304
V. Melnik et al.
One promising type of ZnO-based structures suitable for photovoltaic applications
employs undoped ZnO layers grown on Si wafers [2]. Zinc oxide is also a piezoelectric and optical waveguide material, which was used in sensor and ultraviolet (UV)
detector, light emitting diode (LED), surface acoustic wave (SAW), and solar cell
technologies, as well as transparent electrodes, particularly, carrier-selective contacts
with wide band gaps for Si heterojunction solar cells [3–9]. Zinc oxide was also extensively explored for using in transparent thin film transistors (TFTs) [10–12]. High
optical transparency in the visible range and low resistivity make ZnO an important
material for its using as heat mirrors in stoves, conducting coatings in aircraft glasses
to avoid surface icing [13].
The native defects in ZnO, oxygen vacancies V O and zinc interstitials Zn i , form
donor levels in the forbidden gap, so that zinc oxide is naturally an n-type semiconductor [14]. The Si/ZnO heterojunction is also widely employed. The presence of
SiO x native oxide and defects at the interface affects the charge carrier generation
and recombination and drastically changes the electrical and photoelectric properties
of the heterojunction.
Physical properties of ZnO depend on growth method, impurities, temperature,
and other factors, which in turn are important for the effective performance of practical devices. One important prerequisite for the LED applications is the ability to
achieve n and p types of electrical conduction in ZnO [15]. This allowed to fabricate
and realize p-n junction on ZnO and observe electroluminescence in the junction [16,
17]. However, as the acceptor impurities are hardly dissolved, it is still quite difficult
to produce p-type ZnO [18–20]. Moreover, because of a strong polarization field, the
quantum efficiency of ZnO-based LEDs is reduced [21]. It was shown that growing
nonpolar films, such as GaN-based layers, can improve the efficiency [22].
Nickel oxide offers an interesting alternative for fabricating ZnO-based heterojunctions, since it is also a wide direct bandgap semiconductor (E g = 3.7 eV) and
O. Dubikovskyi
e-mail: dubikovsky_o@ukr.net
JU. Gomeniuk
e-mail: yurigom@lab15.kiev.ua
O. Kosulya
e-mail: alexandr250990@gmail.com
V. Shmid (B) · A. Podolian · A. Nadtochiy · O. Korotchenkov
Faculty of Physics, Taras Shevchenko Kyiv National University, Volodymyrska 64/13, Kiev
01601, Ukraine
e-mail: shmdvi@gmail.com
A. Podolian
e-mail: summer.podolian@gmail.com
A. Nadtochiy
e-mail: namobem@gmail.com
O. Korotchenkov
e-mail: olegk@univ.kiev.ua
V. Melnik et al.
One promising type of ZnO-based structures suitable for photovoltaic applications
employs undoped ZnO layers grown on Si wafers [2]. Zinc oxide is also a piezoelectric and optical waveguide material, which was used in sensor and ultraviolet (UV)
detector, light emitting diode (LED), surface acoustic wave (SAW), and solar cell
technologies, as well as transparent electrodes, particularly, carrier-selective contacts
with wide band gaps for Si heterojunction solar cells [3–9]. Zinc oxide was also extensively explored for using in transparent thin film transistors (TFTs) [10–12]. High
optical transparency in the visible range and low resistivity make ZnO an important
material for its using as heat mirrors in stoves, conducting coatings in aircraft glasses
to avoid surface icing [13].
The native defects in ZnO, oxygen vacancies V O and zinc interstitials Zn i , form
donor levels in the forbidden gap, so that zinc oxide is naturally an n-type semiconductor [14]. The Si/ZnO heterojunction is also widely employed. The presence of
SiO x native oxide and defects at the interface affects the charge carrier generation
and recombination and drastically changes the electrical and photoelectric properties
of the heterojunction.
Physical properties of ZnO depend on growth method, impurities, temperature,
and other factors, which in turn are important for the effective performance of practical devices. One important prerequisite for the LED applications is the ability to
achieve n and p types of electrical conduction in ZnO [15]. This allowed to fabricate
and realize p-n junction on ZnO and observe electroluminescence in the junction [16,
17]. However, as the acceptor impurities are hardly dissolved, it is still quite difficult
to produce p-type ZnO [18–20]. Moreover, because of a strong polarization field, the
quantum efficiency of ZnO-based LEDs is reduced [21]. It was shown that growing
nonpolar films, such as GaN-based layers, can improve the efficiency [22].
Nickel oxide offers an interesting alternative for fabricating ZnO-based heterojunctions, since it is also a wide direct bandgap semiconductor (E g = 3.7 eV) and
O. Dubikovskyi
e-mail: dubikovsky_o@ukr.net
JU. Gomeniuk
e-mail: yurigom@lab15.kiev.ua
O. Kosulya
e-mail: alexandr250990@gmail.com
V. Shmid (B) · A. Podolian · A. Nadtochiy · O. Korotchenkov
Faculty of Physics, Taras Shevchenko Kyiv National University, Volodymyrska 64/13, Kiev
01601, Ukraine
e-mail: shmdvi@gmail.com
A. Podolian
e-mail: summer.podolian@gmail.com
A. Nadtochiy
e-mail: namobem@gmail.com
O. Korotchenkov
e-mail: olegk@univ.kiev.ua