Form 1

2019 Report Form for Collaboration with
Research Center for Biomedical Engineering

Year/month/date
Number
Day/Month/Year
Date:
13/03/2020

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

ApplicantTitle:
Name:
Address:

V.E. Lashkaryov Institute of Semiconductor Physics of the
National Academy of Sciences of Ukraine
Ph.D., Senior Scientist
Volodymyr GNATYUKProspekt Nauky 41, Kyiv 03028, UKRAINE

Phone:
Fax:
E-mail:+380 44 5258437+380 44 5258342
gnatyuk@ua.fm

Affiliation:

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:

Day/Month/Year
14/05/2019

To:

Day/Month/Year
31/03/2020

Applicant Organization
Name
Volodymyr
GNATYUK
SergiyLEVYTSKYI
Vitaliy
VELESCHUKKateryna
ZELENSKA

Department
Department of Physics of Optoelectronic Devices,
V.E. Lashkaryov Institute of Semiconductor Physics of the
National Academy of Sciences of Ukraine, Kyiv, Ukraine
Department of Physics of Optoelectronic Devices,
V.E. Lashkaryov Institute of Semiconductor Physics of the
National Academy of Sciences of Ukraine, Kyiv, Ukraine
Department of Physics of Optoelectronic Devices,
V.E. Lashkaryov Institute of Semiconductor Physics of the
National Academy of Sciences of Ukraine, Kyiv, Ukraine
Faculty of Physics, Taras Shevchenko National Universityof Kyiv, Kyiv, Ukraine

Collaboration Partners
in the Research Center

Title

Role

Ph.D.,
Senior Scientist

Leader

Ph.D.,
Senior Scientist

Participant

Ph.D.,
Senior Scientist

Participant

Ph.D.,
Junior Scientist

Participant

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

Research Results (Including Purpose, Results, Figures, etc.)
1. Introduction
Owing to the support of the Cooperative Research Project (No 2022) of the Research Center of Biomedical
Engineering, we performed the research and obtained interesting and important results which were presented at
10 International Meetings and reflected in the abstracts {1-13} (in List of Presentations). Moreover, the project
results have been published in 6 articles cited by Scopus [1-6] (in List of Publications). All the publications were
published during the period of implementation of this project (05.2019-03.2020). The articles [1-6] containacknowledgments to the Cooperative Research Project of the Research Center of Biomedical Engineering.
2. Project purpose and research objectives
The purpose of the project was to develop Cd(Zn)Te-based X/γ-ray detectors with high energy resolution for
security and diagnostic instruments. The research objectives were the study of Cd(Zn)Te properties andelaboration of two techniques of fabrication of Cd(Zn)Te-based diode-type detectors: (i) creating a p-n junctionand (ii) forming a Schottky barrier. The first technique included the doping of the thin semiconductor region withan In impurity by backside laser irradiation, creation of a p-n junction and, thus In/CdTe/Au diode structures.
The second one consisted of formation of Schottky and Ohmic contacts by vacuum deposition of Cr and Au
electrodes onto the CdTe(111) crystal surfaces pre-treated with Ar-ion bombardment in different regimes.
To elaborate the techniques of fabrication of X/γ-ray detectors as In/CdTe/Au p-n junction diodes or
Cr/CdTe/Au Schottky diodes with low reverse dark currents in both the cases, some important semiconductor
properties were investigated, different surface treatments (chemical etching, ion bombardment, laser irradiation,
plasma processing, etc.) of CdTe crystals were studied and efficient methods of formation of electrical contacts
and electrodes (vacuum evaporation, chemical deposition, etc.) were developed.
3. Semiconductor samples
Detector-grade (111) oriented CdTe semiconductor single crystals, grown by the THM by Acrorad Co., wereused in our research [1-6]. Semi-insulating Cl-compensated CdTe showed weak p-type conductivity with a
specific resistivity of 4 × 109 Ω⋅cm at T = 300 K that was close to the intrinsic value [1]. Parallelepiped-like
CdTe(111) wafers with a surface area of 5 × 5 mm2 and different thicknesses (0.5 mm, 0.75 mm, 1.0 mm and 2.0mm), preliminary polished by the manufacturer, were employed [1-6]. Before the experimental procedures, all
CdTe samples were subjected to chemical surface processing for cleaning from contaminants [1-46,].
4. Investigation of some properties of CdTe crystals
The photothermal transformation in the CdTe crystals w studied using the photoacoustic gas-microphone
technique, in particular the thermal conductivity was evaluated [4]. The experimental amplitude-frequency andphase-frequency dependences of the photoacoustic response, obtained by optical irradiation of the reference Si
and investigated CdTe samples, were approximated by the calculations [4]. The qualitative coincidence of thetheoretical curve`s amplitude with the experimental result for the CdTe sample occurred when its thermal
conductivity value as a fitting parameter was equal to 3.7 ± 0.7 W/(m⋅K). This value was used for the
calculations of the CdTe melting thresholds under pulsed laser irradiation [4].
The treatment features of CdTe under laser irradiation with different wavelengths (λ = 300-800 nm) and pulse
durations (τp = 7 ns – 1 ms) were studied [4]. Simulations of the melting thresholds Іth were performed by thethree-stage model of laser-induced excitation and relaxation. Such processes were considered: (i) rapid interband
thermalization, (ii) nonradiative interband and (iii) nonradiative surface recombination. The laser intensity І0required to heat the semiconductor surface from an initial temperature Т0 to a temperature Тf was estimated as:
1
1 f dTc T / ( LT  1)  BNR / ( LT  LD  1)  SNR / LT  ,
 p T0 (1  R)
T

