The Schottky behavior of Ni/Ta and Ni contacts on n-GaN was investigated under various annealing conditions by current-voltage measurements. It is found that with the addition of Ta between the Ni layer and the GaN substrate the thermal stability properties of devices can be significantly improved. Experimental results indicate that a high quality Ni/Ta n-GaN Schottky diode with an ideality factor and barrier height of 1.16 and 1.24 eV, respectively, can be obtained under 1 h annealing, at 700°C.

Photoluminescence (PL) studies of In-doped GaN:Mg films revealed that the Mg-related emission at 3.1 eV is enhanced by more than one order of magnitude on the shoulder of the broad band centered at 2.8 eV for GaN:Mg after an optimal In concentration was added into the films. This enhancement of the 3.1 eV band is believed to be associated with the reduction in the number of self-compensation centers. A slow decay in PL intensity evolution was also observed, which may be ascribed to a local energy barrier that impedes carriers that relax into the valence band. The temperature dependences of the decay time constants were measured and a barrier energy as high as $103 AE 7 meV was obtained for In-doped GaN:Mg as compared with 69 AE 8 meV for GaN:Mg.

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The thermal effects of Ni/Ta/n-GaN Schottky diodes have been investigated for the first time using current-voltage, X-ray photoemission spectroscopy and Auger electron spectroscopy (AES) methods. Their barrier height is found to increase monotonously with increasing annealing temperature up to 800°C. Preliminary results indicate that when a Ta intermediate layer is added into the Ni/GaN diodes, it can prevent the metal-semiconductor interdiffusion and Ni accumulation adjacent to GaN substrate to a large extent so that a more thermally stable device can be obtained.

Multifunctional polymers are highly promising auxiliary agents for the oral delivery of a broad variety of drugs. The main features of multifunctional polymers include controlled release, mucoadhesive, cohesive and permeation enhancing properties and enzyme as well efflux pump inhibitory properties. Within the current review, the most important multifunctional polymers for oral drug delivery as well as various analytical methods including the rotating cylinder method, tensile studies, confocal laser scanning microscopy, permeation studies, and also enzyme and efflux pump inhibition studies are discussed.