New$thick$Silicon$Carbide$detectors:$response$to$14$MeV$neutrons$and$comparison$1"
with$single-crystal$diamonds"2"
"3"
M."Rebai
1,2
,"D."Rigamonti
1,2
,"S."Cancelli
3
,"G. "Croci
2,3
,"G. "Gorini
2,3
,"E ."Perelli"Cippo
1
,"O."Putignano
3
,"M.""4"
Tardocchi
1,2
,"C."Altana
4
,
"
M."Angelone
5
,"G."Borghi
6
,"M."Boscardin
6
,"C."Ciampi
7,8
,"G.A.P."Cirrone
4
,"A."5"
Fazzi
9,10
,"D."Giove
10
,"L."Labate
11
,"G."Lanzalone
4,"
F."La"Via
12,4
,"S."Loreti
5
,"A."Muoio
4
,"P."Ottanelli
7,8
,"G."
6"
Pasquali
7,8
,
"
M."Pillon
5
,"S.M.R."Puglia
4
,"A."Santangelo
13
,"A."Trifiro
14,15
"and"S."Tudisco
4
"
7"
"8"
!
"#$%$&$'()*+(,-(./%*01-(*(2*/0','3%-(4*%(5,-#6%(7'0#%3,%'(8-1%'0-,*(4*,,*(9%/*+/:*;(<%,-0';("$-,="9"
>
("8?8(#*1%'0 * (4 %(<%,-0'@A%/'//-;(<%,-0';("$-,="10"
B
C%)-+$%6*0$'(4%(?%#%/-(‘DE(F//:%-,%0%’;(G0%H*+#%$I(4%(<%, - 0 '@A%/'//-;(<%,-0';("$-,="11"
J
("#$%$&$'(8-1%'0-,* (4%(?%#%/-(8 & /,*-+* (K"8? 8L;(M- N' +-$' +%(8- 1%'0 -,%(4* ,(.&4 (KM8 .L;(O%- (.E(.'P%- (Q>;(RS! >B (7-$- 0 %-;("$-,="12"
S
T##'/%-1%'0*(UG9T2F<@U8UT(#&,,-(?&#%'0*(U8UT(7E9E(?+-#/-$%;(O%-(UE(?*+6%;(JS;(VVVJJ(?+-#/-$%(K9'6-L;("$-,="13"
Q
2+*0$'("0#$%$&$*(P'+(?&04-6*0$-,(5:=#%/#(-04(T)),%/- $%' 0 #(K2"?5 TL ;(K"8?8 L;(?'04 - 1 %'0 * (A+&0 ' (W*##,*+(K?AW@2+*0$'L;(O%-(
14"
.'66-+%H*(!J;(BX!>B(5'H'(2+*0$';("$-,="15"
Y
"8?8Z.*1%'0*(4%(?%+*01*;(O%-(DE(.-0#'0*(!;(SVV!R(.*#$'(?%'+*0$%0';("$-,="16"
X
(C%)-+$%6*0$'(4%(?%#%/-;(G0%H*+#%$I(4%(?%+*01*;(O%-(DE(.-0#'0*(!;(SVV!R(.*#$'(?%'+*0$%0';("$-,="17"
R
C*)-+$6*0$('P(U0*+3=('P(5',%$*/0%/'(4%(<%,-0';(O%-(M-6N+&#/:%0%(J;(>V!SQ;(<%,-0'"18"
!V
("8?8@.*1(<%,-0';(O%-(7*,'+%-(!Q;(>V!BB(<%,-0'"19"
!!
