Evaluation of fluence dependent variations of capacitance and generation current parameters by transient technique E.Gaubas, T.Čeponis, J.Kusakovskij, A.Uleckas, S.Sakalauskas, and J.Vaitku Vilnius University, Institute of Applied Research, Vilnius, Lithuania (VU) Outline Motivation for alternative techniques vs. impedance based frequency domain one Principles of Barrier Evaluation by Linearily Increasing Voltage (BELIV) technique Fluence dependent BELIV characteristics Temperature dependent BELIV characteristics for reverse- biased diodes Detector- barrier evaluation summary Photo-conductivity gain in heavily irradiated full-depleted detectors
Transcript
Evaluation of fluence dependent variations of capacitance and generation current parameters by transient technique
E.Gaubas, T.Čeponis, J.Kusakovskij, A.Uleckas, S.Sakalauskas, and J.Vaitkus
Vilnius University, Institute of Applied Research, Vilnius, Lithuania (VU)
Outline
Motivation for alternative techniques vs. impedance based frequency domain one
Principles of Barrier Evaluation by Linearily Increasing Voltage (BELIV) technique
Fluence dependent BELIV characteristics
Temperature dependent BELIV characteristics for reverse-biased diodes
Detector- barrier evaluation summary
Photo-conductivity gain in heavily irradiated full-depleted detectors
Summary
Applicable only when diode can be emulated by the linear elements Uac<<kT/e
CP CS (UR) Cb0 (1+U/Ubi)-1/2
Cb0=(eND0S2/2eUbi)1/2 slope C-2 vs U ND; intersect. Ubi-UF=0 Ubi
Ubi=(kT/e)ln(NAp+ND/ni2)
at least Uac/URdc<<1`
Motivation for alternative techniques vs. impedance based frequency domain one
Limitations for impedance, frequency domain based C-V (LRC) techniques Principle (LCR meter) “works” only if complexity (jXC) appears due to conductance/impedance
LRC phasor
Whether standard paradigm of C-V technique is valid when diode current iCigen, icapt for UR -?
Applicable only when diode can be emulated by the linear elements Uac<<kT/e
CP CS (UR) Cb0 (1+U/Ubi)-1/2
Cb0=(eND0S2/2eUbi)1/2
Ubi=(kT/e)ln(NAp+ND/ni2)
at least Uac/URdc<<1`
Motivation for alternative techniques vs. impedance based frequency domain one
Limitations for impedance, frequency domain based C-V (LRC) techniques Principle (LCR meter) “works” only if complexity (jXC) appears due to conductance/impedance
LRC phasor
Whether standard paradigm of C-V technique is valid when diode current iCigen, icapt & how to correlate with I-V -?
-200 -150 -100 -50 0 5010-13
10-11
10-9
10-7
10-5
10-3
I (A
)
U (V)
Neutron irradiated diodes:
=1E13 cm-2
=1E14 cm-2
=1E16 cm-2
Why huge difference in CP and Cs appears for heavily irradiated diode -?Why C-V measurements are improved at high frequencies-?Why extracted depletion voltage depends on frequency -?
100 kHz
50 100 150 200 250101
102
Neutron irradiated diodesf=100 kHz
Cp, =1012 cm-2
Cs, 1012 cm-2
Cp, 1014 cm-2
Cs, 1014 cm-2
Cp, 1016 cm-2
Cs, 1016 cm-2C
(pF
)
UR (V)
Motivation for alternative techniques vs. impedance based frequency domain one
Limitations for impedance, frequency domain based C-V (LRC) techniques Principle (LCR meter) “works” only if complexity (jXC) appears due to conductance/impedance
LRC phasor
Whether standard paradigm of C-V technique is valid when diode current iCigen, icapt for UR -?
Why huge difference in CP and Cs appears for heavily irradiated diode -?Why C-V measurements are improved at high frequencies-?Why extracted depletion voltage depends on frequency -?
108 109
UFD-non
108 109108 109
UFD-non
30 Hz
Applicable only when diode can be emulated by the linear elements Uac<<kT/e
CP CS (UR) Cb0 (1+U/Ubi)-1/2
Cb0=(eND0S2/2eUbi)1/2
Ubi=(kT/e)ln(NAp+ND/ni2)
Motivation for alternative techniques vs. impedance based frequency domain one
i*gen
LRC phasor becomes multi-dimensional
Limitations for impedance, frequency domain based C-V (LRC) techniques Principle (LRC meter) “works” only if complexity (jXC) appears due to impedance
How are the generation and carrier capture currents included into standard C-V for (heavily) irradiated pin diodes-? with large igen=eniw(U)S/gen
gen=2cosh(EL-Ei)/vTNL- short i=iC+(igen+idiff - complex quatn.)
