Aluminum gallium nitride alloys and heterostructures: Growth, characterization and application

AlGaN alloys and heterostructures were grown by MOCVD and characterized by using Hall measurement, time-resolved photoluminescence (PL) and x-ray diffraction (XRD).; Si-doped n-type AlxGa1-xN alloys with x up to 0.5 and Mg-doped p-type AlxGa1-xN alloys with x up to 0.27 were grown. Highly conductive n-type AlxGa 1-xN alloys were obtained for x up to 0.5. Emission lines of band-to-impurity transitions of free electrons with neutral Mg acceptors as well as localized excitons have been observed in the p-type AlxGa1-xN alloys. PL spectra showed that Mg acceptor activation energies EA increase with Al content and the results agrees with Hall measurement.; Picosecond time-resolved PL was used to study the optical properties of GaN/AlxGa1-xN MQWs with varying structural parameters. The optimal GaN/AlxGa1-xN ( x ∼ 0.2) MQW structures for UV light emitter applications are those with well (barrier) widths ranging from 12 to 42 A (40 to 80 A). The decreased quantum efficiency in GaN/AlxGa1-xN MQWs with well width Lw < 12 A is due to the enhanced carrier leakage to the underlying GaN epilayers, while the decreased quantum efficiency in MQWs with well width Lw > 42 A is associated with an increased nonradiative recombination rate as Lw approaching the critical thickness of MQWs.; InxAlyGa1-xN quaternary alloys were grown on sapphire substrates. The dominant optical transition at low temperatures in InxAlyGa1-xN quaternary alloys was due to localized exciton recombination, while the localization effects in InxAlyGa1-xN quaternary alloys were combined with those of InGaN and AlGaN ternary alloys with comparable In and Al compositions. We can achieve not only higher emission energies but also higher quantum efficiency in InxAlyGa1-x N quaternary alloys than that of GaN.; AlN epilayers with high optical qualities have been grown on sapphire substrates by MOCVD. Band-edge emission lines have been observed both at low and room temperatures and are at 6.017 and 6.033 eV at 10 K Both the optical quality and the quantum efficiency of AlN epilayers are comparable to GaN.; AlGaN/GaN-based heterostructure field-effect transistors (HFETs) by employing the delta-doped barrier and the SiO2 insulated-gate are fabricated and characterized. The device grown on sapphire substrate has a high drain-current-driving and gate-control capabilities as well as a very high gate-drain breakdown voltage of 200 V for a gate length of 1 mum and a source-drain distance of 3 mum. The incorporation of the SiO2 insulated-gate and the delta-doped barrier into HFET structures reduces the gate leakage and improves the 2D channel carrier mobility.