Shallow energy levels induced by γ rays in standard and ... · PDF fileShallow energy...

1

Shallow energy levels induced by γ rays in standard and oxygenated floating zone

silicon

David Menichelli1 Monica Scaringella Stefania Miglio and Mara Bruzzi

Dipartimento di Energetica Via S Marta 3 50139 Florence Italy and INFN Firenze via G Sansone

1 50518 Sesto Fiorentino (FI) Italy

Ioana Pintilie

National Institute of Materials Physics 76900 Bucuresti-Magurele Romania

Eckhart Fretwurst

Institute for Experimental Physics Hamburg University D-22761 Germany

Abstract Shallow defect levels in Floating Zone (FZ) and Diffusion Oxygenated FZ (DOFZ) Silicon

before and after irradiation with a 60Co γ-source up to 300 Mrad have been studied by Thermally

Stimulated Currents (TSC) and Deep Level Transient Spectroscopy (DLTS) in the temperature range

42-110 K Besides vacancy oxygen (VO) and interstitial-substitutional carbon (CiCs) emissions

several TSC peaks have been observed A trap with activation energy 11 meV has been observed at 6 K

only in irradiated DOFZ Two hole traps at 80 meV and 95 meV have been observed both in irradiated

FZ and DOFZ while a trap at 100 meV related to interstitial-oxygen (IO2) complex has been revealed

only in irradiated DOFZ A TSC peak close to 24 K has been resolved into two components whose

concentrations are independent of irradiation fluence a trap at 55 meV and a level which remains

charged after emission at 80 meV Our measurements confirm the formation only in DOFZ of a

radiation induced donor at 230 meV It appears to be responsible for the improved radiation hardness of

oxygenated Si together with the suppression of deep acceptors since no shallower radiation-induced

donors have been detected in DOFZ samples

PACS 7155Cn 2940Wk 6180Hg 6182Fk

1 Corresponding author Electronic address davidmenichellicernch

2

1 Introduction

In the ever increasing need for extremely radiation hard detectors to be employed in the forthcoming

elementary particle physics experiments silicon is regarded to be the best choice as the sensor-based

material because of its unsurpassed material quality high technological sophistication and low cost for

mass production [1-3] Nonetheless the high radiation fluences in the operative environment will cause

a significant deterioration of silicon detector performances due to the formation of lattice defects [4] A

complete study of radiation damage and an intense research and development activity on material and

device engineering in order to increase its radiation hardness is therefore mandatory

It has been already proved that defect formation kinetics strongly depends on the engineering steps

adopted during device processing Appreciable improvements in radiation hardness has been obtained

by enriching standard high resistivity Floating Zone (STFZ) silicon with oxygen [56] Recent results

have shown that the beneficial effect of oxygen in moderating the radiation induced modifications of

space charge density (which tends to become more and more negative as the irradiation fluence is

increased) is mainly determined by the partial suppression of a deep acceptor and by the enhanced

generation of a radiation-induced donor The donor has been observed by Thermally Stimulated

Currents (TSC) spectroscopy close to 100 K after gamma irradiation [7-9] while the acceptor (usually

labeled as I) produces a TSC peak close to 200K It is created via second order processes and is

believed to be associated with divacancy-oxygen complexes [7910] In any case further studies are

needed to investigate if other radiation-induced shallow donor levels participate to this phenomenon

The purpose of this work is a thorough identification of shallow levels in STFZ and Diffusion

Oxygenated FZ (DOFZ) Si before and after irradiation with a 60Co γ-source up to 300 Mrad Irradiation

of silicon with γ rays is a relevant means to study radiation-induced point defects and defect formation

kinetics This is because γminusirradiation causes low energy recoils of silicon atoms which lead only to the

formation of point defects This is in contrast to irradiation by fast hadrons or high energy electrons

which cause a significant amount of vacancy related extended defects These extended defects produce

deep levels close to midgap [4] and heavily worsen the signal to noise ratio of TSC and Deep Level

