Acceptor Decoration of Threading Dislocations in (Al,Ga)N/GaN Heterostructures

Abstract

We demonstrate that threading dislocations in $(\mathrm{Al},\mathrm{Ga})\mathrm{N}/\mathrm{Ga}\mathrm{N}$ heterostructures can be spontaneously decorated by acceptors during the epitaxial process. First-principles calculations show that the threading dislocation introduces detrimental deep electronic states both above the valence-band maximum (VBM) and below the conduction-band minimum (CBM) of $\mathrm{Ga}\mathrm{N}$. Because of the electron transfer between the occupied level above the VBM of the threading dislocation and the defect states of acceptors, acceptors will decorate the threading dislocation, which leads to the shift of the dislocation states. For the occupied deep states above the VBM, the acceptor decoration shifts the deep states toward the VBM, which may constructively contribute to the dislocation tolerance of $(\mathrm{Al},\mathrm{Ga})\mathrm{N}/\mathrm{Ga}\mathrm{N}$ heterostructures. For the unoccupied states below the CBM, the acceptor-decorated dislocation provides an additional electron-transfer channel besides that through the pure threading dislocations. These two distinct electron-transfer channels are observed in reverse-biased $(\mathrm{Al},\mathrm{Ga})\mathrm{N}/\mathrm{Ga}\mathrm{N}$ Schottky diodes, which is characterized by two distinct Frenkel-Poole-emission states.