Relaxation process features of photoconductivity in p-i-n structures
We studied the relaxation processes of photoconductivity in Si(Li) p-i-n structures. It has been shown that a clearly pronounced “well” is observed in time dependences of the photovoltage pulse after photoexcitation of these structures. Our experimental data are indicative of abnormal relaxation...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2010
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| Цитувати: | Relaxation process features of photoconductivity in p-i-n structures / R.A. Mumimov, Sh.K. Kanyazov, A.K. Saymbetov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 3. — С. 259-261. — Бібліогр.: 12 назв. — англ. |
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irk-123456789-1183982017-05-31T03:07:37Z Relaxation process features of photoconductivity in p-i-n structures Mumimov, R.A. Kanyazov, Sh.K. Saymbetov, A.K. We studied the relaxation processes of photoconductivity in Si(Li) p-i-n structures. It has been shown that a clearly pronounced “well” is observed in time dependences of the photovoltage pulse after photoexcitation of these structures. Our experimental data are indicative of abnormal relaxation of photoconductivity in silicon pi-n diodes. 2010 Article Relaxation process features of photoconductivity in p-i-n structures / R.A. Mumimov, Sh.K. Kanyazov, A.K. Saymbetov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 3. — С. 259-261. — Бібліогр.: 12 назв. — англ. 1560-8034 PACS 61.20.Lc, 74.62.Dh http://dspace.nbuv.gov.ua/handle/123456789/118398 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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| description |
We studied the relaxation processes of photoconductivity in Si(Li) p-i-n
structures. It has been shown that a clearly pronounced “well” is observed in time
dependences of the photovoltage pulse after photoexcitation of these structures. Our
experimental data are indicative of abnormal relaxation of photoconductivity in silicon pi-n
diodes. |
| format |
Article |
| author |
Mumimov, R.A. Kanyazov, Sh.K. Saymbetov, A.K. |
| spellingShingle |
Mumimov, R.A. Kanyazov, Sh.K. Saymbetov, A.K. Relaxation process features of photoconductivity in p-i-n structures Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Mumimov, R.A. Kanyazov, Sh.K. Saymbetov, A.K. |
| author_sort |
Mumimov, R.A. |
| title |
Relaxation process features of photoconductivity in p-i-n structures |
| title_short |
Relaxation process features of photoconductivity in p-i-n structures |
| title_full |
Relaxation process features of photoconductivity in p-i-n structures |
| title_fullStr |
Relaxation process features of photoconductivity in p-i-n structures |
| title_full_unstemmed |
Relaxation process features of photoconductivity in p-i-n structures |
| title_sort |
relaxation process features of photoconductivity in p-i-n structures |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2010 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/118398 |
| citation_txt |
Relaxation process features of photoconductivity
in p-i-n structures / R.A. Mumimov, Sh.K. Kanyazov, A.K. Saymbetov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 3. — С. 259-261. — Бібліогр.: 12 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT mumimovra relaxationprocessfeaturesofphotoconductivityinpinstructures AT kanyazovshk relaxationprocessfeaturesofphotoconductivityinpinstructures AT saymbetovak relaxationprocessfeaturesofphotoconductivityinpinstructures |
| first_indexed |
2025-07-08T13:54:13Z |
| last_indexed |
2025-07-08T13:54:13Z |
| _version_ |
1837087175009632256 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 3. P. 259-261.
PACS 61.20.Lc, 74.62.Dh
Relaxation process features of photoconductivity
in p-i-n structures
R.A. Mumimov1, Sh.K. Kanyazov2, A.K. Saymbetov1
1Physical-Technical Institute, 100084 Tashkent, Uzbekistan
E-mail: detector@uzsci.net
2Karakalpak State University, 742012 Nukus, Uzbekistan
Abstract. We studied the relaxation processes of photoconductivity in Si(Li) p-i-n
structures. It has been shown that a clearly pronounced “well” is observed in time
dependences of the photovoltage pulse after photoexcitation of these structures. Our
experimental data are indicative of abnormal relaxation of photoconductivity in silicon p-
i-n diodes.
