Solubility and activity of oxygen in liquid germanium and germanium-copper alloys
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1 J.
w h e r e the s t a n d a r d s t a t e for d i s s o l v e d oxygen is that which m a k e s the v a l u e of a c t i v i t y equal to the c o n c e n t r a t i o n (in at. pct), in the l i m i t , as c o n c e n t r a t i o n a p p r o a c h e s z e r o . T h e effect of copper on the a c t i v i t y of oxygen d i s s o l v e d in liquid g e r m a n i u m is found to be in good a g r e e m e n t with that p r e d i c t e d by a q u a s i c h e m i c a l m o d e l i n which each oxygen was a s s u m e d to be bonded to four m e t a l a t o m s and the n e a r e s t n e i g h b o r m e t a l a t o m s to an oxygen a t o m a r e a s s u m e d to lose a p p r o x i m a t e l y half of t h e i r m e t a l l i c b o n d s .
PREVIOUS
s t u d i e s I on dilute s o l u t i o n s of oxygen w e r e m a i n l y confined to t y p i c a l m e t a l l i c s y s t e m s in which t h e r e a r e fewer e l e c t r o n s than n e e d e d to f o r m e l e c t r o n - p a i r bonds to all n e a r e s t n e i g h b o r s . I n v e s t i gation of the b e h a v i o r of d i s s o l v e d oxygen in group IVA e l e m e n t s like g e r m a n i u m , which is a c o v a l e n t l y bonded and t e t r a h e d r a l l y c o o r d i n a t e d s e m i c o n d u c t o r in the s o l i d s t a t e , and of its alloy with group I B e l e m e n t s such as copper, in which the e l e c t r o n c o n c e n t r a t i o n c h a n g e s r a p i d l y with c o m p o s i t i o n , is a n a t u r a l e x t e n s i o n of e a r l i e r s t u d i e s . R e c e n t l y J a c o b a n d A1cock 2 have c o m p l e t e d a s i m i l a r study u s i n g an i s o p i e s t i c t e c h n i q u e on oxygen s o l u b i l i t y in liquid g a l l i u m copper a l l o y s in which there is a well u n d e r s t o o d change in e l e c t r o n - a t o m r a t i o , and whilst the r e s u l t s i n d i c a t e the p r e d i c t e d effects they do not c o v e r the whole c o m p o s i t i o n r a n g e . F u r t h e r m o r e i n f o r m a t i o n on liquid Ge-O and C u - G e - O s y s t e m s is u s e f u l f r o m a p r a c t i c a l as well as a t h e o r e t i c a l point of view. A knowledge of the oxygen s o l u b i l i t y in liquid g e r m a n i u m is i m p o r t a n t i n the p r e p a r a t i o n of g e r m a n i u m b a s e d s e m i c o n d u c t o r s grown f r o m m e l t s . R e c e n t m o d e l s ~'3 for the d e s c r i p t i o n of t h e r m o d y n a m i c p r o p e r t i e s of oxygen i n dilute s o l u t i o n i n b i n a r y K. FITZNER was on leave at the Department of Metallurgy and Materials Science, University of Toronto, when this investigation was undertaken. He has now returned to the Institute for Metals Research, Polish Academy of Sciences, 25 Reymonta St., 30-059 Krakow, Poland, K. T. JACOB is Senior Research Associate and Special Lecturer, Department of Metallurgy and Materials Science, University of Toronto, and C. B. ALCOCK is Professor, Department of Metallurgy and Materials Science, University of Toronto, Toronto, Canada M5S 1A4. Ma
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