I0 

(1)

where c is the specific heat, ρ is the density, R is the reflectivity coefficient, α is the absorption coefficient, ∆Т =Tf - T0 is the temperature rise, LD = (DτB)1/2 is the free carrier diffusion depth, D is the ambipolar carrier diffusion
coefficient, τB is the bulk carrier recombination lifetime, LT(T) is the thermal diffusion depth. The parameters ηT,
ηBNR and ηSNR are the fractions of the laser energy which go into the thermalization of nonequilibrium excess
carriers immediately (1 fs – 1 ps) after excitation (interband relaxation), into both nonradiative interband (bulk)
and surface recombination with surface lifetime τS = LD/S, where S is the surface recombination velocity.

10
8
6

1 - 7 ns
2 - 20 ns
3 - 80 ns
4 - 120 ns
5 - 1 s(a)

Melting threshold (MW/cm2)

Melting threshold (MW/cm2)

The description of the processes under heating of the CdTe surface by nanosecond laser pulses is complicatedbecause of temperature dependences of the thermal and optical parameters, and concentration of photoexcited
nonequilibrium excess carriers. In the calculations, we took the parameters of detector-grade CdTe [4], which
was used to create Cr/CdTe/Au Schottky and In/CdTe/Au p-n junction diodes as X/γ-ray detectors [1-3, 6].
Fig. 1(a) demonstrates the melting thresholds Ith calculated by (1) under pulsed laser irradiation within the
wavelength region λ = 300–800 nm for different pulse durations τp. An increase in τp leads to a sensitivity
decrease of Іth on the excitation wavelength λ. At τp = 7 ns, the threshold laser intensity increases by ΔІth = 5.6
MW/cm2 (from 4.7 MW/cm2 to 10.3 MW/cm2) with a variation of λ from 300 nm to 800 nm (Fig. 1(a), curve 1).
While, at τp = 1 μs, the melting threshold changes only by ΔІth = 0.045 MW/cm2 (curve 5). Such decrease in ΔІthwith increasing τp can be explained by the fact that the thermal diffusion depth LT increases with rising τp andbecomes much larger than 1/α, therefore Іth becomes less dependent on the optical absorption coefficient α(λ) [4].

