Magnetoresistance of High‐Ohmic Semiconductors by a Capacitive Method

Abstract

The measurement of c o n d u c t i v i t y o f semiconductors w i t h methods r e q u i r i n g m e t a l l i c c o n t a c t s s u f f e r f r o m s e v e r a l troubJei because o f t h e p r o p e r t i e s of metal-semiconductor c o n t a c t s , inc l u d i n g imperfect c o n t a c t i n g , especiall'y a t l o w temperatures and w i t h h i g h l y i n s u l a t i n g material. W e t r i e d , t h e r e f o r e , t h e c a T a c i t i v e method of c o n d u c t i v i t y measurements (I), which does not need m e t a l l i c c o n t a c t s w i t h the semiconductor, f o r t h e magnetoresistance e f f e c t w i t h t h e hope t o circumvent such d i ff i c u l t i e s . The method proved indeed t o be l a r g e l y f r e e from severe d i s t u r b i n g i n f l u e n c e s .The c o n d u c t i v i t y and i t s change i n a magnetic f i e l d i s determined from t h e frequency dependence of t h e loss angle of a condenser t h a t c o n t a i n s the semiconducting medium (1 mm t h i c k n e s s ) between two i n s u l a t i n g mylar s h e e t s (10 p t o t a l t h i c k n e s s ) . The m a x i m a l magnetic f i e l d was 19.2 kG. The f r equency ranged f r o m 60 H e t o 20 MHz. The measurements could be made f o r t h e t r a n s v e r s e and t h e l o n g i t u d i n a l e f f e c t s (and f o r o r i e n t a t i o n s i n between) at temperatures between 60 and 295 OK. The c r y s t a l s were c i r c u l a r d i s k s of 1 mm t h i c k n e s s and 8 mm diameter; t h e i r s u r f a c e w a s perpendicular t o t h e [ I l l ] d i r e c t i o n .The r e s u l t s of the measurements w i t h Ge (n-type, donor c o n c e n t r a t i o n about 1 .5x101 ~m -~) agreed w e l l w i t h previous r e s u l t s f r o m current-voltage c h a r a c t e r i s t i c s methods ( 2 ) f o r t h e so-called "physical e f f e c t " (change o f m o b i l i t i e s i n t h e magnetic f i e l d ) i n s p i t e o f a geometry of t h e sample that would provoke a llgeometrical e f f e c t " (3). W e shall d i s c u s s t h i s circumstance i n a more d e t a i l e d r e p o r t t o be published l a t e r .Measurements w i t h G a A s (p-type at room temperature, Pe-5 physica