temperature dependence of reverse current of irradiated si detectors
DESCRIPTION
Temperature dependence of reverse current of irradiated Si detectors. E. Verbitskaya , V. Eremin, I. Ilyashenko Ioffe Physical-Technical Institute of Russian Academy of Sciences St. Petersburg, Russia Z. Li Brookhaven National Laboratory, Upton, NY, USA J. Härkönen , P. Luukka - PowerPoint PPT PresentationTRANSCRIPT
Temperature dependence of reverse currentof irradiated Si detectors
E. Verbitskaya, V. Eremin, I. IlyashenkoIoffe Physical-Technical Institute of Russian Academy of Sciences
St. Petersburg, RussiaZ. Li
Brookhaven National Laboratory, Upton, NY, USAJ. Härkönen, P. Luukka
Helsinki Institute of Physics, CERN/PH, Geneva, Switzerland
20 RD50 Collaboration WorkshopBari, May 30-June 1, 2012
1
Outline
Motivation
♦ Model of bulk generation current based on Shockley-Read-Hall statistics♦ Parameters of investigated detectors and experimental procedure♦ Simulation of generation current of detectors irradiated by 23 GeV protons and neutrons: - single level model - two level model (PTI model with midgap levels) - alternative versions
♦ Lifetime vs. fluence dependence♦ Impact of bulk generation on E(x) profile
Conclusions
E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 20122
Motivation
Goal: Analysis of bulk generation current of irradiated detectors, impact on characteristics of irradiated detectors
Importance: bias voltage applied to p+-n or n+-p junction,power dissipation
Earlier results:
Low neutron fluence (10101012 cm-2): E-center gives the main contribution to the reverse current [E. Borchi and M. Bruzzi, NIM A 310 (1991) 273]. Agreement between calculated and measured damage coefficient was obtained. Activation energy of generation current of neutron irradiated detectors was estimated as 0.6 – 0.65 eV (our earlier data) Recent results on I(T) scaling; simulation and experiment; A. Chilingarov, RD50 notes and presentation at 18 RD50 workshop, May 2011, Liverpool
E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 20123
Earlier results of RD50 collaboration
Linear fit of I(F) is a strong argument to use linear dependence of the concentration of radiation induced defects which act as generation centers on F
a = 3.7x10-17 A/cm
G. Lindström, NIM A 512 (2003) 30
E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 2012 4
Modeling of bulk generation current
Modeling is based on Shockley-Read-Hall statistics
Emission rates ee,h: Generation rate:
kTEE
expkT
EEexp
NnvG
tih
ite
tithhe
kT
EEexpNve;
kTEE
expNve tvvhthhh
ctcethee
Et = Et – Ev; - carrier capture cross section, Nt – deep level concentration
G is determined by a larger energy gap
Assumption for (T):
(T) = o(T/To)-m m = 02
(V. Abakumov, et. al., Sov. Phys. Semicond. 12 (1978) 1)
E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 20125
Experimental
# radiation F, cm-2 kOhm.cm processing d, m923-D26 p 5.00E+12 1,2-3 stand. oxyd. 188923-D35 p 5.00E+13 stand. oxyd. 188923-D39 p 2.00E+14 stand. oxyd. 188921-D12 p 5.00E+12 prol.oxyd.+TD 188899-82 n 1.00E+12 1,2-3 stand. oxyd. 200899-97 n 4.20E+13 stand. oxyd. 200
899-112 n 2.30E+14 stand. oxyd. 200
Irradiated detectors
♦ T = 200400 K♦ Full depletion – bulk generation current is measured♦ Guard ring grounded
E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 20126
Reverse current simulation
1. Carrier generation via single level (SL simulation)
I = evthniNgenSdexp(-Ea/kT) (T) = o(T/To)-2
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
0.0025 0.003 0.0035 0.004 0.0045 0.005 0.0055
I (a
)1/T
neutrons, SL simulation1E+12
simul.
4.2E+13
simul.
2.3E+14
simul.
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
0.0025 0.003 0.0035 0.004 0.0045 0.005 0.0055
I (a
)
1/T
protons, SL simulation
5E+12
simul.
