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Ternary chalcopyrite semiconductors
Mat. Res. Bull. Vol. II, pp. 451-452, 1976. P r i n t e d in the United States.
P e r g a m o n P r e s s , Inc.
NEW BOOKS
T e r n a r y Chalcopyrite Semiconductors. J. L. Shay and J. H. Wernick. Pp. 244. P e r g a m o n P r e s s , Oxford, England, 1975. P r i c e : $25.00. Chalcopyrite s e m i c o n d u c t o r s may n e v e r substitute for Si or even GaAs in our daily lives, but authors J. L. Shay and J. H. Wernick of Bell Labs. have opened the door for physicists, device e n g i n e e r s and m a t e r i a l s s c i e n t i s t s to peek in, look around, and evaluate the potential for further p r o g r e s s in this d i v e r s e class of m a t e r i a l s . I think we owe them accolades for t h e i r efforts. This text c o v e r s it all, from c r y s t a l growth and phase d i a g r a m s to the interactions of uniaxial distortion and spin-orbit splitting in the electronic excitations of chalcopyrites. We a r e taught how to grow the c r y s t a l s , why they behave as they do, and what applications have been developed for t h e m to date. T h e r e is a lot of detail, indeed one has the feeling that the authors have told us nearly everything that they know about t h e s e m a t e r i a l s . And yet t h e text is so c l e a r l y written and so well illustrated that I, for one, r e v e l l e d in the gory details. Regarding contents, the chapter titles taken together indicate the general a r e a s of e m p h a s i s : Chalcopyrite Structure and Crystal Growth; E l e c tronic Structure; Luminescence; Nonlinear Optical Applications; E l e c t r i c a l P r o p e r t i e s ; and Miscellaneous Physical P r o p e r t i e s . The d i s o r d e r e d chalcopyrite s t r u c t u r e s , including wurtzite, zincblende and glassy phases a r e c o v e r e d briefly. E m p h a s i s is focused on the t e r n a r y I-III-VI 2 + II-IV-V 2 (really the IB-IIIA-VIA2 + I1B-IVA-VA2) compounds. The prototypical chalcopyrite phase, the m i n e r a l CuFeS2, is t h e r e f o r e neglected. Some g e n e r a l c o m m e n t s are in order. The c r y s t a l growth and stoichiometry problems for t h e s e t e r n a r y chalcopyrites are, for the most part, horrendous. Many ingenious solutions have been generated and the p r o g r e s s , for example in the development of Liquid P h a s e Epitaxy techniques for h e t e r o junctions by the Bell group, has been r e m a r k a b l e . Future p r o g r e s s in the s c i e n c e and, especially, in the w i d e s p r e a d application of t h e s e m a t e r i a l s will r e q u i r e f u r t h e r m a t e r i a l s p r o c e s s i n g innovations. 451
452
NEW BOOKS
Vol. 11, No. 4
My only c r i t i c i s m of this monograph r e l a t e s to the occasional glibness with which this l a r g e l y unexplored t e r r i t o r y of solid state m a t e r i a l s s c i e n c e is handled. In truth, we know r e m a r k a b l y little about most of the t e r n a r y c h a l co pyri t e s d i s c u s s e d in this monograph, a point the authors chose not to e m phasize. Regarding phase d i a g r a m s , the liquidus cu rv e for Cu2Ga4Te 7 in Fig. 2.14 has an unnatural shape while Figs. 2.33 and 2.42 might be c l e a r e r if all the phase fields w e r e labeled. But the main point is that these t e r n a r y s y s t e m s a r e complex, few good phase d i a g r a m s are available, and p r o b l e m s of s t o i c h i o m e t r y abound. Regarding " e l e c t r o n i c s t r u c t u r e " , it is c l e a r that the t h e o r e t i c a l situation for the energy bands in the t e r n a r y c h a l c o p y r i t e s is in d i s a r r a y . Indeed the authors extol a highly e m p i r i c a l model for the v a l e n c e band s t r u c t u r e which t r e a t s the c r y s t a l - f i e l d and spin-orbit splittings independently and d e r i v e s the c-f splitting from a uniaxia! distortion of the isoe l e c t r o n i c binary zincblende phase (e. g. InP for CdSnP2) c o r r e s p o n d i n g to the m e a s u r e d c / a ratio. This q u a s i - c u b i c model fits the observed splittings much better than m o r e sophisticated calculations do. Why does the simple model w o r k so well when l e s s approximate t h e o r i e s fail ? This point is not e m phasized. E x p e r i m e n t a l l y these c r u c i a l valence band splittings show up as a s e r i e s of dips in the e l e c t r o r e f l e c t a n c e s p e c t r a . Confirmation by XPS or UPS would be most satisfying. In s u m m a r y , this book provides a m a r v e l o u s overview of the t e r n a r y c h a l c o p y r i t e s . It should s t i m u l a t e i n t e r e s t in all as p ects of t h e s e unique m a t e r i a l s . The c l a r i t y of p r e s e n t a t i o n qualifies this o th erw is e highly s p e c i a l i z e d monograph as a good r e f e r e n c e for an introductory graduate c o u r s e in solid state e l e c t r o n i c s . T r y it, you'll like it. JOHN P. DE NEUFVILLE Exxon R e s e a r c h and E n g in eerin g Co.
