Form 1

2017 Report Form for Collaboration with
Research Center for Biomedical Engineering

Year/month/date
2015

Number

20 /March/2018
date:

To Chairman, Board of Directors, Research Center for Biomedical Engineering

ApplicantAffiliation: V.E. Lashkaryov Institute of Semiconductor Physics of the National
Academy of Sciences of Ukraine
Title: Ph.D., Associate Professor, Senior Scientist
Name: Volodymyr GNATYUK
Address: Prospekt Nauky 41, Kyiv 03028, UKRAINE
Phone: +380 44 5258437, +380 67 3239528
Fax: +380 44 5258342
E-mail: gnatyuk@ua.fm
Report Form for Collaboration Research

Research Theme

Development of Cd(Zn)Te-based X/gamma-ray detectors with high resolution for security
and diagnostics instruments

Research Area

1. Biomaterials
2. Bioengineering
3. Functional molecules
4. Chemistry/Electrical Engineering/Mechanical Engineering/Materials Science

Research Period

From:01/07/2017

To: 31/03/2018

Applicant Organization
Name

Volodymyr Gnatyuk

Sergiy Levytskyi

Kateryna Zelenska

Department
Department of Physics of Defects andNonequilibrium Processes in Complex
Semiconductors,
V.E.
Lashkaryov
Institute of Semiconductor Physics of the
National Academy of Sciences of
Ukraine, Kyiv, Ukraine
Department of Detector Physics andNonequilibrium Processes in Complex
Semiconductors,
V.E.
Lashkaryov
Institute of Semiconductor Physics of the
National Academy of Sciences of
Ukraine, Kyiv, Ukraine
Faculty of Physics, Taras Shevchenko
National University of Kyiv, Kyiv,
Ukraine

Title

Role

Ph.D., Associate
Professor, Senior
Scientist

Leader

Ph.D., Research
Scientist

Participant

Ph.D., Engineer

ParticipantCollaboration Partners in the
Research Center

Toru AOKI, Ph.D., Professor
Research Institute of Electronics, Shizuoka University, Japan

Research Results (Including Purpose, Results, Figures, etc.)
1. Introduction
The purpose of the project is the elaboration of methods and technologies of fabrication of uncooled
Cd(Zn)Te)-based X/γ-ray detectors with high energy resolution for instruments designed for detection ofionization sources, identification of radioactive contaminations, monitoring of environment and nuclear power
plants, formation of images in medicine, customs, industry, cosmic astronomy and other application fields.
The main our ideas in the development of Cd(Zn)Te) semiconductor-based X/γ-ray detectors, which allow us
to obtain nuclear radiation sensors with high energy resolution and low leakage current are the application of theadvanced methods of surface processing of semiconductor crystals, laser-induced doping:• Cd(Zn)Te detectors will be developed as M-p-n structured diodes with a built-in shallow and abrupt p-njunction formed by laser-induced solid phase doping;• Cd(Zn)Te detectors will be developed as Schottky diodes using special treatment of the crystal surfaces before
electrode deposition to form a high barrier Schottky contact and Ohmic contact.
2. Semiconductor samples for investigation
For fabrication of diode-based X/γ-ray detectors, commercial CdTe single-crystal wafers produced by Acrorad
Co., Ltd. by THM we used. Semi-insulating Cl-compensated CdTe semiconductor showed weak p-typeconduction with the room temperature resistivity ρ = (2-4) × 109 Ω·cm that was close to the intrinsic value.
Parallelepiped-like (111) oriented CdTe single-crystal samples with the thickness of 0.5 mm and 0.75 mm, andarea of 5×5 mm2 and 10×10 mm2 were used.
3. Development of CdTe-based diodes with a laser induced p-n junction
Laser-induced solid-phase doping of the CdTe surface region was employed to create a shallow and abrupt
built-in p-n junction. Three techniques of In doping of a thin CdTe surface layer and formation of In/CdTe/Au
diodes with a p-n junction under irradiation of CdTe crystals have been developed: (i) liquid-phase doping using athin (20 ns) In dopant film; (ii) solid-phase doping using a thick (300-600 nm) In dopant film; (iii) space-confined
doping by irradiation of the CdTe sample pre-coated with a thick In film from the CdTe side, i.e. directly affecting
the CdTe-In interface with YAG:Nd laser pulses (1064 nm) through the CdTe.
Before doping and metal deposition, the CdTe crystals were subjected to the preliminary surface processing forcleaning and removing of a disordered surface layer. Evaporation of an In dopant (electrode) film and then an Au
electrode was carried out using the masks for contact deposition in the vacuum system for thermal annealing andelectrode deposition. The surface area of the CdTe(111)B face pre-coated with a In dopant film was entirely anduniformly irradiated with single nanosecond laser pulses in different conditions at room temperature.
Fig. 1 shows the procedure (ii) of laser irradiation of the In/CdTe structure thick (400 nm) In dopant film by ananosecond pulse in water. For the simulation of laser-induced thermal processes, the following three-region
structure was considered: environment (water layer with the depth of 3-5 mm) / metal dopant film (In film withthe thickness of 400 nm) / semiconductor substrate (CdTe crystal with the thickness of 0.5 mm) (Fig. 1). The
corresponding data characterizing thermal and optical properties CdTe and In were taken from the literature. The
result of the calculation of the temperature distributions in the structure of water (3-5 mm)/In (400 nm)/CdTe (0.5mm) under laser radiation is shown in Fig. 2. As seen, the temperature increases with increasing laser pulse energy
density, while the shape of the temperature distributions does not change.