Igen,capt=eniw(U)S/gen,capt becomes a complex quantity for ac U~
Is it possible to separate an impact of igen, capt from C-V to correlate with I-V -?
Technical limitations for LRC-meters based measurements- necessary to make measurements in the range of low UR voltages to avoid the impact of igen,~ U1/2 - LRC meters with small ac voltage U~<<kT/e
- dc and ac voltage sources connected in series (dependence on Rin dc), - noise (Uns) suppressed dc voltage sources due to small Uns <<U~,
- no additional loops (capacitors, resistors), limitations to ground for LRC-meters with wide range of external dc voltages
Indications that LRC impedance principle and a paradigm of parameter extraction does not work anymore:- appears huge difference between CP and CS - artefact of principle due to i*
gen,- impossible to separate iC and i*
gen,
- appears crucial reverse voltage drop:
e.g. Ugen=igenRdepl=w2(U)/gen and indefinite voltage drop (on junction and within bulk) Utechn =Ugen UFD shifts crucially to the high voltage/high frequency range due to increase of Ugen with Uext
- depletion width becomes indefinite (un-known gen) - estimation by iteration procedure-- simulations by TCAD/SPICE or approach of positive root w(Uex)=[20 (Ubi+Uext )/{eND(1+20 /eNDgen)}]1/2 – valid for Uac/Udc<<1; necessary additional parameters)
- intricate (w(Uext)) dependence on frequency, temperature, voltage - due to gen
To include dominant physical processes, analysis of Cbj(U)=0S/w(U) is an alternative way with estimation of w(U) by iteration procedure- approach of positive w(U) root using Ugen=w2/gen,capt
valid for Uac/Udc<<1 and leads to different Neff=ND (120 /eND+gen,-capt) for 1/gen (+) and for 1/capt (-)
)2
1(
)(2)(2)(
,
0
,0,,0,
captgenDD
extRbi
D
captgenextRbiextR
eNeN
UU
eN
UUUUw
Motivation for alternative techniques vs. impedance based frequency domain one
Alternative measurement techniques capable to separate components
Evaluation of w(Ujunct) by simulations by TCAD/SPICE etc.
captgen
iC
SUwenUwiUi
,
)()]([)(
BELIV technique
U(t)=UP/PLt =At
LIV ramp A=UP/PL = U/t
PL= 10 ns 500 sUP= 0.01 5 V
Cb= 2 pF 40 µF with resolution 0.2 pF | (2-20 pF)
UC=iC*50 =10 mV 4 pF|A=5*E8 V/s
GLIVpin
diode
RL=50 oscilloscope
GLIVGLIVpin
diode
RL=50 oscilloscope
Cryo-chamber
AT-DSO-6102A
iC
LIV always starts from U(t)=0
BELIV technique, model and simulations
2/30
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21
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gC
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ii
i
Ai
Ut
Reverse bias
Short transient processes acting in series due to tD, DR, capt, gen
etc (to complete a circuit) determine a delay,- reduction of the initial displacement current step. Similar effect perturbs the C-V characteristic at UR0 measured by impedance technique (LRC-meters).
0 2 107
4 107
6 107
8 107
1 106
0
5 105
1 104
1.5 104
2 104
2.5 104
3 104
2.8 104
1.4 108
jc t 4( )
jcM t 4 2 1010
jcM t 4 2 108
jcM t 4 2 107
1 1061 10
11 t
Displacementcurrent
Charge extractioncurrent
te
0 5 107
1 106
0
1 104
2 104
3 104
4 104
3.7 104
5.185 105
jc t 4( )
jcg t 4( )
1 1061 10
11 t
Charge extraction
Charge generation
BELIV technique UF model
U(t)=UP/PLt =At
)1(i))(
1(2
}])(
1[)
)(1(
)2
)(1(
{)(
)()()()()(
)/)(2/10
)(
02/3
0
TkteUdiff
bi
F
R
iTk
teU
B
Fdiff
bi
F
bi
F
bF
diffFRCdiffCFF
BFB
F
eU
tUwene
Tk
teUC
UtU
UtU
Ct
tU
tititititi
Forward biasUF(t)=At-RLiF(t),
Transcendental, iterative simulations
BELIV transients – measurement technique
0 2 4 6 80.00
0.04
0.08
UG
LIV
(a.
u.),
dU
GLI
V/d
t (a.
u.)
t (s)
Ampl
itude
BEL
IV (V
) Si diode A = 4 V/s 2 V/s 1 V/s 0.5 V/s 0.3 V/s
0.0
0.1
0.2
0.3
0.4
0.5
0.6
GLIV signal Differentiated GLIV signal
A = 0.5 V/s
a ba- Barrier evaluation by linearily increasing voltage (BELIV) technique based on charge extraction current transients measured in the non-irradiated and irradiated with small fluence pin diode at reverse (UR) biasing by LIV pulses.
b- Charge injection BELIV transients for forward (UF) biased pin diode irradiated with small fluence varying ramp A of LIV pulses.
