Buried Unstrained Germanium Channels: A Lattice‐Matched Platform for Quantum Technology

ABSTRACT Strained germanium (‐Ge) and strained silicon (‐Si) buried quantum wells have enabled advanced spin‐qubit quantum processors. However, in the absence of suitable lattice‐matched substrates, ‐Ge and ‐Si are deposited on defective, metamorphic SiGe buffers, which may impact device performance and scaling. Here an alternative platform is introduced based on the heterojunction between bulk unstrained Ge and a lattice‐matched strained silicon‐germanium (‐SiGe) barrier, eliminating the need for metamorphic buffers altogether. In a structure with a 52‐nm‐thick ‐SiGe barrier, a low‐disorder two‐dimensional hole gas is demonstrated with a high‐mobility of and a low percolation density of . Quantum transport shows that holes confined in the buried unstrained Ge channel have a strong density‐dependent in‐plane effective mass and out‐of‐plane ‐factor, pointing to a significant heavy‐hole–light‐hole mixing in agreement with theory. Measurements of Zeeman‐split levels in quantum point contacts further highlight this character, showing a two‐fold larger in‐plane ‐factor in Ge than in ‐Ge. The prospects of strong spin–orbit interaction, isotopic purification, and of hosting superconducting pairing correlations make this platform appealing for fast quantum hardware and hybrid quantum systems.