Growth and Optoelectronic Properties ofifi-Nitride Quatemary Alloys

InA1GaiN 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 InAlGaiN quaternary alloys with lattice matched with GaN (y—4.7x) have the highest optical quality. More importantly, we can achieve not only higher emission energies but also higher emission intensities (or quantum efficiencies) in JnMGa1N quaternary alloys than that of GaN. The quantum efficiency of InALGaiN quaternary alloys was also enhanced significantly over A1GaN alloys with a comparable Al content. We have also fabricated ultraviolet (UV) photoconductive detectors based on InAlGai.N/GaN qUaternary alloy heterostructures. We found that with varying In and Al compositions, the cut-off wavelength of the InAlGai.N detectors could be varied to the deep Uv range tnd that the responsivity of the InAlGaiN quaternary alloys exceeded that of A1GaN alloys with comparable cut-off wavelengths by a factor of five. This showed that InAlGai.N quaternary alloys is a very important material for solar-blind UV detector applications particularly in the deep UV range where Al rich A1GaN alloys have problems with low quantum efficiency and cracks due in part to lattice mismatch with GaN. Our results strongly suggested that InAlGai.N quatemary 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.