Performance-Limiting Traps in GaN-Based HEMTs: From Native Defects to Common Impurities
This chapter describes the properties of the performance-limiting defects in GaN-based transistors. The first part of the chapter summarizes the properties of the most common defects in GaN, by describing a database of defects that has been prepared by ou
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Performance-Limiting Traps in GaN-Based HEMTs: From Native Defects to Common Impurities Isabella Rossetto, Davide Bisi, Carlo de Santi, Antonio Stocco, Gaudenzio Meneghesso, Enrico Zanoni and Matteo Meneghini
A significant effort has been recently spent with the aim of investigating the properties of the defects that limit the dynamic performance of GaN-based power transistors and of correlating the results obtained through the different deep-level characterization techniques with the microscopic origin of the defect. A correct identification is important, since it provides useful information about the improve‐ ments needed in the growth process that could enhance the performance of the devices. Several experimental and theoretical issues make the comparison between different papers difficult. The results of deep-level investigation can be significantly dependent on the technique used for the analysis, mainly due to the specific physical quantities and the procedures used for the excitation of the deep level and for the detection of the trap-sensitive parameter. Moreover, the electric field at the trap location plays an important role, since it may lead to an underestimation of the acti‐ vation energy (Ea) through the emission barrier lowering caused by the Poole– Frenkel effect. The presence of a capture barrier implies a further problem, related to the different level of trap filling during temperature- or field-dependent measure‐ ments. For this reason, in the following, we will group together reports that may reasonably refer to the same deep level. If we take into account all the possible growth techniques and used materials, the list of possible defect types may be ascribed to the following categories:
I. Rossetto · D. Bisi · C. de Santi · A. Stocco (✉) · G. Meneghesso E. Zanoni · M. Meneghini Department of Information Engineering, University of Padova, Padua, Italy e-mail: [email protected] © Springer International Publishing Switzerland 2017 M. Meneghini et al. (eds.), Power GaN Devices, Power Electronics and Power Systems, DOI 10.1007/978-3-319-43199-4_9
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• Native defects: These are the defects that may be present in bulk GaN due to its crystalline structure. They can be summarized in: vacancies, i.e., missing nitrogen (VN) or gallium (VGa) atoms in their usual position in the lattice; antisites, when a nitrogen atom occupies the expected location of a gallium atom (NGa) or vice versa (GaN); and interstitials, caused by a nitrogen (Ni) or gallium (Gai) atom in a position where no element should be present. • Impurities: These are foreign atoms inside the gallium nitride. They can be in interstitial or substitutional position if they are located at a typically unoccupied location of the GaN crystal or at the place of a Ga or N atom in the lattice, respec‐ tively. They may be expected dopant atoms (magnesium, silicon, iron, carbon), elements used in the growth chamber in precursors or flow gases (carbon, hydrogen), or impurities incorporated from the atmosphere (hydrogen, oxygen). Altho
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