Highly conductive n-Al_xGa_1-xN layers with aluminum mole fractions above 80%

Published in:
Appl. Phys. Lett., vol. 103, no. 212109 (2013).
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Abstract:
Silicon doping of Al_xGa_1-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 Al_xGa_1-xN:Si layers, a recorded low resistivity of Al_0.81Ga_0.19N:Si was obtained with 0.026Ωcm. The resistivity increases exponentially with increasing aluminum content to 3.35 Ω cm for Al_0.96Ga_0.04N, 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 Al_0.81Ga_0.19N:Si exhibits a carrier concentration of 1.5×10¹⁹ cm^-3 and a mobility of the carriers of 16.5 cm²V^-1 s^-1.

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