ISSN:
2181-3906
2024
International scientific journal
«MODERN SCIENCE АND RESEARCH»
VOLUME 3 / ISSUE 5 / UIF:8.2 / MODERNSCIENCE.UZ
1471
RADIATION DEFECTS IN CDZNTE/ZNTE QUANTUM STRUCTURES
Shamuratova A.
Sharibaev M.B.,
Karakalpak State University named after Berdakh (Nukus., Uzbekistan)
Qalandarova Sh.
Nukus State Pedagogical Institute named after Azhiniyaz (Nukus, Uzbekistan)
https://doi.org/10.5281/zenodo.11401847
Abstract.
Optical studies of ZnCdSe/ZnSe, ZnCdTe/ZnTe heterostructures with singular
and multiple quantum wells and quantum dots arouse interest in connection with investigation of
the hot carriers relaxation generated by electron injection or optical excitation. Multi-phonon
relaxation of the hot electrons under optical excitation of the quantum-size ZnCdSe/ZnSe
heterostructures had been considered before using photoluminescence and Raman scattering [1].
Ключевые слова:
гетероструктуры, теллурид кадмия, квантовые ямы, облучение.
РАДИАЦИОННЫЕ ДЕФЕКТЫ В КВАНТОВЫХ СТРУКТУРАХ CDZNTE/ZNTE
Аннотация.
Оптические исследования гетероструктур ZnCdSe/ZnSe, ZnCdTe/ZnTe
с сингулярными и множественными квантовыми ямами и квантовыми точками вызывают
интерес в связи с исследованием релаксации горячих носителей заряда, генерируемых
инжекцией электронов или оптическим возбуждением. Многофононная релаксация горячих
электронов при оптическом возбуждении квантоворазмерных гетероструктур
ZnCdSe/ZnSe рассматривалась еще до использования фотолюминесценции и
комбинационного рассеяния света [1].
Ключевые слова:
гетероструктуры, теллурид кадмия, квантовые ямы, облучение.
Experiment
A series of
n
narrow and rather intensive peaks in exciton band of the quantum-size
ZnCdTe/ZnTe heterostructures low-temperature photoluminescence spectra, superimposed on the
main photoluminescence hump, had been observed. These peaks are shifted relatively to excitation
photon energy on a value, which is multiple to energy of LO-phonon.
Changes of the quantum-size ZnCdTe/ZnTe heterostructures optical properties after b- and
X-ray irradiation had been studied using low-temperature photoluminescence technique [2]. These
optical data allows to derive additional information about well shape transformation and stress
relaxation after radiation treatment. This rearrangement of the heterostructure is caused with
radiation-stimulated inter-diffusion of the semiconductor compound components and it leads to
noticeable alteration of the multi-phonon relaxation processes.
Undoped CdZnTe/ZnTe structures had been grown by molecular-bean epitaxy.
Amorphous ZnTe was deposited on a (100) semi-insulating GaAs wafers with subsequent soild-
phase crystallization of this seeding coat and epitaxial growth of 1,5 m ZnTe buffer epitaxial
layer on the initial nucleation bed [3]. After this operation Cd
X
Zn
1-X
Te quantum well and tunnel
transparent ZnTe barriers had been composed. Cd content in the quantum wells was controlled
using low-temperature luminescence and reflectance spectra (see Table 1).
Table 1
ISSN:
2181-3906
2024
International scientific journal
«MODERN SCIENCE АND RESEARCH»
VOLUME 3 / ISSUE 5 / UIF:8.2 / MODERNSCIENCE.UZ
1472
№
Quantum wells
Treatment
Deformation ε
(4,2К)
Cd
0.17
Zn
0.83
Te
L
z1
=L
z2
=L
z3
=2
nm
L
B
=2 nm
Initial samples without
radiation treatment
~6,4·10
-4
2
Cd
0.17
Zn
0.83
Te
L
z1
=L
z2
=L
z3
=2
nm
L
B
=2 nm
E
=1.8 MeV
I
=1 mA·cm
-2
F
=6·10
12
cm
-2
·s
-1
D
=4·10
16
cm
-3
~5.0·10
-4
3
Cd
0.17
Zn
0.83
Te
L
z1
=L
z2
=L
z3
=2
nm
L
B
mn
X-ray irradiation
U
=100 kV
F
~10 cm
-2
·s
-1
D
·10
4
rad
·10
-4
E
- electron energy,
I
- current density,
F
- flux density,
D
- absorbed dose
Photoluminescence and reflectance (R(λ)) spectra measurements was made at 4,2 and 80
K using 0,5 meV resolution spectrometer and LGN-503 laser with
1
= 0.5145 and
2
= 0.4880
mkm for excitation. Photoluminescence spectra for initial and irradiated Cd
0.17
Zn
0.83
Te/ZnTe
structures with quantum wells are shown in the Fig.1 [4].
Fig.1.
