Study of X-ray induced conductivity of ZnSe and the development of high-temperature detectors of ionizing radiation

1. Study of X-ray induced conductivity of ZnSe
and the development of high-temperature
detectors of ionizing radiation
Andrii Sofiienko – Chief Physicist, Head of research laboratory, Ph.D.
Volodimir Degoda – Director of RPC “Arvina”, Dr. Sci. Phys.
2011
1

2. Table of contents
 General information about ZnSe.
 Methods to investigate the conductivity and
luminescence.
 Research results.
 Design of detectors based on ZnSe.
2

3. General information about ZnSe
ZnSe - binary diamond-like semiconductors with a
band gap of 2.7 - 2.8 eV.
ZnSe is used for the manufacture of optical
components (windows, lenses, prisms and mirrors) for
the visible and infrared range (0.5-22) microns in
optical systems and laser CO2 optics. ZnSe has a
high transmittance value, strength, hardness, optical
uniformity, wide transparency range, erosion and
thermal stability.
3

4. General information about ZnSe
4
Fig. 1 The samples of ZnSe

5. General information about ZnSe
5
Parameter
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
Т(smelting), 0С 1798 1090 1100 1420 940 1240 2800
ρ, gcm3
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, Ohm∙cm 1011 109 1011 105 104 108 109

6. Experimental methods
The main directions of research on the physical
characteristics of wide band-gap semiconductors:
 photo and X-ray luminescence
 photo and X-ray conductivity;
 relaxation of the current and phosphorescence;
 thermally stimulated luminescence and conductivity.
Generally used for more than 10 techniques to study
the characteristics of semiconductors in the
temperature range from -265 0C to 300 0C.
6

7. Experimental methods
Fig. 2 A schematic of the experimental setup
7

8. Research results
8
0 50 100 150 200 250
10
0
10
1
10
2
10
3
10
4
10
5
up to 1000 times
E ~ 1.0 eV
single crystal
E ~ 0.82 eV
polycrystal
Intrinsicconductivity,pA
T,
0
C
1
2
Fig. 3 Temperature dependencies of intrinsic conductivity of polycrystalline ZnSe (1)
and single-crystal (2), Е0 = 400 V/cm

9. Research results
9
-50 0 50 100 150 200 250 300
10
-12
10
-11
10
-10
10
-9
10
-8
10
-7
10
-6
10
-5
Conductivity,A
T,
0
C
10
3
times10
5
times
1, X-ray conductivity (~ 1 kGy/h)
2, intrinsic conductivity
Temperature stabilization of
X-ray conductivity
Fig. 4 Temperature dependencies of X-ray conductivity of single-crystal ZnSe (1) and
intrinsic conductivity (2), Е0 = 400 V/cm

10. Research results
10
0.0 2.0x10
3
4.0x10
3
6.0x10
3
8.0x10
3
1.0x10
4
0.00
0.06
0.12
0.18
0.24
0.30
0.36 i(600 V) D
1.36
i(400 V) D
1.60
D, Gy/h
IX
(D),A
1
2
3
i(200 V) D
1.75
Fig. 4 Dose dependencies of X-ray conductivity of single-crystal ZnSe:
U = 200V (1), U = 400V (2), U = 600V (3)

11. Design of detectors based on ZnSe
When we design a high-temperature detectors based
on ZnSe, we consider the following requirements:
 high optical quality of crystals;
 minimum intrinsic conductivity;
 possibility of compensating for the intrinsic
conductivity in the on-line;
 temperature range up to 200 0C without cooling;
 high efficiency of absorption of ionizing radiation.
11

12. Design of detectors based on ZnSe
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Fig. 5 Single-crystal multielectrode detector with automatic compensation of intrinsic
conductivity

13. Design of detectors based on ZnSe
13
Fig. 6 Double-crystal multielectrode detector with automatic compensation of
intrinsic conductivity

14. Design of detectors based on ZnSe
14
Fig. 7 Detection efficiency of gamma radiation of ZnSe detectors, [d] = cm

15. Design of detectors based on ZnSe
15
Fig. 8 A Schematic of the measuring system for isotopic thickness gauge

16. CONCLUSIONS
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Change of intrinsic conductivity of ZnSe specimens within the range of
temperatures from 10 0С up to 240 0С showed that single-crystal specially
undoped ZnSe has extremely low intrinsic conductivity. This attribute of obtained
specimens can be used during the designing and manufacturing of gamma and X-
ray radiation detectors for the application in radiation hot rolling thickness gauges
which are widely used in the metallurgy. Distinctive feature of such detectors is
that there is no necessity to perform additional cooldown which considerably
simplifies measuring part of thickness gauge.
It was determined that “dose rate - current” calibrating characteristic of analyzed
specimens approaches to the linear one when electric field is increased in the
specimen up to Е0 ≥ 1400 V/cm. However, since the current of X-ray induced
conductivity is described precisely enough with simple power function of the
following type IX ~ Db, which is linearized in double logarithmic scale, then in
practice significantly lesser electric fields 500-1000 V/cm can be used what
decreases the probability of surface breakdown of sensors.

17. 17
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