1

2
4

3 4
2
300

400

500

600

Wavelength (nm)

700

5

800

101

(b)

3
2

10

10-1

10

1

0

1 - 694 nm
2 - 532 nm
3 - 308 nm

1

2
3

-2

10-8

10-7

10-6

10-5

10-4

10-3

Pulse duration (s)Fig. 1. Dependences of the CdTe melting Ith on laser threshold wavelength for different pulse durations (a)and on pulse duration for different wavelengths (b).

For application, the dependence of Іth on p is also important (Fig. 3(b)). Іth falls drastically with an increasein p in accordance with (1) because the heated-up layer volume increases. If p becomes shorter, the rate of laser
energy delivery becomes higher. With increasing p by six orders of magnitude, Ith decreases by three orders ofmagnitude, e.g. from 8.7 MW/cm2 to 10 kW/cm2 at λ = 532 nm (Fig. (1(b), curve 2). The fact that the curvesintersect at τp ~ 1 μs is explained by temperature dependences of the optical parameters of the semiconductor [4].
It was revealed that in the range τp = 7 ns – 1 μs, Ith mainly depends on the absorption coefficient α(λ). For τp> 1 μs, Ith starts to depend also on the reflectivity R(λ). The results on determination of Ith was used for
optimization of the laser-assisted techniques of surface processing and stimulated doping of CdTe crystals [6].
5. In/CdTe/Au p-n junction diode detectors formed by backside laser irradiation doping
Backside laser irradiation of the In/CdTe structures was employed to dope the thin p-CdTe region with In
atoms (donors), form a shallow abrupt p-n junction and create diode-type X/γ-ray detectors [6]. An In dopant
film with the thickness of 100 nm was thermally evaporated onto the CdTe(111)B crystal surface (Te-terminated)using a mask of sizes of 4 × 4 mm2. Then, the In/CdTe structure was irradiated with single pulses of a YAG:Ndlaser (λ = 1.06 μm, τ = 8 ns) from the CdTe(111)A (Cd-terminated) side [6].
CdTe semiconductor is transparent for the employed laser radiation wavelength and radiation is strongly
absorbed (α ~ 109 cm-1) only by a thin In layer at the In/CdTe interface. After backside laser irradiation doping,an Au electrode was deposited on the CdTe(111)A (Cd-terminated) surface with the same technique andthickness as an In one to form a near Ohmic contact at the Au/CdTe interface [6].
Fig. 2(a) shows the I-V characteristics of the In/CdTe/Au sample fabricated without laser irradiation of the
In/CdTe interface (curve 1) and diode after backside laser doping (curve 2) performed by irradiation of the
In/CdTe structure with 50 laser pulses of output energy E = 11 mJ. Reverse current flowed when the In electrode(rectifying contact) was biased positively with respect to the Au electrode (Ohmic contact). As seen, pulsed laser
irradiation remarkably shifted the forward branch of the I-V characteristics of the In/CdTe/Au structure toward
lower voltages (i.e, forward current increased) and reduced reverse current in comparison with the unirradiatedsample. High forward current and low reverse one (leakage current) were evidence of formation of a high barrier
p-n junction as result of backside laser doping of a thin CdTe layer at the In/CdTe interface (Fig. 2(a), curve 2).

(a)

(b)

Fig. 2. I-V characteristics (a) and spectra of a 137Cs isotope (b) obtained from the unirradiated In/CdTe/Au structure(Schottky diode) (curves 1) and In/CdTe/Au p-n junction diodes formed by the backside laser irradiation doping withlaser pulse energy E = 11 mJ (curves 2) and 2 mJ (curve 3).

