Czochralski growth techniques of germanium crystals grown from a melt covered partially or fully by liquid B2O3

We propose two unique Czochralski (CZ) techniques for growing germanium (Ge) crystals with an extremely low dislocation density and high interstitial oxygen concentration ([Oi]) using boron oxide (B2O3) and a silica crucible. When a Ge melt is partially covered with liquid B2O3, but only on the outer region of the melt surface, germanium-oxide (GeO2)-related particles forming naturally in the melt are effectively dissolved by the liquid B2O3. The clean central portion of the melt produces dislocation-free undoped or Ga-doped Ge crystals. In addition, Ge crystals with [Oi] up to 6×1017 cm−3 can be grown from a melt fully covered by liquid B2O3 with added GeO2 powder. The reaction and transportation of oxygen atoms during the growth process using B2O3 was investigated, revealing that liquid B2O3 acts like a catalyst without heavy contamination of the growing Ge crystal by B and Si atoms.

► We propose two unique Czochralski techniques for growing Ge crystals using B2O3. ► Dislocation-free Ge crystals can be grown from the Ge melt partially covered with liquid B2O3. ► Ge crystals with high oxygen concentration can be grown from a melt fully covered by liquid B2O3. ► The maximum interstitial oxygen concentration in such crystals obtained was 6×1017 cm−3. ► The liquid B2O3 added to Ge melt acts like a catalyst without contamination of the Ge crystal.