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| Home > Publications database > Fermi level pinning at nitride semiconductor surfaces and interfaces |
| Conference Presentation (Invited) | FZJ-2025-03137 |
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2025
Abstract: Fermi level pinning plays a crucial role in nitride semiconductor growth, contact formation, and the engineering of insulating layers. While pinning effects and carrier accumulation have been widely studied at nitride surfaces, their impact on interfaces remains equally significant. In this presentation, we explore Fermi level pinning at non-polar (10-10) surfaces and interfaces using scanning tunneling spectroscopy, off-axis electron holography (EH) in TEM, and complementary DFT calculations.First we discuss the interplay of intrinsic surface states, defects, and air exposure on the Fermi level pinning at non-polar GaN, AlInN, AlGaN, and InN surfaces as well as the origin of electron accumulation. The empty group III-derived dangling bond is found to govern Fermi level pinning on most n-type group III nitrides, but not for InN, where defects dominate. Likewise for p-type doping defects govern the Fermi level pinning, too. Air exposure is found to shift pinning levels toward the band edges, attributed to water adsorption and dissociation, passivating intrinsic and extrinsic gap states. The results demonstrate that for all group III nitride semiconductors, including InN electron accumulation is not intrinsic, but rather extrinsically induced by adlayers. Furthermore, we demonstrate the quantification of Fermi level pinning by EH in TEM using the example of focussed ion beam (FIB) implanted carbon. FIB preparation induces a Fermi level pinning about 0.7 eV above the valence band edge, attributed to C on N sites. Annealing experiments allow to probe the defect dynamics and barriers. Notably, it is demonstrated that carbon undergoes an atomic site-switching process, transitioning from a substitutional to an interstitial site where it becomes electrically inactive upon annealing. These findings provide a profound foundation for understanding the stability of insulating layers in ternary nitrides and offer critical insights for optimizing nitride-based electronic and insulating structures.
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