Both types of In/CdTe/Au diode detectors (with Schottky contact and p-n junction) were tested for detectionof 241Am and 137Cs isotope emissions at T = 300 K [6]. Fig. 2(b) shows the 137Cs isotope spectra taken with threedetectors at reverse bias voltage V = 200 V. The unirradiated In/CdTe/Au structure (Schottky diode) detected 662
keV γ-rays with rather low (FWHM = 5%) energy resolution (Fig. 2(b), curve 1). The In/CdTe/Au p-n junction
diodes, formed by backside laser irradiation doping, demonstrated higher energy resolution, more correct peakchannel position of the 662 keV line and lower background (Fig. 2(b), curves 2 and 3). Attention is drawn to asignificant increase in energy resolution (FWHM = 1.3%) and decrease of the low-energy tail level in the
spectrum taken with the In/CdTe/Au p-n junction diode fabricated by multiple laser irradiation with E = 2 mJ
(curve 3). A broad shoulder and tail, extending toward the low-energy side from the 662 keV peak in the
spectrum taken with the In/CdTe/Au Schottky diode (Fig. 2(b), curve 1), were due to incomplete chargecollection (a part of photogenerated carriers was trapped in the CdTe bulk) along with Compton scattering [6].
6. Cr/CdTe/Au Schottky-diode detectors formed by Ar-ion bombardment
We also developed high energy resolution X/γ-ray detectors as Cr/CdTe/Au Schottky diodes using CdTe
wafers with different thicknesses d: 0.5 mm, 0.75 mm, 1.0 mm and 2.0 mm. Both the Schottky (Cr electrode) andOhmic (Au electrode) contacts were formed on the opposite sides of semi-insulating CdTe(111) crystals after
preliminary Ar-ion etchings using different parameters of such plasma treatment [1-3]. The I-V characteristics of
the Schottky diodes were measured in dark at T = 300 K. Forward current flowed when the Cr electrode wasbiased negatively with respect to the Au one. Based on the I-V measurements, the dominant charge carriertransport mechanisms were determined as: (i) generation-recombination in the space-charge region (SCR) at
reverse bias voltages V = 1-100 V, (ii) the charge transport in the conditions when the SCR width W exceeded thesemiconductor thickness d at elevated V and, finally (iii) currents limited by space charge at even higher V [2].
The spectroscopic performance of the Cr/CdTe/Au Schottky-diode detectors with different CdTe crystal
thicknesses was examined by the measurements of 241Am and 137Cs isotope emissions in dark at T = 300 K
without any charge-loss correction or rise-time discrimination electronics [1-3]. The electronic parameters suchas the uncompensated impurity concentration N, the SCR width W and thus, the depletion region thickness in thediodes, were calculated based on the comparison of the bias voltage dependences of the photopeak heights in the241
Am isotope spectra excited from the Schottky contact side (Cr) and Ohmic contact side (Au), respectively [1].
The Cr/CdTe/Au Schottky diodes demonstrated steep rectification that made it possible to apply high reverse
bias voltages up to V = 1500 V at moderately low dark currents (Table 1). This provided full collection ofphotogenerated charge carriers and, thus high energy resolution. Fig. 3 shows the 137Cs isotope spectra taken by
the Schottky-diode detectors with different CdTe crystal thicknesses d at V = 1200 V (Fig. 3). As seen, theintensity (number of counts) of the 662 keV photopeak in the spectra increases significantly with increasing d.
The CdTe crystal thickness dependences of the photopeak height (curve 1) and energy resolution (curve 2)
are shown in Fig. 4. It follows, that the intensity (number of counts) of the 662 keV photopeak in the 137Cs
isotope spectra increases approximately in 4 times (curve 1) and energy resolution (FWHM at the 662 keV peak)of the detectors varies from 0.5 % to 3 % (curve 2), when d increases from 0.5 mm to 2.0 mm (Fig. 4). Both thevalues (height and FWHM) change almost linearly (Fig. 4).

