QDev Seminar: Petr Sennikov

High-pure, high-enriched Si and Ge isotopes in form of gases (SiF₄, SiH₄, GeF₄, GeH₄), bulk materials and thin films. Past, present and future.

Sennikov Petr G.

Institute of Chemistry of High-Pure Substances of RAS

Institute of Applied Physics of RAS

The natural silicon consists of 3 stable isotopes, the natural germanium – of 5 stable isotopes (²⁹Si and ⁷³Ge have odd nuclear spin numbers). The report gives short chronological overview of milestones of application of these isotopes for basic research (from 1942 up to present time). In the period from 1942 (publication of theoretical work of I.Pomeranchuk describing the dependence of thermal conductivity of Si and other semiconductors on isotopic disorder) to beginning of 90s (starting of commercial production of stable isotopes in Russia by centrifugal method) only one experimental work on this subject has been published (T.Geballe, G.Hall, 1958). Since 1993 manufacturing of Ge and later Si isotopes based on chemical recovering of isotopically enriched fluorides has been started. The dependence of their physical properties on isotopic composition has been investigated and new application fields were proposed. The driving force of development of effective chemical method of production of high-pure and high-enriched ²⁸Si was the idea to use the sphere from this material for redefinition of mass unit and redermination of Avogadro constant – the Avogadro project (1994). In 2000-2003 first samples of ²⁸Si (in hundred gram amount) as well as of two other isotopes (in gram amount) of sufficient for Avogadro project quality were obtained. In 2006 the first phase of Avogadro project finished with 6 kg of 99,995% ²⁸Si with extremely low content of oxygen, carbon and boron impurities and new precise value of Avogadro constant was determined. At the same time, this valuable material is used now also for basic research. First of all it concerns solid state spectroscopy and quantum bit storage. The recent outstanding result regarding all-silicon quantum computer design  is the obtaining of coherence time of 39 min at room temperature for ionized ³¹P in 99,995% ²⁸Si (M.Thewalt, 2013). The international GERmanium Detector Array (GERDA) project for search of neutrinoless double beta decay of 76Ge is based on 87% enriched isotop in form of extremely high-pure single crystal. Up to now about 37 kg of this material was used for detector construction. Future requirements are of 1000 kg. That is the challenge for new effective methods of Ge isotopes production.