[Paper Review] Band bending profile and band offset extraction at semiconductor-metal interfaces

Sergej Schuwalow, Niels B. M. Schroeter+12 more|arXiv (Cornell University)|Oct 7, 2019

Advanced Semiconductor Detectors and Materials28 references4 citations

TL;DR

This paper presents a novel method to accurately extract band bending profiles and band offsets at buried semiconductor-metal interfaces using core-level photoemission spectroscopy combined with self-consistent electronic structure simulations. By leveraging high-signal-to-noise core level spectra and a reference system with known conduction band states, the method achieves sub-0.1 eV accuracy in band offset determination without requiring direct measurement of conduction band states, enabling reliable characterization of complex interfaces like InAs/Al with strong band bending.

ABSTRACT

The band alignment of semiconductor-metal interfaces plays a vital role in modern electronics, but remains difficult to predict theoretically and measure experimentally. For interfaces with strong band bending a main difficulty originates from the in-built potentials which lead to broadened and shifted band spectra in spectroscopy measurements. In this work we present a method to resolve the band alignment of buried semiconductor-metal interfaces using core level photoemission spectroscopy and self-consistent electronic structure simulations. As a proof of principle we apply the method to a clean in-situ grown InAs(100)/Al interface, a system with a strong in-built band bending. Due to the high signal-to-noise ratio of the core level spectra the proposed methodology can be used on previously inaccessible semiconductor-metal interfaces and support targeted design of novel hybrid devices and form the foundation for a interface parameter database for specified synthesis processes of semiconductor-metal systems.

Motivation & Objective

• To overcome the challenge of accurately measuring band alignment at buried semiconductor-metal interfaces where strong band bending distorts conventional spectroscopy.
• To develop a method that bypasses the need for direct conduction band measurements, which are often inaccessible in metal-encapsulated heterostructures.
• To enable high-accuracy band offset determination using only core-level photoemission spectra, leveraging a reference system with well-characterized electronic states.
• To establish a robust, transferable framework for extracting key interface parameters such as band offsets and core level shifts for use in device engineering.
• To support the creation of a standardized interface parameter database for specific semiconductor-metal synthesis processes based on experimental validation.

Proposed method

• Utilizes soft X-ray angle-resolved photoemission spectroscopy (SX-ARPES) to measure core level spectra from buried InAs/Al interfaces with high signal-to-noise ratio.
• Employs self-consistent Schrödinger-Poisson simulations to model the band bending profile and confining potential in the presence of strong Fermi level pinning.
• Uses electron accumulation layers in a reference semiconductor (e.g., InSb) as a benchmark to determine the core level shift parameter Δ_CL, which links core level binding energy to the conduction band edge.
• Applies the determined Δ_CL to the buried InAs/Al system to extract the interface band offset Φ_int via fitting of core level spectra under the same self-consistent potential model.
• Validates the extracted band offset by comparing simulated core level positions with directly measured quantum well states from SX-ARPES, ensuring consistency.
• Relies on the physical consistency between core level binding energy and band bending profile through a unified self-consistent potential model, eliminating independent fitting parameters.

Experimental results

Research questions

• RQ1 Can core-level photoemission spectroscopy be used to accurately extract band offsets at buried semiconductor-metal interfaces where direct conduction band measurements are experimentally inaccessible?
• RQ2 How can the intrinsic uncertainty in core level shift (Δ_CL) be minimized to enable high-accuracy band offset determination?
• RQ3 To what extent can self-consistent electronic structure simulations improve the reliability of band offset extraction from core level spectra?
• RQ4 Can the method be applied to systems with strong band bending, such as InAs/Al heterostructures with 2DEG formation, without requiring angular resolution or high surface quality?
• RQ5 Is the core-level-based approach quantitatively comparable to direct measurement of quantum well states in terms of band offset accuracy?

Key findings

• The method achieves a band offset determination accuracy of ±0.04 eV, with extracted values of Φ_int,CL = -0.39(4) eV and Φ_int,direct = -0.35(5) eV, showing excellent agreement.
• The core level binding energy shift Δ_CL was determined with high precision using the reference InSb(110) system, enabling reliable transfer to the InAs/Al interface.
• Quantum well state energies extracted from the core level fitting (ε₁,CL = -0.17 eV, ε₂,CL = -0.07 eV) matched directly measured values (ε₁,direct = -0.16 eV, ε₂,direct = -0.06 eV) within experimental uncertainty.
• The use of self-consistent potentials ensures a physically consistent relationship between core level energy and band bending, eliminating arbitrary energy offsets.
• The method enables accurate band offset extraction through core level spectra alone, even under up to 6–8 nm of metallic capping layers, significantly reducing acquisition time and surface quality requirements.
• The approach is robust and generalizable, supporting the development of a standardized interface parameter database for semiconductor-metal systems based on controlled synthesis processes.