p-ZnO Films Research Articles

Enhanced Thermochemical Stability of CH3NH3PbI3 Perovskite Films on Zinc Oxides via New Precursors and Surface Engineering

Hydroxyl groups on the surface of ZnO films lead to the chemical decomposition of CH3NH3PbI3 perovskite films during thermal annealing, which limits the application of ZnO as a facile electron-transporting layer (ETL) in perovskite solar cells. In this work, we report a new recipe that leads to substantially reduced hydroxyl groups on the surface of the resulting ZnO films by employing polyethylenimine (PEI) to replace generally used ethanolamine in the precursor solutions. Films derived from the PEI-containing precursors are denoted as P-ZnO and those from the ethanolamine-containing precursors as E-ZnO. Besides the fewer hydroxyl groups that alleviate the thermochemical decomposition of CH3NH3PbI3 perovskite films, P-ZnO also provides a template for the fixation of fullerene ([6,6]-phenyl-C61-butyric acid methyl ester, PCBM) owing to its nitrogen-rich surface that can interact with PCBM. The fullerene was used to block the direct contact between P-ZnO and CH3NH3PbI3 films and therefore further enhance the thermochemical stability of perovskite films. As a result, perovskite solar cells based on the P-ZnO/PCBM ETL yield an optimal power conversion efficiency (PCE) of 15.38%. We also adopt P-ZnO as the ETL for organic solar cells that yield a remarkable PCE of 10.5% based on the PBDB-T:ITIC photoactive layer.

Characterization and device applications of p-type ZnO films prepared by thermal oxidation of sputter-deposited zinc oxynitride

Formation of nitrogen-doped p-type ZnO (p-ZnO) and related homojunction devices has been reported extensively using a variety of techniques with the exception of thermal oxidation of ZnON that is a simple and less explored method. We converted sputter-deposited ZnON films to p-ZnO at relatively low oxidation temperatures (400–500 °C) as compared with other reports. Chemical bonding states of nitrogen in p-ZnO films were examined by XPS analysis and the mechanism of p-type doping was discussed. Films were characterized by XRD, SEM, photocurrent spectroscopy, and photoluminescence (PL) measurement. Films were composed from nano-size crystallites with (100) preferential orientation. A shallow acceptor level with a 70–90 meV binding energy and a 1.72-eV deep level were measured and identified. PL thermal quenching of the films had activation energy of 34 meV. Schottky barrier (SB) and homojunction diodes, with two different types of n-ZnO, were fabricated on films and their parameters were compared with the reported data. The SB and both types of homojunction diodes had high rectification factors (104-105) and good device parameters. The conductance of homojunction diode based on sputter-deposited n-ZnO showed thermal activation energies of 0.08–0.12 eV, 0.16–0.20 eV, and 0.40–0.50 eV. The homojunction diode based on n-ZnO nano-rods exhibited strong electroluminescence in the visible region from which two defect-related transition energies of 2.21 eV and 2.66 eV were obtained. In conclusion, good quality p-ZnO films and related devices can be prepared by thermal oxidation of ZnON films.

Structural Properties of P-Type ZnO Thin Film Post-Treated by NH<sub>3</sub> Plasma Method

In this paper, a simple method is reported to obtain nitrogen-doped p-ZnO film. In this method NH3 plasma, generated in a plasma-enhanced chemical vapor deposition system, was employed to treat ZnO thin film. By hall-effect measurement a p type conductivity was observed for the treated film with the hole density of 3.6×1016. XPS result confirmed nitrogen was incorporated into ZnO film during the treatment process to occupy the oxygen positions.

Realization of reliable p-type ZnO thin films by nitrogen implantation using plasma immersion ion implantation

Plasma immersion ion implantation was used to dope nitrogen in ZnO thin films to achieve p-type films. The doped samples were subsequently annealed at temperatures between 700°C and 1000°C. A strong A°X peak around 3.35eV was detected in the photoluminescence spectra for samples annealed at high temperatures. The p-ZnO films were stable after 9months and were reproducible. The current–voltage relationship for a p–n heterojunction diode exhibited rectifying behavior with a built-in voltage of 1.6V.

Fabrication of p-ZnO:ZrN thin films by RF magnetron sputtering

An attempt has been made to fabricate p-ZnO thin films from the ZrN mixed ZnO targets by RF magnetron sputtering. The targets of different ZrN concentrations (0, 1, 2, and 4 mol%) have been prepared by solid-state reaction route. The ZrN-codoped ZnO films grown on semi-insulating Si (100) substrates have been characterized by X-ray diffraction (XRD), photoluminescence (PL), Hall effect measurement, time-of-flight secondary ion mass spectrometer (ToF-SIMS), and atomic force microscopy (AFM). XRD studies reveal that all films are oriented along (002) plane. The Hall measurements showed p-conductivity for 1 and 2 mol% ZrN-codoped ZnO films. Further, it has been found that 1 mol% ZrN-codoped film has low resistivity (7.5 × 10−2 Ω cm) and considerable hole concentration (8.2 × 1018 cm−3) by optimum incorporation of nitrogen due to best codoping. The red shift in near-band-edge emission observed from PL well acknowledged the p-conduction in 1 and 2 mol% ZrN-codoped ZnO film. The incorporation of N and Zr atoms in the ZnO matrix has been confirmed by ToF-SIMS analysis. The increase in peak to valley roughness (R pv) with increase of doping concentration has been observed from AFM analysis. ZnO homojunction has also been fabricated with the best codoped p-ZnO film and it showed typical rectification behavior of a diode. The junction parameters have also been determined for the fabricated homojunction.

${\rm NH}_{3}$ Sensing by $p$-ZnO Thin Films

AlN and AlAs codoped <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> -ZnO thin films are fabricated by RF magnetron sputtering for gas sensing applications. For comparison, Al monodoped <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -ZnO film is also grown. The conductivity of the films is confirmed by the Van der Pauw Hall effect measurement system. The structural and elemental properties of the films are studied by X-ray diffraction and time-of-flight secondary ion mass spectroscopy. Sensitivity measurements are performed with the fabricated <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> -and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -ZnO films for different concentrations of ammonia (200-1200 ppm) at different operating temperatures (room temperature: 100 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C and 150 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C). It is found that both <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> -ZnO films have higher sensitivity than that of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -ZnO film. Furthermore, both <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> -ZnO films exhibit lower response and recovery times than <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -ZnO film.

Preparation of ZnO:Mo Thin Films by RF Sputtering

ABSTRACTBased on the electron configurations of Mo and Zn, the valence electron difference between Mo6+ and Zn2+ is 4. Therefore, a small amount of Mo doping can produce sufficient free carriers to reduce the ion scattering effects. The Mo doped ZnO (MZO) thin film prepared by RF sputtering was studied in this research. Structural, electrical, and optical characteristics of the films were discussed. The MZO film shows a resistivity of 1.1 × 10-2 Ω⋅cm, a carrier concentration of 2.2 × 1021 cm-3,a mobility of 0.63 cm2/V⋅s, and average transparency of 81.0% at both the powers of 20 W to the Mo target and of 125 W to the ZnO target. The MZO film becomes a stable p-type semiconductor at high power process toward Mo target. The film preserves its p-type characteristics after exposure to air for one and a half months. The crystal structure of the p-ZnO films is amorphous with an average transparency of 34.5%.

Study of p-ZnO Fabricated by Thermally Oxidized Zn3N2

The ZnO thin films prepared by the oxidation of Zn3N2 thin film with different oxidation temperature were characterized. The surface morphology analyzed by scanning electron microscope was studied. A smooth surface morphology can be achieved with the oxidation temperature reached 500°C. X-ray diffraction patterns show that the ZnO structure can be formed with the oxidation temperature higher than 300°C. P-type ZnO with concentration around 1017 cm−3 can be achieved stably within the temperature 400 to 600°C. The p-ZnO/n-Si diode was achieved and characterized by applying the p-ZnO film on the n-Si substrate. For such heterostructure diode, the enhancement of the ultraviolet band responsivity can be characterized. The p-ZnO resulted from the oxidation of Zn3N2 show a promising responsivity enhancement in Si-contained heterostructure p-n diode.

