This document summarizes research on the effects of thermal annealing on the spectral responsivity and specific detectivity of Al/NiO/PSi/Si/Al photodetectors. NiO nanoparticles were deposited on porous silicon (PSi) substrates via drop casting and annealed at 250°C and 500°C. X-ray diffraction analysis showed the NiO formed a cubic crystal structure. Annealing increased the NiO grain size and decreased the bandgap. Atomic force microscopy images showed annealed films had larger, more homogeneous grains. Photoluminescence measurements demonstrated light emission from the PSi layer. The spectral responsivity and specific detectivity of the photodetectors increased after annealing, indicating improved performance of

1. International Journal of Advanced Science and Technology
Vol. 29, No. 5, (2020), pp. 5438 - 5447
5438ISSN: 2005-4238 IJAST
Copyright ⓒ 2020 SERSC
Thermal Annealing Influence on Spectral Responsively and Specific
Detectivity for Al/NiO/PSi/Si/Al Photodetectors
Muhammid H. AL-Baghdadi1
Esraa H. Hadi2
Hiba Noori Thakir3
Nadir F. Habubi2*
1
Physics Department/ College of Education for pure science/ Kerbala University/ Iraq
2
Physics Department/ College of Education/ Mustansiriyah University/ Iraq
3
Ministry of education /Baghdad/Iraq
*
Corresponding author E-mail: nadirfadhil@uomustansiriyah.edu.iq
Abstract:
Al/p-NiO/PSi/n-Si/Al sandwich structure was synthesis and studied utilizing drop casting method DCM . NiO NPs
subjected to thermal annealing at (250 and 500)°C, NiO thin films show a decreases in the energy bandgap from 3.5eV
to2.9eV, which was calculated from optical properties. AFM images of NiO films confirm a ball-shape with perfect
homogeneity, the measurements of XRD revealed that NiO were cubic crystal structure, the spectral responsivity and
specific detectivity of photodetector after annealing showed an increasing and enhancing in characterization of porous
silicon in response.
Keywords: Nickel oxide, Thermal annealing, Photodetector, Structure, Optical.
1. Introduction:
There is a contrast between conventional semiconductors and the functions of semiconductor
junctions, which was somewhat limited, although the optical transparency and chemical sensing are
unique functions of semiconductors and excellent stability in photovoltaic [1]. To take advantage of
full potential of semiconductors from oxide, for electronic applications the composition of two
types: P-type semiconductors and Ni oxidation as semi-conductive type is used, such as optical
diodes, transistors, rectification of diodes and optical detectors [2–6]. Therefore, the produce of
semiconductors that depends on type p-oxide poses a major challenge when the formation of p-n
intersections. Although the mechanism of conducting for NiO thin film that is from a long time
been the subject of much argument, the increasing of Ni3+
ions will lead to decrease the resistivity
for NiO film, which is due to the overflow oxygen in the NiO crystallite. Recently, there are some
reports were written related to NiO as well as for oxide-based heterojunction with characteristics of
rectifying and photon sensing [5-7]. These innovative applications and materials and have pushed
steadily the forward of oxide-based semiconductors. In this paper, the p-n heterojunction diodes which
based on nickel oxide NiO/porous silicon were fabricated. The characteristics of p-n heterojunction diodes at
different thermal annealing are exhibited by I-V curves.
2-Experimental works:
The nickel oxide solution was prepared from NiNO3 using a chemical method. Two different
bathroom combinations were used. The first is the preparation of pure nickel oxide solution which
is achieved by dissolving 5g of NiNO3 in 50ml of water and 1M of NaOH. They were mixed slowly

