Undoped Strained Ge Quantum Well with Ultrahigh Mobility of Two Million

Wedevelop a method to fabricate an undoped Ge quantum well (QW)under a 32 nm relaxed Si0.2Ge0.8 shallow barrier.The bottom barrier contains Si0.2Ge0.8 (650 degrees C) and Si0.1Ge0.9 (800 degrees C) such thatvariation of Ge content forms a sharp interface that can suppressthe threading dislocation density (TDD) penetrating into the undopedGe quantum well. The SiGe barrier introduces enough in-plane parallelstrain (epsilon(parallel to) strain -0.41%) in the Gequantum well. The heterostructure field-effect transistors with ashallow buried channel obtain an ultrahigh two-dimensional hole gas(2DHG) mobility over 2 x 10(6) cm(2)/(V s)and a very low percolation density of (5.689 +/- 0.062) x10(10) cm(-2). The fractional indicationis also observed at high density and high magnetic fields. This strainedgermanium as a noise mitigation material provides a platformfor integration of quantum computation with a long coherence timeand fast all-electrical manipulation.

Automated summary

We have developed a method to fabricate an undoped Ge quantum well (QW) under a 32 nm relaxed Si0.2Ge0.8 shallow barrier, which can suppress the threading dislocation density (TDD) penetrating into the undoped Ge quantum well. The Ge quantum well exhibits in-plane parallel strain introduced by the SiGe barrier. The heterostructure field-effect transistors with a shallow buried channel exhibit an ultrahigh two-dimensional hole gas (2DHG) mobility and a very low percolation density.