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Bright-field transmission electron micrograph of the superlattice. The ⟨0001⟩ growth direction is from bottom to top. (a) Multibeam image of region containing the superlattice. (b) Enlargement of the rectangular box showing the graded nature of the barrier. The layers appear with brighter contrast.
Low-magnification electron hologram: (a) phase and (b) amplitude images used to analyze the uniformity of 2DEG formation in the superlattice.
Potential energy profile obtained from the phase and amplitude informations shown in Fig. 2, assuming an inelastic mean-free path of .
Potential energy profile across the heterostructure for the top two periods derived from a high-magnification electron hologram.
Comparison of conduction band energy diagrams from a self-consistent one-dimensional Schrödinger-Poisson calculation for different Al grading schemes in AlGaN layer: linear (dashed line) and parabolic (dotted line), with the measured electrostatic potential by electron holography (solid line). (b) Electron density distribution for the 2DEG region.
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