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Si-doped n-type AlxGa1MINxN alloys with x up to 0.5 and Mg-doped p-type AlxGa1-xN alloys with x up to 0.27 were grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrates. For the n-type AlxGa1-xN, we achieved highly conductive alloys for x up to 0.5. An electron concentration as high as 1x1018cm-3 was obtained in Si-doped Al0.5Ga0.5N alloys with an electron mobility of 16 cm$_2)Vs at room temperature, as confirmed by Hall-effect measurements. Our results also revealed that the conductivity of AlxGa1-xN alloys continuously increases with an increase of Si doping level for a fixed value of Al content (X<0.5), the conductivities of AlxGa1-xN alloys decrease with increasing Al content for a given doping level; the critical Si-doping concentration needed to convert insulating AlxGa$1-x)N with high Al contents (X>=0.4) to n- type conductivity is about 1 x 1018cm-3. Time- resolved photoluminescence studies carried out on these materials have shown that Si-doping reduces the effect of carrier localization in AlxGa1-xN alloys and a sharp drop in carrier localization energy occurs when the Si doping concentration increases above 1x1018cm-3, which directly correlates with the observed electrical properties. For the Mg-doped AlxGa1-xN alloys, p-type conduction was achieved for x up to 0.27, as confirmed by variable temperature Hall measurements. 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. The Mg acceptor activation energies EA were deduces from photoluminescence spectra and were found to increase with Al content and agreed very well with those obtained by Hall measurements. From the measured activation energy as a function of Al content, EA versus x, the resistivity of Mg-doped AlxGa1-x with high Al contents can be deduced. Our results have also shown that PL measurements provide direct means of obtaining EA especially where this cannot be obtained accurately by electrical methods due to high resistance of p-type AlxGa1-xN with high Al content.
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