Phonon-Kick Mechanism for Defect Reactions in Semiconductors

Defects in GaN can cause degradation in the active regions of GaN-based devices; however, the origin of such defects remains unclear. Here, the electron–phonon interaction around Ga vacancies (VGa) in GaN is investigated quantitatively using first-principles calculations. It is shown that the energy shift in an electronic system with a localized phonon mode has the same order of magnitude as that in an atomic system. Next, the phononic structures of a system in a positively charged state are calculated. It is demonstrated that localized modes in the neutral state are still localized under slightly shifted frequencies. These results indicate that a VGa satisfies all conditions for the phonon-kick mechanism. This characteristic is expected to result in enhancement of the amplitude of the localized modes, which should cause N atoms to migrate toward VGa sites and form a NGa–VN complex defect. Hence, the migration energies of N atoms from VGa sites to NGa–VN complex defects in both neutral and positively charged states are investigated. It is revealed that the migration barrier is smaller in the positively charged state than in the neutral state and that the NGa–VN complex is more stable than a VGa. In light of these findings, the conformation change from a VGa to a NGa–VN complex may serve as a microscopic mechanism for the first stage of the defect reactions around VGa sites in GaN. These findings are expected to be useful in the future development of light-emitting diodes and transistors with longer lifetimes and higher efficiencies.

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First-principles calculation of electron–phonon coupling at a Ga vacancy in GaN

Tsujio¹,

Oda²,

Shinozuka³

2017

Jpn. J. Appl. Phys.

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We investigate the dependence of the electronic band structure on the localized phonon mode at a Ga vacancy in GaN. The electronic states and phonon modes are both calculated using a first-principles method based on the density functional theory. Comparing the calculated electronic band structures and phonon-frequency densities of states of GaN without and with a Ga vacancy, we find that 1) there are localized electronic midgap states closely above the top of the valence band, 2) localized phonon modes appear above the acoustic and optical phonon bands, 3) one of these localized phonon modes contains asymmetric distortions in which one of the four N atoms around a Ga vacancy strongly oscillates, and 4) the localized electronic midgap states strongly couple with the localized asymmetric mode. These results indicate that a Ga vacancy can act as a nonradiative recombination center and may trigger defect reactions in GaN-based devices.

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Phonon-Kick Mechanism for Defect Reactions in Semiconductors

Cited by 3 publications

References 29 publications

Annealing effects of 850 nm vertical-cavity surface-emitting lasers after proton irradiation

Annealing effects of 850 nm vertical-cavity surface-emitting lasers after proton irradiation

Investigation of the electron–phonon interactions around Ga vacancies in GaN and their role in the first stage of defect reactions

First-principles calculation of electron–phonon coupling at a Ga vacancy in GaN

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