The hot-wall metal-organic chemical vapor deposition (MOCVD), previously shown to enable superior III-nitride material quality and high performance devices, has been explored for Mg doping of GaN. We have investigated the Mg incorporation in a wide doping range ([Formula: see text] cm−3 up to [Formula: see text] cm−3) and demonstrate GaN:Mg with low background impurity concentrations under optimized growth conditions. Dopant and impurity levels are discussed in view of Ga supersaturation, which provides a unified concept to explain the complexity of growth conditions impact on Mg acceptor incorporation and compensation. The results are analyzed in relation to the extended defects, revealed by scanning transmission electron microscopy, x-ray diffraction, and surface morphology, and in correlation with the electrical properties obtained by Hall effect and capacitance–voltage (C–V) measurements. This allows to establish a comprehensive picture of GaN:Mg growth by hot-wall MOCVD providing guidance for growth parameters optimization depending on the targeted application. We show that substantially lower H concentration as compared to Mg acceptors can be achieved in GaN:Mg without any in situ or post-growth annealing resulting in p-type conductivity in as-grown material. State-of-the-art [Formula: see text]-GaN layers with a low resistivity and a high free-hole density (0.77 [Formula: see text] cm and [Formula: see text] cm[Formula: see text], respectively) are obtained after post-growth annealing demonstrating the viability of hot-wall MOCVD for growth of power electronic device structures.

Ellagic acid (EA), an antioxidant from fruits or other plants, has recently evoked interest in the field of organic electronics because of its weak electron donor properties. In this work, the preparation of uniaxial π-stacked EA films by thermal evaporation on different surfaces is reported for the first time. The (102) lattice plane of the π-electron system was confirmed as the contact plane for one monolayer equivalent on Ag(111) by lowelectron energy diffraction. X-ray and atomic force microscopy measurements revealed nanocrystalline grains with an average inplane size of 50 nm and considerably smaller average out-of-plane crystallite sizes (16−25 nm) in films of 16−75 nm thickness. The influence of different substrates was minor compared to the effect of the film thickness. An increase in the in-plane density of grains at larger film thicknesses was deduced from the trend in their uniaxial optical properties. Weak and strong intermolecular H-bonding interactions were identified in the EA crystal lattice, while a surplus of weak H-bonding was observed for the nanocrystallites in thin films, as compared to bulk EA. Finally, EA was coevaporated with the semiconducting thiophene molecule DCV4T-Et 2 to demonstrate principle interactions with a guest molecule by H-bonding analysis. Our results illustrate the feasibility of applying EA films as alignment layers for templating other semiconducting organic films used in organic electronic devices.

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High performance organic transistors have been realized via airbrush technique, using small molecule-insulating polymer blends.

Note: This paper is part of the Special Topic on Wide Bandgap Semiconductor Materials and Devices.