2. International Journal of Advanced Science and Technology
Vol. 29, No. 5, (2020), pp. 5438 - 5447
5439ISSN: 2005-4238 IJAST
Copyright ⓒ 2020 SERSC
for 60minutes using a stirrer magnetic device, then get a pure homogeneous solution, we get the
green solution. The TEM (type CM10 pw6020, Philips-Germany) image for NiO nanoparticles is
shown in figure (1) is well-defined spherical nanoparticles with average particle size about 20nm.
Fig. 1: TEM image of NiO Colloidal suspensions.
A 100μl of NiO colloidal solution and drop it onto the substrate (glass and porous silicon) using a
circulating device, an electric oven was used to dry substrate at 80°C for 5min to take out the
solvent (water). Figure (2) shows SEM (Jeol JSM-6335F) image for NiO thin film prepared at room
temperature. The morphology of these NPs consists of many small irregular nanoparticles, which is
meant not uniform, as stars with 100 to 120nm average size ranging.
Fig.2:SEM image for NiO Nanocrystalline thin film deposited at room temperature.
Finally, the samples were annealed by (250 and 500)o
C for 1hr to reduce the crystal defects and
increasing the conductivity of the samples.

3. International Journal of Advanced Science and Technology
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5440ISSN: 2005-4238 IJAST
Copyright ⓒ 2020 SERSC
Crystalline of n-type Silicon wafer is used as a substrate which has (2-20)Ω.cm resistivity, (100)
orientation and 508 µm thickness. The substrate has (2.0×2.0)cm. Photoelectrochemical etching
PEC was performed in solution (1:1) HF(47%)-Ethanol (99.99) which are mixture at normal
environment (room temperature) and using an (Au) electrode as shown in figure (3). To produce an
etched area of sample around (0.785cm2
) a current density (20mA/cm2
) was applied for 15min
using.
Fig. 3 :The photographic image for PEC system.
The X-ray diffractometer device (XRD-6000, Shimadzu) was examined the structure and crystalline
of deposited films. To study morphology films, an Atomic Force Microscope (AFM) (AA
3000scanning probe microscope) was used. The (CARY 100 CONC plus UV-Vis-NIR, Split- beam
Optics, Dual detectors) spectrophotometer device was examined the optical properties which
equipped with a xenon lamp at a wavelength range at (300-900nm). Photoluminescence (PL) is an
important physical phenomenon which used to characterize porous silicon, it depicts energy
structure of samples to reveal other important material properties. The samples transition energy is
measured via (ELICO, SL174, SPECTROFLUORO-METER, Xe LAMP POWER SUPPLY). A
double-beam UIR-210A spectrophotometer device is used to measure the spectral responsivity
which operated through the range (200-1000)nm of wavelengths. A 8010 DMM Fluke digital
multimeter device is used to measure the current. By using the following equation, the spectral
responsivity is calculated [8]:
𝑅() =
𝐼 𝑝ℎ
𝑝𝑖𝑛
(1)
Where pin is the input power and Iph is the photocurrent. The important function, which used to
know how match signal of detector will be available when used them in some application is
spectral responsivity [8].
The symbol D* represents detectivity, which defined as the squared value of NEP and declare as D-
star:
𝐷∗
= 𝑅
𝐴1/2
.  𝑓1/2
𝐼 𝑛
( 2 )
𝐼 𝑛 = √2𝑞𝐼 𝑑 √ 𝑓 ( 3 )

4. International Journal of Advanced Science and Technology
Vol. 29, No. 5, (2020), pp. 5438 - 5447
5441ISSN: 2005-4238 IJAST
Copyright ⓒ 2020 SERSC
Where Δ is the noise bandwidth. D* is a parameter that is independent on the area of detector. The
intrinsic quality of detector material itself was examined by finding the directivity. When an optical
detector D* value is measured (with a system in which the AC signal is produced by using
modulated incident light or chopped at a frequency ). Then with an amplification bandwidth Δ, it
is amplified. There are some quantities must be specified as: the frequency at which the
measurement is made, the bandwidth and the dependence of D* on the wavelength λ are expressed
by the notation D* (f, ΔF , λ). The bandwidth has a reference value which is often 1Hz. The units of
D* (λ, , ΔF) indicate that the detector can be detecting weak signals even the noise is presence or
not [9,10].
3. Results and discussion
The XRD patterns for NiO films which deposited at a substrate of glass and annealing (250 and 500)o
C are
shown in Figure (4), and thicknesses about 200nm. The films were found to be polycrystalline with the
diffraction peak along (200) and (012) planes for cubic NiO phase (JCPOS 047- 1049). Also, single peak
along (012) Plane has appeared when the thin film was annealed at 500o
C temperature.
Fig.4: The peaks appear by XRD patterns of prepared films.
By using the Scherrer′s equation the crystallite size was determined for prepared samples as follows
[11].
𝐷 =
0.9 
𝛽 𝐶𝑂𝑆 (𝜃)
… … … … … … . . (4)
Where 𝜃 refer to the Braggs angle (in radians), D to the crystal size, λ to the wavelength of X-ray
and β to the full width at half maximum for the peak (in radians), by using the following relations
[11] the microstrain value ‘η’ and the dislocation density ‘δ’ was estimated and the values are listed
in table (1).
0
100
200
300
400
500
600
700
20 30 40 50 60 70 80
Intensity(a.u.)
2 Theta (deg)
250 C
500 C