UR pulse duration dependent BELIV transients at a constant LIV ramp is equivalent to Cb -V~t
BELIV transients on WODEAN pad-detectors neutron-irradiated with fluences 1012 -1016 n/cm2
a ba- LIV pulse duration (LIV ramp) dependent BELIV transients at reverse (UR) bias. b- Comparison of charge extraction (UR) and
injection (UF) BELIV transients measured on diodes irradiated by neutrons of different fluence.
To separate the displacement, generation/capture and diffusion currents, a wide range of duration/voltage and perfect LIV pulses are necessary.
For diodes irradiated with rather small fluence charge extraction current prevails for Rev biasing, while charge storage (diffusion) capacitance dominates for Frw biased diodes.
In heavily irradiated material generation and recombination currents dominate. Voltage on junction is governed by Ujnc=At-iRL
Reverse bias Reverse & Forward bias
0.0 0.2 0.4 0.6 0.8 1.00.0
0.1
0.2
0.3
0.4
0.5
0.6
Am
plitu
de B
ELI
V (V
)
t (s)
MCZ n-type Si diode, = 1012 n/cm2 T=300K, U
pulse-reverse= 5V
tpulse
= 1 s 0.2s 0.1s 0.05s
Barrier capacitance prevails for short LIV pulses
0.0 0.5 1.0 1.50.000
0.002
0.004
0.006
0.008
0.010
0.00
0.01
0.02
0.03
0.04
1015 n/cm2 Up= 2V
Forward Up= 2V
Reverse 0.2V Reverse 2V
Ampl
itude
BEL
IV (V
)
t (s)
1012 n/cm2
Forward Up= 0.2V
Reverse Up= 0.2V
Reverse Up= 2V
Cb
dominates for1E12 n/cm2
Igen & irecdominate for1E16 n/cm2
BELIV results –dependence on fluence
a ba- Variations of BELIV transients with irradiation fluence for reverse biased Si pin pad-detector at the same LIV parameters (A= 3 MV/s, PL =1.5 s). b- Injection current BELIV transients for different fluence neutron irradiated Si pin diodes. The extreme points (te, tFk) are denoted on transients.
0.0 0.4 0.8 1.210-4
10-3
10-2
10-1
Am
plit
ud
e B
EL
IV (
V)
t (s)
MCZ n-type Si diode T=300K, U
pulse-reverse=5V, t
pulse=1.5s
=1E12 n/cm2
1E13 n/cm2
1E14 n/cm2
1E16 n/cm2
0.0 0.4 0.8 1.2
10-3
10-2
10-1
tFk
iR(t)
iCdiff
(t)
iCF
(t)
MCZ n-type Si diode T=300K, U
F,GLIV=0.3V,
PL=1.5s
=1E12 n/cm2
1E13 n/cm2
1E14 n/cm2
1E16 n/cm2
Am
plit
ud
e B
EL
IV (
V)
t (s)
iC(t)
te
BELIV results –dependence on temperature
Temperature dependent variations of BELIV transients in heavily (with fluence of 1016 n/cm2) irradiated Si pin diode.
0.0 0.1 0.2 0.3
10
20
30
40
50
Am
plit
ud
e B
EL
IV (
mV
)
t (s)
1016 n/cm2 , U
pulse-reverse= 8V, t
pulse=0.25s
T = 170K 200 250 273 294
-200 -150 -100 -50 0 5010-13
10-11
10-9
10-7
10-5
10-3
I (A
)
U (V)
Neutron irradiated diodes:
=1E13 cm-2
=1E14 cm-2
=1E16 cm-2
T=294 K
Ubi still exists (for 1E16 n/cm2) but diode at RT resembles a photo-resistor at large Ubias
Photo-conductivity gain (PCG)
PCG=tdr,h/tdr,e CCE>1 if tdr,e<tdr,h<Rec
CCE0 for Rec<tdr
- radiation induced generation (trapping) centers (increased density with fluence) enhance probability for PCG processes;
- reduction of tdr by enhancement of U>UFD and by reduction of d~lh;
- resolvable PCG pulses if time gap tar between arrival of HE particles tar>tr
p+ n+
iat FD
-+
tdr,h=lh2/hU
tdr,e=le2/eU
for tdr,e<tdr,h to keep el. neutrality additional carrier(s) is injected from electrode or thermally generated in vicinity of electrode
tr
Rec
gT
n, H+
Summary: detector- barrier evaluation by LIV
For barrier evaluation better to control Ubi=(kT/e)ln(NAND/ni2)
BELIV shows ND is invariable, barrier exists, detector functional, but necessary to shift the operational range towards high () frequency/short time domain range, to decrease bias voltage (to suppress igen) etc.