Electrical characterization of Cr Schottky contacts on undoped and Ni-doped p-ZnO films grown by pulsed laser deposition on Si (100) substrates

Wide band gap semiconducting layers of undoped and Ni-doped p-type ZnO thin films were developed on (100) silicon substrates by pulsed laser deposition (PLD) at a constant oxygen partial pressure of 1.0x10^-^4 Torr and at constant temperature of 250^oC. The electrical properties of the films were studied by resistivity and Hall coefficient measurements at room temperature. P-type conductivity was found to be dominant in these films at room temperature although the incorporation of Ni dopants caused a reduction in the p-character of ZnO films. The surface morphology of the films was evaluated by contact mode atomic force microscopy (AFM) in air. Cr-Schottky contacts were deposited on these p-type ZnO films, and the rectifying properties of the contacts were evaluated. The current-voltage (I-V) characteristics of the Cr/ZnO Schottky diodes were measured at room temperature. Due to series resistance, the Cheung and Cheung functions were used to determine the barrier height and ideality factor of the diodes while Norde function was used to determine barrier height. Ideality factors of 1.07 and 1.22 were obtained for the Cr/undoped ZnO and Cr/Ni-doped ZnO diodes, respectively, while the barrier height was 0.59eV by the Norde model, and in good agreement with 0.62eV of the Cheung-Cheung model, for both undoped and Ni-doped samples.

Fabrication of Al3+ and large radii mismatch As5+ codoped p-ZnO thin film and homojunction

We report Al3+ and large radii mismatched As5+ codoped p-ZnO thin films by As back diffusion from GaAs substrate and sputtering Al2O3 (1, 2 and 4 at%) mixed ZnO target. Hall effect measurements showed that the hole concentration increased upon codoping (As5+ and Al3+) compared to the monodoped (As5+) film. Also, it showed that 1 at% Al doped ZnO:As has low resistivity with high hole concentration due to best codoping. The crystallinity of the films has been studied by X-ray diffraction. The p-type formation mechanism has been investigated by X-ray photoelectron spectroscopy and low temperature photoluminescence analysis. It implies that As5+ substitutes on Zn2+ instead on O2− site that leads to the formation of (AsZn–2VZn) complex which gives rise to p-conductivity. Further, the fabricated p-n homojunction using best codoped p-ZnO film shows typical rectifying characteristics of a diode.

Influence of Al concentration on electrical, structural and optical properties of Al–As codoped p-ZnO thin films

We report the influence of Al concentration on electrical, structural, optical and morphological properties of Al–As codoped p-ZnO thin films using RF magnetron sputtering. Al–As codoped p-ZnO films with different Al concentrations were fabricated using As back diffusion from the GaAs substrate and sputtering Al2O3 mixed ZnO targets (1, 2 and 4at%). The grown films were investigated by Hall effect measurement, X-ray diffraction (XRD), electron probe microanalysis (EPMA), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and atomic force microscopy (AFM) to study the electrical, structural, optical and morphological properties of the films. From the XRD, it was observed that both full-width at half-maximum (FWHM) and c-axis lattice constant have similar trends with respect to Al concentration. Hall measurements showed that the hole concentration increases as the Al concentration increases from 1015 to 1020cm−3. The increase in hole concentration upon codoping was supported by the red shift in the near-band-edge (NBE) emission observed from room temperature PL spectra. The proposed p-type mechanism due to AsZn–2VZn complex was confirmed by low temperature PL and XPS analysis. The low FWHM, resistivity and peak-to-valley roughness observed by XRD, Hall measurement and AFM, respectively, suggest that 1at% Al-doped ZnO:As film is the best codoped film.

