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In this work we report on the electrical characterization of nonpolar cubic GaN metal-insulator-semiconductor (MIS) structures. Si 3 N 4 layers were deposited in situ on top of cubic GaN grown on 3C-SiC (0 0 1) substrates. The electric characteristics of the MIS structures are determined by current-voltage measurements and by capacitance and admittance spectroscopy techniques. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) was used to investigate the composition of our samples. From the flat band voltage in the MIS capacitors and a detailed band diagram analysis, the conduction band discontinuity of Si 3 N 4 and cubic GaN was evaluated 1.17 eV, which is slightly lower than reported for hexagonal GaN. By admittance spectroscopy interface state densities are calculated. Current-voltage characteristics were used to evaluate the influence of the substrate temperature on the insulating properties of the MIS structures. The energetic position of the interface traps was found to be about 0.3 eV below the conduction band of cubic GaN. The density of these traps is 2.5 × 10 11 cm −2 eV −1 . We find a conductivity minimum in the MIS structure grown at 600 • C.

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Cubic Al 0.3 Ga 0.7 N/GaN heterostructures were grown by plasma-assisted molecular beam epitaxy on 3C-SiC (001) substrates. A profile of the electrostatic potential across the cubic-AlGaN/GaN heterojunction was obtained using electron holography in the transmission electron microscope. The experimental potential profile indicates that the unintentionally doped layers show n-type behavior and accumulation of free electrons at the interface with a density of 5.1 Â 10 11 /cm 2 , about one order of magnitude less than in wurtzite AlGaN/GaN junctions. A combination of electron holography and cathodoluminescence measurements yields a conduction-to-valence band offset ratio of 5:1 for the cubic AlGaN/GaN interface, which also promotes the electron accumulation. Band diagram simulations show that the donor states in the AlGaN layer provide the positive charges that to a great extent balance the two-dimensional electron gas. V C 2012 American Institute of Physics. [http://dx.

We report on the growth of non‐polar cubic GaN/AlxGa1‐xN heterostructures by plasma‐assisted molecular beam epitaxy on free standing (001) 3C‐SiC substrates. The samples consist of 600 nm thick GaN buffer and 30 nm AlxGa1‐xN layer. The growth was observed by in‐situ reflection high energy electron diffraction (RHEED). Layer thickness was determined by AlxGa1‐xN RHEED growth oscillations and by reflectance measurements after growth. The morphological and the structural properties are analyzed by high resolution x‐ray diffraction (HRXRD) and atomic force microscopy (AFM). Using a metal oxide semiconductor heterostructure (MOSH), capacitance voltage (CV) characteristics were measured. The oxide layer consists of SiO2, the thickness was varied between 15 nm and 30 nm. SiO2 layer was produced by plasma enhanced chemical vapour deposition (PECVD). The contact structure is lithographically deposited on top of the sample. Metal contacts have a diameter of 300 μm and were thermally evaporated consisting of 15 nm Ni and 50 nm Au. By CV measurements of the MOSH structures we obtain clear evidence for the existence of an electron accumulation layer at the GaN/AlGaN interface. The sheet carrier concentration at the hetero‐interface is calculated from experimental data (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)