Formation and Transient Photovoltaic Properties of ZnO/Si …
305
can much simpler be obtained with a p-type conductivity [23, 24]. Consequently, p-n
junctions utilizing NiO/ZnO and MgZnO/NiO were successfully fabricated [25–27].
In this respect, metal oxide semiconductor nanocomposite heterojunctions, which
combined n-type zinc oxide and p-type nickel oxide, offered an interesting approach
for enlarging the free charge separation lengths increasing their lifetimes [28–34].
Different low-dimensional structures with ZnO, e.g., thin films, nanotubes,
nanowires, nanofibers, were fabricated using various deposition techniques, such
as MBE, CVD, sol–gel method [35, 36]. Microwaves and sonochemical synthesis
were also used [37–40].
Using magnetron sputtering technique, ZnO-on-p-Si LEDs were obtained [41].
It was reported in this work that the electroluminescence behavior of the ZnO/Si
depends sensitively on the growth conditions. Morphology aspects in thin films of
ZnO synthesized with magnetron sputtering method were recently addressed by
Nagabharana et al. [42], and a crucial role of the deposition rate in the substrate-ZnO
interface bonding was demonstrated.
As reported by Wang et al., changing the deposition temperature of wurtzite
ZnO FAZO films, co-doped with fluorine and aluminum, modified the film surface
morphology such that “pyramid” and “crater” shapes were observed [43]. These
transformations were detected by combining different techniques, e.g., XRD, SEM,
AFM, XPS, and optical spectroscopy.
When doping ZnO with Mg, Al, and Ga (AGMZO), the properties of the films,
such as structure, morphology, resistivity, and optical transmittance, were found to
depend upon the Mg content, as reported by Liu and Zhu [44].
Kim et al. studied ZnO films integrated in the ITO cathodes as transparent buffer
layers in inverted polymer solar cells (IPSCs) [45]. Comparing magnetron sputtering and solution-based growth techniques, the authors demonstrated that the power
conversion efficiency was much lower in the former growth method. Meanwhile, it
exhibited improved performance of ZnO buffers due to the formation of a suitable
heterojunction structure
Photoelectrical properties of Cr-doped magnetron-sputtered ZnO layers were
studied by Fareed et al. [46]. It was shown that the barrier height in ZnO/Pt Schottky
diodes was lowered due to such a doping of ZnO. Moreover, the ideality factor of
the diode was made better. Furthermore, the doping induced the diode responsivity
in the visible region, although an undoped ZnO film in the photodiode did not show
appropriate response. This effect was attributed to the reduction in E g due to Cr
doping.
Frequently, ZnO is doped by the IIIA group elements to obtain a layer with
modified properties. Aluminum is the most suitable for this purpose because Al
dopant atoms offer an enhanced concentration of free electrons, which increases
the electrical conductivity [47]. Besides, adding aluminum into ZnO (AZO films)
changes E g . ZnO:Al/Si heterojunctions have a higher switching speed and lower
temperature budget in comparison with typical silicon p-n or p-i-n junctions. The
heterojunction quality depends on the number and type of defects on the interface
and in the thin film. Ion implantation with the next temperature treatments allows to
305
can much simpler be obtained with a p-type conductivity [23, 24]. Consequently, p-n
junctions utilizing NiO/ZnO and MgZnO/NiO were successfully fabricated [25–27].
In this respect, metal oxide semiconductor nanocomposite heterojunctions, which
combined n-type zinc oxide and p-type nickel oxide, offered an interesting approach
for enlarging the free charge separation lengths increasing their lifetimes [28–34].
Different low-dimensional structures with ZnO, e.g., thin films, nanotubes,
nanowires, nanofibers, were fabricated using various deposition techniques, such
as MBE, CVD, sol–gel method [35, 36]. Microwaves and sonochemical synthesis
were also used [37–40].
Using magnetron sputtering technique, ZnO-on-p-Si LEDs were obtained [41].
It was reported in this work that the electroluminescence behavior of the ZnO/Si
depends sensitively on the growth conditions. Morphology aspects in thin films of
ZnO synthesized with magnetron sputtering method were recently addressed by
Nagabharana et al. [42], and a crucial role of the deposition rate in the substrate-ZnO
interface bonding was demonstrated.
As reported by Wang et al., changing the deposition temperature of wurtzite
ZnO FAZO films, co-doped with fluorine and aluminum, modified the film surface
morphology such that “pyramid” and “crater” shapes were observed [43]. These
transformations were detected by combining different techniques, e.g., XRD, SEM,
AFM, XPS, and optical spectroscopy.
When doping ZnO with Mg, Al, and Ga (AGMZO), the properties of the films,
such as structure, morphology, resistivity, and optical transmittance, were found to
depend upon the Mg content, as reported by Liu and Zhu [44].
Kim et al. studied ZnO films integrated in the ITO cathodes as transparent buffer
layers in inverted polymer solar cells (IPSCs) [45]. Comparing magnetron sputtering and solution-based growth techniques, the authors demonstrated that the power
conversion efficiency was much lower in the former growth method. Meanwhile, it
exhibited improved performance of ZnO buffers due to the formation of a suitable
heterojunction structure
Photoelectrical properties of Cr-doped magnetron-sputtered ZnO layers were
studied by Fareed et al. [46]. It was shown that the barrier height in ZnO/Pt Schottky
diodes was lowered due to such a doping of ZnO. Moreover, the ideality factor of
the diode was made better. Furthermore, the doping induced the diode responsivity
in the visible region, although an undoped ZnO film in the photodiode did not show
appropriate response. This effect was attributed to the reduction in E g due to Cr
doping.
Frequently, ZnO is doped by the IIIA group elements to obtain a layer with
modified properties. Aluminum is the most suitable for this purpose because Al
dopant atoms offer an enhanced concentration of free electrons, which increases
the electrical conductivity [47]. Besides, adding aluminum into ZnO (AZO films)
changes E g . ZnO:Al/Si heterojunctions have a higher switching speed and lower
temperature budget in comparison with typical silicon p-n or p-i-n junctions. The
heterojunction quality depends on the number and type of defects on the interface
and in the thin film. Ion implantation with the next temperature treatments allows to