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Switchable Ferroelectric
Diode andPhotovoltaic Effect in
BiFeO3
(Science, Vol 329, April 29!
"o#e Antonio Pe$a %arcia
&art' %tierre) *atorre
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Switchable Diode
Diode+ r-#talline piece with a p.n /nction connectedto two electrical ter0inal#
Switchable Diode+ the polarit- of the diode can bereprodcibl- #witched b- the rever#ion of the appliedelectric field
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Photovoltaic Effect
1t i# the creation of voltae or electriccrrent in a 0aterial pon to epo#re toliht
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&ain propertie# of ferroelectric#
4he- #witch the cr-#tal #trctre at a certain te0peratre
5ih #-00etr- (non ferroelectric!
6ever#ible
*ow #-00etr- (ferroelectric!
*ow #i00etr- enerate# polar direction#, hencepolari)ation
4he- 0aintain the polari)ation #tate in the ab#ence of avoltae and the po##ibilit- to rever#e the polari)ationdirection b- appl-in an electric field
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&ain propertie# of ferroelectric#
4he- #how photocrrent when ill0inated, bt not li7e#e0icondctor# (and that8# the point!
4here8# onl- photocrrent in the polari)ation direction,the oriin i# #till nclear, bt it wor7#
Photocrrent den#it- i# low, bt it i# proportional to thelenth in the polari)ation #o it8# o7
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BiFeO3Perov#7ite t-pe nit cell with
a:3;9< = and >:?9;3@
6ho0boedral #trctre (63c!
rie 4e0peratre+
Cel 4e0peratre+ .pha#e i# 0eta#table in air Vacc0 condition#
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4hree BiFeO3 r-#tal# are #tdied
One ferroelectric do0ain, #a0e #pace di#po#ition,different thic7ne##e# (H, ? and 9I0!
JDia0eter.circlar thic7
Samples BFO thickness(μm)/A(mm2) Electrodes
BFO HK 22 AK ;< 00JBFO2 ?K 2;2; AK ;
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Sa0ple#
A
BFO
A
BFO
A
A
BFO
BFO2
A
A
BFO
BFO3
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Eperi0ent
Sa0ple+ AKBFOKAL Dar7 condition#
Fir#t the diodeli7e behavior and te0peratre effect are#tdied
ABFO
A
BFO
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6e#lt#
Diodeli7e behavior i# ob#erved
rrent den#it- increa#e with 4e0peratre
6ectification ratio(6:"(E:M;3!K"(E:.;3! increa#e with4e0peratre
Polari)ation #witch doe# not occr
Temperature (K) Rectiication ratio
2 3
2 93 N??
3 N9
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Eperi0ent 2
4he polari)ation direction clearl- ha# relevance
Pl#e#: V (E:H7VKc0!K t: ; #
PF&+ Vr0# and f:H 75)
A
A
BFO
BFO3
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6e#lt#
Flip in the electric polari)ationafter .V pl#e#
4he diode forward and rever#e
direction# #witch when thedirection of P i# rever#erd
4he aplication of the #econd #et of M.V pl#e doe#not re#tore oriinal confiration
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Eperi0ent 3
Sa0ple+ AKBFO2KAL %reen liht (:32 n0!
4hen the photocrrent i# #tdied
A (
A (
B F O
6iht*eft
A
A
BFO
BFO2
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6e#lt#
Qhen a bia# potential i# applied to the 0aterial thephotocrrent follow# the bia#
Qhen there i# no bia#, it follow# the polari)ation direction,and i# alwa-# neative
*eft.#ide ill0ination wor7# better than riht.#ideill0ination
!llumination"side #hotocurrent($%&)' (μA)
Reerse $ias(μA/cm2)
*eft.#ide .;3 ?;29
6iht.#ide .;3 ;?N9
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Eperi0ent N
4he #ide of the il0ination i# relevant beca#e thephotocrrent i# a##-0etric (de to ther0oelectricit-,probabl-R!
A
A
BFO
BFO2
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6e#lt#
4he crrent withot liht decrea#ed to ; pA
Sa0e )ero.bia# photocrrent direction in both #ide#
&ch 0ore inten#e with hih ener- liht
Photovoltaic effect ha# been de0on#trated
6iht.left a#-00etr- 0a- re#lt fro0 a ther0oelectric
power effect andKor ncontrolled a#-00etrie# in theconfiration
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Eperi0ent
4he anle between the #a0ple and Polari)er affect# too
Ble ircle#+ 1nitial po#ition
%reen ircle#+ 1nitial po#ition M polari)er rotation of 9@
A
A
BFO
BFO2
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6e#lt#
4he PV effect i# 0ai00 when the polari)ed.lihtelectric field i# parallel to the in.plane co0ponent offerroelectric polari)ation (:9@!
4he PV effect i# 0ini00 when the polari)ed.lihtelectric field i# perpendiclar to the in.planeco0ponent of ferroelectric polari)ation (:@!
After the rotation b- 9@, the chane of photocrrent i#
#i0ilar, ecept for a 9@ pha#e
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oncl#ion#
Diodeli7e behavior and Photovoltaic effect ha# been#hown
Qhen a electical field larer than the coercitive field i#applied the diode polari)ation #witche#
4he )ero bia# photocrrent den#it- i# #ide dependent
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on#trctive critici#0
Are the #a0ple# trl- 0onodo0ain#T
10ae# cold be better eplained
1# the crrent den#it- proportional to lenthT
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