The enhancement of electron field emission efficiency due to illumination by low energy photon light has been investigated. Illumination of electron field emitting GaN cathodes with light energy lower than the bandgap caused an increase of the emission current and a change of the slope of emission curves as evidenced by Fowler-Nordheim characteristics. The observed properties suggest a change of the effective emission barrier due to charge carrier excitation. The influence of light modulation on field emission current was also investigated. An increase of emission current was only observed at lower light modulation frequencies. Two slopes were observed in the Fowler-Nordheim curves without illumination, namely a higher slope at lower voltages and a lower slope at higher voltages. Such behavior can be explained by emission from the Γ- and X-valley respectively. Key field-emisision parameters were determined from the Fowler-Nordheim plots and are reported. Another important feature is the relative decrease of the ratio of illuminated to dark current at very high voltages.