"#$%$&$'(8-1%'0 - ,* (4 %(F $$ %/-;(7'0#%3,%'(8-1%'0-,*(4*,,*(9%/*+/:*;(O%-(DE(<'+&11%(!;(SQ!>J(5%#-;("$-,="
20"
!>
"0#$%$&$*(P'+(< %/+ ' *,* /$ +' 0 %/# (-0 4 (<%/+'#=#$*6#;(7'0#%3,%' (8 - 1 %' 0- ,* (4 * ,,*(9 %/ *+ /: * (O """(.$ +- 4 - ;(S;(R S! > !(7 - $- 0 %- ;("$- ,="
21"
13
".2<%/+'*,*/$+'0%/#;(.$+-4-,*(5+%6'#',*;(SV;(RS!>!(7-$-0%-;("$-,="22"
!J
C%)-+$%6*0$'(4%(./%*01*(<"?2(4*,,[G0%H*+#%$\(4%(<*##%0-;(OE,*(?E(.E(C[T,/'0$+*#(B!;(RX!QQ(<*##%0-;("$-,=(23"
!S
"8?8@.*1(7-$-0%-;(O%-(.-0$-(.'P%-;(QJ(@(RS!>B(7-$-0%-"24"
$25"
$26"
Abstract"27"
"28"
In"this"work"we"present"the"response"of"a"new"large"volume"4H"Silicon"Carbide"(SiC)"detector"to"14"29"
MeV"neutrons."The"device"has"an"active"thickness"of"100"μm"(obtained"by"epitaxial"growing)"and"an"30"
active"area"of"25"mm
2
."Tests"were"conducted"at"the"ENEA-Frascati"Neutron"Generator"facility"by"31"
using"14.1" MeV" neutrons." The"SiC" detector" performance" was" compared"to" that" of" Single-Crystal"32"
Diamond"(SCD)"detectors."The"SiC"response"function"was"successfully"measured"and"revealed"a"very"33"
complex" structure" due" to" the" presence" in" the" detector" of" both" Silicon" and" Carbon" atoms."34"
Nevertheless," the" flexibility" in" the" SiC" manufacturing" and" the" new" achievements" in" terms" of"35"
relatively" l arge" areas" (u p" 1x1" cm
2
)" and" a" wide" range" of" thicknesses" makes" them" an" interesting"36"
alternative"to"diamond"detectors"in"environments"where"limi ted"space"and"high"neutron"fluxes"are"37"
an"issue,"i.e."modern"neutron"cameras"or"in-vessel"tokamak"measurements"for"the"new"generation"38"
fusion" machines" such" as" ITER." The" absence" of" instabilities" during" neutron" irradiation" and" the"39"
capability" to" withstand" high" neutron" fluences" and" to" follow" the" neutron" yield" suggest" a"40"
straightforward"use"of"these"detectors"as"a"neutron"diagnostics.""41"
1. Introduction$42"
$43"
The"range"of"application" o f"high"band-gap"solid"state"detectors"is"expanding"in"those"environments"44"
where"the"high"neutron"flux"is"an "issue,"such"as"in"the"high-flux"spallation"neutron"sources"and"in"45"
the"thermonuclear"fusion"environment.""An"example"of"the"former"is"the"ISIS"spallation"neutron"46"
source"(Didcot,"U.K.)[1],"where"neutrons"are"produced"by"800"MeV"protons"impinging"on"a"heavy"47"
material."Being"a"pulsed"neutron"source,"instant"neutron"flux"can"be"very"high,"therefore"the"small-48"
size" and" the" fast" response-time" features" of" high" band-gap" solid" state" detectors" make" them" an"49"
interesting" solution" to" monitor" and" measure" the" neutron" flux." Single-crystal" Diamond" (SCD)"50"
detectors"have"been"characterized"in"the"past"[2][3][4]"and"they"are"currently"installed"at"the"ChipIr"51"
beam-line" at" ISIS " as" beam" monitors" [5]." ChipIr," built" for" measuring" the" Single" Events" Effects" on"52"
electronic"devices,"is"a"fast"neutron"beam-line"that"directly"faces"the"spallation"target:"the"neutron"53"
flux"exceeds"10
6
"n/s
∙
cm
2
above"10"MeV"and"therefore"dedicated"fast-neutron"detectors"are"still"in"54"
development"fo r"the"measurement"of"the"neutron"flux"in"the"1-800"MeV"energy"range"and"able"to"
55"
work"at"high"rates"(">"1"MHz).""
