Improved calculations of the complex dielectric constant of semiconductors
Improved calculations of the complex dielectric constant of semiconductors
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改进半导体复杂介电常数的计算
DOI:
10.1103/physrevb.10.2483
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发表时间:
1974
影响因子:
3.7
通讯作者:
A. Sher
中科院分区:
文献类型:
--
作者:
R. A. Breckenridge;R. Shaw;A. Sher
Im proved e x p re s s io n s a re o b ta in e d f o r th e r e a l , s t a t i c p a r t €i(<0 and th e im ag inary p a r t €a.(.uj) o f th e d i e l e c t r i c c o n s ta n t o f sem i co n d u c to rs in th e lo n g w aveleng th l i m i t u s in g th e i s o t r o p i c , n e a r ly f r e e e l e c t r o n band ap p ro x im atio n (Penn m odel). E a r l i e r c a lc u la t io n s o f th e s e fu n c t io n s do n o t s a t i s f y th e K ram ers-K ronig r e l a t i o n s and y i e l d an e x c e s s iv e ly l a r g e r e s u l t f o r th e f -sum r u l e . The c o r r e c te d e x p re s s io n s e l im in a te th e s e in c o n s i s te n c ie s . V alues o f th e energy gap betw een th e bond ing and a n ti-b o n d in g s t a t e s a re o b ta in e d f o r diam ond, s i l i c o n and germanium. £ i s o b ta in e d from €a.(w) th ro u g h th e u se o f th e K ram ers-K ronig r e l a t i o n . The t h e o r e t i c a l cu rv es f o r and £ a (uj) a re compared w ith e x p e rim e n ta l r e s u l t s . C o rre c te d p a ra m e te rs f o r th e P h i l l ip s -V a n V echten th e o ry o f i o n i c i t y a re o b ta in e d th ro u g h th e u se o f th e im proved e x p re s s io n f o r G^Co) . I . INTRODUCTION A lthough d e ta i l e d band s t r u c tu r e c a lc u la t io n s have been u sed to e v a lu a te th e d i e l e c t r i c c o n s ta n t f o r sem ico n d u cto rs w ith e x c e l le n t r e s u l ts ,^ " th e a p p e a l Of approx im ate c a lc u la t io n s b a sed on th e i s o t r o p i c , n e a r l y f r e e e l e c t r o n ap p ro x im atio n rem ains s tro n g due t o p h y s ic a l i n s ig h t g a in e d from th e s im p l ic i t y o f th e a n a ly t i c a l r e s u l t s . P r io r to P e n n 's in t r o d u c t io n o f a n e a r l y f r e e e l e c t r o n m odel, i s o t r o p i c a l l y ex ten d ed t o th r e e d im ensions (Penn m o d e l) , o n ly two crude approxim a t io n s t o th e s t a t i c (1 0 = o) t r e a l p a r t o f th e d i e l e c t r i c c o n s ta n t e x is t e d . The f i r s t ap p ro x im atio n was t o u se th e f r e e 3 H e le c t r o n gas v a lu e f o r C ± > \̂ ) • ’ In th e lo n g w aveleng th (cj-*-o) l i m i t , ( Ojo)-»-e»« in th e f r e e e le c t r o n gas m odel. However, th e t r e n d o f th e «i dependence o f 6 . (o. d 'j i s re a s o n a b ly approx im ated * ^ away from <j= o by th e f r e e e le c t r o n e x p re s s io n f o r m a te r ia ls whose G l ( o j o) v a lu e s a re l a r g e . Then, Callaw ay^ r e f in e d th e f r e e e le c tr o n gas ap p ro x im atio n by i n s e r t i n g a r t i f i c i a l l y an energy gap betw een th e v a le n c e and c o n d u c tio n bands w i th o u t , how ever, m od ify ing th e wave f u n c t io n s . U n like th e s e two a p p ro x im a tio n s , th e Penn model a llo w s f o r th e fo rm a tio n o f s ta n d in g waves a t th e zone edge and acco u n ts f o r th e c o n tr ib u t io n s from Umklapp p r o c e s s e s . Penn c a lc u la te d ^ i C°j ^ ) by ap p ro x im atin g th e m a tr ix e lem en ts f o r th e norm al and Umklapp p ro c e s s e s and o b ta in e d an e x p re s s io n f o r £ ^ ( o ^ o ) . He a ls o d e m o n stra ted t h a t Umklapp p ro c e s s e s make th e dom inant c o n t r ib u t io n t o £^(o j ) f o r sm a ll «|. 1