Characterization of traps in AlGaN/GaN HEMTs with a combined large signal network analyzer/deep level optical spectrometer system

A study of the effects of traps on the RF characteristics of AlGaN/GaN HEMTs is conducted using small and large-signal microwave measurements with deep-level optical spectroscopy. Different variations of the drain current swing are observed for illuminations of different photon energies. The time evolution of the current swing in transient measurements enabled to determine the optical transient time-constant and the equilibrium relaxation time-constant. The dependence of the S-parameters upon the illumination yielded results consistent with the variation of the drain current swing under illumination. A variation in the small signal transconductance and drain conductance was extracted at 2 GHz which presumably arises from the variation of the drain resistance under illumination. In addition, it was verified that the SiN passivation greatly helps in mitigating the RF performance degradation arising from deep trapping centers.