Research project:

X-ray induced conductivity of ZnSe and

development of high-temperature detectors of

ionizing radiation

Volodymyr Degoda – Director of R&D Center “Arvina”, Ph.D.

Andrii Sofiienko – Physicist, Ph.D.

1

NATIONAL TARAS SHEVCHENKO

UNIVERSITY OF KYIV

R&D Center “ARVINA”

Kyiv - 2012

Table of contents

General information about ZnSe;

Methods of the experimental studies;

Research results;

Designing and manufacturing of the high-temperature

ZnSe detectors.

2

General information about ZnSe

ZnSe is binary diamond-like semiconductor with a band-gap of

2.7 - 2.8 eV at the temperature of 300 K.

ZnSe is used to make optical components (windows, lenses,

prisms and mirrors) for the visible and infrared range (0.5-22 m)

for the optical systems and laser CO2-optics.

ZnSe has a high transmittance value, strength, hardness, optical

uniformity, wide transparency range, erosion and thermal

stability.

3

General information about ZnSe

4

Fig. 1 A photo of several ZnSe samples.

General information about ZnSe

5

Parameters

Semiconductors

ZnSe CdTe CdZnTe Si Ge GaAs SiC

Eg (300 K), eV 2.80 1.51 1.57 1.11 0.67 1.43 2.86

Тsmelting, 0С 1798 1090 1100 1420 940 1240 2800

ρ, g\cm3 5.4 5.9 6.0 2.3 5.3 5.3 --

μе, cm2/V∙s

μh, cm2/V∙s

700

25÷40

1050

100

1000

100

1500

480

4500

1900

8500

450

1200÷800

80÷140

α (300 К), К-1 7.5 4.9 5.0 2.4 5.8 6.0 ≈ 3.0

Radiation

resistance to γ,

Gy

107 < 105 < 106 < 105 < 106 ≈ 3∙105 ≈ 106

Radiation

resistance to n,

1/cm2

1016 < 1013 < 1014 < 1012 < 1014 < 1012 < 1015

The threshold

energy for defect

formation, eV

~ 40 6 ÷ 8 6 ÷ 8 11 ÷ 20 12 ÷ 20 8 ÷ 20 50 ÷ 150

ρR, Оhm∙cm 1011 109 1011 105 104 108 109

Methods of the experimental studies

Experimental investigation of the physical characteristics of wide-

gap semiconductors includes:

Photo-and X-ray induced luminescence;

Photo- and X-ray induced conductivity;

Relaxation of the current and phosphorescence;

Thermally stimulated luminescence and conductivity.

In general, more than 10 techniques were used to study the

physical properties of ZnSe semiconductor in the temperature

range from -265 0C up to +300 0C.

6

Methods of the experimental studies

Fig. 2 A schematic of the experimental set-up used for the investigation of ZnSe. 7

Research results

8

Fig. 3 Sketch of the experimental set-up adopted for the characterization of X-ray

induced conductivity of ZnSe samples (U0 = 0-1500 V; d = 2-5 mm)

Since X-ray radiation was used as an exciting radiation which is

absorbed completely in the thickness of ZnSe about 80 μm (ЕX = 20

keV), the specific geometry of metal electrodes on the sample surface

was selected as it is shown in Fig. 3. The area between electrodes was

uniformly irradiated with X-rays.

Research results

9

Fig. 4 Test sample of monocrystalline ZnSe (used for the testing and investigation

in the cryostat)

Research results

10

0 50 100 150 200 25010

0

101

102

103

104

105

up to 1000 times

E ~ 1.0 eV

single crystal

E ~ 0.82 eV

polycrystal

Intr

insic

co

nd

uctivity, pA

T, 0C

1

2

Fig. 5 Temperature dependencies of intrinsic (dark) conductivity of one

polycrystalline ZnSe (1) and one monocrystalline ZnSe (2), Е0 = 400 V/cm

Research results

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-50 0 50 100 150 200 250 30010

-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

C

urr

ent,

A

T, 0C

103 times10

5 times

1, X-ray conductivity (~ 300 Gy/h)

2, intrinsic conductivity

Temperature stabilization of

X-ray conductivity

Fig. 6 Temperature dependencies of X-ray conductivity of single-crystal ZnSe (1)

and intrinsic (dark) conductivity (2), Е0 = 400 V/cm

~ 200 pA at 150 0C

Research results

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Fig. 7 Temperature dependence of X-ray induced conductivity of ZnSe sensor, E0

= 1600 V/cm

Insignificant change of the sensitivity of

ZnSe detectors to X-rays at the heating up

to 200 0C is a prerequisite to use ZnSe as

a high-temperature X-ray detector.