56"
"As"for" "thermonuclear"fusion"environments,"it"has"been"sho wn"that"SCDs"can"be"used"as""excellent"
57"
spectrometers"for"14"MeV"neutrons"[6]"and"a"SCD"detector"matrix"has"been"installed,"e.g.,""at"JET "58"
(Joint"European"Torus)"for"the"diagnosis"of"the"plasma"in"the"upcoming"Deuterium-Tritium"campaign"59"
[7]." Measurements" performed" with" Deuterium" (D)" plasmas" at" JET" have" demonstrated" that"60"
spectroscopy" with" a" moderate" energy" resolution" can" also" be" performed" [8][9]" with" 2.5" MeV"61"
neutrons."The"limited"availability"of"large"size"commercial" single-crystal" diamonds" has"led"to"the"62"
development"of"a"12-pixel"(4.5"x"4.5"mm
2"
each)"matrix"to"boost"the"counting"rate,"especially"in"D"63"
plasmas,"instead"of"having"a"single"diamond"detector"with"equal"area."""
64"
Diamond"detectors"have"been"shown"to"withstand"neutron"fluence"up"to"2*10
14
"n/cm
2
"as"shown"in"65"
[10]""for"single"crystal"and"in"[11]""for"polycrystalline"diamonds."The"latter,"after"irradiation"with"66"
8*10
14
"n/cm
2
,"recovers"up"to"70%"of"their"initial"performance"after"a"suitable"annealing."Moreover,"67"
transient" effects" have" been" noticed" for" SCD" detectors" irradiated" with" high" energy" neutrons" and"68"
alpha"particles"[13][14].""Transient"effects"are"due"to"partial"trapping"of"the"charge"carries"within"69"
the"detector"bulk"d efects"and"in"the"interfaces"between"the"diamond"crystal"and"the"ohmic"contacts."
70"
These"are"known"as"polarization"effects"and"depend"on "the"type,"and"amo unt,"of"crystal"defects,"
71"
naturally"present"or"induced"b y"neutron"irradiation"[15][16]."The"polarization"effect"can"be"reset"by"72"
inverting"the"bias"voltage,"as"discussed"in"[14],"but"it"could"affect"energy"resolution"if"not"accounted"73"
for."""74"
In"thi s"paper"we"investigate"the"performance"of"new"SiC"detectors"as"an"alternative"to"SCDs."SiC"75"
devices"have"been"already"used"in"the"past"to"measure"the"thermal"neutron"flux"in"reactors"[17]"and"76"
the"14"MeV"neutrons"from"DT"reactions"[18]."As"shown"in"[19]"good"quality"SiC"detectors"are"now"77"
available"and"measurement"of"the"fast"neutron"spectrum"is"possible"also"at"high"temperatures"as"78"
done"with"diamond"detectors"[20].""79"
The"device"used"in"present"work"was"manufactured"by"SiCILIA"(.%,%/'0(7- +N%4*( 4 *$*/$'+#(P' +( "0$*0#*(80"
M&6%0'#%$=("0H*#$%3-$%'0#(-04(T)),%/-$%'0#)"[21]"project"which"is"a"collaboration"between"IMM-CNR"81"
and"INFN"totally"funded"by"INFN."The"main"goal"of"th e"project"was"the"processes"innovation"and"82"
production"of"relatively"l arge"area"SiC"detectors"for"many"applications"[22][23][24][25][26][27],"with"83"
thicknesses"dependin g"on"the"experiment"requirements."Today,"thanks"to"the"SiCILIA"R&D,"SiC" can"84"
be"produced"in"relatively"large"areas"(up"to"1.5"cm
2
)"[28]"and"with"thicknesses"up"to"250"μm"which"85"
represent"an"excellent"enhancement"in"the"SiC"growth"technology."Moreover"in"the"near"future"they"86"
could"be"worked"in"Geiger"mode,"in"order"to"detect"single"photons"[29][30]."""87"
Moreover,"the"possibility"of"growing"SiC"layers" with"large"area"and"with"different"thickness,"makes"88"
this"material"an"interesting"candidate"for"applications"in"fusion"plasma"physics,"like"for"instance"for"89"
