4/5/2023 0 Comments Ion bonding coating![]() ![]() However, the low exciton binding energy of ZnSe makes room temperature excitonic lasing difficult even in cases where the binding energy is enhanced by quantum confinement. The advantage of excitonic laser gain has been demonstrated for ZnSe-based quantum wells ( Ding et al. The ZnO exciton has a binding energy of 60 meV, which is significantly larger than the effective thermal energy at room temperature thus excitonic gain mechanisms could be expected to play a significant role in ZnO-based devices. Thus crystal field splitting and spin-orbit coupling give rise to three two-fold degenerate valence bands: A(Γ 9), B(Γ 7), and C(Γ 7) from the valence band maximum. Because of the lower symmetry of the wurtzite structure, the crystal field further lifts the valence band degeneracy. Spin–orbit splitting leads to a partial lifting of the valence band degeneracy: the six-fold degenerate valence band splits into a four-fold ( j=3/2) and a two-fold band ( j=1/2). The conduction band of ZnO is predominantly s-like, while the valence band is p-like. ZnO has a direct bandgap with the conduction band minimum and the valence band maximum located at k=0 in the Brillouin zone. Although the ideal wurtzite structure has four-fold coordination with a hexagonal unit cell having two lattice parameters of a and c ( c/ a= 8/3=1.633), the actual lattice of ZnO deviates from the ideal lattice with c/ a=1.602. A phase transition to the rock-salt structure occurs under high pressure. The most stable phase under thermal equilibrium is the wurtzite structure. ZnO can crystallize in the wurtzite, zinc blende, and rock-salt structures. The chemical bonding in ZnO is predominantly covalent but with a significant contribution from ionic bonding. Yao, in Encyclopedia of Materials: Science and Technology, 2001 1 Material Properties ![]()
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