P-46

Cd(Zn)Te semiconductor-based diodes for detection of Xand gamma-ray photons with high energy resolution andimaging formation[1] Organization
Project Leader: Volodymyr Gnatyuk, Ph.D.,
Assoc. Prof., Senior scientist (V.E.
Lashkaryov Institute of Semiconductor
Physics of the National Academy ofSciences of Ukraine, Kyiv, Ukraine)
Representative at RIE: Toru Aoki, Ph.D., Prof.)
Research Institute of Electronics, Shizuoka
University, Japan).
Participants:
Oleksandr Vlasenko (Dr., Prof., Head oflaboratory (V.E. Lashkaryov Institute ofSemiconductor Physics of the National
Academy of Sciences of Ukraine, Ukraine).
Sergiy Levytskyi, M.Sci., Junior researchscientist (V.E. Lashkaryov Institute ofSemiconductor Physics of the National
Academy of Sciences of Ukraine, Ukraine).
Kateryna Zelenska, M.Sci., Engineer (TarasShevchenko National University of Kyiv,Ukraine).

 Dr. V. Gnatyuk was a member of theInternational Committee, and Prof. T. Aoki andMs. K. Zelenska were members of theOrganizing Committee of The 16th Intern.
Young Scientists Conf. “Optics & HighTechnology Material Science” SPO 2015 heldat the Faculty of Physics of Taras Shevchenko
National University of Kyiv (22-25 Oct. 2015,Kyiv, Ukraine).
 Dr. V. Gnatyuk presented the project-related
results at The 14th Intern. Conf. on Global
Research & Education: Inter-Academia-2015)
held at Shizuoka University (28-30 Sep. 2015,Hamamatsu, Japan).
 Prof. T. Aoki and his students presented theproject-related results at The 16th Intern. Young
Scientists Conf. “Optics & High Technology
Material Science” SPO 2015 held at the Facultyof Physics of Taras Shevchenko National
University of Kyiv (22-25 Oct. 2015, Kyiv,Ukraine).

[2] Progress of Scientific Activity
The CRP participants actively collaborated
through electronic media and face-to-face at themeetings when Prof. Toru Aoki and hisstudents visited Ukraine in Sep. and Oct., inparticular to attend The 12th Intern. Conf. onCorrelation Optics and The 16th Intern. Young
Scientists Conf. “Optics & High Technology
Material Science” SPO-2015, respectively, andwhen the Ukrainian scientists (V.G. and K.Z.)
visited Hamamatsu in Sep. (14th Intern. Conf.
on Global Research & Education: InterAcademia-2015) and Nov.-Jan. 2016 (researchvisits owing to CRP). They reported achieved
results, exchanged ideas about join work inframes of cooperative projects, and discussed
further cooperation between the institutions.
Apart from achieving the research results,
described in the next section, the CRP teammembers were involved in the organization ofseveralinternational
scientificforums,
workshops and meetings in Ukraine to discuss
the work concerning the project topics andgeneral cooperation.

[3] Research Results
The main purpose of the project is thedevelopment of effective techniques andtechnological procedures for creation ofCd(Zn)Te-based X/gamma-ray detectors, whichallow us to design various devices for imaging
formation with high energy resolution andstable electrical and spectral characteristics.
Nowadays, the bottleneck in manufacturing
Cd(Zn)Te-based detectors is pre-treatment of
the crystal surface and formation of electricalcontacts with desired and predicted properties.
Therefore, the main attention in our projectwork was devoted to the elaboration of efficientmethods and techniques of surface processingof Cd(Zn)Te crystals, including chemical
etching, thermal annealing and laser irradiation,
to obtain the surface states with thecorresponding band bending or a thin surface
layer with the modified structure and electricalparameters (including doping layer), and finallyto form Ohmic or barrier contacts using
differentelectrodemetals,
deposition
procedures and following treatments [1-14].

Water output Water input

Laser radiation pulse

Laser Cooling System
Optics Mountwith Quick Release
Mounting Carriage
Neutral density
Water cooling of laser
FGL850
optical filters
Colored Glass Filter,
800-2600 nm
Mirror
850 nmwith dielectric multilayer coating
Right-Angle Prism
Laser
st harmonic,
1
YAG:Nd1064 nm
2nd harmonic,
532 nmLaser Controler

Beam Dump

1st harmonic,
1064 nm, 8 nsLens Mountwith Retaining Ring

DGUV10-1500
Silica Ground Glass Diffuser

SampleGlass container with water

Fig. 1. Experimental setup of the optical equipments for irradiation and laser-induced doping of CdTe samples inwater with YAG:Nd laser pulses (λ = 1064 µ, τ = 8 ns ). The insert schematically shows laser-stimulated thermaland stress processes (a) and doping of a thin CdTe layer near the CdTe-metal interface with In or Al atoms (b).