Fig. 1. Schematic illustration of irradiation of the In film - CdTe
crystal structure with a single nanosecond laser pulse in water
environment.

Fig..2. Temperature distribution in the structure ofwater environment/In film/CdTe crystal underirradiation from the In film side with laser pulse
energy density E (J/m2): 1100 (a), 1300 (b), 1500 (c).
The time (a) and coordinate (b) distribution profiles, depending on the laser energy density, are shown in Fig.3
1.3. According to the calculation results, the temperature increases linearly (not counting the region where theindium melts) that is associated with high laser pulse energy density. The influence of the cooling water layer andcooling due to “evaporation” of In atoms from the dopant film surface is small and it does not have a noticeable
effect during the irradiation of this structure by a short laser pulse. In order to finally verify this, the heating fluxof transmitted laser radiation into the In film (~1012 W/m2) and fluxes of the cooling indium surface are compared(Fig. 4). As seen, the cooling flows from surfaces film are several orders of magnitude lower than the heating flowof the structure of water (3-5 mm)/In (400 nm)/CdTe (0.5 mm) under pulse laser radiation.
The whole In film (400 nm) was melted at laser pulse energy densities above 1300 J/m2. The melting time at E
= 1500 J/m2 was about 13 nanoseconds, but the temperature at the boundary of the In film and CdTe substrate did
not reach the semiconductor melting threshold (Fig. 1.3(b)). There was no melting of a CdTe layer near the
In/CdTe interface (Fig. 5). Thus, mixing of these substances (In and CdTe) in liquid (melted) state could not occur.
550

550

(b)

(a)

500

500
450

T (K)

T (K)

450
400

400

350

350

300

300
250

250
5

0

10

15

20

25

30

0

500

1000

t (ns)

1500

2000

2500

x (nm)

Fig.3. Temperature distribution in the structure of water environment/In film/CdTe crystal under irradiationfrom the In film side in dependence on laser pulse energy density vs time for the maximum temperature layer(a) and vs coordinate in 20 ns after irradiation starts (b).
60
10-3

(a)

(b)

10-4

Qbw (µW/m2)

Qevap (µW/m2)

50

10-5
10-6

40
30
20
10

10-7
10

12

14

16

18

20

t (ns)

22

14

22

28

30

0

0

5

10

15

20

25

30

t (ns)

Fig.4. Cooling flows from the In film surface in the structure of water environment/In film/CdTe crystal due to
In evaporation (a) and boiling of water near the In film surface (b) in dependence on laser energy density.

