Fotoenergetikada nanostrukturali yarimo‘tkazgich materiallar II xalqaro ilmiy anjumani

Fotoenergetikada nanostrukturali yarimo‘tkazgich materiallar

II xalqaro ilmiy anjumani 
 
19-20 noyabr 2021 yil 
42 
then re-crystallized by heating up to the growth temperature. The subsequent 
procedure was the growth of a ZnTe epilayer 1.5

3.2 

m thick. The growth rate 
was about 0.6 

m/h. The growth temperatures were ~350 

C for ZnTe and ~300

C 
for Cd
x
Zn
1-
x
Te layers. Three types of structures with QWs were grown: (i) the 
structure consisted of Cd
0.2
Zn
0.8
Te single well of 5 nm width; (ii) three 
Cd
0.3
Zn
0.7
Te QWs of 8 nm, 4 nm and 2 nm widths and (iii) three tunnel-coupled 
Cd
0.2
Zn
0.8
Te QWs of 2 nm width. All the structures were sandwiched between cap 
ZnTe layer 4 nm thick and buffer ZnTe layer 1.5 

m thick. Details of the sample 
growth were described previously [2]. Photoluminescence (PL) was excited with 
the 488.0 nm and 514.5 nm lines of Ar
+
ion laser or the 632.8 nm line of He

Ne 
laser. Luminescence was detected with a photomultiplier tube in the current-flow 
regime using a grating spectrometer MDR-23. The ZnTe-based structures were 
irradiated with 1.8 MeV-energy electrons or X-ray radiation. The electron 
irradiation was performed at a beam current density of 1 

A·cm
-2
up to a dose of 
4·10
16
cm
-3
(the flux was ~6

10
12 
cm
-2
·s
-1
) using an electron accelerator. The X-ray 
irradiation was performed by means of an X-ray RAP 150/300 apparatus with tube 
voltage 
U
= 100 kV (continuous spectrum). The former kind of radiation produced 
Frenkel defects and e-h pairs in ZnTe [3], and X-ray radiation produced e-h pairs 
only. The effect of electron and X-ray irradiation on the low-temperature 
luminescence properties of QWs is shown in Figs.1 and 2. They represent PL 
spectra from a sample with three tunnel-coupled QWs of both the same width (
L
Z 
= 
2 nm) and composition. In the excitonic region of the as-grown sample (Fig.1, 
curve 1) the following lines that are typical of ZnTe epilayer are present: 
I
2
Ga
+ 
I
FX
lh
at 2.3736 eV (522.4 nm) - the line of an exciton bound to a neutral donor 
(probably Ga [4]) that overlaps with the light-hole component of a free exciton 
I
FX
; 
I
1

at 2.37 eV (523.2 nm) - an exciton bound to a complex of As atoms [4-5] or to 
V
Zn
complex [6]; 
I
1
C
at 2.3568 eV (526.13 nm) is ascribed to dislocation- related 
centers. 
At lower energies a sharp peak at 2.3275 eV (532.8 nm) from three Cd
x
Zn
1-
x
Te QWs (
I
QW
) is observed (Fig.2a, curve 1).
As Figs.1 and 2 show, PL intensity after irradiation became somewhat 
lower. Concurrently the 
I
2
Ga
+ 
I
FX
lh
band in the excitonic region of a ZnTe layer 
divided into two components. This was obviously due to a change in the ratio 
between intensities of these components (Fig.1, curve 2). 
Spectral positions of bands of free excitons and those bound to point defects 
shifted to the high-energy region after both types of irradiation. 

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