Self-compensation in heavily Ge doped AlGaN: A comparison to Si doping
Shun Washiyama, Kelsey J. Mirrielees, Pegah Bagheri, Jonathon N. Baker, Jihyun Kim, Qiang Guo, Ronny Kirste, Yan Guan, M. Hayden Breckenridge, Andrew Klump, Pramod Reddy, Seiji Mita, Douglas L. Irving, Ramón Collazo, Zlatko Sitar
Abstract
Self-compensation in Ge- and Si-doped Al0.3Ga0.7N has been investigated in terms of the formation of III vacancy and donor-vacancy complexes. Both Ge- and Si-doped AlGaN layers showed a compensation knee behavior with impurity compensation (low doping regime), compensation plateau (medium doping regime), and self-compensation (high doping regime). A maximum free carrier concentration of 4–5 × 1019 cm−3 was obtained by Ge doping, whereas Si doping resulted in only half of that value, ∼2 × 1019 cm−3. A DFT calculation with the grand canonical thermodynamics model was developed to support the hypothesis that the difference in self-compensation arises from the difference in the formation energies of the VIII-n•donor complexes relative to their onsite configurations. The model suggested that the VIII-2•donor and VIII-3•donor complexes were responsible for self-compensation for both Ge- and Si-doped AlGaN. However, a lower free carrier concentration in Si-doped samples was due to a high VIII-3•Si concentration, resulting from a lower energy of formation of VIII-3•Si.