Studies of grown-in defects and defects produced by the one-MeV electron irradiation in Al sub 0.3 Ga sub 0.7As p-n junction solar cells fabricated by liquid phase epitaxial (LPE) technique were made for the unirradiated and one-MeV electron irradiated samples, using DLTS and C-V methods. Defect and recombination parameters such as energy level, defect density, carrier capture cross sections and lifetimes were determined for various growth, annealing, and irradiation conditions

Li, S. S.

Rahilly, W. P.

Schoenfeld, D. W.

Teng, K. W.

English

NASA Technical Reports Server

GKOWN-IN DEFECTS A N D  DEFECTS PKODUCED BY 1-MeV ELECTRON IKKADIATION 
I N  A10,3Cao 7As P-N JUNCTION SOLAR CELLS* 
Sheng S. Li, K.W. Teng, and  D.W. Schoenfeld 
Universi ty  o€ Flor ida  
Gainesville, F lor ida  
W.P. Kahilly 
Ai r  F o r c e  Aeropropulsion Labora tory  
Wright-Pat terson Air  F o r c e  Base, Oh io  
EXTENDED ABSTRACT 
Studies  of grown-in d e f e c t s  and d e f e c t s  produced by t h e  one-MeV e l e c t r o n  i r r a d i -  
a t i o n  i n  A10,3Ga0 7 A s  p-n j u n c t i o n  s o l a r  cel ls  f a b r i c a t e d  by l i q u i d  phase e p i t a x i a l  
(LPE) technique have been made f o r  t h e  u n i r r a d i a t e d  and one-MeV e l e c t r o n  i r r a d i a t e d  
(with e l e c t r o n  f luence  of 1014 ,  1015, and 1016 e/cm2) samples, us ing  DLTS and C-V 
methods. Defect and recombination parameters such as en2rgy level,  d e f e c t  dens i ty ,  
carrier cap tu re  c r o s s  s e c t i o n s  and l i f e t i m e s  were determined f o r  va r ious  growth, 
anneal ing,  and i r r a d i a t i o n  condi t ions .  The r e s u l t s  obtained from t h i s  s tudy  are 
d iscussed  as fol lows:  Al,Gal-,As p-n j u n c t i o n  s o l a r  ce l l s  (a rea  1 mm2) grown by 
LPE technique were f a b r i c a t e d  by S .  Bedair a t  t h e  Research Tr i ang le  I n s t i t u t e  i n  
conjunct ion wi th  t h e i r  Al,Gal-,As cascade p-n j u n c t i o n  s o l a r  c e l l  program supported 
by t h e  A i r  Force Aeropropulsion Lab. F ig .  1 shows t h e  four  d i f f e r e n t  s o l a r  c e l l  
s t r u c t u r e s  which have been f a b r i c a t e d  f o r  our  DLTS, C-V, and I-V measurements. F ig .  
1 (b) i s  t h e  ce l l ' s  s t r u c t u r e  used i n  our  s tudy of deep-level  d e f e c t s  produced by t h e  
one-MeV e l e c t r o n  i r r a d i a t i o n .  This  s t r u c t u r e  i s  i d e n t i c a l  t o  t h e  top  c e l l  of t h e  
cascade s o l a r  c e l l ,  repor ted  by Bedair e t  a l [ l l .  
e l e c t r o n  t r a p  (E,-0.31 eV) f o r  t h r e e  Al,Gal-,As p-n j u n c t i o n  s o l a r  cel ls  shown i n  
