PACS : 73.40.Kp; 73.61.Ey; 81.15.Gh Crack-free Al x Ga 1--x N films with an Al mole fraction of up to 37% were successfuly grown on a sapphire substrate by introducing a 10 nm-thick low-temperature (LT) Al x Ga 1--x N interlayer. Three AlGaN layer structures were tested for application to solar-blind UV photodetectors. Among them, Schottky diodes with a Pt/0.5 mm thick Al 0.33 Ga 0.67 N/10 nm thick LT-Al 0.33 Ga 0.67 N interlayer/ 2 mm thick n + -GaN layer exhibited the best behavior with a reverse leakage current of 9 nA at À5 V, UV-visible extinction ratio of $10 4 , and responsivity of 0.15 A/W at 280 nm.

The effects of the isoelectronic Al-doping of GaN grown by metal organic chemical vapor deposition were investigated for the first time using scanning electron microscopy (SEM), Hall measurements, photoluminescence (PL), and time-resolved PL. When a certain amount of Al was incorporated into the GaN films, the room temperature photoluminescence intensity of the films was approximately two orders larger than that of the undoped GaN. More importantly, the electron mobility significantly increased from 130 for the undoped sample to 500 cm2/Vs for the sample grown at a TMAl flow rate of 10 νmol/min, while the unintentional background concentration only increased slightly relative to the TMAl flow. The incorporation of Al as an isoelectronic dopant into GaN was easy during MOCVD growth and significantly improved the optical and electrical properties of the film. This was believed to result from a reduction in the dislocation-related non-radiative recombination centers or certain other defects due to the isoelectronic Al-doping.