Achieving highly conductive AlGaN alloys with high Al contents

Si-doped n-type ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ alloys were grown by metalorganic chemical vapor deposition on sapphire substrates. We have achieved highly conductive n-type ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ alloys for x up to 0.7. A conductivity (resistivity) value of 6.7 Ω⁻¹ cm⁻¹ (0.15 Ω cm) (with free electron concentration ${\text{2.1×10}}^{18}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}}$ and mobility of 20 cm²/Vs at room temperature) has been achieved for ${\mathrm{Al}}_{\text{0.65}}{\mathrm{Ga}}_{\text{0.35}}\mathrm{N},$ as confirmed by Hall-effect measurements. Our experimental results also revealed that (i) the conductivity of ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ 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 ${\text{1×10}}^{18}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}}$ that is needed to convert insulating ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ with high Al content $\text{(x⩾0.4)}$ to n-type.