Keywords: photoconductivity, relaxation, well.
Manuscript received 24.02.10; accepted for publication 08.07.10; published online 30.09.10.
1. Introduction
It is known that the most striking example of the
inhomogeneous field created by a movable space charge
in the semiconductor is the space charge region in p-n,
p-i-n structures of a large size. Studied in [1, 2] was
topography of the photo-emf signal associated with the
heterogeneity of the electric field in the space charge
region in germanium radiation detectors. Silicon p-i-n
radiation detectors were studied using the topography of
the amplitude spectrum by scanning with a collimated
beam of alpha particles [3]. It is important that these
studies enabled to reveal significant inhomogeneous
distribution of impurities in certain local areas. Study of
physical processes in these areas could find unknown
physical processes as a base for new fundamental
functional principles. Consequently, in semiconductor
physics, they can cause a wide interest both of
theoreticians and experimentalists [4, 5].
2. Experimental
In this paper, we consider the relaxation processes for
charge carriers in the space charge region inherent to Si
(Li) p-i-n structures. These structures were fabricated by
us on the base of wafers made of a p-type silicon single
crystal with the diameter 50 mm and thickness 2.5 mm,
as well as initial parameters: resistivity
ρ = 5000 Ohm⋅cm, carrier lifetime τ = 300 μs. After
certain chemical-and-technological operations, lithium
diffusion was made on one of plate sides in vacuum at
T = 450 °C down to the depths 320 to 350 μm. Then, to
compensate the whole thickness of the plate, the drift of
lithium ions was performed over the entire thickness of
it. The drift was carried out in two stages: at T = 80-
100 °C and reverse bias voltage 80 to 120 V and with
increasing the latter up to approximately 300 V at the
same temperatures. The end of the drift was fixed by a
sharp increase in reverse current through the structure
[6, 7]. The plates prepared using the above-mentioned
method were used to measure photoconductivity in their
various parts by probing all over the surface. When
measuring the photoconductivity, we used LED AL-402
(λ = 0.69 μm) with a radiated power close to 5 mW.
Features of the sample photoconductivity were studied
using the relaxation curves both for the rise and decay of
the photovoltage pulse [8].
3. Results and discussion
In separate parts of the investigated samples, the
photoconductivity relaxation curves for the decaying
photovoltage had a clearly pronounced “well”. Fig. 1
shows a typical oscillogram for this type of
photoconductivity relaxation. The time is scaled as
1 ms/10 mm and directed along the abscissa, while the
ordinate corresponds to the voltage scaled as
0.05 V/10 mm.
After reaching the maximum photovoltage value
0.3 V, its drop occurs within 1.025 ms, the relaxation
curve being of a usual form. Then, in 2.1 ms one can
observe the following sharp drop, and the photovoltage
reaches its minimum value equal to 0.05 V. At the
beginning of this drop, the photovoltage value was
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
259
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 3. P. 259-261.
0.12 V. Thus, the slope of the relaxation curve in the
interval 1.025-2.1 ms is –0.065 V/ms, while at the
beginning of the recession in the interval 0-1.025 ms the
slope of the curve was –0.175 V/ms. Consequently, the
slope of the second drop is approximately 3 times less
than that in the first recession. Between the first and
second drops, in the time moment 0.425 ms the
relaxation curve has a minimum slope and can be
considered as nearly parallel to the abscissa.
In 2.1 ms after photoexcitation, the photovoltage is
set at the level 0.05 V. In this point of oscillogram, the
drop is changed by its growth, i.e., the slope of the
curves changes its sign here. Then, in the interval 2.1 to
2.6 ms the photovoltage increases from 0.05 V up to
0.075 V, hence, the slope of the curves reaches
0.05 V/ms. Then again, a slow drop with a slope –
0.006 V/ms takes place. Thus, the relation curve
demonstrates three specific turning points, with one of
them where the drop is changed by a growth [3].
It is known that in presence of trapping levels in
silicon, the photovoltage pulse value is decreased
monotonically during these relaxation processes [9].
