Calculation of phase equilibria in the Ga-Bi and Ga-P-Bi systems based on a theory of regular associated solutions
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BISMUTH
i s an i s o e l e c t r o n i c c e n t e r s u b s t i t u t i n g for P in GaP. At low t e m p e r a t u r e s (20 K) it is a n efficient e m i t t e r with a n o r a n g e hue. 1 R e c e n t l y , it has b e e n shown that the addition of Bi to N-doped GaP leads to yellow i n s t e a d of g r e e n light e m i s s i o n . 2 I n view of the d e m o n s t r a t e d u s e f u l n e s s of t e r n a r y p h a s e d i a g r a m s in the p r e p a r a t i o n and c h a r a c t e r i z a t i o n of doped c o m pound s e m i c o n d u c t o r s , it is d e s i r a b l e to know the det a i l s of s o l i d - l i q u i d e q u i l i b r i a in the G a - P - B i s y s t e m over a wide t e m p e r a t u r e and c o m p o s i t i o n r a n g e . It i s the m a j o r o b j e c t i v e of this p a p e r to c o n s t r u c t the G a - P - B i l i q u i d u s s u r f a c e c o n s i s t e n t with the m e a g e r e x p e r i m e n t a l data. In a f o r t h c o m i n g c o m m u n i c a t i o n , the r e s u l t s of this a n a l y s i s will be applied to the c a l culation of the solid s o l u b i l i t y i s o t h e r m s for Bi in GaP .3 In p r e v i o u s c a l c u l a t i o n s of s o l i d - l i q u i d e q u i l i b r i a in t e r n a r y s y s t e m s i n v o l v i n g Group III-V s e m i c o n d u c t o r s , the r e q u i r e d c o m p o n e n t a c t i v i t i e s i n the liquid p h a s e w e r e o b t a i n e d f r o m the t e r n a r y r e g u l a r (or s i m p l e ) s o l u t i o n model* (Refs. 4-6). In g e n e r a l , *In accordwith the terminologyadvocatedby Panishand n e g e m s , 4 a solution is consideredto be simplewhenthe regulaxsolutioninterchangeenergy,a, is a linearor higherorder functionof temperatureli.e., tx = a + b T , e t c . the r e a s o n a b l e n e s s of the r e g u l a r s o l u t i o n a p p r o a c h is d e m o n s t r a t e d by the good a g r e e m e n t a c h i e v e d b e tween the t h e o r e t i c a l and e x p e r i m e n t a l l i q u i d u s i s o t h e r m s . O c c a s i o n a l l y , however, the d a t a p e r m i t a m o r e s t r i n g e n t t e s t of the m o d e l . F o r e x a m p l e , in the A. S. JORDAN is a Member of Technical Staff, Bell Laboratories, Murray Hill, NJ 07974. Manuscript submitted September 25, 1975. METALLURGICALTRANSACTIONSB
G a - A s - Z n s y s t e m the m e a s u r e d As and Z n p a r t i a l p r e s s u r e s a l o n g the liquidus i s o t h e r m s w e r e found to be in good a g r e e m e n t with the p r e s s u r e s d e r i v e d f r o m an a n a l y s i s of the t e r n a r y liquidus data. 5 L i k e w i s e , i n the G a - A s - S i s y s t e m the t e r n a r y e u t e c t i c v a l l e y and the G a - S i b i n a r y w e r e s u c c e s s f u l l y p r e d i c t e d f r o m t e r n a r y l i q u i d u s d e t e r m i n a t i o n s .6 However, the t h e r m o d y n a m i c p r o p e r t i e s of the G a Bi s y s t e m do not obey r e g u l a r s o l u t i o n b e h a v i o r . F i r s t , the G a - B i s y s t e m e x h i b i
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