Optimization of the detector’ functionality is possible only by a trade-off among desirable parameters:
- necessity to shift the time domain TD towards short shaping time TD1/ is compatible with LHC operation regime, but, to reduce an impact of igen, rec , it is desirable to keep rec,gen >TD>DR (reduction of DR is possible by enhancement of doping);
- to suppress igen, rec - reduction of the operational voltages, temperature and base thickness d;
- to reach full-depletion – enhancement of operational voltage, but increases a problem with igen~U1/2 ;
- to reduce impact of g-r noises – enhancement of detector volume V=Sd through base thickness or area S ( 3-D detectors); - to approach a photo-conductivity gain regime (to increase CCE) enhancement of operational voltage and proper reduction of base thickness d;
Summary
Validity of a simple paradigm (standard C-V method) of the parameter extraction from C-V characteristics in irradiated diodes should be verified for every experimental regime and adjusted by selecting , UR, Uac, T parameters
Developed BELIV transient technique enables one to control variations of Ubi and generation current dependent on fluence and temperature. Increase of generation current for reverse biased diode and reduction of diffusion capacitance/current due to recombination of injected carriers in forward biased diodes leads to the symmetric (Rev/Frw) I-V/C-V transient characteristics. Symmetry of these characteristics indicate the dominant mid-gap centers/clusters with pinned EF.
BELIV shows Ubi and ND is invariable and detector is functional, while in heavily irradiated detectors for 20 Hz< <10 MHz deterioration of characteristics is determined by capt,gen.
Optimization of the detector’ functionality is possible only by a trade-off among desirable parameters. CCE can be increased through proper design of detector (d) and applied detection regimes (U, response) to reach PCG.
Thank You for attention!
ni/ND
20 10 0 10 201
10
10015
1
taug x( )
taur x 0.01( )
taur x 0.001( )
taur x 0.0001( )
2020 xEDL-Ei
Gen
erat
ion
lif
etim
e
Rec
om
bin
atio
n li
feti
me
re
c, g
en
=h/e=n0/p0
Trivial remarks concerning SRH relations between recombination – generation lifetime
n-Si
Photo-injection URT
ne pe > ni2
ne · pe < ni2ne · pe - ni
2 =0
n-Si
Photo-injection URT
ne pe > ni2
ne · pe < ni2ne · pe - ni
2 =0
Without applied E field
With applied dc E field
Eqv.
R>0
G<0
ni/ND
20 10 0 10 201
10
10015
1
taug x( )
taur x 0.01( )
taur x 0.001( )
taur x 0.0001( )
2020 x(EDL-Ei)/kT
Gen
erat
ion
lif
etim
e
Rec
om
bin
atio
n li
feti
me
re
c, g
en
DLnn
iDLei
DLrec NvkT
EE
n
n
NvR
ni
e 1
|]cosh(2
1[1
DL
iDL
igen NvkT
EE
Gn
)cosh(2
/
Calibration of LRC-meters
0 200 400 600 800 1000
103
104
105
C
(pF
)
Uac
(mV)
Neutron irradiated diode
=1013 cm-2, UR=0V, f=10 kHz
Waine Kerr 6440B C
p
Cs
QuadTech 7600 C
p
Cs
0 300 600 900
300
400
500
C (
pF)
Uac
(mV)
Neutron irradiated diode, =1013 cm-2
UR=1V, f=10 kHz
Waine Kerr 6440B C
p
Cs
QuadTech 7600 C
p
Cs
BELIV results –dependence on fluence
0.0 0.4 0.8 1.210-4
10-3
10-2
10-1
ig(t)
iC(t)
te
Am
plitu
de B
ELI
V (V
)
t (s)
MCZ n-type Si diode T=300K, U
R, GLIV=5V,
PL=1.5s
=1E12 n/cm2
1E13 n/cm2
1E14 n/cm2
1E16 n/cm2
0.0 0.4 0.8 1.2
10-3
10-2
10-1
tFk
iR(t)
iCdiff(t)
iCF(t)
MCZ n-type Si diode T=300K, U
F,GLIV=0.3V,
PL=1.5s
=1E12 n/cm2
1E13 n/cm2
1E14 n/cm2
1E16 n/cm2
Am
plit
ude
BE
LIV
(V
)t (s)
a ba- Variations of BELIV transients with irradiation fluence for reverse biased Si pin pad-detector at the same LIV parameters (A= 3 MV/s, PL =1.5 s). b- Injection current BELIV transients for different fluence neutron irradiated Si pin diodes. The extreme points (te, tFk) are denoted on transients.