Fast"Ions"Loss"Detectors"(FILD)"that"measure"the"fast"ions"lost"by"the"plasma"before"they"hit"the"first"90"
wall." Currently," FILD" systems" are" based" on" scinti ll ator" crystals" coupled" to" optical" fibres" leading"91"
scintillation"light"towards"a"CDD"[12]."They"work"in"an"environment"where"neutrons"are"the"highest"92"
source" of" background." An" advantage" of" SiC" in" this" application" is" that," by" decreasing" the" crystal"93"
thickness," the" detector" efficiency" for" neutrons" can" be" accordingly" decreased" to" as" low" as" 10
-5
,"94"
without"losing"efficiency"for"500"keV"ions."95"
As"in"SCDs,"neutron"detection"in"SiC"is"based"on"the"collection"of"electron-hole"pairs"produced"by"96"
charged"particles"generated"by"neutron"interaction"with"C"and"Si"nuclei."Due"to"their"abundances"in"97"
natural" C"and"Si,"in"this"work"we"will"consider"only"interaction"on"
12
C"an d"
28
Si." T hi s"paper"describes"98"
measurements"performed"at"the"Frascati"Neutron"Generator"(FNG)"at"Enea"(Frascati,"Italy)"by"using"99"
a" SiCILIA" SiC" detector" prototype" and" two" SCDs" with" different" thicknesses" irradiated" by" 14" MeV"100"
neutrons."The"SiC"detector"was"irradiated"up"to"a"total"fluence"of"4.45*10
11
"neutrons/cm
2
."101"
The"paper"is"organized"as"follows:"in"Section"2"the"neutron-induced"reactions"on"
12
C"and"
28
Si"are"102"
summarized"and"the"detectors"are"compared"in"terms"of"construction"parameters"and"features."In"
103"
Section"3"the"experiment"performed"at"FNG"is" described," while" in" Section"4"the"most"important"
104"
results"will"be"illustrated.""
105"
"106"
"107"
Figure)1)"Cross"section"of"the"SiC"detectors)108"
2. The$detectors$109"
$110"
A. C*$*/$'+#()+'4&/$%'0"111"
$112"
The"SiC"detectors"were"designed"and"manufactured"at"the"CNR-IMM"(Institute"for"Mi croelectronics"
113"
and"Microsystems)"in"Catania,"starting"from"the"growth"of"thick"4H"epitaxial"layers"on"four"inch"4H-114"
SiC"wafers"by"means"of"a"CVD"(Chemical"Vapour"Deposition)"process."During"this"phase"dopants"are"115"
provided" by" means" of" gaseous" precursors" such" as" N
2
" for" n-type" doping" and" Al
2
(CH
3
)
6"
116"
(Trimethylaluminium)"fo r"p-type"doping"in"order"to"realize"p-n"junction"devices."The"process"was"117"
performed"at"a"low-pressure"and"high"temperature"(1630"°C)"regime.""118"
The" wafers" were" subsequently" treated" with" several" photolithographic" steps," a" first"119"
photolithography"for"the"definition"of"the"detector"area"by"Inductive"Coupled"Plasma"(ICP)"etching"120"
was" performed." Then," a" second" lithography" was" performed" for" the" construction" of" the" edge"121"
structures,"aimed"at"reducing"the"electrical"field"at"the"device"borders."The"process"continues"with "122"
the"deposition "of"an"isolation"oxide"and"the"openin g"of"the"contacts"with"a"further"photolithographic"123"
process" and" a" subsequent" annealing" to" perform" a" good" electric" contact" on" p
+
" region." Along" the"124"
border"of"the"active"area"of"the"detector"a"200nm"layer"of"Ti"and"Al"was"deposited"in"order"to"obtain"125"
a" region" well-suited" for" ultrasonic" micro-bonding." Finally," the" ohmic" contact" was" formed" by"126"
Titanium/Nickel/Gold" d eposi tio n." A" cross-section" of" the" SiC" detector" used" for" the" neutron"127"