Transient Spectroscopy (DLTS) making a detailed analysis of shallow levels difficult

The TSC technique already used in the past by some of the authors to investigate shallow levels in

silicon [1112] has been applied by us together DLTS to determine activation energy E apparent cross

section σ and concentration N of those levels which activate below 100 K TSC has been used also to

reveal the charge state of each energy level by performing a detailed study of the Poole-Frenkel effect

3

during the heating scan

2 Experimental details

The samples studied in this work are p+nn+ diodes produced from n-type STFZ and DOFZ silicon

These diodes have been produced by CiS Institute for Microsensors Erfurt Germany from Si with an

initial resistivity of about 5 kΩcm The crystal orientation is lt111gt and the thickness is w = 285 microm

The electrode active area on the p+ side is Ap = 25 mm2 while the electrode on the n+ side has an area

An=100 cm2 The oxygen diffusion process on DOFZ samples was performed for 72 hours at 1150degC

and the resulting average oxygen concentration is [O]=121017 cm-3 All diodes have been irradiated at

Brookhaven National Laboratory with γ rays from a 60Co source up to a dose of 300 Mrad After

irradiation the STFZ diodes exhibited type inversion at room temperature with a change of the

effective doping concentration from Neff =121012 cm-3 before irradiation to Neff =-601010 cm-3 [7]

Conversely the DOFZ Si diodes are not inverted after irradiation showing rather a slight increase of

Neff from 831011 cm-3 (before irradiation) to 901011 cm-3 (after irradiation) The samples have been

stored for six months at room temperature before carrying out the measurements reported in this work

Twin non irradiated samples have been used as references in order to discriminate between native and

radiation induced defects

TSC [13] and current-Deep Level Transient Spectroscopy (i-DLTS) experiments [14-16] have been

carried out at Department of Energetics of Florence (DEF) using the same cryogenic system The

sample holder is mounted on a hollow steel tube and then lowered inside the liquid helium dewar at

different heights above the liquid surface The distance between the sample and the liquid helium

surface determines the injection temperature A heating resistor wound around the sample support

allows one to vary the temperature of the diode above the initial value The heating rate is β=007-02

Ks depending on the explored temperature range The temperature sensor is a silicon diode (Lake

Shore DT-470-CU11) In TSC measurements an electrometer (Keithley 6517A) provides sample bias

low temperature forward injection and current reading In i-DLTS measurements reverse bias Vrev and

forward voltage pulses Vp for sample excitation are provided by a pulse generator (Systron Donner

110D) The current transients i(tT) are measured using a custom readout circuit [17] The readout

circuit output is monitored by a 500 MHz digital oscilloscope (Tektronix TDS520D) which samples the

current transients Some of the TSC spectra in the range 30-100 K have been measured at Institute for

Experimental Physics of Hamburg University [9]

4

3 Experimental results and discussion

The TSC spectra of STFZ and DOFZ samples measured in the 42-80 K temperature range before and

after irradiation are shown in fig1 Several TSC peaks are observed depending on irradiation and

material The TSC peaks generated by unidentified defects are labeled by means of the peak

temperature given in Kelvin degrees as L(6) D(24) and so on The labels L H and E denote traps

which are electrically neutral after carrier emission Labels H and E indicate hole traps whose charge

state changes during emission as (+0) and electron traps (-0) respectively The label L indicates that

the available information does not permit to determine whether the level is an electron or a hole trap

The label D denote levels which are charged after emission ie donors (0+) and acceptors (0-)

The spectral feature at 55-75 K corresponds to the well known vacancy oxygen (VO) and

interstitial-substitutional carbon (CiCs) defects The phosphorous peak appears close to 15 K in all

investigated samples This peak exhibits a clear Poole-Frenkel shift in temperature by changing the

reverse voltage

The group of peaks at 40-50 K has been already observed on similarly irradiated Si samples [9]

