Incomplete ionization in aluminum-doped 4H-silicon carbide

In this work, we investigate the degree of incomplete ionization of Al doped 4H-SiC. In particular, we perform analysis on a comprehensive list of published measurements of ionization energy, resistivity, and Hall mobility for varying Al concentration. These data are used to construct two separate models with which we calculate the fraction of mobile holes to dopant atoms p/N-A. First, we create a physics-based theoretical model which includes the effects of doping-dependent ionization energy, quantum-mechanical spreading of the acceptor density of states, and density of states smearing due to disorder effects. Our second model is derived mainly from experimental Hall and resistivity data, and we use the results of this calculation to verify our results from the theoretical model. We find good agreement between the two approaches which gives confidence to our resulting p/N-A calculations. At doping above 10(20) cm(-3), we observe an increase in the p/N-A ratio which is likely due to the onset of a parallel impurity conduction mechanism which does not require dopant ionization. We also provide an easily evaluated expression which predicts p/N-A at higher temperatures based on our full theoretical model. Published under license by AIP Publishing.