The I-V characteristics of the In/CdTe/Audiodes showed that multiple laser irradiationincreased forward current and decreased reverse
one (Fig. 2). Extreme conditions in the confinedarea at the CdTe-In interface under irradiation
resulted in formation a heavily doped CdTelayer and a high barrier p-n junction [7, 8].

(a)

(b)

I, µA

We have suggested the principally optimized
technique of the laser-induced doping of a thinlayer of CdTe crystals and formation of a builtin p-n junction by irradiation of the CdTe-metal
structure from the CdTe side with YAG:Ndlaser pulses (λ = 1064 nm, τ = 8 ns) [1, 2, 7, 8,11, 14]. The experimental setup for laser
treatment has been designed (Fig. 1).
A relatively thick (0.1-2 µm) dopant metal
film was deposited in vacuum on the p-like
CdTe(111)B crystal surface. The whole area ofthe sample was irradiated from the CdTe side indistilled water. CdTe is transparent for this laser
wavelength and it was possible to irradiate theCdTe-metal structure through the CdTe bulkand directly affect the interface (Fig. 1, insert).
In or Al was used as a doping source and themetal film also served as an electrode. An Au
electrode was evaporated on the opposite sideof the sample, i.e. on the CdTe(111)A surface.

V, VFig. 2. I-V characteristics of the In/CdTe/Au diodebefore (1) and after (2 and 3) laser irradiation by 10
pulses with intensity F = 5.3 MW/cm2 (2) and by 50
pulses with F = 1.8 MW/cm2.

Fig. 3. Time dependences of the temperature at thefront (1) and back surface (2) of the In (a) and Al (b)film deposited on the CdTe crystal. The simulated
laser pulse and metal melting points are shown bydashed orange curve and red (a) and green (b) lines.

The computer simulation of laser heating
and temperature calculations were performed tochoose the optimal regimes for achieving theeffective doping of thin and thicker CdTe layers
under laser irradiation of the CdTe-In andCdTe-Al interfaces through the CdTe bulk [2, 8,14]. The calculation was based on the thermal
conduction equation and it was performed forthe three-layer structures of CdTe-In-Water andCdTe-Al-Water. Water and CdTe wereassumed as transparent media for the chosen
laser wavelength (λ = 1064 nm) and radiation
was absorbed only by a thin metal layer
adjoining to the CdTe. Temperature
distributions inside all the layers were obtainedfor different laser intensities and metal film
thicknesses. The calculated time dependencesof the temperature in the CdTe-In-Water andCdTe-Al-Water structures are shown in Fig.
3(a) and (b), respectively. The results were usedto find the optimal laser irradiation regimes foreffective doping of thin or thicker CdTe layers.
The obtained In/CdTe/Au detectors weretested by radioisotope spectra measurements
and demonstrated high sensitivity to X/gammarays and satisfactory energy resolution [14].
[4] Publications (published and submitted by
the CRP participants during the project
period 29.05.2015-06.03.2016)
1.

2.

3.

4.

5.

K.S. Zelenska,
D.V. Gnatyuk,
T. Aoki,
Modification of the CdTe-In interface byirradiation with nanosecond laser pulses throughthe CdTe crystal, Program & Technical Digest,
LAPM2015 - The 7th Intern. Congress on Laser
Advanced Materials Processing, 2015, Th2-LO16, 184. (26-29 May 2015, Kitatyushu, Japan).
K.S. Zelenska,
D.V. Gnatyuk,T. Aoki,
Modification of the CdTe-In interface byirradiation with nanosecond laser pulses throughthe CdTe crystal, Proceed. of LAMP2015 - the7th Intern. Congress on Laser Advanced
Materials Processing, (2015) 5 pages.
A.I. Vlasenko,
V.P. Veleshchuk, V.A. Gnatyuk, S.N. Levitskii,
Z.K. Vlasenko, G.D. Ivlev, E.I. Gatskevich,
Acoustic response to the action of nanosecond
laser pulses on an In/CdTe thin-film
heterostructure, Physics of the Solid State, 57(6),(2015) 1089-1094.
V.A. Gnatyuk, O.I. Vlasenko, S.N. Levytskyi,
T. Aoki, Laser-induced modification ofproperties of CdZnTe crystals, Advanced
Materials Research, 1117, (2015) 15-18.
D.V. Gnatyuk,T. Ito,
T. Aoki,Photoluminescence spectra of CdTe single crystals
subjected to nanosecond laser irradiation,

