FREE CARRIER ABSORPTION TECHNIQUES
- MICROWAVE & IR –
FOR CHARACTERIZATION OF IRRADIATED SILICON
E.Gaubas, J. Vaitkus
OUTLINE
Characteristics of the techniques and instrumentation
RT applications to control radiation induced recombination
Excess carrier decay temperature variations
Evaluation of carrier decay parameters
☼ Recombination (fast) and trapping (slow) constituents within transients of microwave absorption by free carriers (MWA) can be distinguished by combining analyses of the excess carrier decays dependent on the excitation intensity and bias illumination (BI).
Carrier recombination and trapping
Variation of MWA decays with excitation intensity (proportional to the initial amplitude) with and without additional cw illumination
0 1000 2000 3000 4000
101
102
103
104
BI off BI on BI off BI on BI off BI on BI off BI off BI on BI off BI off BI on BI off
UM
WA(a
.u.)
t(s)
0 100 200 300 400 500
101
102
103
104
105
U
MW
R (
a.u
.)
t s
Si 1012
e/cm2
Bengt Svensson diode T= 328 K 300 K 268 K 255 K 196 K 175 K
RT Transients at different temperatureselectrons-irradiated Si
0 10 20 30 40 50
0.1
1
Si : - 400 Mrad
T=297K
290K
287K
284K
233K
192K
94K
UM
WA/U
MW
A,O
t (s)
protons-irradiated Si
Principle of the transient techniques
IRA =(4/c)dc {/[1+(sc )2]} 2 MWA >100m 0 =(4/c )dc, < 0
Transient:
(t) (t) FC nexFC (t)
Density of free carriers is controlled
Characteristics of the MW & IR techniques and instrumentation
k
E
IR, MW cw probe
laser lightpulsed excitation
R
Advantages:
☼ direct control of carrier decay process:
- to separate impact of different recombination and trapping mechanisms,
- to determine type of defects ( ~F(nex/ndop)), parameters of traps ( ~F(T)), etc.
- to reveal complicated systems of defects, barriers, non-linear decay processes etc,
☼ contact-less and fast measurement procedure,
☼ non-destructive and distant measurement techniques:
IR (tens of cm), MW (from tens of m to tens of mm),
☼ wide range of lifetime variations ( 1 ns (NR 102) – 10 ms (NR 10-5), RT),
☼ relatively high spatial resolution (from tens of m to tens of mm integration area),
☼ wide range of injection levels (nex/ndop from 0.01 to 100 - for MW. and 1- 103 for- IR).
Limitations:
☼ optically polished surfaces and relatively high excitation levels (nex 1016 cm-3) for IR,
☼ metallised areas are un-acceptable for examination,
☼ MW probing depth depends on material resistivity (decreases with resistivity),
☼ resolution of very short lifetimes ( <1 ns) is limited by oscilloscopic instrumentation and detector (MW / IR) circuits,
☼ examination of thin layered structures is complicated
Analyser of the recombination parameters
0 1000 2000 3000 4000 50000,0
0,2
0,4
0,6
0,8
1,0
1,2
3
2
1
1 <n1/n
0> MCz Si IR probe
2 U 3 <n
1/n
0>
d NTD Si fiber spot
<n
1/n
0>,
d
y1 (m)
2
4
6
8
U (
a.u.
)
0 50 100 150 200 250Y
1 (m)
0 200 400 600 80010
-2
10-1
100
5
1
M-Cz Sid=5000 m
1- y1= 0 m
2- 1003- 3004- 6005- 2000
<n
/n0>
t (s)
Rload
MB tiltas
MW oscillator with adjustable power
and frequency
MB cirkulatorius
MB tiltas
MW circulator
f0.5 GHz,U1 mV/pdf0.5 GHz,U1 mV/pd
TDS-5104
Microchip laser STA-01
exc ~700 ps, Eexc 10 J
MW slitantenna
sample
MW bridge
Attenuatorof light density Sliding short
Sliding short
Sliding short
Amplifier (>50)
MW detector
x-
Ge
zLaser-fiber beam-
Coaxial needle-tip MW antenna
Si
d
0 20 40 60 80
10-1
100
A1
d
5
4
32
1
NTD oxidizedfiber = 3 m
1 Y1 = 5 m
2 253 2704 405 140
<n
/n 0>d
t (s)
Main instrument
Supplementary regimes
Fiber excitation
Coaxial MW cable
Coaxial needle-tip antenna together with fiber beam
Ge waferX-Y-Z actuator of 2 µm
localization precision Nd:LSB laser driver
Coaxial MW cable
Coaxial needle-tip antenna together with fiber beam
Ge waferX-Y-Z actuator of 2 µm
localization precision Nd:LSB laser driver
Lifetime-temperature variations Lifetime depth-scans
Moderate and high excitation level IR probe
stepper sample holder
collimator
fiber
sample
IR beam
spectral filter
PHD
LED
pulsed laser beam
MW techniques for:
0 50 100 150 200 250100
101
102
z=50 m z=300 m
Si
UM
WA (
a.u
.)
