Band gap and defect states of MgO thin films investigated using reflection electron energy loss spectroscopy

Abstract

The band gap and defect states of MgO thin films were investigated by using reflection electron energy loss spectroscopy (REELS) and high-energy resolution REELS (HR-REELS). HR-REELS with a primary electron energy of 0.3 keV revealed that the surface F center (FS) energy was located at approximately 4.2 eV above the valence band maximum (VBM) and the surface band gap width (E g S ) was approximately 6.3 eV. The bulk F center (F B ) energy was located approximately 4.9 eV above the VBM and the bulk band gap width was about 7.8 eV, when measured by REELS with 3 keV primary electrons. From a first-principles calculation, we confirmed that the 4.2 eV and 4.9 eV peaks were F S and F B , induced by oxygen vacancies. We also experimentally demonstrated that the HR-REELS peak height increases with increasing number of oxygen vacancies. Finally, we calculated the secondary electron emission yields (γ) for various noble gases. He and Ne were not influenced by the defect states owing to their higher ionization energies, but Ar, Kr, and Xe exhibited a stronger dependence on the defect states owing to their small ionization energies. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Controlling the non-linear optical properties of MgO by tailoring the electronic structure

“…In pure MgO (Fig.4a), we note an optical band gap of bulk MgO of around 4.7 eV. This lies in clear contrast to the accepted band-gap of around 7.8 eV [30]. The discrepancy between the accepted band-gap and the value reported here is due to the choice of xc functional used.…”

“…Here we use the GGA to the xc functional, which is known to underestimate the band-gap. In fact, calculations similar to those presented here have yielded similar bulk band-gaps from 4.6 to 5 eV for bulk MgO [30,31]. It should be noted that surface band gaps of MgO have been shown elsewhere to be in the 5 eV range.…”

“…It has been shown elsewhere that band-gaps of MgO can be well reproduced with other, more computationally expensive methods [30]. Calculations of the band-structure of MgO have been shown to match experimental values when more complex approaches (using hybrid Hartree-Fock methods) to the xc functional have been employed [31].…”

Energy band offsets of dielectrics on InGaZnO4

“…The matter is further complicated by the presence of surface carbon, which is not discussed in these articles. The traditional components of the O1s spectrum on metal oxides consist of three peaks of 530-531 eV for lattice oxygen, 531-533 eV for C-O and C¼O, and 533-534 eV for O-H and C-O-H groups [235][236][237][238] and are also shown in Figure 27. The mid-binding energy component for C-O/C¼O lies at the same energy assigned to the oxygen defects and separating the contributions of each will be difficult to determine.…”

Wet-cleaning of MgO(001): Modification of surface chemistry and effects on thin film growth investigated by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy

“…The same observation was made on the O1s ( figure 3-f and g). show that defects in MgO may affect the optical properties 26,27 . Figure 6 shows the XPS analysis of the Mg2s peak of the surface of the six samples after annealing and a summary of the composition of the surface evaluated after fitting of the Mg2s peak.…”