Fig. 3. Spectra of a 137Cs isotope, measured by the Cr/CdTe/Au Schottky-diode detectors with different CdTe crystal
thicknesses d at reverse bias voltage V = 1200 V for d (mm): 0.5 (a), 0.75 (b), 1.0 (c) and 2.0 (d).
Table 1. Leakage currents of the Cr/CdTe/Au
Schottky-diode detectors with different thicknesses d
at different applied reverse bias voltages (T = 293 K).
Applied bias (reverse) voltage (V)
CdTe crystal
thickness d 100 200 400 500 600 1000 1500
(mm)
Reverse dark (leakage) current (nA)
0.50

0.58 0.92 1.40 1.72 2.00 2.70 4.60

0.75

0.39 0.60 0.98 1.18 1.40 2.50 3.60

1.00

0.26 0.40 0.72 0.88 1.04 1.60 2.50

2.00

0.26 0.40 0.60 0.75 0.88 1.30 2.10

Fig. 4. Thickness dependences of the height (curve 1) andenergy resolution (curve 2) of the 662 keV photopeak in the137
Cs isotope spectra (Fig. 3); circles and squares are theexperimental data; the curves are linear approximations.

From the comparison of the detection efficiency dependences on the crystal thickness with the corresponding
calculated dependences, the uncompensated impurity concentration in CdTe was obtained as N ≈ 4 × 1010 cm-3
[1, 3]. N determines the SCR width W in Schottky diodes, therefore the effect of this value on the detection
efficiency was analyzed [3]. A key feature of the efficiency calculation was the correct evaluation of the electricfield strength in the CdTe crystals and using the integration limit d rather than W when W > d [1- 3].
7. Summary
In the frames of the Cooperative Research Project (No 2022, May 2019 – March 2020), we have carried out
the investigations according to the research plan, achieved new important results which have been reported at theinternational meetings {1-13} and published in the articles [1-6]. This is the following.
 Based on the study of photothermal transformation and features of processing of CdTe crystals by laser
irradiation with different wavelengths (λ = 300–800 nm) and pulse durations (τp = 7 ns – 1 ms), the CdTe
parameters have been evaluated, in particular, the dependencies of the melting threshold on λ and τp [4].
 The controllable technique of solid-phase doping of the thin semiconductor region near the metal-CdTe
interface by backside laser irradiation has been elaborated and In/CdTe/Au p-n junction diodes have beencreated for X/γ-ray detectors [6].
 High energy resolution Cr/CdTe/Au Schottky-diode detectors have been created using the developed Ar-ion
bombardment-based technique of semiconductor surface processing to create both the rectifying (Cr/CdTe)and Ohmic (Au/CdTe) electrical contacts [1-3].
 Studying the effect of CdTe thickness d on the detection efficiency of the Cr/CdTe/Au Schottky-diodeX/γ-ray detectors, the uncompensated impurity concentration in the semiconductor was estimated as N ~ 4 ×
1010 cm-3. The SCR width at bias voltage V = 0 V is W ~ 0.15 mm that was a significant part of the CdTe
crystals and with increasing V, W extends over the entire crystal and can be formally greater than d [1, 3].
 Quite high energy resolution has been achieved in the developed Cr/CdTe/Au Schottky-diode detectors
formed on thin CdTe crystals (FWHM = 0.5 %@662 keV for d = 0.5 mm) and higher detection efficiency atlower resolution has been obtained for the thicker detectors (FWHM = 3.0 %@662 keV for d = 2.0 mm) [3].
 The elaborated techniques of the formation of Schottky and Ohmic contacts, based on Ar-ion bombardmentof the semiconductor crystal surfaces, have also been successfully employed for creation of Schottky-diodeIR detectors with low leakage current at high operating voltages [5].