A Codoping Route to Realize Low Resistive and Stable p-Type Conduction in (Li, Ni):ZnO Thin Films Grown by Pulsed Laser Deposition

We report on the growth of Li-Ni codoped p-type ZnO thin films using pulsed laser deposition. Two mole percent Li monodoped ZnO film shows highly insulating behavior. However, a spectacular decrease in electrical resistivity, from 3.6 × 10(3) to 0.15 Ω cm, is observed by incorporating 2 mol % of Ni in the Li-doped ZnO film. Moreover, the activation energy drops to 6 meV from 78 meV with Ni incorporation in Li:ZnO lattice. The codoped [ZnO:(Li, Ni)] thin film shows p-type conduction with room temperature hole concentration of 3.2 × 10(17) cm(-3). Photo-Hall measurements show that the Li-Ni codoped p-ZnO film is highly stable even with UV illumination. XPS measurements reveal that most favorable chemical state of Ni is Ni(3+) in (Li, Ni): ZnO. We argue that these Ni(3+) ions act as reactive donors and increase the Li solubility limit. Codoping of Li, with other transitional metal ions (Mn, Co, etc.) in place of Ni could be the key to realize hole-dominated conductivity in ZnO to envisage ZnO-based homoepitaxial devices.

A reproducible route to p-ZnO films and their application in light-emitting devices

Although great efforts have been made, reproducible p-type doping is still one of the largest hurdles that hinders the optoelectronic applications of ZnO. In this Letter, a reproducible route to p-type ZnO films employing lithium-nitrogen as a dual-acceptor dopant has been demonstrated, and p-i-n structured light-emitting devices (LEDs) have been constructed. Obvious purple emissions have been observed from the LEDs, confirming the applicability of the p-type ZnO films in optoelectronic devices. The results reported in this Letter provide a reproducible route to p-type ZnO films, and thus may lay a solid ground for future optoelectronic applications of ZnO.

Influence of grain size on the properties of AlN doped ZnO thin film

Thin films of AlN codoped ZnO have been grown successfully for the realization of p-type conduction. With the intention of using the grown p-ZnO films for the fabrication of optoelectronic devices, the film has been study to observe the dependency of structural, optical and electrical properties on dopant concentration using powder X-ray diffraction, reflectance and measurements, respectively. It has been observed from the X-ray diffraction results that the dopant concentration controls the grain size depending on the incorporation of Al and N into the ZnO film. It is also observed that the optical and electrical properties are strongly influenced by the grain size and grain boundaries. In order to check the efficiency of the material for device fabrication, the figure of merit has been calculated and it is observed that the grain size influences the figure of merit. The effect of grain size on properties of AlN doped ZnO films has been discussed in detail.

Electrical characterization of p-ZnO/p-Si heterojunction

Nitrogen doped p-ZnO film, with urea as nitrogen source, is fabricated by pulsed laser deposition on well-cleaned p-type (1 0 0) Si substrates. The structural and electrical properties of the p–p heterojunction are investigated by current–voltage ( I– V) and capacitance–voltage ( C– V) measurements. It shows a diode-like behavior with turn-on voltage of 0.5 V. The ideality factor η determined by applying positive potential in p-ZnO and negative potential along p-Si is found to be 6. Such a high value of η is attributed to lattice mismatch between ZnO and Si. and other factors responsible are thermoionic emission, minority carrier injection and recombination. C– V results indicate an abrupt interface and a band bending of 0.9 V in the silicon. Heterojunction band diagram for p-ZnO/p-Si is proposed.

Fabrication of p-Type ZnO Thin Films Using rf-Magnetron Sputter Deposition

p-Type ZnO thin turns were prepared on phosphorus (P)-doped poly-Si by sputter deposition under various ambient ratios of Ar and O 2 and subsequent annealing process at temperatures ranging from 400 to 600°C. The effects of the ambient sputtering gas and annealing temperature on the electrical and material characteristics of ZnO films were investigated. The formation of p-ZnO film on P-doped poly-Si was confirmed through comparisons involving the conduction type of the ZnO film deposited on insulating SiO 2 . The film deposited in Ar ambient and annealed at 500°C showed a maximum hole concentration of 5.92 X 10 19 cm -3 .

