Highly conductive n-AlxGa1−xN layers with aluminum mole fractions above 80%

Silicon doping of AlxGa1−xN layers with high aluminum mole fractions (0.8 < x < 1) was studied. The AlGaN:Si layers were pseudomorphically grown by metalorganic vapor phase epitaxy on low defect density epitaxially laterally overgrown AlN/sapphire templates. The effects of SiH4/III ratio and aluminum content on the resistivity, the carrier concentration, and the mobility have been investigated. By variation of the SiH4/III ratio during the growth of AlxGa1−xN:Si layers, a recorded low resistivity of Al0.81Ga0.19N:Si was obtained with 0.026 Ω cm. The resistivity increases exponentially with increasing aluminum content to 3.35 Ω cm for Al0.96Ga0.04N, and the optimum SiH4/III ratio is shifted towards lower values. Hall effect measurements show that the increase of the resistivity with increasing aluminum mole fraction is mainly caused by a decrease of the carrier density. The optimized Al0.81Ga0.19N:Si exhibits a carrier concentration of 1.5 × 1019 cm−3 and a mobility of the carriers of 16.5 cm2 V−1 s−1.