List of Publications Related to the Collaboration Research.
Article with acknowledgments to the Cooperative Research Project of the Research Center of Biomedical Engineering[1] V.M. Sklyarchuk, V.A. Gnatyuk, T. Aoki, Depletion region in CdTe Schottky diode X- and γ-ray detectors,
IEEE Transactions on Nuclear Science, Vol. 66, Issue 9 (Sep. 2019) 2140-2144. DOI: 10.1109/TNS.2019.2935836[2] V.M. Sklyarchuk, V.A. Gnatyuk, X. Fang, T. Aoki, Effect of the thickness of CdTe crystals on electrical anddetection properties of Cr/CdTe/Au Schottky-diode detectors, Proceedings of SPIE, Vol. 11114, Hard X-Ray,
Gamma-Ray, and Neutron Detector Physics XXI, (Sep. 2019) 111141S-1-7. DOI: 10.1117/12.2529965[3] V.M. Sklyarchuk, V.A. Gnatyuk, T. Aoki, Effect of CdTe crystal thickness on the efficiency of Cr/CdTe/Au
Schottky-diode detectors, Nuclear Instruments and Methods in Physics Research A, Vol. 953 (Feb. 2020)
163224-1-5. DOI: 10.1016/j.nima.2019.163224[4] V.P. Veleschuk, V.A. Gnatyuk, T. Aoki, Z.K. Vlasenko, S.M. Levytskyi, A.V. Shefer, A.G. Kuzmich,
K.V. Dubyk, V.V. Kuryliuk, M.V. Isaiev, Melting threshold and thermal conductivity of the CdTe underpulsed laser irradiation, in: A.R. Varkonyi-Koczy (ed.) Engineering for Sustainable Future. Inter-Academia
2019. Lecture Notes in Networks and Systems (LNNS), Vol. 101 (2020) 101-109, Cham: Springer. DOI:
10.1007/978-3-030-36841-8_10[5] V.M. Sklyarchuk, V.A. Gnatyuk, V. Pylypko, T. Aoki, Schottky diode detectors with low leakage current athigh operating voltage, in: A.R. Varkonyi-Koczy (ed.) Engineering for Sustainable Future. Inter-Academia 2019.
Lecture Notes in Networks and Systems (LNNS), Vol. 101 (2020) 159-167, Cham: Springer. DOI:
10.1007/978-3-030-36841-8_16[6] Controllable Doping of CdTe and formation of PN junction diodes by backside laser irradiation, 2019 IEEE
Nuclear Science Symposium and Medical Imaging Conference, 26th International Symposium on
Room-Temperature Semiconductor X-Ray and Gamma-Ray Detectors. Proceedings, (2019) 4 pages, in press.