measurements"described"i n"this"paper"is"shown"in"Fig.1."It"features"a"300"nm"thick"p-layer"with"a"128"
doping"concentration"N
A
=1x10
19
cm
-3"
and"a"100"]m"thick"n-layer"with"a"doping"concentration,"N
D
,"129"
between" 8x10
13
cm
-3"
and" 1x10
14"
cm
-3
." The" detector" has" an" active" area" of" about" 10x10" mm
2
,"130"
segmented"in"four"regions"of"5x5"mm
2
,"and"was"mounted"on"a"PCB"board"(Figure" 3"A)"designed"to"131"
be"housed"in"an"aluminium"box."132"
The"SCD"detectors"were"designed"and"built"at"the"CNR-IFP"(Institute"of"Plasma"Physi cs)"in"Milan"and "133"
at" the" CNR-ISM" institute" in" Rome" (Italy)" [31][32][33]." The" first" SCD" is" made" of" a" single-crystal"134"
diamond"sample"(4E5^4E5^0E5mm
3
)"grown"with"a"CVD"technique"with"boron"concentration"[A]"_5"135"
ppb"and"nitrogen"concentration"[8]"_1"ppb),"provided"by"Element"Six"Ltd."[34]."The"second,"equal"136"
to"the"first"one,"has"been"thinned"by"laser"cutting"to"a"layer"thickness"of"150"]m."Ohmic"contacts"137"
were"obtained"on"the"top"and"bottom"surfaces"of"the"samples"by"subsequ ent"sputtering"depositions"138"
of"a"multilayer"metal"structure"(patent"pending),"followed"by"a"final"gold"layer"deposition,"in"order"139"
to"improve"weldability"with"microwires"and"to"prevent"oxidation"of"the"underlying"structure."The"140"
contact"thickness"is"200"nm"with"a"lateral"dimension"of"4E2^4E2mm
2
."A"dedicated"1mm"thick"alumina"141"
Printed" Circuit" Board" (PCB)" was" designed" and" fabricated;" the" bottom" surfaces" of" the" diamond"142"
samples"were"glued"with"a"thin"layer"of"conductive"silver"paste"on"the"pad,"whereas"the"top"surfaces"143"
were"wire-bonded"(by"means"of"25"]m"thick"Al/Si"wires)"on"the"ground"plane."The"alumina"PCB"is"144"
housed"inside"a"properly"designed"aluminium"metal"case"in"order"to"shield"it"from"electromagnetic"
145"
interference"and"to"give"the"detectors"the"mechanical"resistance"necessary"for"handling.""
146"
"
147"
)148"
Figure)2)Cross"sections"for"neutron"interaction"on"Carbon"(left)"and"on"Silicon"(right).""Data"from"the"ENDF/B-VI.0"for"
12
C"and"149"
ENDF/B-VIII.0"for"
28
Si[35].)150"
(151"
A. 8*&$+'0(4*$*/$%'0"152"
"153"
Neutron"detection"is"based"on"the"collection"of"th e"electron-hole"(e-h)"pairs"produced"by"neutron"154"
interaction"with "
12
C"in"SCDs"and"with"both"
12
C"and"
28
Si"in "SiC"detectors."The"most"important"reactions"
155"
induced"by"neutrons"in"the"MeV"energy"range"on"Carbon"and"Silicon"are"reported"in"Table"1"and"156"
their"cross-sections"in"Figure"2.""The"most"relevant"neutron-induced"process"in"both"Carbon"and"157"
Silicon"is"the"*,-#$%/(#/-$$*+%03((black"lines"in "Figure"2),"in"which"on ly"a"fraction"of"the"neutron"energy"158"
is" released" into" the" detector," by" means" of" the" energy" of" the" recoiling" atom," gi ven" by"159"
E
d
=E
n
*cosθ(4A)/(1+A)
2
,"where"E
n
"is"the"incoming" neutron" energy," θ is" the"recoil"angle" and" A" the"160"
mass"number"of"the"recoiling"atom."The"maximum"energy"that" can "be"released"into"th e"detector"is"161"
E
d,max
=4.00" MeV" and" E
d,max
=1.87" MeV" for" recoils" of" Carbon" and" Silicon" ions," respectively." All" the"162"
energy"values"smaller"than""E
d,max""
can"possibly"be"released"by"this"process"into"the"detector;"as"a"163"