Research results

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0.0 2.0x103

4.0x103

6.0x103

8.0x103

1.0x104

0.00

0.06

0.12

0.18

0.24

0.30

0.36

i(600 V) D1.36

i(400 V) D1.60

D, Gy/h

I X(D

),

A

1

2

3

i(200 V) D1.75

Fig. 8 Dose dependencies of X-ray induced conductivity of single-

crystal ZnSe: U = 200V (1), U = 400V (2), U = 600V (3)

Designing and manufacturing of ZnSe detectors

Following requirements should be considered for the designing

of high-temperature ZnSe detectors:

high optical quality of the crystals;

minimum intrinsic (dark) conductivity;

wide operating temperature range up to 200 0C without

cooling;

high absorption efficiency to ionizing radiation.

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Designing and manufacturing of ZnSe detectors

15

Fig. 9 One polished ZnSe crystal developed for the gamma-ray detector

(10 x 15 x 40 mm)

Control of the optical quality

16

Fig. 10 Measuring of the light absorption with use a green semiconductor laser.

µ < 0.1 cm-1

Absorption of the

green light (650 nm)

Design and manufacturing of ZnSe detectors

17

Fig. 11 A system of vacuum deposition VUP-5 used for vacuum deposition of

multi-layered metal electrodes on ZnSe crystals.

Design and manufacturing of ZnSe detectors

18

Fig. 12 ZnSe multi-electrode integral detector with automatic compensation of

intrinsic (dark) conductivity

For the detection of strong X-

ray flux in the range up to

200 keV a special ZnSe

detector can be developed

with automatic compensation

of the intrinsic (dark)

conductivity.

Design and manufacturing of ZnSe detectors

19

Fig. 13 Absorption efficiency of ZnSe to X-ray and gamma radiation at

different thicknesses.

Design and manufacturing of ZnSe detectors

20

Fig. 14 A schematic of the measuring system developed for isotopic thickness

gauges utilized strong sources of X-ray or gamma radiation.

An example of the measuring

system for isotopic / X-ray

thickness gauges utilized

strong sources for the greater

range of the measured

thickness.

Operating temperature range:

-40 0C to +200 0C

Multielectrode detectors for X-ray thickness gauges

21

Fig. 15 Several samples of multielectrode detectors based on the

monocrystalline undoped ZnSe

Multielectrode ZnSe detectors were developed for the measuring of

the thickness profile of the metal sheet during the hot rolling (R&D

Center “ARVINA”).

Multielectrode detectors for X-ray thickness gauges

22 Fig. 16 A schematic of the experimental set-up used for the testing and verification

of ZnSe multielectrode detectors.

Special equipment and methods are necessary for the testing and

verification of ZnSe multielectrode detectors.

CONCLUSIONS

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Undoped monocrystalline ZnSe has extremely low intrinsic

conductivity in wide temperature range from +10 0С up to +200 0С and

small decreasing of X-ray conductivity. This feature can be used for the

designing and manufacturing of X-ray radiation detectors for the

following applications:

Radiation thickness gauges for hot rolling which are widely used

in the metallurgy;

Emergency control in the confinement of Nuclear power plant;

Detecting of high-energy particles (High-energy physics

applications).

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R&D Center “ARVINA”, Kyiv, Ukraine (R&D center was founded at the National

Taras Shevchenko University of Kyiv)

Director: Ph.D. Degoda Volodymyr Yakovych

01033, Ukraine, Kyiv, Saksaganskogo str., 31,

E-mail: degoda@univ.kiev.ua

Contact information: