The Distribution Coefficient of Boron in Germanium

Abstract

The equilibrium distribution coefficient of boron in germanium was found to be 12.2. The variation with growth rate was interpreted in terms of a theory by Burton, Prim, and Slichter. As the growth rate was increased the width of the diffusion dominated layer initially increased followed by a later decrease. This was due to a change from a thermally produced melt flow pattern to a hydrodynamically produced pattern. The results show that a slow growth rate and a high rotation rate should be used to obtain equilibrium distribution coefficients.

Segregation of boron in germanium crystal

“…From the present result, the equilibrium segregation coefficient is considered to be k 0 =5-6 for B in Ge. In addition, it is seen that the decrease of B concentration obtained experimentally is much slower than those predicted with the equilibrium segregation coefficient k 0 =17 and 12.2 reported previously [4,5]. These features suggest the necessity of reevaluating the B segregation behavior in order to utilize the potential of Ge for a wide range of semiconductor applications.…”

“…Thin lines show simulated variations with the previously reported equilibrium segregation coefficient k=k 0 =17[4] and 12.2[5].…”

“…The acceptor concentration, $2.5 Â 10 18 cm À3 in maximum at the shoulder part of the crystal (region TO), decreases gradually with the increase of solidification fraction in the B-doped Ge crystal and reaches a value smaller than that of the TO region by one order of magnitude at g=0. 5.…”

“…It is found that the evaluated effective segregation coefficient obtained in the present study with the rather slow growth rate of 10 mm/h is very low. Thus, it seems to be difficult to derive the equilibrium segregation coefficient k 0 =17 or 12.2 [4,5], even including the effect of the difference of the rotational rate. From the present result, the equilibrium segregation coefficient is considered to be k 0 =5-6 for B in Ge.…”

“…As a p-type dopant, boron (B) is most popular in Si technology, while highly volatile gallium or indium, rather than B, is used in Ge. To date, B has been recognized as having a large segregation coefficient of k=12.2-22 with some scatter [3][4][5][6], together with a low solid solubility around 2 Â 10 18 cm À3 [4,7] and rather slow diffusivity 10 À11 À10 À14 cm 2 /s, even at temperatures close to the melting point [7,8]. The above characteristics of B in Ge might lead to serious difficulties for device applications.…”