500

T (K)

450
400

Fig. 5. Temperature distribution at the boundary of
the In film/CdTe crystal in the structure of water
environment/ In film/CdTe crystal under irradiationfrom the In film side with different laser pulse
energy densities.

350
300
250

0

5

10

15

20

25

30

t (ns)(b)

8x10-46x10-4

1x10-3(c)

8x10-46x10-4Current (A)1x10-3Current (A)(a)

Current (A)Thus, the computational simulation of thermal processes and calculations of the time-dependent temperature
distributions in the structure of water environment (3-5 mm)/In film (400 nm)/CdTe crystal (0.5 mm) underirradiation from the In film side in water with KrF excimer laser pulses (λ = 248 nm, τ = 20 ns) (Figure 1.1) has
demonstrated that the In film was completely melted at laser pulse energy density E = 1300-1500 J/m2, however
the temperature at the In film/CdTe crystal boundary was still much lower the melting point of CdTe. Cooling due
to “evaporation” of In atoms and boiling of the surrounding water layer did not significantly affected the laser
heating process. As shown, the cooling flows were several orders of magnitude lower than the heating flux of laser
radiation. The results can be used for optimization of the laser-induced doping of CdTe and formation of
In/CdTe/Au diodes with a p-n junction for X/γ-ray detectors.
The fabricated In/CdTe/Au diodes, created, by laser-induced doping, demonstrated high rectification I-V
characteristics (Fig. 6(c)). The spectroscopic performance of the fabricated M-p-n structured In/CdTe/Au detectors
was tested for radiation detection of a 137Cs radioisotope. Good results were obtained with detectors formed on thebase of CdTe crystals with sizes of 5×5×0.75 mm3 by laser-induced doping according to the procedure (ii), in
particular the best energy resolution (FWHM) was less than 1%@662keV (Fig. 7).
1x10-38x10-46x10-44x10-44x10-44x10-42x10-4-100 -80 -60 -40 -20 0

2x10-4-100 -80 -60 -40 -20 0

2x10-440 -100 -80 -60 -40 -20 0

20

40

60

Voltage (V)20

Voltage (V)-1x10-7-2x10-9-4x10-10-7-4x10-9-8x10-10

-2x10

20

40

Voltage (V)Fig. 6. I-V characteristics of the In/CdTe/Au structures before (a) and after (b, c) irradiation from the In film
coated side (procedure (ii)) by nanosecond laser pulses energy densities: E (J/m2): 1000 J/m (b) and 1200 J/m (c).

Fig. 7. Room temperature spectrum of a 137Cs
radioisotope taken by the In/CdTe/Au detector witha p-n junction at applied bias voltage of 700 V.

4. Development of CdTe-based diodes with a Schottky barrier
The Schottky diode detectors were prepared using CdTe crystals with sizes of 10×10×0.75 mm3 by formationof a rectifying Schottky contact on the CdTe(111)B-face (Te-terminated) by thermal deposition of a Ni film in
vacuum. An Ohmic contact was created on the opposite CdTe(111)A-face (Cd-terminated) by chemical depositionof an Au film. Before Ni and Au electrode deposition, both the CdTe crystal surfaces were treated with an Ar ion
plasma in different regimes (voltage, current and time), respectively. The fabricated Schottky diode type detectors
were tested by for radiation of 241Am and 137Cs radioisotopes. The spectroscopic performance of ten Ni/CdTe/Au
detectors with a Schottky barrier is shown in Fig. 8.
Detector G25