t (s)
RDL minmin
- estimation of carrier transport parameters
D 67 cm2/s p-Ge
D 21 cm2/s p-Si
☼Parallel MWR ☼Oblique MWR
x
laser beam
coaxial needle-tip MW antenna
3 mm
d
Ge
x
laser beam
coaxial needle-tip MW antenna
3 mm
d
Ge
☼ Perpendicular MWR
laser beam
d Ge
MW slit antenna
laser beam
d Ge
laser beam
d Ge
MW slit antenna
Si or laser beam
coaxial needle-tip MW antenna
Ged(x)
laser beam
coaxial needle-tip MW antenna
Ged(x)
or SiSi or
x-
dGe
zlaser beam-
Si orGe
Coaxial needle-tip MW antenna
z
0 200 400 600 800 1000 1200
10-2
10-1
100
UM
WA (
a.u
.)
z (m)
Ge LD = 580 m
Si LD = 320 m
Laser beam
60 m
RT applications to control radiation induced recombination
Calibrated RT lifetime variations with fluence for definite particles,exploited for the same material and structures, would enable oneto control the density of the radiation induced dominant traps
Proton irradiation
- not covered the range of moderate and the highest fluences,
- samples from different material (sources) exploited
0 5 10 15 2010-1
100
101
102
20 mm
20 mm
0 - 20 mm
25 mm
n-Si (H07) TD
10 MeV 5*1012 cm-2 (
s)
x (mm)
Lateral lifetime variation due to irradiation geometry with proton beam spot of 25 mm.
109 1010 1011 1012 1013 1014 1015
101
102
103
104
MWR technique /low injection level CE24 diodes Hamburg FZ Si CH22 diodes Hamburg protons 10 MeV IMEC Leuven FZ Si MCZ n-Si Helsinki MCZ p-Si Helsinki
high injection level CE24 diodes Hamburg CH22 diodes Hamburg
R (
ns)
Fluence of protons (p/cm2)
N|~10-16 =1017 cm-3
N|~10-14 =81010 cm-3
1011
1012
1013
1014
1015
1016
101
102
103
104
105
FZ Si diodes samples: CERN (F.Lemeilleur)
FZ NTD Si samples: BNL (H.Kraner)
(n
s)
neutron irradiation fluence (cm-2)
Detection limit in the low fluence wing – density of the intrinsic recombination centers, thickness, quality of surface preparationResolution in the high fluence range - RC of the MW detector-oscilloscope circuit ~1-2 ns
Neutron irradiation
- too small set of samples examined
0 100 200 300 400
100
101
102
T= 300 K
MCZ p-Si A1, A2
, , MCZ Si n-Si B1, B2
, , FZ Si 400 Mrad
R - open signs
tr - solid signs
(
s)
Dose of -rays (Mrad)
- rays irradiation (BNL-Helsinki samples)for n-Si a non-linear dependence can be implied
0 100 200 300 400
0,0
0,5
1,0
T= 300 KMCZ p-Si A1, A2 , MCZ n-Si B1, B2 , FZ Si (400 Mrad)
R
-1 (s
-1)
Dose of -rays, Mrad
1/R = 1/* + vthN = 1/* + vth(N0 + D),
* - carrier capture lifetime attributed to the intrinsic centers;
N0 –concentration of radiation defects at low dose;
D – irradiation dose;
= 5.7 108 1/Mrad [Z Li]; > 4 10-19 cm2
Excess carrier decay temperature variations
-irradiated MCZ Sie-irradiated FZ Si
150 200 250 300 3500
300
600
FZ Si 3 1012 e/cm2
tr
R
(s
)
T (K)
DLTS
0.17 eV
DLTS
0.24 eV DLTS
0.42 eV
100 150 200 250 300 350 400 45010
-2
10-1
100
101
102
103
T (K)
-rays irradiation dose 210 Mrad p-Si n-Si
tr (s
)DLTS
DLTS
Excess carrier decay temperature variations
MWR proton-irradiated Si
100 150 200 250 300
10-1
100
101
102
0.23 eV
2
1
MCz n-Si
1 10 MeV protons 1013
cm-2
2 50 MeV protons 9x1012
cm-2
(
s)
T (K)
Evaluation of carrier decay (trap) parameters
1) Separation of traps from the transient decay shape and variation with external factors;
2) Estimation of the parameters for a dominant recombination center:
NR 1/vth,Tminority from absolute values of minority if S-R-H approximation holds,
- estimation of the ratio e/h from the dependency on excitation level,
- evaluation of ER from -T slope if no additional traps compete;
Detection limitations: ex<< R; simple system of the dominating traps; for radiation defects (NRD>NR, intrinsic)
3) Evaluation of the parameters of trapping centers from temperature peaks/slopes in -T dependence
(variations of the trapping caused -T as usually prevails in T<TRT, when density of trapping centers is high enough)
Hole thermal release lifetime
Recombination center, e h
Generation lifetime
Electron capture lifetime
Hole capture lifetime
Recombination lifetime
Hole capture lifetime
Trapping center, e << h
Trapping lifetime
Generation lifetime
Precise simulation of the temperature dependent lifetime variations correlating with DLTS peaks – J.Vaitkus’ method
Common DLTS peaks
MWR decay as peak
Single act of capture/thermal releaseMulti-trapping
process
V-O
V2-/oV2
=/-
Summary
☼ Calibrated RT lifetime variations with fluence for definite particles, exploited for the same material and structures, would enable one to control radiation induced density of the dominant traps. However, calibration curves are not determined.
☼ Tentative examination of recombination characteristics dependent on fluence and particle species, by MWR using (T), Iexc, exc, BI are carried out; as(T) variations are correlated with those determined by DLTS technique in the range of relatively low fluences.
Thank You for attention!
