VGF growth of germanium single crystals without crucible contact

Experimental results on the vertical gradient freeze growth of germanium single crystals without crucible contact are presented. Two different approaches to establish a stable pressure difference necessary for avoiding the contact between crystal and crucible on solidification are described. Germanium crystals with a diameter of up to 3 in were grown almost without contact to the crucible wall. The effect of detachment is discussed with respect to the microscopical surface roughness and dislocation density of the grown crystals. In comparison to conventionally grown reference crystals the structural perfection of the detached-grown crystals is found to be much higher which can be attributed to the reduced thermal and thermo-mechanical stress in growth without wall contact.

Source: Journal of Crystal Growth

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Czochralski-growth of germanium crystals containing high concentrations of oxygen impurities

Oxygen-containing germanium (Ge) single crystals with low density of grown-in dislocations were grown by the Czochralski (CZ) technique from a Ge melt, both with and without a covering by boron oxide (B₂O₃) liquid. Interstitially dissolved oxygen concentrations in the crystals were determined by the absorption peak at 855 cm⁻¹ in the infrared absorption spectra at room temperature. It was found that oxygen concentration in a Ge crystal grown from melt partially or fully covered with B₂O₃ liquid was about 10¹⁶ cm⁻³ and was almost the same as that in a Ge crystal grown without B₂O₃. Oxygen concentration in a Ge crystal was enhanced to be greater than 10¹⁷ cm⁻³ by growing a crystal from a melt fully covered with B₂O₃; with the addition of germanium oxide powder, the maximum oxygen concentration achieved was 5.5×10¹⁷ cm⁻³. The effective segregation coefficients of oxygen in the present Ge crystal growth were roughly estimated to be between 1.0 and 1.4.

Source: Journal of Crystal Growth

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Double-hump diffusion profiles of copper and nickel in germanium wafers yielding vacancy-related information

Diffusion of Cu and Ni into Ge was investigated between 700 and 900 °C with the aid of rapid isothermal lamp annealing and spreading-resistance profiling. Using low-dislocation-density single-crystal Ge wafers with a backside gold layer, we observed typical double-hump diffusion profiles of both Cu and Ni. These profiles can be described within the dissociative model by taking into account that the front surface acts as source for both vacancies (V) and Cu or Ni while the back surface combines the V-source feature with a Cu, Ni-sink property. Profile fitting yields data regarding the V-assisted Ge self-diffusion coefficient and the equilibrium concentration of vacancies as a function of temperature.

Source:IEEE

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