Codoped (AlN) and monodoped (Al) ZnO thin films grown by RF sputtering: A comparative study

We present the comparative study on AlN codoped ZnO (ANZO) and Al doped ZnO (AZO) thin films of different concentrations (0.5–4 mol%) grown by RF magnetron sputtering. X-ray diffraction (XRD), reflectance and Hall measurements have been carried out on both codoped ANZO and monodoped AZO films grown on Si (1 0 0) substrates. XRD studies reveal that all the films in both systems are polycrystalline. Further, it has been inferred that all the Al-doped films are under compressive strain while in the AlN-doped (codoped) films, 0.5 and 1 mol% are under tensile strain and others are in compressive strain. The reflectance measurements suggest that the optical band gap increases with Al concentration in monodoped systems whereas the band gap decreases upto 1 mol% and then increases for codoped system. The Hall measurements indicate that interestingly 0.5 and 1 mol% codoped ZnO films exhibit p-type conduction and obviously all the monodoped films show n-type conduction. FTIR spectra also confirm the larger density of Al N bonds in p-ZnO films of codoped system.

Characteristics of nitrogen-doped p-ZnO thin films and ZnO/ZnSe p–n heterojunctions grown on a ZnSe substrate

We investigate p-type doping in ZnO prepared by the method of radical beam gettering epitaxy using NO gas as the oxygen source and nitrogen dopant. A narrow (0 0 2) peak is observed in the x-ray diffraction spectra, which indicates that the N-doped ZnO films are oriented along the c-axis. Secondary ion mass spectroscopy measurements demonstrate that N is incorporated into a ZnO film with a concentration of about 2.5 × 1019 cm−3. The hole concentration of the N-doped p-ZnO films was between 1.4 × 1017 and 7.2 × 1017 cm−3, and the hole mobility was 0.9–1.2 cm2V−1 s−1 as demonstrated by Hall-effect measurements. The emission peak of 3.312 eV is observed in the photoluminescence spectra at 4.2 K of N-doped p-ZnO films, probably neutral acceptor bound excitons and the band of 3.24 eV, connected with a donor–acceptor pair recombination. The activation energy of the nitrogen acceptor was obtained by the temperature-dependent Hall-effect measurement, and is about 145 meV. The p–n heterojunctions ZnO/ZnSe were grown on the n-type ZnSe substrate, and have a turn-on voltage of about 3.5 V.

Optical and electrical properties of p-type ZnO fabricated by NH 3 plasma post-treated ZnO thin films

In this paper, a simple method is reported to obtain nitrogen-doped p-ZnO film. In this method NH 3 plasma, generated in a plasma-enhanced chemical vapor deposition system, was employed to treat ZnO thin film. By Hall-effect measurement, a p-type conductivity was observed for the treated film with the hole density of 2.2 × 10 16 cm −3. X-ray photoelectron spectroscopy (XPS) results confirmed that nitrogen was incorporated into ZnO film during the treatment process to occupy the oxygen positions. In low temperature photoluminescence spectra, an emission peak corresponding to acceptor–donor pair was observed. From this emission peak we calculated the N-related acceptor binding energy to be 130 meV.

Fabrication of p-type ZnO thin films via magnetron sputtering and phosphorus diffusion

ZnO thin films were deposited on heavily phosphorus-doped (n +-Si) substrates by radio frequency magnetron sputtering. The films were changed from n-type to p-type by phosphorus diffusion from the n +-Si substrates to the ZnO films and being activated thermally during deposition. n-Type ZnO (n-ZnO) films were also deposited onto the p-type ZnO (p-ZnO) films to form n-ZnO/p-ZnO/n +-Si multilayer structures. The cross section of the multilayer structure was examined by scanning electron microscopy. Crystal structures of the p-ZnO films were studied by X-ray diffraction and were confirmed to be highly c-axis oriented primarily perpendicular to the substrate. Photoluminescence spectra of the p-ZnO films showed that band-edge UV emission predominated. The hole concentration of the p-ZnO films was between +1.78×10 18 cm −3 and +1.34×10 19 cm −3, and the hole mobility was 13.1–6.08 cm 2/V s measured by Hall effect experiment. The formation of p-ZnO films was confirmed by the rectifying characteristics of the p-ZnO/n +-Si heterojunctions and the n-ZnO/p-ZnO homojunction on the multilayer structure as well as by the experimental results of Hall effect.