Heteroepitaxial GaAs on aluminum oxide. I: Early growth studies
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The n u c l e a t i o n and i n i t i a l growth of GaAs f i l m s p r e p a r e d from t r i m e t h y l g a l l i u m and a r s i n e on (0001) A1203 s u b s t r a t e s have b e e n e x a m i n e d by m e a n s of e l e c t r i c a l m e a s u r e m e n t s and r e f l e c t i o n e l e c t r o n diffraction and e l e c t r o n m i c r o s c o p y t e c h n i q u e s . The e a r l y stage of growth of GaAs, u n d e r conditions which a r e c o n s i s t e n t with epitaxial film f o r m a t i o n , a p p e a r s to be by the f o r m a t i o n of m a n y d i s c r e t e n u c l e i which c o a l e s c e to f o r m l a r g e i s l a n d s and e v e n t u a l l y produce complete s u r f a c e coverage. E l e c t r o n d i f f r a c t i o n r e s u l t s provide e v i d e n c e of a high d e n s i t y of defects n e a r the i n t e r f a c e with a c o n s i d e r a b l e i m p r o v e m e n t in c r y s t a l q u a l i t y as the film thickn e s s i n c r e a s e s . E l e c t r i c a l m e a s u r e m e n t s show the film at the i n t e r f a c e to be p type. The t h i c k n e s s of the p l a y e r v a r i e s t y p i c a l l y from ~1 to ~5 ~m, depending on the c o n c e n t r a t i o n of donor i m p u r i t i e s in the r e a c t a n t g a s e s . The f i l m s a r e found to c o n v e r t to n type upon s u b s e quent growth, s u g g e s t i n g that the p - t y p e b e h a v i o r may be r e l a t e d to the defect s t r u c t u r e n e a r the GaAs/A1203 i n t e r f a c e .
T H E R E has r e c e n t l y b e e n c o n s i d e r a b l e a c t i v i t y in the m i c r o e l e c t r o n i c s i n d u s t r y in the d e v e l o p m e n t of epitaxial GaAs for device a p p l i c a t i o n s . This i n t e r e s t has b e e n s t i m u l a t e d by the s u i t a b i l i t y of GaAs for high f r e q u e n c y d e v i c e s and the high quality of h o m o e p i t a x i a l m a t e r i a l that is b e c o m i n g a v a i l a b l e . This l a b o r a t o r y has been studying the f o r m a t i o n and p r o p e r t i e s of h e t e r o e p i t a x i a l GaAs on i n s u l a t i n g oxide s u b s t r a t e s , c o m p o s i t e s which m a y have a d d i t i o n a l a d v a n t a g e s for some a p p l i c a t i o n s . T h e s e s u b s t r a t e s provide e n h a n c e d e l e c t r i c a l i s o l a t i o n of c o m p o n e n t s and in some c a s e s p o s s e s s s u p e r i o r t h e r m a l p r o p e r t i e s , of p a r t i c u l a r i m p o r t a n c e for high power a p p l i c a t i o n s . I n i t i a l efforts have been d i r e c t e d toward the deposition of GaAs on s a p p h i r e , s p i n e l , b e r y l l i u m oxide, and t h o r i u m oxide s u b s t r a t e s . * In the growth of h e t e r o epitaxial GaAs, there a r e a n u m b e r of f a c t o r s which can a d v e r s e l y influence the quality and p u r i t y of the epitaxial film. T h e s e include, for e x a m p l e , lattice m i s m a t c h and t h e r m a l e x p a n s i o n d i f f e r e n c e s between s u b s t r a t e and f i l m ,
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