Disorder effects on the band structure of ZnGeN₂: Role of exchange defects

Journal Article · Tue Nov 01 00:00:00 EDT 2016 · Physical Review B

DOI:https://doi.org/10.1103/physrevb.94.205201· OSTI ID:1535800

Skachkov, Dmitry ^[1]; Quayle, Paul C. ^[1]; Kash, Kathleen ^[1]; Lambrecht, Walter L. ^[1]

---

1. Case Western Reserve Univ., Cleveland, OH (United States)

The role of exchange defects on the band structure of ZnGeN₂ is investigated. Exchange defects are defined through the exchange of cations Zn and Ge starting from the ideal Pna2₁ crystal structure, which obeys the local octet rule. Each such exchange creates several nitrogen-centered tetrahedra which violate the local octet rule, although overall charge neutrality is preserved. We study several distributions of exchange defects, some with all antisites making up the exchange defect close to each other and with increasing numbers of exchange defects, and others where the two types of antisites Zn_Ge and Ge_Zn are kept separated from each other. We also compare the results for these models with a fully random distribution of Zn and Ge on the cation sites. We show that for a single-nearest-neighbor exchange defect, the band gap is narrowed by about 0.5 eV due to two effects: (1) the Zn_Ge antisites form filled acceptor states just above and merging with the valence-band maximum (VBM) of perfect crystal ZnGeN₂ and (2) the Ge_Zn antisites form a resonance in the conduction band which lowers the conduction-band minimum (CBM). When more exchange defects are created, these acceptor states broaden into bands which can lower the gap further. When tetrahedra occur surrounded completely by four Zn atoms, states even deeper in the gap are found localized all near these tetrahedra, forming a separate intermediate band. Finally, for phase-segregated Zn_Ge and Ge_Zn, the gap is significantly more reduced, but no separate band is found to occur. The Zn_Ge acceptorlike states now form a percolating defect band which is significantly wider and hence reaches deeper into the gap. In all cases, the wave functions near the top of the new VBM remain, to some extent, localized near the Zn_Ge sites. For a fully random case, the gap is even more severely reduced by almost 3 eV. The total energy of the system increases with the number of octet-rule-violating tetrahedra and the energy cost per exchange defect of order 2 eV is quite high.

• Research Organization: Case Western Reserve Univ., Cleveland, OH (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
• Grant/Contract Number: SC0008933; DMREF-1533957; DMR-140-9346
• OSTI ID: 1535800
• Alternate ID(s): OSTI ID: 1330598
• Journal Information: Physical Review B, Vol. 94, Issue 20; ISSN 2469-9950
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
materials science
physics
band gap
density of states
point defects
crystal strucutres
doped semiconductors
band structure methods
density functional theory
electronic structure