Journal Article

Direct observation of a two-dimensional hole gas at oxide interfaces

Lee, J W, Campbell, N, Lee, J, Lee, H, Tsymbal, E Y, Oh, S H, Eom, C B, Paudel, T R, Asel, T J, Park, B, Rzchowski, M S, Zhou, H, Seo, J, Noesges, B, Brillson, L J

2018

Overview

The discovery of a two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface1 has resulted in the observation of many properties2–5 not present in conventional semiconductor heterostructures, and so become a focal point for device applications6–8. Its counterpart, the two-dimensional hole gas (2DHG), is expected to complement the 2DEG. However, although the 2DEG has been widely observed9, the 2DHG has proved elusive. Herein we demonstrate a highly mobile 2DHG in epitaxially grown SrTiO3/LaAlO3/SrTiO3 heterostructures. Using electrical transport measurements and in-line electron holography, we provide direct evidence of a 2DHG that coexists with a 2DEG at complementary heterointerfaces in the same structure. First-principles calculations, coherent Bragg rod analysis and depth-resolved cathodoluminescence spectroscopy consistently support our finding that to eliminate ionic point defects is key to realizing a 2DHG. The coexistence of a 2DEG and a 2DHG in a single oxide heterostructure provides a platform for the exciting physics of confined electron–hole systems and for developing applications.

• Publisher: Nature Publishing Group
• Subject: Cathodoluminescence / Electron gas / Electrons / Epitaxial growth / First principles / Heterostructures / Holography / Partial pressure / Point defects / Strontium titanates