All the presented spectra were studied using exitation light
EXC
= 0.51453 мкм. Energy
(
E
g
= 1.60 эВ, 4.2 К) and well-localised electron-hole pair recombination energy. The spectrum
consists of few stripes in exciton band from bufer ZnTe epitaxial layer and dominating peaks from
quantum wells, I
QW
.
Photoluminescence spectra was measured using excitation light with 0.51453 mkm
wavelength, so E
ext
> E
g
ZnTe
(2.39 ev, 4.2 K)> E
g
CdTe
(1.60 ev, 4.2 K) and exceeds quantum-well
localised electron-hole pair recombination energy. There are few stripes in exciton band of the
ISSN:
2181-3906
2024
International scientific journal
«MODERN SCIENCE АND RESEARCH»
VOLUME 3 / ISSUE 5 / UIF:8.2 / MODERNSCIENCE.UZ
1473
low-temperature photoluminescence spectra, from the ZnTe buffer layer, accompanied with
intense quantum-well photolumiescence peaks [5].
There was irregular peak intensity increasing as it comes near resonance stripes (I
QW
, I
C
).
Inter-peak interval was independent from excitation light wavelength and was equal to ~ 210 cm
-
1
. Measured energeis of the LO-phonon for ZnTe and CdTe bulk crystals were ~208 cm
-1
and ~169
cm
-1
respectively. Consequently, observed phonon repetitions correspond to LO-phonon of the
ZnTe barrier[6].
Discussion
The resonance amplification of the narrow stripes intensity in a quantum wells shine being
observed in quantum-size CdZnSe/ZnSe heterostructures [7] could be interpreted using a model
from [8]. In obedience to this "cascade model" light-induced hot electrons can relax with sequential
phonon emission. In our work an optical phonon frequency of the CdZnTe/ZnTe quantum-sized
structures had been shifted into a biggest frequency range in a comparison with LO-phonon value
for bulk mono-crystalline ZnTe.
Using constant optical excitation level (P
exc
= 1 10
19
quanta/cm
2
sec) and
EXC
= 0.5145
mm) we revealed that resonance gain of the LO-phonon intensification on the resonance stripes
persists in the samples with three tunnel-coupled quantum wells after high energy electrons
treatment as well as after X-ray irradiation, despite different nature of the radiation impact for X-
ray (excitation of the electron subsystem only) and for the -irradiation (creation of the intrinsic
defects also [2]).
For the -irradiated samples (curve 2) there was excessive single-order increasing of the
resonance LO-phonon peak intensity(
n
=3, =207 cm
-1
).
For the X-ray irradiated samples (curve 3) there was inessential raise of the resonance LO-
phonon peak intensity (
n
=3) and a frequency had been diminished against initial sample.
Earlier a shift of the photoluminescence peak into big energies from a quantum well (so
called "blue shift" [9]) for the same heterostructures after -irradiation had been found. This dose-
dependent shift was of 1 meV for the irradiation dose 4 10
16
cm
-3
. Numerical calculation [9]
indicated that such a displacement of the photoluminescence maximum could be provided with
well shape transformation due to radiation-induced diffusion of cadmium atoms and compound
variation of a well's brink. From the one hand, there are conditions for the perfect congruence of
the resonance and LO-phonon (
n
=3); from the other hand, the well smoothing reduces electron
localization inside the well, making energy transfer between hot electrons in a quantum well and
LO-phonons of the barrier layers easier.
Reduction of the edge photoluminescence from the barrier and buffer layers due to
radiation-induced traps generation in ZnSe and increasing of nonradiative recombination makes
an observation of this effect more clear.
Optical phonon energy shift indicates stress changes in ZnTe buffer layer on a ~1 10
-5
.
This disparity with other optical data regarding mechanical stresses in the heterostructures should
be studied later.
There was negligible low-temperature luminescence peak shift to lower energies (red shift)
after X-ray treatment of the samples. This shift was equal 0 0.5 meV for the dose ~10
4
Rad.
Notwithstanding this shift of the photoluminescence spectrum maximum couldn't be explained
ISSN:
2181-3906
2024
International scientific journal
«MODERN SCIENCE АND RESEARCH»
VOLUME 3 / ISSUE 5 / UIF:8.2 / MODERNSCIENCE.UZ
1474
with a smoothing of the quantum well shape, we suppose an influence of the stress reduction in
the barrier layer. Optical phonon energy shift also indicates a variation of the deformation of the
epitaxial structure.
Conclusion
Hereby, possibility of the multi-phonon relaxation of the hot electrons generated by optical
excitation by dint of energy exchange with barrier layer and LO-phonon emission in quantum-size
CdZnTe/ZnTe heterostructures had been demonstrated (cascade process). Exploration of the
electron and X-ray irradiated samples, which subsurface region, barrier layer and shape of the
quantum well was transformed after radiation treatment, accentuates dominant factors of this
optical process. These factors are localization extent of an exciton as well as resonance between
the incident light frequency and fundamental transition in the quantum well.
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