating these green emitting defects.