Fig.  1 (a)  through 1 ( c ) .  From our DLTS d a t a ,  i t  i s  found t h a t  t h e  Ge-doped 
Al,Gal_,As p-n j u n c t i o n  s o l a r  cells  usua l ly  have lower d e f e c t  d e n s i t y  than  t h a t  of 
t h e  Be-diffused p-n j u n c t i o n  s o l a r  c e l l s  shown i n  F ig .  1 (a)  and Fig.  1 (b ) .  This  i s  
a l s o  t h e  case f o r  t h e  hole  t r a p  shown i n  Fig.  3 ,  where one ho le  t r a p  wi th  energy of 
Ev+0.18 e V  w a s  de t ec t ed  i n  both t h e  Ge-doped and Be-diffused A10,3Ga0.7As p-n junc- 
t i o n  c e l l s .  Another i n t e r e s t i n g  study i s  t o  i n v e s t i g a t e  t h e  e f f e c t  of low tempera- 
t u r e  thermal annea l ing  on t h e  d e f e c t  d e n s i t y  i n  t h e  A10.3Ga0.7As s o l a r  ce l l .  F ig .  4 
shows t h e  DLTS scans  of e l e c t r o n  t r a p  vs. anneal ing t i m e  (2  and 5 h r s .  a t  300'C). 
The r e s u l t s  showed t h a t  t h e  e l e c t r o n  t r a p  d e n s i t y  w a s  indeed decreased wi th  increas-  
ing  annea l ing  t i m e .  Table  1 summarizes t h e  d e f e c t  parameters  deduced from t h e  DLTS 
and C-V d a t a  f o r  t h e  u n i r r a d i a t e d  A10.3Ga0,7As and G a A s  s o l a r  c e l l s  shown i n  F ig .  1 
f o r  d i f f e r e n t  anneal ing t i m e s .  Table  2 summarizes t h e  d e f e c t  parameters f o r  t h e  un- 
annealed and annealed A10e3Ga0.7As and G a A s  s o l a r  ce l l s  shown i n  Fig.  4 .  
t h e  e f f e c t  of one-MeV e l e c t r o n  i r r a d i a t i o n  on t h e  d e f e c t s  i n  t h e  Al,Gal-,As p-n 
j u n c t i o n  s o l a r  cel ls  grown by t h e  LPE technique,  w e  performed (done a t  t h e  A i r  Force 
Aeronaut ica l  Lab.) t h e  one-MeV e l e c t r o n  i r r a d i a t i o n  on t h e  A10.3Gao 7 A s  p-n j u n c t i o n  
s o l a r  ce l l s  shown i n  Fig.  1 (b) f o r  e l e c t r o n  f luence  of 1014, 1015,'and 1016 e / c m 2 .  
The r e s u l t s  are  shown i n  F ig .  5 and Fig.  6. Fig.  5 shows t h e  DLTS scan of e l e c t r o n  
t r a p s  f o r  t h e  one-MeV e l e c t r o n  i r r a d i a t e d  A10.3Ga0,7As s o l a r  ce l l s  as a func t ion  of 
e l e c t r o n  f luence .  Note t h a t  t h r e e  e l e c t r o n  t r a p s  wi th  ene rg ie s  of E,-0.12, 0.20, and 
0.31 e V  w e r e  observed i n  t h e  one-MeV e l e c t r o n  i r r a d i a t e d  A10.3Ga0.7As c e l l s ;  t h e  dom- 
i n a n t  e l e c t r o n  t r a p  w a s  due t o  E,-0.31 e V .  The d e n s i t y  of t h i s  E,-0.31 e V  t r a p  w a s  
found t o  inc rease  wi th  inc reas ing  e l e c t r o n  f luence ,  whi le  t h e  o the r  two shal lower 
Fig.  2 shows t h e  DLTS scans of t h e  
To s tudy 