consequence,""a"typical"edge-type"shape"is"produced"into"the"Pulse"Height"Spectrum"(PHS)"of"th e"164"
detector." Concerning" the" reactions"
A
X(n,α)
A-3
Y" and"
A
X(n,p)
A
Y," being" two-body" reactions," all" the"165"
neutron"energy"minus"the"reaction"Q-value"is"deposited"into"the"detector.""166"
"167"
Table) 1:) Main" 14"MeV" neutron-induce d" reactio n s" on" Carbon " and" Silicon." For" each" reaction," the" thresho ld ," the" Q-value" and" the"168"
position"of"the"peak"in"the"PHS"are"given."The"last"column"is"the"label"of"the"peak"observed"in"the"experimental"PHS"shown"in"Figure)169"
6."If"the"nucleus"is"left"in"an"excited"state"the"energy"which "can "be"release d "into"the"det ec to r"is"given"for"the"first"nine"excited"states.)170"
Reaction"
Threshold$
[MeV]"
Q
value
$[MeV]"
E
d
$[MeV]"
Label"
12
C(n,n)
$12
C"
-"
-"
E
d,max
=4.0"
0"
12
C(n$,α)
9
Be"
6.2"
-5.702"
"
"
Ground"state"
8.398"
1"
1st"excited"state"
6.761"
"
12
C(n,p)
12
B"
13.645"
-12.587"
"
"
Ground"state"
1.513"
"
1st"excited"state"
0.56"
"
12
C(n,n’)3α"
"
7.886"
-7.275"
6.825"
2"
28
Si(n,$n)$
28
Si"
-"
-"
E
d,max
=1.87"
"
28
Si(n,$α)$
25
Mg"
2.749"
-2.654"
"
"
Ground"state"
11.446"
3a"
1st"excited"state"
10.861"
3b"
2nd"excited"state"
10.471"
3c"
3rd"excited"state"
9.834"
3d"
4th"excited"state"
9.481"
3e"
5th"excited"state"
8.644"
3f"
6th"excited"state"
8.041"
3g"
7th"excited"state"
8.032"
3h"
8th"excited"state"
7.538"
3i"
9th"excited"state"
7.475"
3j"
$171"
$172"
3. Experimental$set-up"173"
"174"
The"response"function"of"both" S CDs"and"of"the"SiC"detector,"together"with"their"neutron"resistance"
175"
and"stability,"has"been"investigated"by"irradiating"the"detectors"with"14.1"MeV"neutrons"at"FNG."
176"
Here,"neutrons"are"produced"by"Deuterium-Tritium"(DT)"reactions"obtained"from"deuterium"ions"
177"
accelerated"up"to"300"keV"impinging"on"a"tritiated-titanium"target"[36]." The"detectors"were"placed"178"
at"90"degrees"with"respect"to"the"beam"direction"(see"Figure"3)"at"a"distance"between"13"and"18"cm"179"
from"the"target."The"expected"neutron"spectrum"at"the"detector"position,"calculated"through"MCNP"180"
simulations"[37],"features"a"main"component,"peaked"at"14.1"MeV"with"a"130"keV"broadening"and"181"
a"scattered"neutron"component"at"lower"energies"(see"Figure"4)."182"
During"the"measurements,"the"FNG"neutron"yield"has"been"monitored"as"a"function"of"time"by"the"183"
standard"FNG"monitor"which"detects"the"alpha"particles"produced"by"the"DT"reactions"in"the"target.""184"
"
185"
"186"
Figure)3)Pictures"of"the"Silicon"Carbide"(A)" and"Single-crystal"Diam ond " (B)"d etectors" and " their"installation"at"the"FNG"facility"(C)."The"187"
SiC"detector"used"for"the"m easurement"was"the"one"labelled"“A”"in"the"top"left"panel.)188"
A"dedicated"custom"electronic"chain"was"used"to"bias"and"collect"charge"carriers"from"each"detector."189"
In" particular," the" SCDs" were" coupled" (through" a" 5" cm" RG62" cable)" to" a" CIVIDEC" C6" fast" charge"190"
preamplifier"[38]"with"rise"time"of"3.5"ns"and"a"shaping"time"of"25"ns." Si gnal s"were"directly"fed"into"191"
a" CAEN" DT5730B" digitizer" (500" MSample/s" and" 14" bits)" equipped" with" CAEN" software" able" to"192"
perform"on-line"measurements"of"the"pulse"area"[39].""193"