5E+13
simul.
2E+14
simul.
7E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 2012
Fp (cm-2) 5x1012 5x1013 2x1014 Feq (cm-2) 3.1x1012 3.1x1013 1.24x1014 Ec - Et (eV) 0.65 0.65 0.65 e (cm2) 1x10-13 1x10-13 1x10-13 Ngen (cm-3) 1.35x1013 1.4x1014 5.3x1014
F (cm-2) 1x1012 4.2x1013 2.3x1014 Ec - Et (eV) 0.65 0.65 0.65 e (cm2) 5x10-14 7x10-14 1x10-13 Ngen (cm-3) 1.6x1011 1.5x1014 1x1015
Reverse current simulation
1. Carrier generation via single level (SL simulation)
0.0E+00
2.0E+14
4.0E+14
6.0E+14
8.0E+14
1.0E+15
1.2E+15
0.E+00 1.E+14 2.E+14 3.E+14
Nge
n (c
m-3
)
Feq (cm-2)
protons
protons eq.
neutrons
Ngen vs. fluence dependence
Linear dependence of Ngen vs. F agrees with data on I(F)
8E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 2012
Reverse current simulation
2. Carrier generation via two levels (TL simulation) – two independent processes
NDA/NDD = 1.2; kDD = 1
Contributions to current from DD and DA are close
DD: Ev + 0.48 eV; DA: Ec – (0.5250.005) eV – midgap levels used in all PTI simulations and fits
NDA/NDD = 2; kDD = 0.5
Contribution from DA prevails(at F≥1013 cm-2)
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
0.0025 0.003 0.0035 0.004 0.0045 0.005 0.0055
I (A
)
1/T
protons, TL simulation
5E+12
simul.
5E+13
simul.
2E+14
simul.
9E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 2012
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
0.0025 0.003 0.0035 0.004 0.0045 0.005 0.0055
I (A
)
1/T
neutrons, TL simulation
1E+12
simul.
4.2E+13
simul.
2.3E+14
simul.
Parameters of two level simulation
protons
neutrons Generation via two midgap levels, DDs and DAs, adequately describes temperature dependence of reverse current
Generation rate is determined by a larger energy gape – sensitive for DDh – sensitive for DA
E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 201210
Fp (cm-2) 5x1012 5x1013 2x1014 Feq (cm-2) 3.1x1012 3.1x1013 1.24x1014 DD DA DD DA DD DA Et-Ev (eV) 0.48 0.6 0.48 0.595 0.48 0.595 Ec-Et (eV) 0.64 0.52 0.64 0.525 0.64 0.525 e (cm2) 1x10-14 1.5x10-14 1x10-14 1x10-14 1x10-14 1x10-14 h (cm2) 1.4x10-14 1x10-14 1.4x10-14 1x10-14 1.4x10-14 1x10-14 Nt (cm-3) 5x1012 6x1012 5x1013 6x1013 2x1014 2.4x1014
F (cm-2) 1x1012 4.2x1013 2.3x1014 DD DA DD DA DD DA Et-Ev (eV) 0.48 0.6 0.48 0.59 0.48 0.59 Ec-Et (eV) 0.64 0.52 0.64 0.53 0.64 0.53 e (cm2) 1x10-15 1x10-14 1x10-14 1x10-14 1.4x10-14 1x10-14 h (cm2) 1x10-14 4x10-16 1x10-14 1.2x10-14 1x10-14 3x10-14 Nt (cm-3) 5x1011 1x1012 8.4x1012 4.2x1013 1.15x1014 2.3x1014
