Can photoemission measure valence-band discontinuities?

Abstract

The progress in understanding heterojunction band lineups has increasingly become dependent upon the availability of accurate and reliable measurements. The reported values of the band offset for the Si/GaAs system measured by photoemission range from 0.05 to 0.70 eV. Such a large scatter in experimentally determined discontinuities is common for other systems as well and not only makes the evaluation of different theories difficult, but raises the question as to whether such variations are real and representative of technological variations in the offset. Clearly the understanding and control of these variations is essential before any device applications can be realized. We attempted to study the source of these variations in the Sil GaAs( 110) heterojunction. We altered the growth conditions to effect modifications in the overlayer crystalline order, strain, and chemical reactivity. While some ofthese studies have been previously reported, their collective consideration gives us a much more coherent overview of the problems involved in discontinuity measurements. In our studies we found the offset to be 0.23 ± 0.05 e V for both amorphous and crystalline overlayers, either strained or unstrained. We did, however, observe discontinuities as large as 0.7 e V for room temperature growths. We show that such large discontinuities are due to dangling bond type states which extend into the band gap and change the apparent valence band maximum energy. These states can be removed by annealing the sample without crystallization. Offsets as small as 0.05 e V may be inferred from our data if we fail to account for the contributions of rather subtle chemical effects at the interface. Overall, we found the discontinuity to be more dependent on the interpretation of the data than on technological variations. If we discern and properly account for extrinsic effects and unambiguously define the discontinuity, photoemission can yield accurate and single valued measurements of the valence band discontinuity.1228

Energy band offsets of dielectrics on InGaZnO4

“…[23][24][25][26][27] The valence band offset between the dielectric and IGZO is directly measured and the conduction band offset is derived from this and the differences in bandgaps. 124,125 One of the key methods for determining valence band offsets is XPS in conjunction with techniques for obtaining bandgaps, like absorption or various types of electron energy loss spectroscopies, [126][127][128][129][130][131][132][133][134][135][136][137][138] so it is worth briefly reviewing the need for accounting for sample charging in dielectrics and curve fitting of the data. Nichols et al 134 provide a discussion of the precision of the XPS approach in determining core levels.…”

Determination of the valence band offset of a heterojunction using low energy yield spectroscopy

“…This determination was made using a sample on which a thin [14] microcrystalline graphite layer had developed over the SiC layer. Finally, the valence band alignment between the silicon substrate and the microcrystalline graphite film E V (C/Si) was determined by the difference between E V (SiC/Si) and E V (C/SiC) , corrected for the rigid shift of the bands due to the band bending in the SiC layer after the microcrystalline graphite layer had developed [18]. Their shift (β) was obtained from the change in the position of the Si 2p core level in the SiC layer after the thin microcrystalline graphite layer had developed.…”

X-Ray Photoemission Investigation of the Beryllium Oxide Band Alignment with Magnesium Oxide and Estimates for Other Insulating and Conducting Oxides

“…The peak positions for all XPS core levels were determined via curve fitting using a mixed Gaussian-Lorentzian lineshape and Shirley background with Casa XPS software (53). The VBM was determined via linear regression analysis of the steepest slope of the turn-on for the photoemission valence band spectra (54).…”