Development of Pulsed-Envelope Techniques Tailored to On-Wafer RF GaN HEMTs

Modern communication systems are driving the demand for advanced semiconductor technologies. Gallium Nitride (GaN) High-Electron-Mobility Transistors (HEMTs) have become a key technology in the design of high-efficiency microwave power amplifiers, where optimizing power efficiency while preserving linearity over a broad bandwidth is critical. However, these devices are susceptible to various dynamic effects that can degrade performance, particularly in wideband modulated signal applications. The major contributing factor to these performance limitations is charge trapping, which arises at semiconductor level from lattice mismatches during the epitaxial growth process. This phenomenon involves the capture and release of mobile charge carriers, influenced by factors such as voltage and temperature variations. Traditional methods for characterizing trapping effects primarily rely on low frequency techniques, such as current deep-level transient spectroscopy (I-DLTS), continuous-wave (CW) measurements, and pulsed current-voltage characterization. Although these techniques provide valuable insights, dynamic characterization directly at microwave frequencies allows for a more realistic evaluation of device behavior and the development of more accurate compact models. This thesis explores a recently proposed double-pulsed radio-frequency (RF) measurement technique for characterizing the dynamic behavior of GaN HEMTs. By systematically varying the prepulse duration (which induces the trapping state) and the interval between the prepulse and the measurement pulse (associated with the release time constant), a comprehensive evaluation of charge trapping dynamics is conducted. Finally, the extracted time constants provide valuable information for the development of advanced compact models, enhancing the predictive accuracy of GaN HEMT performance under practical operating conditions.