Ordering-induced direct-to-indirect band gap transition in multication semiconductor compounds

Abstract

Using first-principles calculations and symmetry analysis, we show that as cation atoms in a zincblende-based semiconductor are replaced through atomic mutation (e.g., evolve from ZnSe to CuGaSe 2 to Cu 2 ZnGeSe 4 ), the band gaps of the semiconductors will become more and more indirect because of the band splitting at the zone boundary, and in some cases will even form the segregating states. For example, although ZnSe is a direct band gap semiconductor, quaternary compounds Cu 2 ZnGeSe 4 and Cu 2 ZnSnSe 4 can be indirect band gap semiconductors if they form the primitive mixed CuAu ordered structures. We also find that the stability and the electronic structure of the quaternary polytypes with different atomic ordering are almost negative-linearly correlated. We suggest that these intrinsic properties of the multi-cation semiconductors can have a large influence on the design and device performance of these materials.2

Opposing effects of stacking faults and antisite domain boundaries on the conduction band edge in kesterite quaternary semiconductors

“…The CBO, on the other hand, is −70 and −77 meV, respectively, indicating that the ADBs can easily trap electrons, which is opposite to the SFs. This opposite effect of the ADB on the conduction band is consistent with a previous DFT calculation with symmetry analysis [28]. The ADB, a polytype with infinite length, has [110] faults increase the formation energy of the polytype as shown in a previous study [28].…”

“…Such planes are also formed in primitive-mixed CuAu phases (PMCA), which is another polytype of CZTS [6]. Generally speaking, such faults in this category of materials result in higher formation energy and lower band gap, predicted by a previous first-principles calculation [28]. The octet rule is broken at the other ADBs, and thus some S or Se atoms are bonded to two Sn atoms (the coordination in bulk kesterite is one Sn, one Zn, and two Cu).…”

“…The ADB, a polytype with infinite length, has [110] faults increase the formation energy of the polytype as shown in a previous study [28]. The electronic band gap of the polytype is negative-linearly correlated with the formation energy of polytypes [28], and thus the ADB should lower the band gap. Moreover, as it has been shown that the kesterite, stannite, and PMCA Cu 2 ZnGeS 4 have similar valence band edge position, and the change of the band gap is mainly explained by the change of the conduction band [37].…”

Electronic Structure and Optical Properties ofCu2ZnGeSe4: First-Principles Calculations and Vacuum-Ultraviolet Spectroscopic Ellipsometric Studies

“…The direct-indirect bandgap transition in Cu 2 ZnGeSe 4 has also been predicted in a previous theoretical study [7]. The details of the ordering-induced direct-indirect bandgap transitions are discussed elsewhere [44]. The lattice parameters used in our calculations and the resulting E 0 for three structural phases are summarized in Table I.…”

Nonisovalent Si-III-V and Si-II-VI alloys: Covalent, ionic, and mixed phases

“…The dotted line in Fig. 3(a) Because of the reduced symmetry, the four-fold L 3' -derived valence-band states split into four segregating levels [18], among which the highest energy level is localized on the Sication sublattice, while the lowest energy level is localized on the Si-anion sublattice. For Si 2 AlP (not shown here), the energy splitting between the highest and lowest levels is 2.05 eV, which is still not large enough to push the highest L 3' -derived level above the 25'derived states.…”