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GaN(Si)/AlInN multiple quantum wells were grown on GaN/Al2O3 (0001) templates by metalorganic vapor-phase epitaxy. Transmission electron microscopy observations showed well-defined GaN quantum wells and AlInN barrier layers. Electrostatic potential profiles across the heterostructure have been measured using off-axis electron holography. A polarization-induced electric field with magnitude of ∼2.2 ± 0.1 MV/cm was measured across the GaN quantum wells, in reasonable agreement with simulated values. However, the measured fields across the AlInN barriers were considerably less than predicted from simulations: possible reasons are briefly discussed. [ABSTRACT FROM AUTHOR]

Off-axis electron holography has been used to measure the built-in potential profile across an Al0.85In0.15N/AlN/GaN high electron mobility transistor heterostructure. Profile measurements indicated a polarization-induced electric field of 6.9 MV/cm within the AlN layer. A two-dimensional electron gas with a density of ∼2.1×1013 cm-2 was located in the GaN layer at ∼0.8 nm away from the AlN/GaN interface in reasonable agreement with the reported simulations. Electron microscopy confirmed that the Al0.85In0.15N layer was uniform and that Al0.85In0.15N/AlN and AlN/GaN interfaces were abrupt and well defined. [ABSTRACT FROM AUTHOR]

The microstructure of InxAl1-xN/GaN heterostructures (where x∼0.13–0.19), grown by molecular beam epitaxy, was investigated by transmission electron microscopy. Observations in the cross-section and plan-view geometries show evidence for lateral phase separation originating at the GaN surface that results in a vertical honeycomblike structure within the InAlN layers. The lateral dimensions of the honeycomb cells are ∼5–10 nm. The vertical walls are In rich with a width of ∼1–2 nm and align roughly perpendicular to <1120> and <1100> directions. The phase separation is attributed to random compositional fluctuations during the early stages of growth, possibly associated with misfit-strain relaxation. [ABSTRACT FROM AUTHOR]