Detector G25

Detector G26

Detector G26

Am-241 (59.5 keV)
Vbias = 400 V

Cs-137 (662 keV)
Vbias = 800 V

Am-241 (59.5 keV)
Vbias = 400 V

Cs-137 (662 keV)
Vbias = 800 V

Detector G31

Detector G31

Detector G32

Am-241 (59.5 keV)
Vbias = 400 V

Cs-137 (662 keV)
Vbias = 800 V

Detector G32

Am-241 (59.5 keV)
Vbias = 400 V

Cs-137 (662 keV)
Vbias = 800 V

Detector G34

Detector G34

Am-241 (59.5 keV)
Vbias = 400 V

Cs-137 (662 keV)
Vbias = 800 V

Detector G36
Am-241 (59.5 keV)
Vbias = 400 V

Detector G35

Detector G35

Am-241 (59.5 keV)
Vbias = 400 V

Cs-137 (662 keV)
Vbias = 800 V

Detector G36

Detector G37

Detector G37

Cs-137 (662 keV)
Vbias = 800 V

Am-241 (59.5 keV)
Vbias = 400 V

Cs-137 (662 keV)
Vbias = 800 V

Detector G44

Detector G44

Am-241 (59.5 keV)
Vbias = 400 V

Cs-137 (662 keV)
Vbias = 800 V

Detector G45

Detector G45

Am-241 (59.5 keV)
Vbias = 400 V

Cs-137 (662 keV)
Vbias = 800 V

Fig. 8. Room temperature energy spectra of 241Am and 137Cs radioisotopes taken by ten Ni/CdTe/Au Schottky
diode detectors.
5. Conclusion
M-p-n structured diodes and Schottky diodes have been fabricated using semi-insulating p-like CdTe wafers
and two principal technologies, which have been developed: (I) laser-induced doping of a thin CdTe region andformation of a p-n junction, and (II) creation of both rectifying (Schottky) and Ohmic contacts using preliminary
treatment of the CdTe surface by an argon ion bombardment. The In/CdTe/Au diodes with a p-n junction and
Ni/CdTe/Au diodes with a Schottky barrier showed good detection efficiency as X/γ-ray detectors anddemonstrated high energy resolution. The highest energy resolution, achieved in the best samples, was FWHM =0.7-1.5%@662keV.

List of Publications Related to the Collaboration Research
1.

2.

3.

4.
5.

6.

7.

8.

V.A. Gnatyuk, V.L. Dubov, D.V. Fomin, A.Yu. Seteikin, T. Aoki, Temperature fields in the In/CdTe structure
under laser-induced doping in liquid, Recent Advances in Technology Research and Education. Inter-Academia
2017. Advances in Intelligent Systems and Computing, Vol. 660 (Sep. 2018) 87-95.
O.L. Maslyanchuk, M.M. Solovan, V.V. Kulchynsky, V.A. Gnatyuk, T. Aoki, Space-charge limited transport in
CdTe-based X- and γ-ray detectors, 2016 IEEE Nuclear Science Symposium, Medical Imaging Conference andRoom-Temperature Semiconductor Detector Workshop (NSS/MIC/RTSD), Conference Record, (Oct. 2017) 2
pages.
O.L. Maslyanchuk, M.M. Solovan, V.V. Kulchynsky, V.V. Brus, P.D. Maryanchuk,
I.M. Fodchuk, V.A. Gnatyuk, T. Aoki, C. Potiriadis, Y. Kaissas, Possibilities of CdTe-based X/γ-ray detectors
with MoO x contacts, 2016 IEEE Nuclear Science Symposium, Medical Imaging Conference andRoom-Temperature Semiconductor Detector Workshop (NSS/MIC/RTSD), Conference Record, (Oct. 2017) 3
pages.
V.M. Sklyarchuk, V.A. Gnatyuk, W. Pecharapa, Low leakage current Ni/CdZnTe/In diodes for X/γ-ray
detectors, Nuclear Instruments and Methods in Physics Research A, Vol. 879 (Jan. 2018) 101-105.
O.L. Maslyanchuk, M.M. Solovan, E.V. Maistruk, V.V. Brus, P.D. Maryanchuk, V.A. Gnatyuk, T. Aoki,
Prospects of In/CdTe X- and γ-ray detectors with MoO Ohmic contacts, Proceedings of SPIE, Vol. 10612(Jan. 2018) 10612V-1-6.
O. Maslyanchuk, M. Solovan, V. Brus, P. Maryanchuk, E. Maistruk, I. Fodchuk, V. Gnatyuk, T. Aoki,
C. Lambropoulos, C. Potiriadis, Comparative study of X- and γ-ray detectors with MoO x , TiO x and TiN
Schottky contacts, 2017 Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature
Semiconductor Detector Workshop (NSS/MIC/RTSD), Conference Record, (2018) 5 pages, in press.
V.M. Sklyarchuk, V.A. Gnatyuk, T. Aoki, Determination of the depletion region thickness in X/γ-ray detectors
with a Schottky contact, 2017 Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature
Semiconductor Detector Workshop (NSS/MIC/RTSD), Conference Record, (2018) 2 pages, in press.
V.A. Gnatyuk, K.S. Zelenska, V.M. Sklyarchuk, T. Aoki, Enhanced X/γ-ray detection efficiency in CdTe-based
Schottky diode detectors operated in a stacked mode, 2017 Nuclear Science Symposium, Medical Imaging
Conference and Room-Temperature Semiconductor Detector Workshop (NSS/MIC/RTSD), Conference Record,(2018) 2 pages, in press.