5. International Journal of Advanced Science and Technology
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5442ISSN: 2005-4238 IJAST
Copyright ⓒ 2020 SERSC
η=
𝛽 𝐶𝑂𝑆 (𝜃)
4
… … … … … …… (5)
Table 1: Parameters of all prepared films structural
Annealing temperature 2 (deg) β (deg) D (nm) η x10-4 lines-2/m4
500 0C
29.28 0.86 09.46 36.62
31.79 0.715 11.49 30.14
250 0C 31.77 0.1893 43.40 7.98
The NiO tin film which prepared and annealed at 250o
C have ball-shape with good dispensability,
homogenous grains and aligned vertically are agglomerated to form larger particles (52nm). The
average grain size with 500o
C increases to reach 97nm.
Fig. 5: 2D AFM image and the distribution of Granularity accumulation chart for NiO thin
films.
2 (deg)β (deg)2 (rad)β (rad)D (nm)δ E14 µ m-2
η E-4 lines-2
/m4
31.77290.18930.278710.00332143.408855.3069317.982243
Figure (6) shows the relationship between the optical absorption as a function of wavelength. A
maximum absorption spectrum is observed for NiO thin films of temperatures at 200°C and 500°C.
250 C
500 C

6. International Journal of Advanced Science and Technology
Vol. 29, No. 5, (2020), pp. 5438 - 5447
5443ISSN: 2005-4238 IJAST
Copyright ⓒ 2020 SERSC
The thin films were prepared by deposit it on a substrate of glass by using a drop casting
techniques, UV-regain, the absorption is sharply decreasing towards NIR region because particle
size has wide absorbed.
Fig .6: The absorption spectra for NiO thin films.
Figure (7) shows that the plotting between the square value of (αhv) versus photon energy hv ,can
use to measure the bandgap of NiO thin films, where α is the absorption coefficient. By
extrapolating the tangent for those two curves to cross the axis of photon energy, it was found to be
(2.9 and 3.5)eV for NiO thin films annealed at 250O
C and 500O
C respectively, these values are
because of the density of state variation with the level of energy and the structure of energy band.
Fig.7: The relationship between (αhν)2 versus optical energy gap for NiO thin films.
Figure (8) shows X-ray diffraction for n-Si, which observed a sharp peak at diffraction angle 69.92o
and reflecting plane (211) of cubic structure n-Si, according to (1997 JCPDS 17-0901), which
approved the c-Si has single crystal structure. Figure (2-b) shows the X-ray diffraction for p-PSi
sample that etching at 20mA/cm2
current density during 15min etching time.
0.1
0.15
0.2
0.25
0.3
0.35
300 400 500 600 700 800 900
Apsorption
Wavelength (nm)
250 C
500 C
0
50
100
150
200
250
300
350
0 1 2 3 4 5
(αhv)2(eV/cm)2x1012
photon energy (eV)
250 C
500 C

