Improvement of low-intensity ultraviolet photodetectors based on AlGaN with low threading dislocation density

We report on the fabrication and the characterization of low-intensity ultr aviolet metal-semiconductor-metal photodetectors based on AlGaN (0 less tha n or equal to x less than or equal to 0.44) with low threading dislocation density. Active layers were grown by organometallic vapor phase epitaxy on: GaN. For comparison, AlGaN layers grown on sapphire were also prepared. Ph otodetectors on low threading dislocation layers present a very low dark cu rrent level, constant responsivity with optical power, a rejection over two orders of magnitude at the band gap, and an improved response speed. The r esults were uniform over the whole AlN mole fraction investigated. On the o ther hand, samples on sapphire present degraded behaviors when the AlN mole fraction becomes higher than 0.11.