n-Type conductivity bound by the growth temperature: the case of Al 0.72 Ga 0.28 N highly doped by silicon

High-Al-content AlxGa1−xN layers, x ∼ 0.72, have been grown by metal organic chemical vapour deposition (MOCVD) at a temperature ranging from 1000 to 1100 °C, together with high flow rate of the dopant precursor silane (SiH4) in order to obtain highly Si-doped Al0.72Ga0.28N layers, ∼1 × 1019 cm−3 as measured by secondary ion mass spectrometry (SIMS). Further characterization of the layers by capacitance–voltage (C–V), electron paramagnetic resonance (EPR), and transmission electron microscopy (TEM) measurements reveals the complex role of growth temperature for the n-type conductivity of high-Al-content AlxGa1−xN. While increasing temperature is essential for reducing the incorporation of carbon and oxygen impurities in the layers, it also reduces the amount of silicon incorporated as a donor.