Characterization of Mercury Cadmium Telluride Using Nondestructive Transverse Acoustoelectric Voltage Measurements

Hgl-x Cd, Te is e x t e n s i v e l y used today as a v e r s a t i l e i n f r a r e d d e t e c t o r m a t e r i a l w i t h i n c r e a s i n g impor t ance i n t h e f a b r i c a t i o n o f f o c a l p l a n e a r r a y s . e r t i e s a r e i n v e s t i g a t e d u s i n g n o n d e s t r u c t i v e SAW techn ique . The t r a n s v e r s e a c o u s t o e l e c t r i c v o l t a g e (TAV) i s moni tored a c r o s s t h e Hgl-x Cd, Te sample which i s p l aced i n p rox imi ty of a LiNbOj de lay l i n e . TAV is developed due t o t h e n o n l i n e a r i n t e r a c t i o n between t h e e l e c t r i c f i e l d accompanying SAW, and t h e f r e e c a r r i e r s n e a r t h e Hgl-x Cd, T e s u r f a c e . C o n t a c t l e s s TAV and s u r f a c e p h o t o v o l t a g e s p e c t r o scopy a r e performed t o de t e rmine t h e bandgap and t h u s t h e a l l o y compos i t ion (x ) of Hgl-x Cd, Te. I n t h i s work Hgl-x Cd, T e e l e c t r o n i c propThe TAL' v e r s u s v o l t a g e measurements are a l s o per formed f o r f u r t h e r i n v e s t i g a t i o n of Hgl-x Cd, Te s u r f a c e p r o p e r t i e s ( such as c o n d u c t i v i t y t y p e and p o s s i b l e s u r f a c e i n v e r s i o n due t o p a s s i v a t i o n by ZnS). I n t r o d u c t i o n F u l l s c a l e p roduc t ion f o r c u r r e n t and f u t u r e g e n e r a t i o n m i l i t a r y i n f r a r e d sys tems w i l l r e q u i r e l i n e a r a r r a y s and mosaic f o c a l p l a n e s w i t h a l a r g e number of i n f r a r e d d e t e c t o r s . Mercury cadmium t e l l u r i d e p r o v i d e s a predominant r o l e a s t h e materi a l f o r t h e s e d e t e c t 0 r s . l pho to -de tec to r p r o d u c t i o n and maximum y i e l d f o r sys t ems such as Advanced FLIR Technology (AFT), Thermal Weapon S i g h t s (TWS) and t h e S h u t t l e I n f r a r e d Te le scope F a c i l i t y (SIRTF), advanced n o n d e s t r u c t i v e c o n t a c t l e s s t echn iques w i l l b e needed. To m a i n t a i n h i g h volume For example, a f a s t , r e l i a b l e c o n t a c t l e s s t e c h n i q u e i s h i g h l y d e s i r a b l e f o r c h a r a c t e r i z i n g semiconductor m a t e r i a l s a t s e v e r a l key p r o d u c t i o n p o i n t s b e f o r e comple t ion of t h e f i n a l p h o t o d e t e c t o r . These p o i n t s may i n c l u d e a n n e a l i n g , s l i c i n g , p o l i s h i n g , e t c h i n g , s u r f a c e p a s s i v a t i o n and implan t prof i l i n g . C o n t a c t l e s s t e s t i n g p r o v i d e s c o n s i d e r a b l e s a v i n g s i n l a b o r and m a t e r i a l s by r e j e c t i n g a f a u l t y d e v i c e e a r l y d u r i n g p r o d u c t i o n and by making t h i s d e t e r m i n a t i o n w i t h r e l a t i v e e a s e compared w i t h o t h e r t e c h n i q u e s r e q u i r i n g ohmic c o n t a c t s o r m e t a l l i z a t i o n . The c o n t a c t l e s s t e c h n i q u e chosen f o r t h i s pape r u s e s S u r f a c e Acous t i c Wave (SAW). D i f f e r e n t imp lemen ta t ions 'of t h e SAW technique2-10 have been used f o r s emiconduc to r s such as S i l i c o n , CadmiumS u l p h i d e , Indium Arsen ide , Indium Phosphide , Gal l ium Arsen ide and Gal l ium Phosphide . I n t h i s p a p e r , i t 0090-5607/83/0000~0421 $01.00