Two of the peaks of this group are due to hole traps (H(42) and H(47)) while the latter is related to an

electron trap (E(50)) [9] The signature of these three traps is determined in this work for the first time

With the exception of E(50) which has been related to the IO2 defect [8 9 18] the correlation of the

other two energy levels with specific point defects is still uncertain

The other spectral features are reported and studied in this work for the first time The signal at 24 K

can be split into two components due to a trap L(24) plus a level D(24) which we recognize as charged

after emission by investigating Poole-Frenkel effect L(24) and D(24) are observed even before

irradiation in both STFZ and DOFZ Si The emission from the traps L(6) and L(35) are observed only

in irradiated samples In particular L(6) is present only in DOFZ Si while L(35) is observed in both the

materials its amplitude is too small to permit the determination of its signature

31 L(6) peak

L(6) is the shallowest level detected by our TSC experiments and the related TSC peak is shown in fig

2 This level is formed during irradiation only in oxygen rich material Several measurements have

been carried out using different reverse voltages in the range 10-100 V without detecting any evidence

5

of Poole-Frenkel barrier lowering The saturated amplitude corresponds to a trap concentration of about

1012 cm-3 Since the peak is isolated from any other TSC feature it is possible to determine its complete

signature by fitting the line-shape and taking into account its peak temperature However it is not

possible to discriminate whether it is a hole or an electron trap The fitting procedure resulted in the

activation energy E=11plusmn2 meV and an effective cross section of either σsim08sdot10-15 cm2 (if it was a hole

trap) or σsim02sdot10-15 cm2 (if it was an electron trap) The small capture cross section and the absence of

Poole Frenkel effect indicate that this trap is neutral after carrier emission

32 L(24K) and D(24) peaks

The signal close to 24 K is generated by the superposition of contributions from two levels L(24) and

D(24) This is evidenced in fig 3 where the TSC spectra measured with different reverse biases are

shown The spectral line is split into two components if the reverse bias exceeds Vrev=100 V because

the peak related to D(24) exhibits field enhanced emission Phonon assisted tunneling and pure

tunneling are not expected to be important below 104 Vcm [1920] and are impossible for such a large

thickness thus the peak shift must be explained in terms of the Poole-Frenkel effect [24] This implies

that D(24) becomes charged after emission Anyway in our TSC experiments energy levels are filled

by forward biasing the sample As a consequence both electrons and holes are injected in the device

and it is not possible to determine whether D(24) is a donor or an acceptor The separation between

D(24) and L(24) peaks is observed also in i-DLTS spectra as shown in fig 4(a) DLTS and TSC

spectra (measured using the same reverse bias) can be compared to obtain the complete signature of the

two levels by requiring the (Eσ) pairs to be consistent with both measurements A possible σ(T)

dependency is neglected in this analysis The energy value obtained in this way for D(24) can be used

to evaluate the barrier lowering ∆E (relative to the spectrum with Vrev=10 V) for every measurements

of fig 3 The average electric field F across the junction can be evaluated as F~Vrevw and the plot of

∆E versus F12 can be compared with the prediction of one-dimensional Poole-Frenkel law

2121

0

3

)( FFZqFE απεε

=⎟⎟⎠

⎞⎜⎜⎝

⎛=∆ (1)

where Z is the charge state of the emitting center This formula provides a simple approximated

description of Poole-Frenkel enhanced emission even if somewhat overestimates the barrier lowering

of a three dimensional Coulombic well [2223] According to this model the slope of the plot should be

6

αcong022 meV(cmV)12 The plot deduced from our measurements is shown in the inset The slope of the

line fitting experimental data is about 01-03 meV(cmV)12 in fair agreement with theory The

activation energy deduced from TSC measurement at Vrev=10 V must be consequently increased by

about 4 meV to extrapolate the zero-field energy

Similar TSC measurements carried out on irradiated and non-irradiated samples revealed that D(24)

is observed even before irradiation and that its concentration is independent of oxygen concentration

irradiation fluence and annealing time (up to 110 min at 150 degC)