Advanced Materials Research, 1117, (2015)
102-106.
6. V.A. Gnatyuk, O.I. Vlasenko, S.N. Levytskyi, T. Aoki, Photoconductivity of CdTe-based
semiconductor solid solutions subjected to laser
irradiation, The 14th Intern. Conf. on Global
Research and Education: Inter-Academia 2015,Extended Abstract Digest, 2015, 220-221. (2830 Sep. 2015, Hamamatsu, Japan).
7. D.V. Gnatyuk, T. Aoki, Mechanism of laserinduced doping under direct irradiation ofCdTe-In interface through the CdTe crystals,
The 14th Intern. Conf. on Global Research andEducation: Inter-Academia 2015, Extended
Abstract Digest, 2015, 166-167. (28-30 Sep.
2015, Hamamatsu, Japan).
8. K.S. Zelenska,D.V. Gnatyuk,
T. Aoki,
Modification of the CdTe-In interface byirradiation with nanosecond laser pulses throughthe CdTe crystal, Journal of Laser
Micro/Nanoengineering, 10(3), (2015) 298-303.
9. V.A. Gnatyuk, O.I. Vlasenko, S.N. Levytskyi, T. Aoki, Modification of the surface state ofCdZnTe crystals and contact formation, The
22nd Intern. Symp. on Room-Temperature
Semiconductor X-Ray and Gamma-Ray
Detectors, 2015NSS/MIC/RTSD, Conf. Program
Book, 2015, Abstract R3A-40. (31 Oct. - 7 Nov.
2015, San Diego, CA, USA).
10. D.V. Gnatyuk, T. Ito, T. Aoki, Photoluminescence of the CdTe single crystal surface layer
after nanosecond laser irradiation, The 22ndIntern.
Symp.
onRoom-Temperature
Semiconductor X-Ray and Gamma-RayDetectors, 2015NSS/MIC/RTSD, Conf. Program
Book, 2015, Abstract R3A-51. (31 Oct. - 7 Nov.
2015, San Diego, CA, USA).
11. K.S. Zelenska,
D.V. Gnatyuk,
T. Aoki,Formation of diode detectors by laser irradiationof CdTe-In interface from the semiconductorside, The 22nd Intern. Symp. on RoomTemperature Semiconductor X-Ray andGamma-Ray Detectors, 2015NSS/MIC/RTSD,
Conf. Program Book, 2015, Abstract R3A-52.
(31 Oct. - 7 Nov. 2015, San Diego, CA, USA).
12. V.A. Gnatyuk, O.I. Vlasenko, S.N. Levytskyi, T. Aoki, Modification of the surface state ofCdZnTe crystals and contact formation, 2015
Nuclear Science Symposium and MedicalImaging
Conference
Record(2015NSS/MIC/RTSD), (2015), in press.
13. D.V. Gnatyuk, T. Ito, T. Aoki, Photoluminescence of the CdTe single crystal surface layer
after nanosecond laser irradiation, 2015 Nuclear
Science Symposium and Medical Imaging
Conference Record (2015NSS/MIC/RTSD),(2015), in press.
14. K.S. Zelenska,
D.V. Gnatyuk,
T. Aoki,Formation of diode detectors by laser irradiationof CdTe-In interface from the semiconductorside, 2015 Nuclear Science Symposium andMedicalImaging
ConferenceRecord

(2015NSS/MIC/RTSD), (2015), in press.

Traveling Report
Name:
Affiliation and address:

Period of time:
Destination:
Purpose:Name of receiver:

Volodymyr Gnatyuk
V.E. Lashkaryov Institute of Semiconductor Physics of the National
Academy of Sciences of Ukraine, Prospekt Nauky 41, Kyiv 03028,Ukraine
15 November 2015 – 13 January 2016
Research Institute of Electronics, Shizuoka University
Preparation of the experimental setup and carrying out experiments onelaboration of novel methods and techniques of fabrication of effective
uncooled Cd(Zn)Te semiconductor-based X/gamma-ray detectors.
Participation in scientific forums and meetings at Research Institute ofElectronics, Shizuoka University during the staying period. Educational
activity with students of the laboratory headed by Prof. Toru Aoki.
Prof. Toru Aoki