Direct observation of Al-doping-induced electronic states in the valence band and band gap of ZnO films

Simultaneous enhancement of carrier mobility and concentration via tailoring of Al-chemical states in Al-ZnO thin films

“…12,19 However, the one additional band $1.2 eV is attributed to DOS in the forbidden band gap region as Al impurity band state, which pins the Fermi level just below the conduction band minimum. 21 As a consequence, higher values of conductivities are found in these samples. The overall strength of Zn 3d band is found maximum for the power density 2 W/cm 2 , which suggests that increase in O vacancies saturates at 2 W/cm 2 , and further increase in power density does not affect the O vacancies, which is in agreement with the calculated stoichiometry of ZnO as mentioned in XPS results.…”

“…In particular, transparentconductive characteristics of AZO films depend on E g modulation by controlling dopants concentration and defects creation by O vacancies. 11 To enhance the transparentconductive characteristics, effect of growth conditions under spray pyrolysis, 12 magnetic field alignment process, 10 laser molecular beam epitaxy, 13 atomic layer deposition, 11,14 pulsed laser deposition, 15,16 chemical bath technique, 17 plasma based chemical vapor deposition, 18 RF sputtering, [19][20][21] and DC sputtering [22][23][24] have been utilized. Among these, plasma based sputtering techniques have the advantage for large area and fast deposition, but require substrate heating for good conductivity.…”

Effects of Al-Impurity Type on Formation Energy, Crystal Structure, Electronic Structure, and Optical Properties of ZnO by Using Density Functional Theory and the Hubbard-U Method

“…They used the optimal effective Hubbard-U (U eff ) of 8.5 eV and calculated the ZnO band gap (2.13 eV), which was lower than the experimental value of 3.4 eV. Gabás et al [ 20 ] indicated the decrease in the AZO film resistivity is due to the filling of the Al impurity band state by using the DFT+U method. According to the calculated results regarding the formation energy, Li et al [ 21 ] indicated that a single doping of Al forms easily, particularly at the extreme O-rich limit.…”

Hard X-ray PhotoElectron Spectroscopy of transition metal oxides: Bulk compounds and device-ready metal-oxide interfaces

“…Interestingly, it has been soon clear that a further parameter enters into play, namely the relative ratio of states with different symmetry that strongly favors extended s states with respect to localized p, d and f ones [18,19]. Such differences and the experimental observation of a similar enhancement of s states for many metal oxides turned to be a new and unique probe of metal s character within the total density of states of an oxide [20][21][22][23]. Important examples of such approach include doped ZnO, CdO, In 2 O 3 and SnO 2 , systems with potentially relevant applications in optoelectronic and spintronics, where doping produces a degenerate electron gas with carrier concentrations in the range up to about 10 21 cm −3 .…”