33 H(42) H(47) and E(50) peaks

The activation energies of these centers have been evaluated from Arrhenius plots following the

fractional heating procedure [24] The analysis of H(47) is complicated by the fact that its TSC peak is

very close to the E(50) peak which has a higher amplitude Anyway H(42) and E(50) centers anneal

out after 2 hours of annealing at 150 degC [89] The annealing procedure permits to isolate H(47) signal

and to determine the activation energy of the center via Arrhenius plots from the increasing part of the

corresponding TSC peak The results are given in Fig 5

By using the activation energies deduced from Arrhenius plots for the H(42) H(47) and E(50)

defects TSC spectra can be nicely fitted as shown in fig6 The fitting procedure allows one to

determine the apparent cross sections which are reported in table 1 as well The signature of E(50) is

consistent with the activation energy (112 meV) of the electron trap formerly found in 10 MeV

irradiated silicon [25] by means of Thermally Stimulated Capacitance (TSCAP) spectroscopy

34 D(97) peak

A further peak can be observed close to 97 K but only using a reverse bias of some hundreds of volts

as shown in fig 7 This signal can be related to the defect previously identified as a bistable donor

center (labeled as BD in [8 9]) generated by irradiation in oxygen rich material Oxygen dimers have

been suggested to be part of the defect The signature (E=230 meV) and the donor behavior of this

level are consistent with the peak position and the Poole Frenkel line shift shown in fig7 This level is

observed only in DOFZ silicon and its concentration is about [D(97)]sim3sdot1011 cm-3

The energy levels cross sections and trap concentrations related to the peaks studied in this work are

7

summarized in table 1 The concentrations have been evaluated at signal saturation and in the case of

levels exhibiting Poole Frenkel effect the extrapolated zero-field energy is reported Since it was not

possible to reveal whether the levels L(6) L(24) and D(24) are related to hole or electron emissions

the cross sections corresponding to the two cases have been reported in the table The concentrations

are the same within the experimental uncertainty in STFZ and DOFZ with the exception of L(6) E(50)

and D(97) which are observed only in DOFZ and of the group L(24)-D(24) whose overall

concentration is significantly higher in STFZ Si (4sdot1011 cm-3) than in DOFZ (15-3sdot1011 cm-3)

4 Conclusion

A study of shallow levels in Float Zone and Diffusion Oxygenated FZ (DOFZ) silicon before and

after irradiation with a 60Co γ-source up to 300 Mrad has been performed by Thermally Stimulated

Currents (TSC) and current-Deep Level Transient Spectroscopy (i-DLTS) in the temperature range 42-

110 K Besides the well known spectral feature corresponding to vacancy oxygen (VO) and interstitial-

substitutional carbon (CiCs) defects several TSC peaks are observed depending on irradiation and

material kind Some of them have never been cited in literature before

A level characterized by activation energy 11meV is detected at 6 K only in DOFZ after irradiation

It is found in a neutral state after TSC emission Two traps with energy levels at 80 meV and 95 meV

are observed both in FZ and DOFZ Si before and after irradiation while a trap at 010 eV previously

identified as interstitial-oxygen related (IO2) has been revealed only in irradiated DOFZ Si The peak

close to 24 K whose concentration is significantly higher in STFZ Si has been resolved into two

components One of them is identified through the investigation of the Poole-Frenkel effect as related

to a level which becomes charged after emission Its concentration is independent of oxygen

concentration irradiation fluence and annealing time (up to 110 min at 150 degC) and it cannot explain

the different radiation hardness of STFZ and DOFZ Our measurements confirm the formation of a

donor level only seen in DOFZ Si after irradiation with activation energy 023 eV and concentration

of about 3sdot1011 cm-3 This signal can be related to the defect previously identified as a bistable donor

center [9] generated by radiation in oxygen rich material The donor-like nature of this level is

consistent with the Poole Frenkel effect investigation presented in this paper The detailed investigation

of shallow levels presented here reveals no other radiation-generated donors up to the dose of 300

