High electron concentrations in Si-doped AlN/AlGaN superlattices with high average Al content of 80%

Uniformly Si-doped AlN/Al_0.5Ga_0.5N superlattices were shown to have a high electron concentration. Even with high average Al content of approximately 80%, the high electron concentration reached 3.2 × 10¹⁸ cm^-3, which is about eight times higher than that of a bulk Si-doped AlGaN layer with the same Al content. In the AlN/AlGaN system, the conduction band offset is larger than the ionization energy of the Si donor in AlN. Therefore, the Si donors in the AlN barriers are fully activated and the corresponding electrons are transferred to the AlGaN wells. In addition, the large band bending caused by the strong strain-induced piezoelectric and spontaneous polarization increases the activation of the donors in the AlGaN wells.