Fluence–dependent lifetime variations in neutron irradiated MCZ Si measured by microwave probed photoconductivity and

dynamic grating techniques

E.Gaubas, A.Kadys, A.Uleckas, and J.Vaitkus

Vilnius university, Institute of Materials Science and Applied Research, Sauletekio av. 10, LT-10223, Vilnius, Lithuania

Outline

Objectives of investigations

Setup of MWR and DG experiments

Fluence and heat-treatment dependent lifetime variations

Characteristics of lifetime cross-sectional profiles

Summary

Objectives of investigation

- Direct measurements of recombination lifetime:

combined investigations of of MWR and DG applied in the range of the highest fluence;

- Control of possible anneal of defects:

heat treatments 80C 5 min, 30 min and 24 h,- WODEAN standard;

- Cross-sectional scans within wafer depth to control of oxygen out-diffusion

Measurement techniques and instruments

Microwave probed photoconductivity (MW-PCD)

in MW reflection mode (MWR) Dynamic gratings (DG)

Diffraction efficiency (=I-1/I0) on light induced dynamic grating is a measure   (N)2 of excess carrier density, while its variations in time (t)  exp(-2t/G) by changing a grating spacing () enable one to evaluate directly the parameters of grating erase 1/G = 1/R + 1/D  through carrier recombination (R) and diffusion D = 2/(42D) with D as a carrier diffusion coefficient.

K.Jarasiunas, J.Vaitkus, E.Gaubas, et al. IEEE Journ. QE, QE-22, (1986) 1298.

k

E

cw MW probe

laser lightpulsed excitation R

kk

E

cw MW probe

laser lightpulsed excitation R

(t)

MWR >100m 0 =(4/c )dc, transient:(t) (t) FC nexFC (t)

E.Gaubas. Lith. J. Phys., 43 (2003) 145.

Rload

MB tiltas

MW oscillatorwith 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

Rload

MB tiltas

MW oscillatorwith 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

MB tiltasMB tiltas

MW oscillatorwith adjustable power

and frequency

MW oscillatorwith 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

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 detectorThe microwave probed photoconductivity (MW-PCD) technique is based on the direct measurements of the carrier decay transients by employing MW absorption by excess free carriers. Carriers are photoexcited by 1062 nm light generated by pulsed (700 ps) laser and probed by 22 GHz cw microwave probe.

1012 1013 1014 1015 101610-4

10-3

10-2

10-1

100

101

=1

Okmetic MCZ<100> 1kOhm·cm 300 m non-processed CISSamples 8556- 14 1 - 63 passivated wafers

- directly measured values &extracted from the decrease of amplitude UMWR

wafers 54-60 measured by DG

R

-1 (

ns-1)

Fluence (n/cm2)

Direct measurements of recombination lifetime by MWR

0 5 10 150

5

10

15

20

- H1-1012 n/cm2

-H61

- H2-1013 n/cm2

- H62

- H3-1014 n/cm2

- H63

- H4-3·1014

n/cm2

- H64

- H53-1015

n/cm2

- H54

- H55-3·1015

n/cm2

- H56

- H57-1016

n/cm2

- H58

- H59-3·1016

n/cm2

- H60

UM

WR (

a.u

.)

t (s)

R t|U ~ exp(-1)

R gexcRs/gexcRL (UMWRs<2 ns /UMWRL>5 ns)

1012 1013 1014 1015 1016

10-1

100

101

102

103

104

Laser pulse limit

Electr. circuitry limit

Okmetic MCZ<100> 1kOhm·cm 300 m non-processed CISSamples 8556- 14 1 - 63

- directly measured values - extracted from the decrease of amplitude U

MWR

Eff

ect

ive

life

time

(n

s)Neutron fluence (cm

-2)

Direct measurements of recombination lifetime by DG

0 200 400 600 800

10-3

10-2

10-1

100

Diff

ract

ion

effic

ienc

y (a

. u.)

Delay (ps)

I0=0.4 mJ/cm

2,

G=(2658) ps

I0=0.8 mJ/cm

2,

G=(2404) ps

I0=1.6 mJ/cm

2

G=(2042) ps

MCZ wafer 60=13 m

D (cm2/s) R (ps)

15.40.4 2203

0 500 1000

10-2

10-1

100

101

Diff

ract

ion

effic

ienc

y (a

. u.)

Delay (ps)

I0=0.4 mJ/cm

2,

G=(515) ps

I0=0.8 mJ/cm

2,

G=(514) ps

I0=1.6 mJ/cm

2

G=() ps

wafer 58 =13 m

D (cm2/s) R (ps)

15.40.2 51510

11016 n/cm2 31016 n/cm2

Recombination lifetime in wafer and diode samples measured by MWR

1012 1013 1014 1015 1016

10-4

10-3

10-2

10-1

100

Okmetic MCZ<100> 1kOhm·cm 300 m MWR, CIS 8556- 14 wafers 1 - 63 passivated CIS 8556- 14 wafers measured by DG technique CIS 8556-01 diodes neutron irradiated

1/ R

(n

s-1)

Fluence (n/cm2)

Lifetime under heat treatments at 80C for 5 min, 30 min and 24 h

1012

1013

1014

1015

1016

10-4

10-3

10-2

10-1

100

101

Okmetic MCZ<100> 1kcm as-irradiated

Heat treated at Tann= 800 C

for tanneal = 5 min 30 min 24 h

Rec

ombi

natio

n lif

etim

e (

s)

Neutron fluence (n/cm2)

Lifetime variation with neutron irradiation fluence in MCZ Si

61,62,63,64, 54,56,58, and 60 wafers for the as-received and heat treated material

Cross-sectional scans within wafer depth

fiber

MW coaxial needle-tipantenna

sample

0 100 200 30010

0

101

102

103

MCZ 1 k·cm, d= 300 m neutron fluence

1012

cm-2

3·1014

cm-2

1015

cm-2

3·1015

cm-2

MWR amplitude R(n

s),

MW

R a

mpl

itude

(a.

u.)

Z (m)

SUMMARY

Lifetime decreases from few s to about of 200 ps with enhancement of neutron irradiation fluence ranging from 1012 to 31016 n/cm2, as measured directly by exploiting microwave probed photoconductivity transients and verified by dynamic grating technique.

Lifetime values are nearly the same for wafer and diode samples.

Small increase of lifetime values under annealing can be implied.

Lifetime values are nearly invariable within wafer thickness, as determined from the lifetime cross-sectional scans within wafer depth.

Investigation of the lifetime – temperature variations in the range of more than RT is anticipated, to determine the activation factors for the dominant recombination centers. However, annealing and instability of defects would be a problem for precise extraction of these parameters.

Thank You for attention!