Experimental determination of valence band maxima for SrTiO3, TiO2, and SrO and the associated valence band offsets with Si(001)

Abstract

We address the issue of accurate determination of the valence band maximum (VBM) for SrTiO3(001) single crystals and epitaxial films, as well as TiO2(001) anatase and SrO epitaxial films. These measurements are of critical importance in determining valence band offsets in heterojunctions of these oxides with Si. Three different methods are analyzed: (1) fitting a Gaussian broadened theoretical density of states to the x-ray photoelectron valence band spectrum; (2) finding the intersection of a regression line that spans the linear portion of the x-ray photoelectron valence band leading edge with the background between the valence band maximum and the Fermi level; and (3) determining the energy at which high-resolution ultraviolet photoemission intensity at the leading edge goes to zero. We find that method 1 yields physically unreasonable results when used in conjunction with density functional theory because the latter does not predict the detailed shape of the valence bands in these oxides with sufficient accuracy. In contrast, methods 2 and 3 give physically reasonable results that are in good mutual agreement. The difference in VBM between method 1 and methods 2 and 3 is 0.4–0.6 eV, depending on the oxide. Methods 2 and 3 yield the most reliable VBM, provided the experiments are carried out with adequate energy resolution.

Energy band alignment of atomic layer deposited HfO2 oxide film on epitaxial (100)Ge, (110)Ge, and (111)Ge layers

“…Truly, the VBM value is sensitive to the choice of points on the leading edge used to obtain the regression line. 30,31 Several different sets of points were selected over the linear region of the leading edge to perform regressions, and the uncertainty of DE v and DE c values were found to be in the range of 0.05-0.1 eV in the present work. Figure 1(a) shows the VBM for the (100)Ge film.…”

Valence band offset of InN∕AlN heterojunctions measured by x-ray photoelectron spectroscopy

“…12 The position of the valence band maximum ͑VBM͒ is calculated by extrapolating a linear fit to the leading edge of the valence band photoemission to the background level in order to take account of the finite resolution ͑0.45 eV͒ of the spectrometer. 13 A low-energy electron flood gun was utilized for the measurements of the AlN sample to achieve charge compensation. Calibration to a universal energy reference was not required as it is the relative energy separation of spectral features that is of importance for the determination of a valence band offset ͑VBO͒.…”

Band offset determination of mixed As/Sb type-II staggered gap heterostructure for n-channel tunnel field effect transistor application

“…Curve fittings were used to separate the spin-orbit splitting of 13,16 According to Kraut's method, 13 the VBM was determined by fitting a instrumentally broadened valence band density of states (DOS), for which the VBM is uniquely identified as the energy at which the DOS goes to zero, to the leading edge of the experimental valence band spectrum. 13,16 Based on this method, the insets of Figs. 4(a) and 4(b) show the corresponding magnified VB spectra of In 0.7 Ga 0.3 As and GaAs 0.35 Sb 0.65 , respectively.…”