195 
https://ntrs.nasa.gov/search.jsp?R=19830007557 2020-03-22T00:05:42+00:00Z
2 
e l e c t r o n  t r a p s  showed less dependence on t h e  e l e c t r o n  f luence .  I n  c o n t r a s t  t o  t h e  
G a A s  p-n j u n c t i o n  cells ,  no mid-gap deep-level  t r a p s  w e r e  de t ec t ed  i n  t h e  A10~3Ga0.7- 
A s  p-n j u n c t i o n  s o l a r  cells. Fig.  6 shows t h e  DLTS scans  of ho le  t r a p  f o r  t h e  s a m e  
cells  shown i n  Fig.  5; only one h o l e  t r a p  w i t h  energy of Ev+0.18 e V  w a s  observed i n  
t h e s e  cel ls ,  and t h e  d e n s i t y  w a s  found t o  vary  from 2 . 7 5 ~ 1 0 1 5  ( f o r  $e = 1014 e/cm2) 
t o  5 . 9 3 ~ 1 0 1 5  cm-3 (at  $e = 1 O I 6  e/cmz). 
w a s  observed i n  t h e s e  e l e c t r o n  - i r r a d i a t e d  Al,Gal_,As p-n j u n c t i o n  s o l a r  cells. 
Table  3 summarizes t h e  d e f e c t  parameters deduced from t h e  DLTS d a t a  f o r  t h e  e l e c t r o n  
t r a p s  shown i n  Fig.  5. From t h e  r e s u l t s  of t h i s  s tudy ,  i t  is concluded t h a t :  (1) f o r  
t h e  u n i r r a d i a t e d  A10.3Ga0.7As p-n j u n c t i o n  cells ,  t h e  dominant e l e c t r o n  t r a p  is  due 
t o  E,-0.31 e V  and t h e  dominant ho le  t r a p  is  due t o  Ev+0.18 e V ;  thermal  annea l ing  w i l l  
e f f e c t i v e l y  reduce t h e  d e n s i t y  of bo th  e l e c t r o n  and ho le  t r a p s ,  (2) Ge-doped A10.3- 
G a O e 7 A s  p-n j u n c t i o n  ce l l s  con ta in  lower d e f e c t  d e n s i t y  than  t h e  Be-diffused cel ls ,  
(3) one-MeV e l e c t r o n  i r r a d i a t i o n  i n  t h e  A10,3Ga0,7As p-n j u n c t i o n  cel ls  produces 
only  one ho le  t r a p  ( i .  e. , Ev+0.18 eV) and t h r e e  e l e c t r o n  t r a p s  (Ec-0.12, 0.20, and 
0.31 e V ) ;  no mid-gap deep level d e f e c t s  w e r e  observed, (4) d e f e c t  d e n s i t y  does in-  
crease w i t h  inc reas ing  e l e c t r o n  f luence ,  and (5) t h e  DLTS d a t a  showed t h a t  A10.3- 
G a o . - / A s  p-n j u n c t i o n  s o l a r  ce l l s  may have more r a d i a t i o n  t o l e r a n c e  than  t h a t  of G a A s  
p-n j u n c t i o n  s o l a r  ce l l s  r epor t ed  i n  our prev ious  paperL21. 
Again, no mid-gap h o l e  t r a p  o r  new h o l e  t r a p  
*Research supported by A i r  Force Aeropropulsion Lab., AFWAL, subcont rac t  through 
(1) S. M. Bedair,  M. Lamorte, and J. Hauser, Appl. Phys. L e t t . ,  vo l .  34, p .  38 (1979). 
(2) I n  t h e  same proceeding of t h i s  workshop. 
Universa l  Energy System Inc . ,  t a s k  6. 
196 
Table 2 .  oefect Parameters for the Unannealed and the Annealed A10.3Ga0.7AS and 
GaAs LPE Layers. 