List of Presentations ( Conference, Meeting, etc.)
1.

2.

3.

4.

5.

6.

7.

V. Gnatyuk, K. Zelenska, T. Aoki, Doping and metallization of the CdTe crystal surface by laser
irradiation of the metal substrate through the semiconductor, The conference on Hard X-Ray,
Gamma-Ray, and Neutron Detector Physics XIX (Conference 10392), Part of 2017 SPIE Optics + Photonics:
Optical Engineering + Applications, Technical Program, 2017, Abstract No 10392-46, 161. (6-10 August
2017, San Diego, CA, USA).
O. Maslyanchuk, M. Solovan, E. Maistruk, V. Brus, V. Gnatyuk, T. Aoki, Prospects of In/CdTe X- andγ-ray detectors with MoO Ohmic contacts, The 13th International Conference on Correlation Optics“Correlation Optics’17”, Programme, 2017, Abstract No M25, 1 page. (11-15 September 2017, Chernivtsi,
Ukraine).
V.A. Gnatyuk, Laser modification of electronic properties of semiconductors: formation ofphotosensitive structures, The 16th International Conference on Global Research and Education,
Inter-Academia 2017 (iA-2017), Book of Abstracts, 2017, Abstract No IL.04, 6. (25-28 September 2017, Iasi,
Romania). (Invited report).
K. Zelenska, V. Sklyarchuk, V. Gnatyuk, T. Aoki, Spectroscopic studies of Ni/CdTe/Au Schottky diode Xand γ -ray detectors, The 16th International Conference on Global Research and Education, Inter-Academia
2017 (iA-2017), Book of Abstracts, 2017, Abstract No O.06, 16. (25-28 September 2017, Iasi, Romania).
V.A. Gnatyuk, V.L. Dubov, D.V. Fomin, A.Yu. Seteikin, T. Aoki, Temperature fields in the In/CdTe
structure under laser-induced doping in liquid, The 16th International Conference on Global Researchand Education, Inter-Academia 2017 (iA-2017), Book of Abstracts, 2017, Abstract No O.12, 22. (25-28
September 2017, Iasi, Romania).
O. Maslyanchuk, M. Solovan, V. Brus, I. Fodchuk, P. Maryanchuk, V. Gnatyuk, T. Aoki, C. Lambropoulos,
C. Potiriadis, Comparative study of X- and γ-ray detectors with MoO x , TiO x and TiN schottky contacts,
The 24th International Workshop on Room-Temperature Semiconductor Detectors (RTSD 2017), 2017 IEEE
Nuclear Science Symposium & Medical Imaging Conference (2017 NSS/MIC), Conference Program &Abstracts, 2017, Abstract #2524. (21-28 October 2017, Atlanta, USA).
O. Maslyanchuk, M. Solovan, V. Brus, I. Fodchuk, P. Maryanchuk, V. Gnatyuk, T. Aoki,
Graphene/semi-insulating CdTe X-ray and γ-ray radiation detectors, The 24th International Workshop
on Room-Temperature Semiconductor Detectors (RTSD 2017), 2017 IEEE Nuclear Science Symposium &Medical Imaging Conference (2017 NSS/MIC), Conference Program & Abstracts, 2017, Abstract #2546.

