Growth and optoelectronic properties of III-nitride quaternary alloys

InxAlyGa1-xN quaternary alloys with different In and Al compositions were grown on sapphire substrates with GaN buffer by metal-organic chemical vapor deposition (MOCVD). Optical properties of these quaternary alloys were studied by picosecond time-resolved photoluminescence. Our studies have revealed that InxAlyGa1-xN quaternary alloys with lattice matched with GaN (y similar to4.7x) have the highest optical quality. More importantly, we can achieve not only higher emission energies but also higher emission intensities (or quantum efficiencies) in InxAlyGa1-xN quaternary alloys than that of GaN. The quantum efficiency of InxAlyGa1-x-yN quaternary alloys was also enhanced significantly over AlGaN alloys with a comparable Al content. We have also fabricated ultraviolet (UV) photoconductive detectors based on InxAlyGa1-xN/GaN quaternary alloy heterostructures. We found that with varying In and Al compositions, the cut-off wavelength of the InxAlyGa1-x-yN detectors could be varied to the deep UV range and that the responsivity of the InxAlyGa1-x-yN quaternary alloys exceeded that of AlGaN alloys with comparable cut-off wavelengths by a factor of five. This showed that InxAlyGa1-x-yN quaternary alloys is a very important material for solar-blind UV detector applications particularly in the deep UV range where Al rich AlGaN alloys have problems with tow quantum efficiency and cracks due in part to lattice mismatch with GaN. Our results strongly suggested that InxAlyGa1-x-yN quaternary alloys open a new avenue for the fabrication of many novel optoelectronic devices such as high efficient light emitters and detectors, particularly in the UV region.