High-Al-content AlxGa(1-x)N layers, x similar to 0.72, have been grown by metal organic chemical vapour deposition (MOCVD) at a temperature ranging from 1000 to 1100 degrees C, together with high flow rate of the dopant precursor silane (SiH4) in order to obtain highly Si-doped Al0.72Ga0.28N layers, similar to 1 x 10(19) 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.