(21-28 October 2017, Atlanta, USA).
V.M. Sklyarchuk, V.A. Gnatyuk, T. Aoki, Determination of the depletion region thickness in X/γ-ray
detectors with a Schottky contact, The 24th International Workshop on Room-Temperature Semiconductor
Detectors (RTSD 2017), 2017 IEEE Nuclear Science Symposium & Medical Imaging Conference (2017
NSS/MIC), Conference Program & Abstracts, 2017, Abstract #2991. (21-28 October 2017, Atlanta, USA).
9. J. Nishizawa, V.A. Gnatyuk, K. Zelenska, A. Koike, T. Aoki, Doping of CdTe by indium or aluminumwith Nd:YAG laser, The 24th International Workshop on Room-Temperature Semiconductor Detectors(RTSD 2017), 2017 IEEE Nuclear Science Symposium & Medical Imaging Conference (2017 NSS/MIC),
Conference Program & Abstracts, 2017, Abstract #3897. (21-28 October 2017, Atlanta, USA).
10. V.A. Gnatyuk, K.S. Zelenska, V.M. Sklyarchuk, T. Aoki, Enhanced X/γ-ray detection efficiency in
CdTe-based Schottky diode detectors operated in a stacked mode, The 24th International Workshop on
Room-Temperature Semiconductor Detectors (RTSD 2017), 2017 IEEE Nuclear Science Symposium &Medical Imaging Conference (2017 NSS/MIC), Conference Program & Abstracts, 2017, Abstract #4164.
(21-28 October 2017, Atlanta, USA).
11. V.A. Gnatyuk, Laser-stimulated modification of surface state and photoelectrical properties of crystals
and films of CdTe-based solid solutions, The First Materials Research Society of Thailand International
Conference (1st MRS Thailand International Conference), Abstract Book, 2017, 15_2. (31 October – 3
November 2017, Chiang Mai, Thailand). (Keynote report).
8.

List of Awards
Owing to the obtained results, the leader of the research team Dr. Volodymyr A. Gnatyuk was awarded by threefinancial grants to visit and carry out the synchrotron measurements at Synchrotron Light Research Institute in
Thailand in July and November (Project No 2885 and No 2888) 2017, respectively:
1. Characterization of CdTe-based structures with a surface nanolayer doped with an In or Al impurity using
nanosecond laser irradiation.
2. Characterization of Cd(Zn)Te crystals subjected to different surface processing (chemical etching, thermal
heating, nanosecond laser irradiation.
3. Characterization of CdTe and Cd(Zn)Te crystal surfaces and interfaces after laser deposition of a metal contact
film.
Research plan for the next year (from April 1, 2018 to March 31, 2019), if the collaboration research is continued.
Prior consent from the collaboration partner in the Research Center is necessary.
Different techniques of laser processing of semi-insulating p-like CdTe crystals and CdTe-metal interfaces will be
developed to create X/γ- ray radiation diode type detectors:(i) laser transfer of a thin In film, pre-deposited on the glass substrate by laser ablation of an In target irradiatedthrough the glass, on the CdTe surface;(ii) laser deposition of In on the CdTe surface by irradiation of an In target through the CdTe crystal;(iii) activation of the CdTe-In interface by laser irradiation of CdTe crystals, pre-coated with an In dopant(electrode) film, (a) from the metal side or (b) through the semiconductor.
Applying infrared nanosecond laser pulses it will be possible to introduce and electrically activate In dopant
atoms with high concentration in the thin surface region of CdTe crystals and thus, to form an In(Al)-doped layer.
Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) with synchrotron radiation as an
excitation light, photoconductivity, I-V characteristics and radioisotope spectrum measurements will be applied to
study laser-induced doping and test the obtained In(Al)/CdTe/Au diodes with a p-n junction.