List of Presentations (Conference, Meeting, etc.){1} V. Gnatyuk, CdTe-based diode-type X/γ-ray detectors with high energy resolution and applications, The
Seminar at Anhui Institute of Optics and Fine Mechanics (AIOFM), Hefei Institutes of Physical Science (HIPS),
Chinese Academy of Sciences (CAS), 2019, 1 page abstract. (7 May 2019, Hefei, China). (Invited report).
{2} K. Zelenska, Laser-induced incandescence of carbon surface, creation of marks in transparent polymers,
formation of CdTe-metal interfaces for diode-type high energy radiation detectors, the same as above, 1page abstract. (Invited report).
{3} T. Aoki, K. Takagi, T. Takagi, T. Terao, H. Kase, V. Gnatyuk, A. Koike, Photon counting X-ray image sensor
by laser doping process, XVII International Freik Conference on Physics and Technology of Thin Films andNanosystems (ICPTTFN-XIVII), Abstract Book, 2019, 6. (20-25 May 2019, Ivano-Frankivsk, Ukraine). (Keyreport).
{4} J. Nishizawa, V. Gnatyuk, A. Koike, T. Aoki, Doping of p-n junction CdTe diode by backside laser doping,
Monday Morning Forum, Research Institute of Electronics, Shizuoka University, Program & Abstract, 2013, 1-2.
(27 May 2019, Hamamatsu, Japan).
{5} O.P. Kulyk, V.A. Gnatyuk, K.S. Zelenska, O.V. Podshyvalova, A. Koike, T. Aoki, High-performancesemiconductor X/γ-ray detection system for environment monitoring, Proceedings of the International
Scientific and Technical Conference “Physical and Technical Problems of Energy and Their Solutions 2019”(ISTCPTPES-2019), 2019, 3. (19 June 2019, Kharkiv, Ukraine). (Plenary report).
{6} V. Gnatyuk, Photoelectric properties of semiconductors subjected to laser pulse action, International
Congress on Advanced Materials Sciences and Engineering 2019 (AMSE-2019), Abstract Book, 2019, 43. (22-24
July 2019, Osaka, Japan).
{7} V.M. Sklyarchuk, V.A. Gnatyuk, T. Aoki, Effect of the thickness of CdTe crystals on the detection properties
of Cr/CdTe/Au Schottky diode detectors, The conference on Hard X-Ray, Gamma-Ray, and Neutron Detector
Physics XXI (Conference OP319), Part of 2019 SPIE Optics + Photonics: Optical Engineering + Applications,2019, Abstract No 11114-67, 165. (11-15 August 2019, San Diego, CA, USA).
{8} V.P. Veleschuk, V.A. Gnatyuk, T. Aoki, Z.K. Vlasenko, S.M. Levytskyi, A.V. Shefer, A.G. Kuzmich,
K.V. Dubyk, V.V. Kuryliuk, M.V. Isaiev, Melting threshold and thermal conductivity of the CdTe underpulsed laser irradiation, The 18th International Conference on Global Research and Education in Engineering
for Sustainable Future, Inter-Academia 2019 (iA-2019), Program and Book of Abstracts, 2019, 5. (4-7September 2019, Budapest and Balatonfüred, Hungary).
{9} V.M. Sklyarchuk, V.A. Gnatyuk, V. Pylypko, T. Aoki, Schottky diode detectors with low leakage current athigh operating voltage, the same as above, 16-17.
{10} J. Nishizawa, H. Nakagawa, V. Gnatyuk, A. Koike, T. Aoki, Impeccable regulated doping of p-n junction
CdTe diode by backside laser doping, 2019 IEEE Nuclear Science Symposium and Medical Imaging
Conference, 26th International Symposium on Room-Temperature Semiconductor X-Ray & Gamma-Ray
Detectors, Abstract Booklet, 2019, Contribution R-10-04, Abstract #2606, 363. (26 October - 2 November 2019,
Manchester, United Kingdom).

{11} V. Gnatyuk, Characterization of Cd1-xZnxTe crystals, modification of their properties by surface processing
and formation of diodes for X/γ-ray detectors, The Seminar at the State Key Laboratory of Solidification
Processing, Northwestern Polytechnical University (NPU), 2019, 1 page abstract. (28 November 2019, Xi'an,
China). (Invited report).
{12} K. Zelenska, Techniques of formation of CdTe-based diode-type for X/γ-ray detectors, the same as above, 1page abstract. (Invited report).
{13} V. Gnatyuk, S. Levytskyi, V. Veleschuk, K. Zelenska, J. Nishizawa, T. Aoki, Development of Cd(Zn)Te-based
X/gamma-ray detectors with high resolution for security and diagnostics instruments, The Annual Meetingof 2019 Cooperative Research on Biomedical Engineering, Book of Abstracts, 2020, Abstract No 1-09. (13March 2020, Tokyo, Japan), in press.