L-1383 
0.42 7 . 1 ~ 1 0 ~ ~  0.40 5.5~10~' 2 .8x1Ol5 
0.60 1. 7x1011 0. I1 4 . 1 ~ 1 0 ~ ~  3 . 6 ~ 1 0 ~ ~  
Unannealed 
L-1383 
0.42 1.2x1010 0.40 2.7xio10 2.lx1ol5 
3OO0C,2 hrs 
0.60 4.7~10~' 0.71 2.4~10~' 2 . 4 ~ 1 0 ~ ~  
Table3 . Electron Traps in One-MeV Electron Irradiated 
A10.3Ga0.7As P-N Junction Solar Cells 
L-1383 
Electron Pluence 
(elm ) 
2 
1 . 3 ~ 1 0 ~ ~  2.5~10'~ 
1 . 5 ~ 1 0 ~ ~  2.4~10'~ 
0.42 1 . 0 ~ 1 0 ~  0.40 
0.60 6 . ~ ~ 1 0 ~  0.71 
3OO0C,5 hrs 
0 
1.03~10~~ 
l0l6 
Ec-0.i2 2 . 1 ~ 1 0 ~ ~  - 
Ec-0.20 4 . 3 ~ 1 0 ~ '  2.63~10-l~ 8.84 
E--0.31 7 . 8 ~ 1 0 ~ ~  1.64~10-l~ 0.078 
17 
1.26~10 
1.16~10~' 
Ec-0.12 1.9~10 15 - 
Ec-0.20 6 . 5 ~ 1 0 ~ ~  2.63~10-l~ 5.85 
Ec-0.31 1 . 1 1 ~ 1 0 ~ ~  1.64~10-l~ OD55 
Ec-0.12 2.2~10~' - 
Ec-0.20 3 . 9 ~ 1 0 ~ ~  2.63~10-l~ 9. 75 
Ec-0.31 1 . 8 ~ 1 0 ~ ~  1.64~10-l~ QC34 
197 
4 
AI Go As 
AIe3 Go, As 
G a  As 
(SUBSTRATE) 
0.9 0.1 
P' (Be) 
n 
n+ 
_ - - _ _ _ - -  ------ 
(UNDOPED) 
f I 
p' (Be) Ga, As 
A I 3  GasAs n 
Ga As n+ 
- - - - - - - - - - - - - - 
(UNDOPED) - 
(SUBSTRATE 1 
I I 
GaAs I n+ 
I I 
I . ( c )  L-119D 
p+ ( Be) A 1 3 G a 7 A s  
I n+ G a A s  1 
I. (dIL-138D 
F i g .  1 S t r u c t u r e  o f  A1 Ga As p-n j u n c t i o n  s o l a r  c e l l s  f o r  DLTS and C - V  s tudy.  
x 1-x 
EcO 31 ev 
I I I I 
' 100 150 200 250 
TEMPERATURE (K)  
0 
AS p-n 0 .  3Gac. 7 F ig.% DLTS scans of e l e c t r o n  t r a p s  i n  Be-d i f fused and Ge-dcped A 1  j u n c t i o n  s o l a r  c e l l s  grown by LPE technique. 
198 
ELECTRON TRAP 
Y-015C 
1 . 5 H R S  300 C 
2. BHRS 300 'C 
3. UNANNEALED 
E,- 0.31 eV 
100 150 200 250 
T (K) 
HOLE TRAPS 
1. Y-015B 
2. L-119D 
77 100 150 200 250 
TEMPERATURE ( K ) 
F i g .  3 DLTS scans o f  e l e c t r o n  t r a p s  
i n  A1  Ga As  p-n j u n c t i o n  
s o l a r  c e l l s  annealed a t  300 C 
f o r  0, 2,  and 5 hours. 
0 
0.3 0.7 
F ig .  4 O p t i c a l  DLTS scans o f  h o l e  t r a p  
i n  Be- and Ge-doped A10.3Ga0.7 As p-n 
j u n c t i c n  so lar  cells. 
199 
ELECTRON TRAP 
I 
E ~ =  E=- 0.31 ev 
I I I 
100 2 0 0  
T (IO 
3 00 
Fig.5 DLTS scans o f  e l e c t r o n  t r a p s  i n  
Ga A s  p-n j u n c t i o n  s o l a r  
one-Mev e l e c t r o n  i r r a d i a t e d  
A10.3  0.7 
- 
H O L E  T R A P  
Ev+0.18 ev 
100 2 00 
T ( K )  
300 
Fig .  6 DLTS scans o f  h o l e  t r a p  i n  cne-Mev 
e l e c t r o n  i r r a d i a t e d  A1 Ga A s  
p-n j u n c t i o n  s o l a r  c e l l s  shown i n  
F ig .  5. 
0 - 3  0 . 7  
c e l l s  f o r  t h r e e  e l e c t r o n  f luences.  
200 


Grown-in defects and defects produced by 1-Me electron irradiated in Al0.3Ga0.7As P-N junction solar cells

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