Impact of mechanical stress on AlGaN/GaN HEMT performance: Channel resistance and gate current

AlGaN/GaN high electron mobility transistors (HEMTs) stand out with superb advantages for high-power, high-temperature, high-frequency applications. Internal stress is inherent to state-of-the-art AlGaN/GaN HEMTs and has the potential to impact performance and reliability. Strain is an integral part of modern semiconductor technology and has been used to extend scaling of Si for nearly a decade, and the performance and reliability implications are well understood. Understanding the impact of mechanical stress on AlGaN/GaN HEMT channel resistance and gate current is crucial for continued improvements in device performance and reliability.;Repeatable gauge factors of an AlGaN/GaN HEMT device were obtained after eliminating parasitic charge trapping effects. Over four orders of magnitude of variation in gauge factors are reported in literature. Charge traps are likely responsible for the huge discrepancy. By employing continuous sub-bandgap optical excitation, the effect of non-repeatable charge trapping transients was effectively minimized, allowing the gauge factor to be accurately measured. The measured gauge factor is compared to a simulated gauge factor, calculated from stress-induced changes in the 2DEG sheet carrier density and mobility.;Stress-altered gate leakage currents in AlGaN/GaN HEMTs are measured as a function of constant applied reverse gate bias. Increasing reverse gate bias decreases the stress sensitivity of the gate leakage current. Poole-Frenkel emission dominates the gate leakage current for gate biases above threshold. Stress changes Poole-Frenkel emission by altering the trap activation energy, which also changes the compensation parameter. Reverse tunneling current which balances the forward Poole-Frenkel current at equilibrium is modeled to explain the experimental results. Tensile (compressive) stress decreases (increases) the trap activation energy, increasing (decreasing) the gate leakage current. Although below threshold, the electric field in the AlGaN barrier saturates in the middle of the gate, the electric field increases at the gate edges because of two-dimensional effects. For larger reverse gate bias much below threshold, the thickness of the AlGaN tunneling barrier decreases which causes Fowler- Nordheim tunneling at the gate edges to dominate the current transport. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html )...