First-principles identification of VI+Cui defect cluster in cuprous iodide: origin of red light photoluminescence

The γ-phase Cuprous Iodide (CuI) emerges as a promising transparent p-type semiconductor for next-generation display technology because of its wide direct band gap, intrinsic p-type conductivity, and high carrier mobility. Two main peaks are observed in its photoluminescence (PL). One is short wavelength (410-430 nm) emission, which is well attributed to the electronic transitions at Cu vacancy, whereas the other long wavelength emission (680-720 nm) has not been fully understood. In this paper, through first-principles simulations, we investigate the formation energies and emission line shape for various defects, and discover that the intrinsic point defect cluster V_I+Cu_i^(2+) is the source of the long wavelength emission. Our finding is further supported by the prediction that the defect concentration decreases dramatically as the chemical condition changes from Cu-rich to I-rich, explaining the significant reduction in the red light emission if CuI is annealed in abundant I environment.

Electronic property of intrinsic point defect system on β–Si3N4 (0001) surface

The intrinsic point defect influence data for [Formula: see text]–Si3N4 by far are incomplete and experimental clarification is not easy. In this contribution, the effects of vacancy ([Formula: see text], [Formula: see text] and [Formula: see text]) and interstitial ([Formula: see text] and [Formula: see text]) defects on the electronic properties of H-passivated [Formula: see text]–Si3N4 (0001) surface are explored based on density functional theory (DFT) calculation. The results show that it is easier to form [Formula: see text] vacancy defects in the surface layer under Si-rich conditions. The existence of N vacancies makes the bottom of conduction bands shift downwards, and the top of valance band is away from Fermi level. The presence of [Formula: see text] makes the system have the characteristics of p-type semiconductor, and the closer to the inner layer, the narrower the range of additional energy bands and the greater the degree of localization of electrons. The closer the Si atom vacancy is to the surface, the smaller the photon energy corresponding to the maximum absorption coefficient is. Compared with the N vacancy system, the Si vacancy system has higher reflection ability in the low energy region. For the interstitial defect systems, [Formula: see text] is easy to form on the surface layer, and [Formula: see text] is easy to produce in the inner layer. The [Formula: see text] system has a new additional energy level at the Fermi level, and as the [Formula: see text] is closer to the inner layer, the energy range of the additional energy level is also narrower. In the [Formula: see text] system, the new additional energy levels appear at the Fermi level and the intermediate band. The results have positive significance for the design of this advanced structural and functional integrated ceramics. The absorption coefficient and reflection coefficient of [Formula: see text] system are much higher than those of other systems when the energy is greater than 2.5 eV.

Structural characterization of off-stoichiometric kesterite-type Cu2ZnGeSe4 compound semiconductors: from cation distribution to intrinsic point defect density

The substitution of Ge4+ for Sn4+ in Cu2ZnSn(S,Se)4 (CZTSSe) kesterite-type absorber layers for thin film solar cells has been proven to enhance the opto-electronic properties of the material.