Microwave effects of UV light exposure of a GaN HEMT: Measurements and model extraction

This paper presents an experimental investigation on the microwave performance of a GaN HEMT subject to UV light exposure. The device, having 0.25 μm gate length and 100 μm gate width, has been characterized by measuring its DC performance, linear scattering parameters, noise parameters in the 2-26 GHz frequency range, either in dark condition and under CW light exposure at 375 nm. Clear variations of the GaN HEMT performance related to the charge generation and the relevant threshold voltage shift within the semiconductor layers are recognizable in the reported results. The scattering parameters and the noise parameters are affected in a similar way as it occurs in GaAs HEMT's under optical irradiation in the visible range. A circuit model extraction has then been performed to analyze more deeply the effects of the UV exposure. The observed changes of the noise parameters might be ascribed to the effects of the increased gate conduction under illumination and have been efficiently modeled by an additional resistor between the internal gate and source terminals with an assigned noise temperature of 3053 °C.