![]() ![]() This is followed by computational modeling and microscopy. Typically, device degradation and failure mechanisms are inferred from the characterization data obtained from time and stress-controlled tests. 10,12 In general, permanent degradation of AlGaN/GaN HEMTs is a complex function of the reverse bias (with respect to pinch-off), drain bias (with respect to breakdown voltage), as well as the device geometry, and more importantly, the crystallographic quality of the device layers. Since there is little or no current output, thermally activated mechanisms are known to be insignificant. Degradation events are known to be concentrated at the drain-side edge of the gate, 6,11 where the electrical field strength is the highest. ![]() 7 Moderate to large scale mechanical defect formation has been widely reported in the literature 8–10 due to the inverse piezo-electric stress. Both of these effects nucleate defects in the semiconducting and passivation layers. The off-state is associated with large mechanical stress from the inverse piezoelectric effect 6 and high kinetic energy or hot electrons. 2 HEMTs can degrade and fail in both “on” (high temperature and electrical fields 3) and “off” (high electrical field 4,5) states. 1 Their reliability is affected by the very high electrical, thermal, and mechanical fields during operation. Gallium nitride based high electron mobility transistors (GaN HEMTs) are particularly attractive for high-power and high-frequency applications. The “seeing while measuring” approach presented in this study can be useful in pinpointing the dominant failure mechanisms and their fundamental origin. Off-state failure studies in the TEM clearly show the critical role of defects and interfaces that lead to punch-through mechanisms at the drain and even source sides. Through the bright-field, diffraction, and energy dispersive spectroscopy techniques, we show that it is possible to characterize the lattice defects and diffusion of the various elements and thus monitor the microstructural quality during the transistor failure. This is demonstrated by operating electron transparent AlGaN/GaN HEMTs inside a transmission electron microscope (TEM). We propose that real-time visualization of the device microstructure can shift this paradigm. ![]() Thus, it is difficult to predict or identify the dominant mechanism under various test protocols adopted in the literature. Degradation and failure phenomena in high electron mobility transistors (HEMTs) are complex functions of electrical, thermal, and mechanical stresses as well as the quality of the device materials and their interfaces. ![]()
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