P e r g a m o n P r e s s , Inc.
NEW BOOKS
T e r n a r y Chalcopyrite Semiconductors. J. L. Shay and J. H. Wernick. Pp. 244. P e r g a m o n P r e s s , Oxford, England, 1975. P r i c e : $25.00. Chalcopyrite s e m i c o n d u c t o r s may n e v e r substitute for Si or even GaAs in our daily lives, but authors J. L. Shay and J. H. Wernick of Bell Labs. have opened the door for physicists, device e n g i n e e r s and m a t e r i a l s s c i e n t i s t s to peek in, look around, and evaluate the potential for further p r o g r e s s in this d i v e r s e class of m a t e r i a l s . I think we owe them accolades for t h e i r efforts. This text c o v e r s it all, from c r y s t a l growth and phase d i a g r a m s to the interactions of uniaxial distortion and spin-orbit splitting in the electronic excitations of chalcopyrites. We a r e taught how to grow the c r y s t a l s , why they behave as they do, and what applications have been developed for t h e m to date. T h e r e is a lot of detail, indeed one has the feeling that the authors have told us nearly everything that they know about t h e s e m a t e r i a l s . And yet t h e text is so c l e a r l y written and so well illustrated that I, for one, r e v e l l e d in the gory details. Regarding contents, the chapter titles taken together indicate the general a r e a s of e m p h a s i s : Chalcopyrite Structure and Crystal Growth; E l e c tronic Structure; Luminescence; Nonlinear Optical Applications; E l e c t r i c a l P r o p e r t i e s ; and Miscellaneous Physical P r o p e r t i e s . The d i s o r d e r e d chalcopyrite s t r u c t u r e s , including wurtzite, zincblende and glassy phases a r e c o v e r e d briefly. E m p h a s i s is focused on the t e r n a r y I-III-VI 2 + II-IV-V 2 (really the IB-IIIA-VIA2 + I1B-IVA-VA2) compounds. The prototypical chalcopyrite phase, the m i n e r a l CuFeS2, is t h e r e f o r e neglected. Some g e n e r a l c o m m e n t s are in order. The c r y s t a l growth and stoichiometry problems for t h e s e t e r n a r y chalcopyrites are, for the most part, horrendous. Many ingenious solutions have been generated and the p r o g r e s s , for example in the development of Liquid P h a s e Epitaxy techniques for h e t e r o junctions by the Bell group, has been r e m a r k a b l e . Future p r o g r e s s in the s c i e n c e and, especially, in the w i d e s p r e a d application of t h e s e m a t e r i a l s will r e q u i r e f u r t h e r m a t e r i a l s p r o c e s s i n g innovations. 451
452
NEW BOOKS
Vol. 11, No. 4
My only c r i t i c i s m of this monograph r e l a t e s to the occasional glibness with which this l a r g e l y unexplored t e r r i t o r y of solid state m a t e r i a l s s c i e n c e is handled. In truth, we know r e m a r k a b l y little about most of the t e r n a r y c h a l co pyri t e s d i s c u s s e d in this monograph, a point the authors chose not to e m phasize. Regarding phase d i a g r a m s , the liquidus cu rv e for Cu2Ga4Te 7 in Fig. 2.14 has an unnatural shape while Figs. 2.33 and 2.42 might be c l e a r e r if all the phase fields w e r e labeled. But the main point is that these t e r n a r y s y s t e m s a r e complex, few good phase d i a g r a m s are available, and p r o b l e m s of s t o i c h i o m e t r y abound. Regarding " e l e c t r o n i c s t r u c t u r e " , it is c l e a r that the t h e o r e t i c a l situation for the energy bands in the t e r n a r y c h a l c o p y r i t e s is in d i s a r r a y . Indeed the authors extol a highly e m p i r i c a l model for the v a l e n c e band s t r u c t u r e which t r e a t s the c r y s t a l - f i e l d and spin-orbit splittings independently and d e r i v e s the c-f splitting from a uniaxia! distortion of the isoe l e c t r o n i c binary zincblende phase (e. g. InP for CdSnP2) c o r r e s p o n d i n g to the m e a s u r e d c / a ratio. This q u a s i - c u b i c model fits the observed splittings much better than m o r e sophisticated calculations do. Why does the simple model w o r k so well when l e s s approximate t h e o r i e s fail ? This point is not e m phasized. E x p e r i m e n t a l l y these c r u c i a l valence band splittings show up as a s e r i e s of dips in the e l e c t r o r e f l e c t a n c e s p e c t r a . Confirmation by XPS or UPS would be most satisfying. In s u m m a r y , this book provides a m a r v e l o u s overview of the t e r n a r y c h a l c o p y r i t e s . It should s t i m u l a t e i n t e r e s t in all as p ects of t h e s e unique m a t e r i a l s . The c l a r i t y of p r e s e n t a t i o n qualifies this o th erw is e highly s p e c i a l i z e d monograph as a good r e f e r e n c e for an introductory graduate c o u r s e in solid state e l e c t r o n i c s . T r y it, you'll like it. JOHN P. DE NEUFVILLE Exxon R e s e a r c h and E n g in eerin g Co.