Vertical gradient freeze

H. Weimann, J. Amon, T. Jung, G. Mueller. Numerical simulation of the growth of 2" diameter GaAs crystals by the vertical gradient freeze technique. J Crys Growth 180 560, 1997. 

VGF Vertical-Gradient Freezing rather rare method of constant-cooling solidification in a vertical temperature gradient ZM (Joule Heat) Zone Melting first simple method of directional solidifica-... 

Due to the relatively poor thermal conductivity and low yield stresses of III-V and II-VI compounds, as compared with Ge and Si, it is not possible to reduce the thermal stresses to a suffidently low level to avoid dislocation multiplication. However, recent developments in vertical gradient freeze techniques have produced a marked reduction ofdislocation density in undoped GaAsand InP. InVGF growth the establishment of a uniaxial heat flow has led to minimum dislocation densities below 10 cm and 10 cm in 4-inch undoped and Si-doped GaAs crystals, respectively. 

A. Kleinwechter, U. Kretzer, Th. Steinegger, B. Weinert, 2001, Development of a vertical gradient freeze process for low EPD GaAs substrates , Mater. Sci. Eng. B 80, 5-9. 

Fig. 5.1 Schematic principle of (a) the vertical gradient freeze method and (b) the vertical Bridgman method.

An important breakthrough was achieved in the late 1980s when the vertical gradient freeze (VGF) technique was developed [3, 4]. In the following period it was possible to improve the crystal-growth conditions continuously with respect to decreased thermal stress, especially by a rigorous application of modeling and process-simulation tools [5, 6]. 

W.A. Gault, E.M. Monberg, and J.E. Clemans, 1986, A novel application of the Vertical Gradient Freeze method to the growth of high quality lll-V crystals , J. Cryst. Growth 74, 491-506. 

Crystal-Growth Technology for Ternary lll-V Semiconductor Production by Vertical Bridgman and Vertical Gradient Freezing Methods with Accelerated Crucible Rotation Technique... 

T. Asahi, K. Kainosho, K. Kohiro, A. Noda, K. Sato, O. Oda, 2003, Growth of III-V and II-VI Single Crystals by the Vertical Gradient-freeze Method, in Crystal Growth Technology, (eds.)... 

Tammann 1914/Stober 1925 Bridgman 1923/Stockbaraer 1936 Vertical gradient freeze VGF... 

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