Determining band alignment using a single core-level photoelectron spectrum

Semiconductor heterostructures are the backbone of modern electronics, enabling advancements in LEDs, transistors and photovoltaics. To achieve the targeted device functionality, energy bands in the individual material layers must align in desired ways.

X-ray photoelectron spectroscopy (XPS) is widely used to measure band alignment. The binding energies of electrons bound to the atoms in the various layers contain all the required information.

One of the materials may not exhibit core-level spectra with the right properties to allow the traditional XPS method to work well. However, Wang et al. discovered, for certain kinds of heterojunctions, a single core-level photoelectron spectrum from an element common to both materials can be used to determine the band alignment.

The key criterion in using this method is the difference in electrostatic potential across the interface has to be large enough to ensure the photoelectron peaks from the two materials are well separated in energy. If this is the case, the binding energy difference between the two peaks can be used to determine the band alignment.

The researchers used a p-n junction of two complex oxide semiconductors, strontium-doped lanthanum ferrite (p-Sr_0.12La_0.88FeO₃) and niobium-doped strontium titanate (n-SrNb_0.01Ti_0.99O₃). Strontium and oxygen are the common elements, where the core-level photoelectron features are far enough apart on the energy scale to enable accurate results.

At first, the authors did not know what was causing the unusual splitting in the strontium and oxygen core-level spectra.

“Once we realized what was causing the strontium and oxygen core-level splittings, we knew we had discovered a new way to determine the band alignment using only one core level,” co-author Scott Chambers said.

Source: “Determining valence band offsets in heterojunctions using a single core-level x-ray photoelectron spectrum,” by Le Wang, Yingge Du, and Scott Chambers, Journal of Vacuum Science and Technology A (2021). The article can be accessed at https://doi.org/10.1116/6.0001103 .

This paper is part of the Special Collection Commemorating the Career of Charles S. Fadley. Learn more here .