Studied in [10] is the influence of the saturation effect
for the electron velocity on switching the n+-p-p+
structure in the quasi-neutral drift mode. It is noted that
the effect of velocity saturation significantly slows down
the passage of the Dean wave [11] of electrons through
the base of n+-p-p+ structure, which causes the sharp
drop. Proposed in [11] mechanism is rather suitable to
explain the appearance of the well in the recession, if we
assume that the band gap of silicon clusters contains
deep recombination centers [12]. Then, the relaxation
time has two components [6]
10
111
τ
+
τ
=
τ
. (1)
Here, τ0 is the relaxation time inherent to p-type
semiconductor in the absence of deep recombination
centers; τ1 – relaxation time when only these centers are
present. Then drop in voltage over time is determined by
the formula
t
st eUU
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
τ
+
τ
−
= 10
11
. (2)
Using the experimental results, we determine the
time dependence. First of all, let us analyze the function
U at the points of extremum, where the first derivative of
U with regard to t is equal to zero. In these points, we
have
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
+
τ
ττ
=⎟
⎠
⎞
⎜
⎝
⎛ τ
1
0
111
it tdt
d
i
. (3)
Here, ti is the value of t when one observes a
minimum of U. The experiment shows that the
functional dependence of U on time t has a three-point
extremal value. This means that the empirical formula U
is a curve of the third power. The equation (3)
determines the conditions where the function U has zero
derivative. Analyzing the various options for empirical
formulas describing the dependence of U on time t, we
have drawn the conclusion that the following formula is
rather convenient for calculations
3
3
2
21ln ⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −
+⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −
+=⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−
k
k
k
k
st t
tt
k
t
tt
ky
U
U . (4)
Here, k2 and k3 depend on the parameters of the
function U at the points of extremum:
3102 kyyk +−= ;
( ) ( )11
10
2
12
3 +
−
−
+
−
=
a
yy
aa
yy
k ;
k
k
t
tt
a
−
= 2 ; ⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
stU
Uy ln .
Then y0 = 0, as in the beginning of recession
U = Ust. We designate ⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
stU
Uy ln1 at t = tk, there tk
corresponds to a voltage minimum and t2 to maximum t.
The initial time is determined in a point of recession,
therefore t1 = 0. At t = t2, one can obtain that k2 and k3
are defined by the formulas
( ) 1
2
2
2
22
2
3
2 y
t
tt
ttt
yt
k k
k
k +
−
−
= ,
( ) 1
2
22
22
3
3 y
t
t
y
ttt
t
k k
k
k −
−
= . (5)
As
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
τ
+
τ
=⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−
10
11ln t
U
U
st
, (6)
it follows from (4) that
3
3
2
21
10
11
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −
+⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −
+=⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
τ
+
τ k
k
k
k
t
ttk
t
ttkyt . (7)
Fig. 1. A relaxation of photoconductivity of p-i-n structures,
у = 0.05 V/10 mm, х = 1 ms/10 mm.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
260
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 3. P. 259-261.
Fig. 2. Graphic dependence of time of a relaxation.
The graphic plot of τ1 versus time is shown in
Fig. 2.
As seen, in the process of approach to the abscissa
the pulse photovoltage value takes its minimum, time of
relaxation starts to decrease, when the speed of reduction
in τ1 value with time up to the certain value determined
using the formula (3) reaches its minimal value. Here, τ1
begins to increase up to a certain maximum, after that one
can observe a quasi-stationary value of the relaxation
time. As it was noted above, the account of trapping levels
does not give extreme points in the range of recession in
the pulse photovoltage value [9]. More exact calculation
of dynamic characteristics n+-p-p+ structures, by means of
Dean waves for electrons gives monotonic recession of a
photovoltage on time, too [10]. However, to ascertain the
specific nature of defects causing this non-monotonic drop
in conductivity inherent to p-i-n diodes, additional
investigations are necessary.
4. Conclusions
Thus, our experimental data are indicative of abnormal
relaxation of photoconductivity in silicon p-i-n diodes.
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© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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