Achieving highly conductive AlGaN alloys with high Al contents

Si-doped n-type AlxGa1-xN alloys were grown by metalorganic chemical vapor deposition on sapphire substrates. We have achieved highly conductive n-type AlxGa1-xN alloys for x up to 0.7. A conductivity (resistivity) value of 6.7 Omega(-1) cm(-1) (0.15 Omega cm) (with free electron concentration 2.1x10(18) cm(-3) and mobility of 20 cm(2)/Vs at room temperature) has been achieved for Al0.65Ga0.35N, as confirmed by Hall-effect measurements. Our experimental results also revealed that (i) the conductivity of AlxGa1-xN alloys continuously increases with an increase of Si doping level for a fixed value of Al content and (ii) there exists a critical Si-dopant concentration of about 1x10(18) cm(-3) that is needed to convert insulating AlxGa1-xN with high Al content (xgreater than or equal to0.4) to n-type. (C) 2002 American Institute of Physics.