The authors have studied In x Ga 1−x N / GaN ͑x Ϸ 15% ͒ quantum wells ͑QWs͒ using atomic force microscopy ͑AFM͒ and picosecond time resolved cathodoluminescence ͑pTRCL͒ measurements. They observed a contrast inversion between monochromatic CL maps corresponding to the high energy side ͑3.13 eV͒ and the low energy side ͑3.07 eV͒ of the QW luminescence peak. In perfect correlation with CL images, AFM images clearly show regions where the QW thickness almost decreases to zero. Pronounced spectral diffusion from high energy thinner regions to low energy thicker regions is observed in pTRCL, providing a possible explanation for the hindering of nonradiative recombination at dislocations.

Compared to the AlGaN alloy, which can only be grown under tensile strain on GaN, the AlInN alloy is predicted by Vegard's law to be lattice-matched ͑LM͒ on fully relaxed GaN templates for an indium content of ϳ17.5%, i.e., it can be grown either tensely or compressively on GaN. The effect of strain on the polarization induced sheet charge density at the Al 1−x In x N / AlN/ GaN heterointerfaces is carefully investigated for 6 and 14 nm thick AlInN barriers including a 1 nm thick AlN interlayer. The barrier indium content ranges at 0.03Յ x Յ 0.23 for 6 nm thick barriers and 0.07Յ x Յ 0.21 for 14 nm thick barriers. It is found that the two-dimensional electron gas ͑2DEG͒ density varies between ͑3.5Ϯ 0.1͒ ϫ 10 13 cm −2 and ͑2.2Ϯ 0.1͒ ϫ 10 13 cm −2 for 14 nm thick barriers. Finally, a 2DEG density up to ͑1.7Ϯ 0.1͒ ϫ 10 13 cm −2 is obtained for a nearly LM AlInN barrier with ϳ14.5% indium on GaN as thin as 6 nm.

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We discuss the characteristics of In0.17Al0.83N/GaN High Electron Mobility Transistors (HEMTs) with barrier thicknesses between 33 nm and 3 nm, grown on sapphire substrates by MOCVD. The maximum drain current (at VG = +2.0 V) decreased with decreasing barrier thickness due to the gate forward drive limitation and residual surface depletion effect. Full pinch-off and low leakage is observed. Even with 3nm ultra thin barrier the heterostructure and contacts are thermally highly stable (up to 1000°C).

Ternary semiconductor alloys based on the A y B1–y C stoichiometry are widely employed in electronic devices, and their composition plays a key role in band gap engineering of heterostructures. We have studied the crucial issue of accuracy in composition measurements of Al y Ga1–y N and Mg y Zn1–y O alloys using atom probe tomography (APT). The results indicate a similar behavior for both nitride and oxide systems. A correct site fraction y is measured at low field conditions, while Ga and Zn preferentially evaporate at high field, yielding an overestimation of y. Furthermore, APT data sets exhibit local biases depending on the distribution of the electrostatic field at the specimen surface. We estimate the detection efficiencies for each species and interpret the results through a model describing preferential evaporation in simple terms.