Mrad

The beneficial effect of oxygen diffusion in floating zone silicon in terms of increasing the radiation

8

hardness is determined by both the suppression of deep acceptors and the creation of donors as

already demonstrated in [910] The experimental results discussed in this work evidence that the

beneficial contribution due to donor creation should be mainly related to the donor at 023 eV as no

appreciable formation of additional radiation-induced shallow donor have been observed in oxygenated

Si after gamma irradiation

Acknowledgment

Authors are grateful to Bengt G Svensson at Physics Department University of Oslo for helpful

discussions

9

References

[1] HFW Sadrozinski IEEE Trans Nucl Sci 48 993 (2001)

[2] The LHC study group The Large Hadron Collider conceptual design (CERNAC95-05 (LHC)

Geneva 20 October 1995)

[3] J Varela Nucl Phys B 37C 121 (1995)

[4] M Bruzzi IEEE Trans Nucl Sci 48 960 (2001)

[5] G Lindstroem Nucl Instr and Meth A 512 30 (2003)

[6] The RD50 collaboration RD50 Status Report 20022003-Radiation hard semiconductor devices

for very high luminosity colliders (CERN-LHCC-2003-058 and LHCC-RD-002 Geneva November

2003)

[7] E Fretwurst G Lindstroem J Stahl I Pintilie Z Li J Kierstead E Verbitskaya R Roeder

Nucl Instr Meth A 514 1 (2003)

[8] I Pintilie M Buda E Fretwurst G Lindstroumlm and J Stahl Nucl Instr and Meth A 556 197

(2006)

[9] I Pintilie E Fretwurst G Lindstroumlm and J Stahl Nucl Instr and Meth A 514 18 (2003)

[10] I Pintilie E Fretwurst G Lindstroumlm and J Stahl Appl Phys Lett 82 2169 (2003)

[11] Borchi E Bruzzi M Pirollo S Sciortino S J Phys D Appl Phys 31 L93 (1998)

[12] Borchi E Bruzzi M Li Z Pirollo S J Phys D Appl Phys 33 299 (2000)

[13] M G Buhler Solid State Electronics 15 69 (1972)

[14] D V Lang J Appl Phys 45 3023 (1974)

[15] B W Wessels J Appl Phys 47 1131 (1976)

[16] Blood P J W Orton The electrical characterization of semiconductors majority carriers and

electron states (Academic London 1992)

[17] D Menichelli M Scaringella M Bruzzi I Pintilie E Fretwurst Phys Rev B 70 195209 (2004)

[18] J L Lindstroem T Hallberg J Hermansson L I Murin B A Komarov V P Markevich M

Kleverman B G Svensson Physica B 308-310 284-289 (2001)

[19] S D Ganichev E Ziemann and W Pretti Phys Rev B 61 10361 (2000)

[20] G Vincent A Chantre D Bois J Appl Phys 50 5484 (1979)

[21] J Frenkel Phys Rev 54 647 (1938)

[22] J L Hartke J Appl Phys 39 4871 (1968)

[23] P A Martin B G Streetman and K Hess J Appl Phys 52 7409 (1981)

[24] J C Muller R Stuck R Berger and P Siffert Solid State El 17 1293-1297(1974)

10

[25] J W Walker and C T Sah Phys Rev B 7 4587 (1973)

11

Figure and Table Captions

Fig 1 TSC spectra of irradiated and unirradiated FZ and DOFZ samples (Vrev=10 V) In the case of

unirradiated samples the signal which has been multiplied by 10 for an easy comparison is flat

outside the interval shown in the figure

Fig 2 TSC spectrum at signal saturation (Vrev=100 V) of L(6) peak detected in DOFZ Si sample

after irradiation

Fig 3 TSC spectra of the irradiated STFZ Si diode measured with different reverse biases ranging

from 10 V to 300 V The reverse bias value is shown close to each peak The component exhibiting

