New methods for determining the band gap behavior of ZnO

Two new methods to determine the band gap behavior of ZnO are proposed. One is fitting based on the relationship of absorption coefficient and reflection, in which photon energy (hv) can be expressed as a function of hν ⋅ ln[(Rmax − Rmin)/(R − Rmin)]. This method can give some characteristic parameters of ZnO such as Eg′ (the sum or difference of band gap (Eg) and phonon energy (Ep)), transition type and transition constant. The other method is fitting based on the relationship between absorption coefficient and transmission as well as reflection, in which hv is expressed as a function of hν ⋅ ln[(1 − R)2/T]. In the latter fitting, we separated the wavelength scope into two independent wavelength ranges for improving analysis accuracy. Based on the second method, the band gap Eg and phonon energy Ep that provide the energy for indirect transition when hv < Eg are determined. Besides, the transition type and transition constant, which are related to states density and transition rate, can also be obtained. The band gap value obtained by the second method is as large as that obtained by extrapolation methods, and larger than that decided by energy loss function. The deviation of the band gap value obtained by our method and that by the energy loss function is also discussed.

► A new method based on simulation to determine the band gap characteristics.
► The band gap characteristic parameters is determined without assumption.
► More important/useful band gap parameters can be obtained.
► Our method is convenient and the results are reasonable.