P-doped ZnO Research Articles

Increasing the Efficiency of Photocatalytic Water Splitting via Introducing Intermediate Bands.

Photocatalytic water splitting is a potential way to utilize solar energy. To be practically useful, it is important to have a high solar-to-hydrogen (STH) efficiency. In this study, we propose a conceptually new photocatalytic water splitting model based on intermediate bands (IBs). In this new model, introducing IBs within the band gap can significantly increase the STH efficiency limit (from 30.7% to 48.1% without an overpotential and from 13.4% to 36.2% with overpotentials) compared to that in conventional single-band gap photocatalytic water splitting. First-principles calculations indicate that N-doped TiO2, Bi-doped TiO2, and P-doped ZnO have suitable IBs that can be used to construct IB photocatalytic water splitting systems. The STH efficiency limits of these three doped systems are 10.0%, 12.0%, and 19.0%, respectively, while those of pristine TiO2 and ZnO without IB are only 0.9% and 1.6%, respectively. The IB photocatalytic water splitting model proposed in this study opens a new avenue for photocatalytic water splitting design.

Binding energy of Sb-related complex in p-doped ZnO film

ZnO and Sb-doped ZnO films were grown on (001) sapphire using metal organic chemical vapor deposition (MOCVD). Diethylzinc (DEZn), trimethylantimony (TMSb) and oxygen were used as the Zn, Sb and oxygen sources, respectively. The reaction mechanism of DEZn and oxygen was investigated. The formation of the SbZn–2VZn acceptor complex is explained, and the effect of the Sb chemical state on the conduction type is discussed. In the low-temperature spectrum of the Sb-doped ZnO film, emissions associated with acceptors, such as the acceptor-bound exciton (3.319 eV) and the transition between free electrons and acceptors (3.244 eV), were observed, which proved the creation of the SbZn–2VZn acceptor complex. According to the energy level of the transition between the free electrons and acceptors, the acceptor binding energy was calculated to be 0.19 eV. Meanwhile, by fitting the integral photoluminescence intensity versus the temperature function, the acceptor binding energy was also estimated and was similar to the calculated value.

Optical and electrical transport properties of ZnO/MoS2 heterojunction p-n structure

The MoS2/ZnO and MoS2/Si heterojunction structures were fabricated by thermal evaporation and sol-gel methods. The crystal structures properties of MoS2/ZnO and MoS2/Si were characterized by X-ray diffraction (XRD) pattern, Raman spectroscopy, and transmission electron microscope (TEM). The XRD and Raman spectroscopy results indicate that the n-MoS2 film was successfully grown on p-doped ZnO or Si. The TEM images of MoS2/ZnO and MoS2/Si heterojunction structures shows the MoS2 stacking layer-by-layer covalented by van der Waals (vdW) force. The current–voltage (I–V) measurement shows the rectifying behavior of the heterojunction structures. The photoconductivity and photoresponsivity properties explore its carrier kinetic decay process. The results shows the potential applicability of MoS2/ZnO and MoS2/Si heterojunction structures as optoelectronic devices.

Influence of pressure on electronic and optical properties of phosphorus-doped ZnO

In this work, the geometrical, electronic structure and optical properties of P-doped ZnO under high pressures have been investigated using first-principles methods. The pressure effects on the lattice parameters, electronic band structures, and partial density of states of crystalline P-doped ZnO are calculated up to 8 GPa. Moreover, the evolution of the dielectric function, absorption coefficient (αω)), reflectivity (R(ω)), and the real part of the refractive index (n(ω)) at high pressure are also presented.

Effect of oxygen pressure performance of PZO thin films deposited by pulsed laser deposition at low temperature

The P doped ZnO (PZO) thin films were deposited by pulsed laser deposition via controlling oxygen pressure at low temperature (200 °C). The structural, surface morphological, electrical and optical properties of the thin films are systematically and detailedly studied. The surface morphologies show that the grain size of PZO thin films increases with oxygen pressure. The change mechanism of morphology is proposed. The increase of mobility is associated with the development of grain size. Thus, the carrier mobility can be improved by grain size control. The average optical transmittance in the visible region (380–780 nm) is above 90%. The estimated optical band gaps of the thin films decrease from 3.49 to 3.39 eV with the oxygen pressure increasing from 0 to 1 Pa, due to the Burstein–Moss effect and band gap renormalization. The highest figure of merit observed in this present study is 8.3 × 10−3 Ω−1, while the thin films are deposited at 0.01 Pa. The qualities of PZO thin films are advantages for the application in solar cells.