Reverse current simulation
3. Neutrons, F = 1x1012 cm-2 Additional generation level?
3rd level: DA2, Ec – 0.43 eV
kDD = 0.5NDA1/NDD = 1 NDA2/NDA1 = 5
Contribution from DA2 prevails - agrees with [E. Borchi and M. Bruzzi, NIM A 310 (1991) 273]
11
E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 2012
DD DA1 DA2 Et-Ev (eV) 0.48 0.6 0.69 Ec-Et (eV) 0.64 0.52 0.43 e (cm2) 1.2x10-15 1x10-15 1x10-15 h (cm2) 1x10-15 1.1x10-15 3x10-15 Nt (cm-3) 5x1011 5x1011 5x1012
Generation lifetime vs. F
Ibgen = eniVol/tgen; Ibgen = aFVol
tgen = (eni /a)F-1
tgen 15ttr
12E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 2012
1.0E-09
1.0E-08
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E+11 1.0E+12 1.0E+13 1.0E+14 1.0E+15 1.0E+16F eq (cm-2)
t gen
, ttr
(s)
tau_gen
tau_tr_e
tau_tr_h
tgen = 4.32x107/Feq
ttr_e = 3.1x106/Feq
ttr_h = 2.9x106/Feq
Feq = 1x1015 cm-2
tgen = 40 nsttr_e,h ≈ 3 ns
I. Mandić, et al., NIM A 612 2010) 474
be = 3.2x10-16 cm2s-1; be = 3.5x10-16 cm2s-1
Trapping: all levels contribute to t since pulse signal is measured withinq = 25 ns that is far less than detrapping time constant for larger energy gap (at RT) Generation: only midgap levels contribute
Whether DLs with Ea ~ 0.4 eV can affect Igen (occupancy of DLs vs. T)
Feq ~ 1014 cm-2 DLs: DD, DA, VV-
NVV = 1x1014 cm-3 NVV = 1x1016 cm-3
NVV = 1x1017 cm-3
In plots: concentration of charged DLs and total Neff
-6.E+12
-4.E+12
-2.E+12
0.E+00
2.E+12
0 50 100 150 200 250 300 350
Ndd
+, N
da-,
Nef
f (cm
-3)
T (K)
DD(0.48eV)
DA(V-V)
DA(0.53eV)
Neff
-4.E+12
-2.E+12
0.E+00
2.E+12
0 50 100 150 200 250 300 350
Ndd
+, N
da-,
Nef
f (cm
-3)
T (K)
DD(0.48eV)
DA(V-V)
DA(0.53eV)
Neff
-4.E+12
-2.E+12
0.E+00
2.E+12
0 50 100 150 200 250 300 350
Ndd
+, N
da-,
Nef
f (cm
-3)
T (K)
DD(0.48eV)
DA(V-V)
DA(0.53eV)
Neff
Deep levels with Ea ~ 0.4 eV (VV, Ci-Oi) hardly affect I(T) dependence
13E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 2012
DLs with Ea ~ 0.4 eV affect:♦ space charge region depth (at very high F);♦ trapping time constant
Impact of Igen on E(x) profile
Key parameters for adequate E(x) description: deep levels and generation current
Impact of Igen – double peak (DP) E(x) Simulation without current – no DP E(x)
0.0E+00
1.0E+04
2.0E+04
3.0E+04
4.0E+04
5.0E+04
6.0E+04
0 0.005 0.01 0.015 0.02 0.025 0.03
E (V
/cm
)
x (cm)
293K, current
293K, no current
253K, current
253K, no current
Igen is important parameter since it gives correct E(x) reference to other characteristics (CCE, tdr)
Alternative approach: Generation may be considered via lifetime – suggested by Delhi University group
14E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 2012
Conclusions
Single level model of I(T): Activation energy of bulk generation current Ea is 0.65 eV independent on proton/neutron fluence Concentration of effective generation level is proportional to Feq
Two level model of I(T): Two midgap levels, DDs and DAs, describe I(T) dependence of generation current Contribution of DAs to the generation current prevails in neutron irradiated detectors whereas in proton irradiated detectors both constituents are close
Generation lifetime is significantly larger than trapping lifetime
Bulk generation current gives adequate description of irradiated detector characteristics
15E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 2012
Acknowledgments
This work was made in the framework of RD50 collaboration and supported in part by:
• Fundamental Program of Russian Academy of Sciences on collaboration with CERN, • RF President Grant # SS-3008.2012.2 • U.S. Department of Energy, Contract No. DE-AC02 -98CH10886
Thank you for attention!
16E. Verbitskaya, et al., 20 RD50 workshop, Bari, May 30 – June 1, 2012