Extremely low energy ARPES of quantum well states in cubic-GaN/AlN and GaAs/GaAlAs heterostructures

TL;DR

This study demonstrates the use of extremely low energy ARPES to probe buried quantum well states in cubic-GaN/AlN heterostructures, revealing surface roughness effects and depth limitations for different materials.

Contribution

It introduces a novel application of low energy ARPES for accessing buried quantum well states in semiconductor heterostructures, highlighting its capabilities and limitations.

Findings

QW states in cubic-GaN/AlN can be observed but not their dispersion due to surface roughness.

QW states in GaAs/AlGaAs are too deep for detection by low energy ARPES.

Surface flatness influences the ability to detect and interpret ARPES spectra.

Abstract

Quantum well (QW) heterostructures have been extensively used for the realization of a wide range of optical and electronic devices. Exploiting their potential for further improvement and development requires a fundamental understanding of their electronic structure. So far, the most commonly used experimental techniques for this purpose have been all-optical spectroscopy methods that, however, are generally averaged in momentum space. Additional information can be gained by angle-resolved photoelectron spectroscopy (ARPES), which measures the electronic structure with momentum resolution. Here we report on the use of extremely low energy ARPES (photon energy $\sim$ 7 eV) to increase its depth sensitivity and access buried QW states, located at 3 nm and 6 nm below the surface of cubic-GaN/AlN and GaAs/AlGaAs heterostructures, respectively. We find that the QW states in cubic-GaN/AlN can indeed be observed, but not their energy dispersion because of the high surface roughness. The GaAs/AlGaAs QW states, on the other hand, are buried too deep to be detected by extremely low energy ARPES. Since the sample surface is much flatter, the ARPES spectra of the GaAs/AlGaAs show distinct features in momentum space, which can be reconducted to the band structure of the topmost surface layer of the QW structure. Our results provide important information about the samples' properties required to perform extremely low energy ARPES experiments on electronic states buried in semiconductor heterostructures.