7. International Journal of Advanced Science and Technology
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5444ISSN: 2005-4238 IJAST
Copyright ⓒ 2020 SERSC
Fig. 8 : XRD spectra for n-PSi sample at 15min etching time and 20mA/cm2etching current
density.
Figure (9) displays 2D AFM image as well as the graph of granularity accumulation distribution for
etched n-Si.
The average pore diameter, root mean square, roughness average and ten points height, which
found to have values about 55nm, 2.13nm and 4.1nm respectively. The pore type from 2D AFM
image was found to be mesoporous.
Fig. 9 : displays 2D AFM and the graph of granularity accumulation distribution for etched n-Si.
Characteristics of visible photoluminescence (PL) in porous silicon layers (PSLs) have given
important impulses to material studies due to the vast possibilities for technological application. The
studies of PSLs have aimed at greater stability in PL over long periods of time. Initial research into
PSLs is directed mainly at establishing the origin of radiative recombination mechanisms. Figure
0
50
100
150
200
250
20 30 40 50 60 70 80
Intensity(a.u.)
2 Theta (deg)

8. International Journal of Advanced Science and Technology
Vol. 29, No. 5, (2020), pp. 5438 - 5447
5445ISSN: 2005-4238 IJAST
Copyright ⓒ 2020 SERSC
(10) shows the PL spectrum for PSi/n-Si heterojunction that is formed at 20mA/cm2
current
densities during 15min etching time, which indicates that emission peak of p-PSi at wavelength
648nm and the fixed excitation wavelength of emission about 440nm. The spectral band at value
1.91eV was pronounced PL, their results may be referred to the luminescence which happened due
to the confined silicon structures, these results are with full agreement with [12].
Fig. 10 : PL spectra for n-PS at 20mA/cm2 current density during 15min etching time.
Drop casting technique was utilized to deposit NiO nanoparticle on PSi by using pipette to take the
solution, then dropped it on substrate which made of PSi. Figure (11) shows cross-sectional view
for NiO layer, which deposited on porous matrix.
Fig. 11 : Diagram of photodetector showing NiO layer deposited on PSi.
The spectral responsivity and specific detectivity of thin film structures is examined at (300–
900)nm wavelength range with bias 5V and those are calculated by equation (1). Figures (12a, b, c)
show the relationship between the spectral responsivity versus the wavelength for Al/PSi/n-Si/Al
structurewhich prepared at 20mA/cm2
current density during 15min etching time. The spectral
responsivity plots have two peaks for PSi and Si but for structure for NiO/PSi/(n,p)Si ,it has three

9. International Journal of Advanced Science and Technology
Vol. 29, No. 5, (2020), pp. 5438 - 5447
5446ISSN: 2005-4238 IJAST
Copyright ⓒ 2020 SERSC
peaks, the first one is between the NiO layers, the second to porous silicon PSi and the last for Si
layer.
The inset figures show the specific detectivity as a function of wavelength for Al/PSi/n-Si/Al and
Al/NiO/PSi/p-Si/Al Photodetectors respectively, they show that is a directly depend on the
detectivity on responsivity and the max. value for Al/NiO/PSi/p-Si/Al Photodetector is 0.7 x 1012
cm. Hz1/2
.W-1
at wavelength 780nm.
(a)
(b)

10. International Journal of Advanced Science and Technology
Vol. 29, No. 5, (2020), pp. 5438 - 5447
5447ISSN: 2005-4238 IJAST
Copyright ⓒ 2020 SERSC
Fig. 12 : Responsivity and detectivity as a function of wavelength a) Al/PSi/n-Si, b)
Al/NiO/PSi/Si/Al at 250C thermal annealing , c) Al/NiO/PSi/Si/Al at 500C thermal annealing
photodetectors.
Conclusions
X-ray diffraction (XRD) measurements for NiO thin films revealed the films were
polycrystalline with a cubic crystal structure. Deposition of NiO NPS on porous silicon (PSi) gives
characteristics of suspensions photodetector, which enhanced the properties of porous
photodetectors. The spectral responsivity (R ) for Al/NiO/PSi/Si/Al photodetector have two values
depend on the absorption edge, the first value is around 0.6A/W at  800nm wavelength for silicon;
the second value is around 0.6A/W at  650nm wavelength for NiO NPS. The specific detectivity
(D) has a maximum value for Al/NiO /PSi/Si/Al photodetector is 0.71012
cm.W-1
.Hz-1
at 780nm
wavelength, which obtained by applied 20mA/cm2
current density for 15min aching time, then the
annealing process was performed for NiO thin film at 200C.
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(c)