Sonochemical Synthesis of a Zinc Oxide Core-Shell Nanorod Radial p-n Homojunction Ultraviolet Photodetector.

We report for the first time on the growth of a homogeneous radial p-n junction in the ZnO core-shell configuration with a p-doped ZnO nanoshell structure grown around a high-quality unintentionally n-doped ZnO nanorod using sonochemistry. The simultaneous decomposition of phosphorous (P), zinc (Zn), and oxygen (O) from their respective precursors during sonication allows for the successful incorporation of P atoms into the ZnO lattice. The as-formed p-n junction shows a rectifying current-voltage characteristic that is consistent with a p-n junction with a threshold voltage of 1.3 V and an ideality factor of 33. The concentration of doping was estimated to be NA = 6.7 × 1017 cm-3 on the p side from the capacitance-voltage measurements. The fabricated radial p-n junction demonstrated a record optical responsivity of 9.64 A/W and a noise equivalent power of 0.573 pW/√Hz under ultraviolet illumination, which is the highest for ZnO p-n junction devices.

Simulation studies of p-doped ZnO MSM Photodetector with Plasmonic Enhancement

This paper presents the simulation studies of Metal-Semiconductor-Metal (MSM) Photodetector (PD) with and without plasmonic enhancement. The simulations were carried out using COMSOL Multiphysics® software. The semiconductor layer was p-type ZnO with a doping concentration of 1016/cm3. The plasmonic layer was of Au nanoparticles. The PD was irradiated with 10W UV radiation of wavelength 280nm. The output currents of MSM PD with and without plasmonic layer were found to be ∼0.9×10-7 A and ∼0.8×10-8 A respectively. It was observed that there is an appreciable increase (factor of 10) in photo current in devices with a plasmonic layer. The effect of change in the size of Au nano particles on output photocurrent was also studied.

Controllable Growth of Ultrathin P-doped ZnO Nanosheets.

Ultrathin phosphor (P)-doped ZnO nanosheets with branched nanowires were controllably synthesized, and the effects of oxygen and phosphor doping on the structural and optical properties were systematically studied. The grown ZnO nanosheet exhibits an ultrathin nanoribbon backbone with one-side-aligned nanoteeth. For the growth of ultrathin ZnO nanosheets, both oxygen flow rate and P doping are essential, by which the morphologies and microstructures can be finely tuned. P doping induces strain relaxation to change the growth direction of ZnO nanoribbons, and oxygen flow rate promotes the high supersaturation degree to facilitate the growth of nanoteeth and widens the nanoribbons. The growth of P-doped ZnO in this work provides a new progress towards the rational control of the morphologies for ZnO nanostructures.

First-principles analysis on Seebeck coefficient in zinc oxide nanowires for thermoelectric devices

The Seebeck coefficient of ZnO〈0001〉 nanowires was simulated on the basis of first- principles calculation, to discuss the potential for future application to thermoelectric devices. Simulation procedure by means of the electronic band structure with one-dimensional periodic boundary condition was presented, and dependences of the Seebeck coefficient on temperature and carrier concentration have been investigated for many kinds of n- or p-doped ZnO〈0001〉 nanowire models with 1.00-2.65 nm diameter. For the direct band-gap semiconducting models, a magnitude of the Seebeck coefficient increases gradually as temperature rises in the p-doped state, and a significant effect of miniaturization to nanowire on the Seebeck coefficient has been brought out, such as about 1000 µV/K in the p-doped state and -820 µV/K in the n-doped state for the (ZnO)24 nanowire model with 1 × 1017 cm-3 carrier concentration at room temperature. Similar characteristics of the Seebeck coefficient were observed for some indirect band-gap semiconducting models. At the end of this paper, the simulation was extended to the no band-gap conducting models with some modification.

Doping of ZnO nanowires using phosphorus diffusion from a spin-on doped glass source

In this article, we report on ZnO nanowires that were phosphorus doped using a spin on dopant glass deposition and diffusion method. Photoluminescence measurements suggest that this process yields p-doped ZnO. The spatial location of P atoms was studied using x-ray near-edge absorption structure spectroscopy and it is concluded that the doping is amphoteric with P atoms located on both Zn and O sites.

