High purity isotopically enriched ⁷⁰Ge and ⁷⁴Ge single crystals: Isotope separation, growth, and properties

Abstract

70Ge and 74Ge isotopes were successfully separated from natural Ge and zone purified. Several highly enriched, high purity 70Ge and 74Ge single crystals were grown by the vertical Bridgman method. The growth system was designed for reliable growth of low dislocation density, high purity Ge single crystals of very small weight (∼4 g). A 70Ge and a 74Ge crystal were selected for complete characterization. In spite of the large surface to volume ratio of these ingots, both 70Ge and 74Ge crystals contain low electrically active chemical net-impurity concentrations of ∼2 × 1012 cm−3, which is two orders of magnitude better than that of 74Ge crystals previously grown by two different groups.1,2 Isotopic enrichment of the 70Ge and the 74Ge crystals is 96.3% and 96.8%, respectively. The residual donors and acceptors present in both crystals were identified as phosphorus and copper, respectively. In addition, less than 1011 cm−3 gallium, aluminum, and indium were found in the 70Ge crystal.

Large Stark tuning of donor electron spin qubits in germanium

“…73 Ge [9,32,33]. This crystal was neutron transmutation doped to a density of 3 × 10 15 75 As donors/cm 3 .…”

Hyperfine interactions at dangling bonds in amorphous germanium

“…The preparation of these crystals is described in more detail in Ref. 23. For the a-Ge films with intermediate 73 Ge concentrations of 31 and 51 %, the appropriate amounts of 70 Ge and 73 Ge were electron-beam melted in a single Be crucible before deposition in order to ensure a homogeneous mixing.…”

Highly tuneable hole quantum dots in Ge-Si core-shell nanowires

“…For spin-based quantum computing, 1 increasing research efforts have focused in recent years on C, Si, and Ge [2][3][4] because they can be isotopically enriched to only contain nuclei with zero spin 5,6 and thus exhibit exceptionally long spin lifetimes. 7,8 The one-dimensional character of Ge-Si core-shell nanowires leads to unique electronic properties in the valence band, where heavy and light hole states are mixed.…”