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

Abstract

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.

Optoelectronic properties and ultrafast carrier dynamics of copper iodide thin films

“…However, the nature (i.e., shallow or deep acceptor) of I i is still controversial. For instance, some studies found that the I i are deep acceptors with ionization energy ~0.5 eV 16 , 38 in contrast to the shallow acceptors as revealed in other investigations 20 . On the other hand, the reduction in N for the CuI thin film upon PTA in air is most likely due to the possible removal and/or annihilation of V Cu and out-diffusion of I i .…”

“…On the other hand, the reduction in N for the CuI thin film upon PTA in air is most likely due to the possible removal and/or annihilation of V Cu and out-diffusion of I i . In addition, the formation of additional compensating donor defects (e.g., V I , Cu i , defect cluster V I + Cu i ) in the Cu-rich condition 38 cannot be ruled out. In order to evaluate the stability of the as-grown CuI thin film on glass substrate, the normalized electrical properties were recorded upon aging in the ambient air with increasing aging time, as shown in Fig.…”

Synthesis of Vacancy-Controlled Copper Iodide Semiconductor for High-Performance p-Type Thin-Film Transistors

“…29,30 The decrease in voids on the vacuum-annealed CuI surface with increasing annealing temperature is similar to a previous report, showing the reduced voids on the CuI surface with increasing substrate temperature in an Ar atmosphere, where it can be ascribed to the increased thermal energy that increases the frequency of the CuI lattice oscillations helping I and Cu to overcome the potential barrier and leave regular sites, 32 generating the I Vac and Cu interstitial defects, which are the most stable defects under Cu-rich condition according to the first-principles calculations. 33 Considering that the release of stored energy can be completed by recrystallization during annealing, 34 the reduction in voids with increasing annealing temperature may be attributed to the increased oscillation, relocation, and recrystallization of the CuI lattice in the vacuum-annealed CuI thin films. The detailed mechanisms need to be explored further.…”

Defect-State Transition Associated Hole Dynamics in Cuprous Iodide Nanosheets

“…Cu vacancies are intrinsic defects of γ-CuI, and their abundance gives γ-CuI the high hole density . First-principles calculations predict that rich V Cu in γ-CuI form shallow energy levels near the valence band, , as manifested by the broad peak in the fluorescence spectroscopy measurement (see Figure d). A recent study reported that the hole density in γ-CuI first increases then decreases with the increase of sample thickness .…”

“…The existence of the defect band in many studies of dynamics involving defect states is indirectly inferred through the recovery of the band-edge bleach peak of transient absorption (TA) spectra, while few studies observe directly the band filling peaks of defect states . To date, the understanding of defects in γ-CuI are mainly based on theoretical calculations . Here, we report femtosecond TA spectroscopic investigations of the dynamics of photoexcited carries and their interactions with defect states in synthesized γ-CuI nanosheets.…”