Effect of Thermal Annealing on the Characteristics of Phosphorus-Implanted ZnO Crystals

A P-doped ZnO surface layer on undoped ZnO wafers was prepared by phosphorus (P) ion implantation. Hall effect measurement revealed p-type conduction in such layers annealed at 800°C. This indicates that acceptor levels are present in P-doped ZnO, even though the ZnO is still n-type. Micro-Raman scattering in −z(xy)z geometry was conducted on P-implanted ZnO. The E 2 high mode shift observed toward the high-energy region was related to compressive stress as a result of P-ion implantation. This compressive stress led to the appearance of an A 1(LO) peak, which is an inactive mode. This A 1(LO) peak relaxed during thermal annealing in ambient oxygen at temperatures higher than 700°C. The P2p3/2 peak observed at 135.6 eV by x-ray photoelectron spectroscopy is associated with chemical bond formation leading to 2(P2O5) molecules. This indicates that implanted P ions substituted Zn sites in the ZnO layer. In photoluminescence spectroscopy, the P-related peaks observed at energies ranging between 3.1 and 3.5 eV originated from (A0, X) emission, because of PZn-2VZn complexes acting as shallow acceptors. The acceptor level was observed to be 126.9 meV above the valence band edge. Observation of this P-related emission indicates that ion implantation results in acceptor levels in the P-doped ZnO layer. This suggests that the P2O5 bonds are responsible for the p-type activity of P-implanted ZnO.

Characteristic properties of Raman scattering and photoluminescence on ZnO crystals doped through phosphorous-ion implantation

P-doped ZnO was fabricated by means of the ion-implantation method. At the Raman measurement, the blue shift of the E2high mode and A1(LO) phonon of the inactive mode were observed after the P-ion implantation. It suggested to be caused by the compressive stress. Thus, Hall effect measurement indicates that the acceptor levels exists in P-doped ZnO while still maintaining n-type ZnO. From the X-ray photoelectron spectroscopy, the chemical bond formation of the P2p3/2 spectrum consisted of 2(P2O5) molecules. Therefore, the implanted P ions were substituted to the Zn site in ZnO. From the photoluminescence (PL) spectra, P-related PL peaks were observed in the energy ranges of 3.1 and 3.5 eV, and its origin was analyzed at PZn-2VZn complexes, acting as a shallow acceptor. With increasing temperatures, the neutral-acceptor bound-exciton emission, (A0, X), shows a tendency to quench the intensity and extend the emission linewidth. From the relations of the intensity and the linewidth as a function of temperature, the broadening of linewidth was believed to the result that the vibration mode of E2high participates in the broadening process of (A0, X) and the change of luminescent intensity was attributed to the partial dissociation of (A0, X). Consequently, these facts indicate that the acceptor levels existed in P-doped ZnO layer by the ion implantation.

Defect mediated highly enhanced ultraviolet emission in P-doped ZnO nanorods

The enhancement in UVPL in hydrothermally grown P-doped ZnO is due to the formation of shallow acceptor PZn–2VZn complex defects.

Controlling phosphorus doping concentration in ZnO nanorods by low temperature hydrothermal method

Phosphorous-doped ZnO nanorods (NRs) were synthesized with controllable morphology and doping concentration on top of the array of undoped natural n-type ZnO NRs by hydrothermal process. By changing the concentration of NH4OH to adjust the pH of the reactant solution containing zinc acetate, hexamethylenetetramine, and ammonium phosphate, it was possible to control the morphology, doping concentration, and band structure of the ZnO nanostructures formed on the top side of the undoped NRs array. When the NH4OH concentration was 1 vol% substitutional dopant P formed shallow acceptor levels in the ZnO NRs, while higher NH4OH concentration resulted in the formation of donor levels as well as the compensation of the acceptors. A model p–n homojunction device based on the P-doped ZnO NRs consecutively attached to the initially synthesized n-type NRs showed a rectifying junction behavior confirming the formation of the p-type ZnO NRs with low doping concentration of P.

Annealing Effect of Phosphorus-Doped ZnO Nanorods Synthesized by Hydrothermal Method

An effect of thermal annealing on activating phosphorus (P) atoms in ZnO nanorods (NR) grown using a hydrothermal process was investigated. used as a dopant source reacted with ions and sediment was produced in the solution. The fact that most of the input P elements are concentrated in the sediment was confirmed using an energy dispersive spectrometer (EDS). After the hydrothermal process, ZnO NRs were synthesized and their PL peaks were exhibited at 405 and 500 nm because P atoms diffused to the ZnO crystal from the particles. The solubility of the initially formed sediment varied with the concentration of . Before annealing, both the structural and the optical properties of the P-doped ZnO NR were changed by the variation of P doping concentration, which affected the ZnO lattice parameters. At low doping concentration of phosphorus in ZnO crystal, it was determined that a phosphorus atom substituted for a Zn site and interacted with two , resulting in a complex, which is responsible for p-type conduction. After annealing, a shift of the PL peak was found to have occurred due to the unstable P doping state at high concentration of P, whereas at low concentration there was little shift of PL peak due to the stable P doping state.

