Experimental and theoretical investigation of geometric and compositional factors in improving the off-state breakdown voltage, reliability, and enhancement-mode operation among GaN channel hetero-structure field effect transistors

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More than two decades of research on polar III-Nitride hetero-structure field effect transistors (HFETs) has resulted in rapidly growing markets in the areas of high-frequency power-amplifiers/RF-switches and high-temperature/high-voltage power electronic switches. As the market-share is passing the billion-dollar mark, innovative solutions in-tune with the particulars of these polar hetero-structures for improving their power-handling/heat-management, and for reliable realization of both enhancement- and depletion-modes of operation (i.e. having positive and negative threshold-voltage, respectively) are gaining a more prominent status. With the improvement in techniques of hetero-epitaxy and availability of reliable sources providing the less explored AlInGaN/GaN hetero-structures, taking advantage of lattice-matching to the GaN channel and examining the less-explored compositional and geometric structures towards improving the long-term reliability, enhancing the possibility of achieving stable enhancement-mode operation, and extending the breakdown voltage are all very timely. Combing the now-proven possibilities of shifting the threshold-voltage towards enhancement-mode operation and reducing the self-heating (both realized through modifying the mesa structure of the isolation-feature), with the offered opportunity to tailor the drain-induced electric-field due to the proximity of Fermi-level pinned sidewall facets is expected to not only offer ways to achieve reliable enhancement-mode III-Nitride HFETs, but also to boost their off-state breakdown voltage. While traditionally off-state breakdown voltage is boosted by employing the so-called field-plates (i.e. extensions to the gate electrode and hence capacitance), tailoring the electric-field via the presence of pinned side-wall facets in the close proximity of the channel can partially lift the burden on the frequency response for a higher breakdown voltage. With the help of the previous Discovery grants, PI's team has proudly managed to develop an e-beam lithography process poised for successfully performing the experimental tasks identified in the current proposal. Along with the contributions of the PI to understanding of the aforementioned phenomena, a few other groups are also currently involved in lively technological endeavors in this area. Under the support of the present Discovery grant application, PI intends to continue his groundbreaking work on exploring the aforementioned alternatives for improving the off-state breakdown voltage, long-term reliability, and frequency response among enhancement mode GaN-channel HFETs. The ideas presented in this proposal have the possibility of generating patentable concepts and in the long-term establishing future joint ventures with automobile and telecommunication industries. The latter of which is presently poised to take advantage of III-Nitride HFETs in 5G networks and developing internet of things (IOT) applications.