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

Dr. HyungWoo Lee
Department of Physics, KAIST

Oct. 12 (Fri.), 04:00 PM
E6-2. 1st fl. #1323

Abstract:
Over the past decade, the discovery of a two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface resulted in the observation of remarkable properties not present in conventional semiconductor heterostructures, and so become a focal point for device applications. Its counterpart, the two-dimensional hole gas (2DHG), is expected to complement the 2DEG. However, although the 2DEG has been widely observed, the 2DHG has proved elusive. In this seminar, I will introduce a highly mobile 2DHG in epitaxially-grown SrTiO3/LaAlO3/SrTiO3 heterostructures. Using electrical transport measurements and in-line electron holography, I provide direct evidence of a 2DHG that coexists with a 2DEG at complementary heterointerfaces in the same structure. The key was to create atomically well-defined interfaces and to minimize oxygen-vacancy defects. Note that precise control of the interfacial atomic structure as well as point defects enabled us to realize the 2DHG at oxide heterointerfaces. 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.