Undoped Strained Ge Quantum Well with Ultrahigh Mobility of Two Million
Zhenzhen Kong, Zonghu Li, Gang Cao, Jiale Su, Yiwen Zhang, Jinbiao Liu, Jingxiong Liu, Yuhui Ren, Huihui Li, Laiming Wei, Guo‐Ping Guo, Yuanyuan Wu, Henry H. Radamson, Junfeng Li, Zhenhua Wu, Hai-Ou Li, Jiecheng Yang, Chao Zhao, Tianchun Ye, Guilei Wang
Abstract
We develop a method to fabricate an undoped Ge quantum well (QW) under a 32 nm relaxed Si 0.2 Ge 0.8 shallow barrier. The bottom barrier contains Si 0.2 Ge 0.8 (650 °C) and Si 0.1 Ge 0.9 (800 °C) such that variation of Ge content forms a sharp interface that can suppress the threading dislocation density (TDD) penetrating into the undoped Ge quantum well. The SiGe barrier introduces enough in-plane parallel strain (ε ∥ strain −0.41%) in the Ge quantum well. The heterostructure field-effect transistors with a shallow buried channel obtain an ultrahigh two-dimensional hole gas (2DHG) mobility over 2 × 10 6 cm 2 /(V s) and a very low percolation density of (5.689 ± 0.062) × 10 10 cm –2 . The fractional indication is also observed at high density and high magnetic fields. This strained germanium as a noise mitigation material provides a platform for integration of quantum computation with a long coherence time and fast all-electrical manipulation.