Trapping Effects in Aluminum Gallium Nitride/Gallium Nitride HEMTs for High Frequency Applications : Modeling and Characterization Using Large Signal Network Analyzer and Deep Level Optical Spectroscopy

Any defect site existing in the AlGaN/GaN HEMTs can be electrically active during device operation. The activated defect site not only could lead to a degradation in the output characteristics but may introduce additional nonlinearity which seriously downgrades the values of devices for various applications. This motivates us to study the detailed path experimentally and theoretically how an electrically-activated defect site could impact the device performances during practical device operation. In this study, the goal is (1) to give device engineers ideas on how further improvements can be devised to strengthen the existing GaN technology and (2) to provide circuit designers with better understanding on how to use GaN devices more efficiently for the development of reliable commercial GaN products for higher power applications in wireless systems.;Single tone characterization results of AlGaN/GaN HEMTs for Class A operation are presented and compared. A new combined large signal network analyzer / deep level optical spectroscopy system is utilized to study the impact of illumination on the CW large-signal load line and small-signal S-parameters variations to identify the possible energy level of the trapping center responsible for the degradation of the device performance.;A new pulsed-IV pulsed-RF "coldFET" technique is introduced to extract parasitic elements existing in the access regions of AlGaN/GaN HEMTs. The observation of bias-dependence is detailed and a simple semi-physical model is proposed which provides a satisfactory description of experimental results.;The low-frequency noise, an important figure of merit in terms of reliability, is briefly-reviewed. Additive phase noise measurements are presented and the effects of illumination and load impedance are examined. A physical expression is derived and simulated which successfully establishes a relationship between the access resistance and the low-frequency noise and provides a qualitative description of the measurement results.