Poole Frenkel effect has been considered to plot the barrier lowering ∆E vs the square root of electric

field F shown in the inset

Fig 4 a) i-DLTS spectrum of the oxygenated Si diode with sampling times t1=02 ms and t2=18 ms

Applied bias is Vrev=10 V b) TSC spectrum of the same sample Vrev=10 V β=0075 Ks Thick

marked lines experimental data Thin solid line and dashed line calculated contributions from donor

D(24) and trap L(24) respectively

Fig 5 Arrhenius plots of levels E(50) and H(42) peaks plotted by using the fractional heating (or

thermal cleaning) procedure prior to any annealing The Arrhenius plot of H(47) peak after annealing

at 150 degC is shown as well

Fig6 Example of fit of the TSC signal in the range 30-55 K using the trap parameters reported in

tab 1 Measurements have been carried out on the oxygenated Si diode with Vrev=10 V

Fig 7 Measurements of the D(97) TSC peak carried out with different reverse voltages as given in

the figure A clear Poole-Frenkel shift can be observed when the bias is risen from 100 V to 500 V

Table 1 Resume of activation energy (E) apparent cross section (σ) and trap concentrations (N) of

all the energy levels detected with TSC and i-DLTS in STFZ and DOFZ Concentrations are evaluated

after irradiation at peak amplitude saturation In the case of emissions exhibiting Poole Frenkel effect

E is the extrapolated zero field energy

12




Fig 2 TSC spectrum at signal saturation (Vrev = 100 V) of L(6) peak detected in DOFZ Si sample after

irradiation

13





14





15




Fig6 Example of fit of the TSC signal in the range 30-55 K using the trap parameters reported in tab

1 Measurements have been carried out on the oxygenated Si diode with Vrev=10 V

16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)

material Related bibliography

L(6) 6 (+0 ) or (-0)

11plusmn2 02 (electron) 08 (hole)

~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)

80plusmn5 1-10times103 (electron) 4-40times103 (hole)

L(24) 24 (+0 ) or (-0)

55plusmn5 005-05 (electron) 02-2 (hole)

~4 (STFZ)

15-3 (DOFZ)

DOFZ and STFZ (even unirradiated)

First observation

H(42) 42 (+0) 80plusmn15 2 7plusmn4 H(47) 47 (+0) 95plusmn10 2 8plusmn1

DOFZ and STFZ (irradiated)

Reported in [15] without signature

E(50) 50 (-0) 100plusmn15 2 16plusmn4 irradiated DOFZ [15] [22] 15[C]

D(97) 97 (0++) 230plusmn5 4-90 3 irradiated DOFZ [15]





2

1 Introduction

In the ever increasing need for extremely radiation hard detectors to be employed in the forthcoming

elementary particle physics experiments silicon is regarded to be the best choice as the sensor-based

material because of its unsurpassed material quality high technological sophistication and low cost for

mass production [1-3] Nonetheless the high radiation fluences in the operative environment will cause

a significant deterioration of silicon detector performances due to the formation of lattice defects [4] A

complete study of radiation damage and an intense research and development activity on material and

device engineering in order to increase its radiation hardness is therefore mandatory

It has been already proved that defect formation kinetics strongly depends on the engineering steps

adopted during device processing Appreciable improvements in radiation hardness has been obtained

by enriching standard high resistivity Floating Zone (STFZ) silicon with oxygen [56] Recent results

have shown that the beneficial effect of oxygen in moderating the radiation induced modifications of

space charge density (which tends to become more and more negative as the irradiation fluence is

increased) is mainly determined by the partial suppression of a deep acceptor and by the enhanced

generation of a radiation-induced donor The donor has been observed by Thermally Stimulated

Currents (TSC) spectroscopy close to 100 K after gamma irradiation [7-9] while the acceptor (usually

labeled as I) produces a TSC peak close to 200K It is created via second order processes and is

believed to be associated with divacancy-oxygen complexes [7910] In any case further studies are

needed to investigate if other radiation-induced shallow donor levels participate to this phenomenon