Effects of (P, N) dual acceptor doping on band gap and p-type conduction behavior of ZnO films

A reproducible p-type P-N codoped ZnO [ZnO:(P, N)] film with high quality was achieved by magnetron sputtering and post-annealing techniques. It has room-temperature resistivity of 3.98 Ωcm, Hall mobility of 1.35 cm2/Vs, and carrier concentration of 1.16 × 1018 cm−3, which is better than electrical properties of the p-type N-doped ZnO (ZnO:N) and p-type P-doped ZnO (ZnO:P) films. Additionally, the p-ZnO:(P, N)/n-ZnO homojunction showed a clear p-n diode characteristic. The p-type conductivity of ZnO:(P, N) is attributed to the formation of an impurity band above the valance band maximum, resulting in a reduction in the band gap and a decrease in the ionization energy of the acceptor, as well as an improvement in the conductivity and stability of the p-type ZnO:(P, N).

Comparative Study of P-Doped and Undoped ZnO Nanostructures Using Thermal Evaporation and Vapor Transport Method

We report the synthesis of phosphorus-doped (P-doped) and undoped ZnO nanostructures using a thermal evaporation and vapor transport on Si(100) substrate without any catalyst and at atmospheric argon pressure. The structural and optical properties of P-doped ZnO nanostructures and undoped ZnO nanostructures have been extensively investigated using filed emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Photoluminescence (PL). FESEM observation reveals that the morphology of ZnO nanostructures was changed from a hexagonal-like shape to a spherical shape when doping with P. While, XRD results indicate that P-doped ZnO nanostructures lost the (002) orientation preference and became randomly oriented. In addition, shifting of (002) diffraction peak has been found due to the incorporation of P into ZnO. Room temperature (PL) spectrum of P-doped ZnO nanostructures shows a high efficiency of green emission which was attributed to the presence of phosphorus atoms in the ZnO nanostructures.

Superior photocatalytic properties of phosphorous-doped ZnO nanocombs

We demonstrated that phosphorous (P)-doped ZnO nanocombs exhibited extremely high photocatalytic efficiency, which was evaluated by photodegrading methylene blue dyes in aqueous solutions. The photocatalyst takes advantage of the large surface to volume ratio (S/V) and abundant surface defect states of ZnO nanostructures. To maximize the S/V for more efficient light irradiation, the morphologies of the P-doped ZnO nanostructures were tailored by controlling the ratio of argon and oxygen in the carrier gas. P-doping caused a bunch of surface defects in ZnO, which could effectively restrain the recombination of photogenerated carriers and improve the photocatalytic behavior. Superior photocatalytic behaviors of P-doped ZnO nanocombs, as well as the availability of catalyst-free large scale synthesis, provide a new paradigm for rational synthesis of high efficient photocatalysts.

Electron doping of ALD-grown ZnO thin films through Al and P substitutions

Several series of Al- and P-doped ZnO thin films have been deposited with atomic layer deposition at different temperatures using diethyl zinc, trimethyl aluminum, trimethyl phosphate, and H2O as the precursors. The optimal deposition temperature range is found at 160–220 °C where the film growth is stable and well-crystallized films with low resistivity are obtained. The effect of the dopant content on the charge carrier density of the films is evaluated based on optical reflectivity, Seebeck coefficient, and electrical resistivity data for the films. Both dopants are found to be effective in controlling the carrier density of ZnO; systematic increase in carrier density is demonstrated for Al-doping up to 2 at.% and for P-doping up to 5 at.%. The conductivity of the as-deposited films remains n-type.

P-Doped <i>p</i>-Type ZnΟ Films Deposited by Sputtering and Diffusing

P-doped ZnO thin films were prepared on different Si substrates by RF magnetron sputtering in Ar and O2mixed atmosphere. The P-doped ZnO films were changed from n-type to p-type by phosphorus diffusing from the n-Si substrates with higher phosphorus concentration into the ZnO films during depositing. The crystal structure of the ZnO films was examined by X-ray diffraction and confirmed to belong to wurtzite and highly c-axis oriented primarily perpendicular to the substrate. The Hall effect measurement results show that the corresponding hole concentration and risistivity of the P-doped ZnO film was 8.982×1017cm-3and 1.489 Ω•cm respectively. This reveals that the P-doped ZnO thin film is really p-type behavior.