We report on admittance spectroscopy (AS) investigations taken on aluminum (Al)-
doped 6H-SiC crystals at low temperatures. Admittance spectra taken on Schottky contacts of
highly doped samples (NA ≥ 7.2×1017 cm-3) reveal two series of conductance peaks, which cause
two different slopes of the Arrhenius plot. The steep slope is attributed to the Al acceptor, while the
flatter one - obtained from the low temperature peaks - is attributed to the activation energy ε3 of
nearest neighbor hopping. We propose a model, which explains the unexpected sharpness of the
low temperature conductance peaks and the disappearance of these peaks for low acceptor
concentrations. The model is verified by simulation, and the AS results are compared with
corresponding results obtained from resistivity measurements taken on 4H- and the identical 6HSiC
samples.