List of Awards
Owing to the results obtained in the frame of the Cooperative Research Project of the Research Center ofBiomedical Engineering (Project No 2022), the Ukrainian leader and participants were awarded by threeresearch grants (international projects were adopted):
A. Short-term Recruitment Program of Foreign Experts in Anhui (APFEP-2019, China). The research topic:“Development of perovskite single crystal X/gamma-ray detectors for environmental radioactive
contamination monitoring”.
B. Program of the Ukraine -The People’s Republic of China scientific and technical collaboration for the periodof 2019-2020 adopted by the Ministry of Science and Technology of The People's Republic of China (Grant
No CU03-15). The research topic: “Exploring novel perovskite single-crystal based gamma-ray detector for
trace environmental radioactivity monitoring”.
C. The Fundamental Research Funds for the Central Universities, (Grant No 3102019ghxm015, 2019-2020,
China). The research topic: “Fabrication and characterization of high energy resolution CdZnTe detectors
for radiation detection applications”.
In the frame of Program (A), the project leader Dr. Volodymyr Gnatyuk and participant Dr. Kateryna
Zelenska were awarded by travel grants to report the project-related results at the seminar in Anhui Institute of
Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences (Hefei, China) in
May 2019 {1, 2}.
In the frame of Program (B), Dr. Volodymyr Gnatyuk was awarded by the two month fellowship (Oct.-Dec.
2019) to implement the project-related results at the institution mentioned above.
In the frame of Program (C), Dr. Volodymyr Gnatyuk and participant Dr. Kateryna Zelenska were awarded bytravel grants to report the project-related results at the seminar at State Key Laboratory of Solidification
Processing, Northwestern Polytechnical University (Xi'an, China) in Nov. 2019 {11, 12}.
Totally, 5 travel grants (in frames of Programs (A-C)) were received to present the project related results.
Registration of research-theme continuation for next year.
Prior consent from the collaboration partner in the Research Center is necessary.

Yes

No

Research plan for the next year (from April 1, 2020 to March 31, 2021), if the collaboration research is continued.
Due to high interest of the scientific community to our research results obtained under implementation of thepresent project (No 2022), that is confirmed by a large number of our publications, presentations (6 articles and
13 abstracts/reports) and received awards (3 research grants (projects) and 5 travel grants) during less than one
year, we have concluded that the investigated research field is very important, the achieved results are interestingand promising, thus the collaborative project work should be undoubtedly continued in the next year.
The project purpose for the next year is development of the laser and ion-plasma techniques for efficientsurface processing of Cd(Zn)Te semiconductor crystals to provide modification of the surface state, formation of
Ohmic and Schottky contacts, doping of a surface layer and creation of a p-n junction, and thus to create room
temperature Cd(Zn)Te-based X/γ-ray detectors with low leakage current, high detection efficiency and energy
resolution, which will be well suitable for using in various security and diagnostic instruments.
Our main idea in the development and fabrication of Cd(Zn)Te-based X/γ-ray detectors, designed as diodestructures, is to overcome the general problem concerning charge losses caused by incomplete collection ofphotogenerated charge carriers. Our brief research plan is the following.

 Theoretical study and computer simulation of the processes which take place under different chemical, laser
and ion-plasma treatments of the surface of Cd(Zn)Te semiconductor crystals.
 Elaboration of efficient chemical-based techniques for preliminary surface processing (cleaning, etching,polishing) of Cd(Zn)Te crystals and surface passivation of the created detector structures.
 Investigation and selection of the most suitable materials (metals, carbon compounds, etc.) for electricalcontacts to Cd(Zn)Te crystals.
 Development of methods of electrical contact formation and electrode deposition techniques to form ahigh-barrier Schottky contact and Ohmic contact on the Cd(Zn)Te crystal surfaces.
 Elaboration of techniques of creation of CdTe p-n junction diode detectors by frontside and backside laser
irradiation doping.
 Development of plasma-assisted techniques of formation of CdTe Schottky-diode detectors in particularusing ion-bombardment etching of the semiconductor surface.
 Fabrication of Cd(Zn)Te Schottky and p-n junction diodes using the developed techniques of semiconductor
surface processing and electrical contact formation.
 Characterization of Cd(Zn)Te diode-type X/γ-ray detectors by measurements of their electrical, photoelectricand spectroscopic properties.
 Simulation of the electronic transport and photogenerated processes in the developed Cd(Zn)Te diodes andevaluation of optimal conditions for detector fabrication.
 Testing of Cd(Zn)Te diode X/γ-ray detectors in devices for detection and identification of ionization sources.
 Application of Cd(Zn)Te X/γ-ray detectors with high energy resolution for security diagnostic instruments.