The purpose of this work is a thorough identification of shallow levels in STFZ and Diffusion

Oxygenated FZ (DOFZ) Si before and after irradiation with a 60Co γ-source up to 300 Mrad Irradiation

of silicon with γ rays is a relevant means to study radiation-induced point defects and defect formation

kinetics This is because γminusirradiation causes low energy recoils of silicon atoms which lead only to the

formation of point defects This is in contrast to irradiation by fast hadrons or high energy electrons

which cause a significant amount of vacancy related extended defects These extended defects produce

deep levels close to midgap [4] and heavily worsen the signal to noise ratio of TSC and Deep Level

Transient Spectroscopy (DLTS) making a detailed analysis of shallow levels difficult

The TSC technique already used in the past by some of the authors to investigate shallow levels in

silicon [1112] has been applied by us together DLTS to determine activation energy E apparent cross

section σ and concentration N of those levels which activate below 100 K TSC has been used also to

reveal the charge state of each energy level by performing a detailed study of the Poole-Frenkel effect

3































4













reverse voltage












31 L(6) peak




5

























2121

0

3

)( FFZqFE απεε

=⎟⎟⎠

⎞⎜⎜⎝

⎛=∆ (1)




6








33 H(42) H(47) and E(50) peaks












34 D(97) peak








7








4 Conclusion





















Mrad


8






Acknowledgment


discussions

9

References









2003)




(2006)



















10


11






after irradiation




















12





irradiation

13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










3































4













reverse voltage












31 L(6) peak




5

























2121

0

3

)( FFZqFE απεε

=⎟⎟⎠

⎞⎜⎜⎝

⎛=∆ (1)




6








33 H(42) H(47) and E(50) peaks












34 D(97) peak








7








4 Conclusion





















Mrad


8






Acknowledgment


discussions

9

References









2003)




(2006)



















10


11






after irradiation




















12





irradiation

13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










4













reverse voltage












31 L(6) peak




5

























2121

0

3

)( FFZqFE απεε

=⎟⎟⎠

⎞⎜⎜⎝

⎛=∆ (1)




6








33 H(42) H(47) and E(50) peaks












34 D(97) peak








7








4 Conclusion





















Mrad


8






Acknowledgment


discussions

9

References









2003)




(2006)



















10


11






after irradiation




















12





irradiation

13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










5

























2121

0

3

)( FFZqFE απεε

=⎟⎟⎠

⎞⎜⎜⎝

⎛=∆ (1)




6








33 H(42) H(47) and E(50) peaks












34 D(97) peak








7








4 Conclusion





















Mrad


8






Acknowledgment


discussions

9

References









2003)




(2006)



















10


11






after irradiation




















12





irradiation

13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










6








33 H(42) H(47) and E(50) peaks












34 D(97) peak








7








4 Conclusion





















Mrad


8






Acknowledgment


discussions

9

References









2003)




(2006)



















10


11






after irradiation




















12





irradiation

13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










7








4 Conclusion





















Mrad


8






Acknowledgment


discussions

9

References









2003)




(2006)



















10


11






after irradiation




















12





irradiation

13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










8






Acknowledgment


discussions

9

References









2003)




(2006)



















10


11






after irradiation




















12





irradiation

13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










9

References









2003)




(2006)



















10


11






after irradiation




















12





irradiation

13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










10


11






after irradiation




















12





irradiation

13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










11






after irradiation




















12





irradiation

13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










12





irradiation

13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










13





14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










14





15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










15






16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










16



Label Peak temp (K)

Charge state E

(meV) σ

(times10-15 cm2)

N (times1011cm-3)


L(6) 6 (+0 ) or (-0)


~5 Irradiated DOFZ

D(24) 24 (0+) or (0-)


L(24) 24 (+0 ) or (-0)


~4 (STFZ)

15-3 (DOFZ)


First observation










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