P-type ZnO Thin Films Research Articles

Room temperature deposition of stable p-type ZnO:N thin films through chemical species modulation using reactive pulsed laser deposition

Low temperature processing as well as long-term electrical stability are required to match p-type ZnO thin films with flexible electronics applications. Herein, ZnO and ZnO:N thin films were deposited at room temperature by reactive pulsed laser deposition of a zinc metallic target. Several ZnO thin films were obtained by varying the oxygen working pressure from 1.2 × 10-5 Torr to 3.5 × 10-2 Torr. Chemical concentration was smoothly tuned as demonstrated by in situ X-ray Photoelectron Spectroscopy. Introducing and varying both N2 and O2 fluxes at a constant pressure, N-doped ZnO films from 0.3 at.% to 5 at.% were deposited. Adjusting the N2/O2 flux ratio, p-type ZnO:N films were successfully achieved, exhibiting a carrier concentration of 5.3 × 1018 cm−3, resistivity of 2 Ωcm, and mobility of 0.5 cm2V-1s−1. Four representative p-type samples were analyzed to confirm chemical and electrical reproducibility. Electrical properties of one of these films were measured again nine months after deposited, and p-type conductivity was still observed. Cathodoluminescence revealed green-dominant emissions in n-ZnO and UV-dominant emissions in p-ZnO:N films as nitrogen doping effect. Finally, a p-n diode was fabricated using photolithography, exhibiting rectification performance even nine months after deposited. P-type ZnO:N presented here are suitable for flexible electronics devices fabrication.

Tailoring Sb doping concentration to achieve p-type nanostructured ZnO thin film grown by sol–gel method

Tailoring Sb doping concentration to achieve p-type nanostructured ZnO thin film grown by sol–gel method

Unfolding the conductivity reversal n- to p-type in phosphorus-doped ZnO thin films by spin-on dopant (SOD) process

Phosphorus doping induced p-type doping in ZnO thin films based on spin-on dopant (SOD) process is reported in this article. Owing to the reduced dependence on the conventional amenities for diffusion/ion-implantation doping, the SOD process provides a simple and cheap doping method. The effect of SOD process temperature on conductivity ZnO thin films is investigated by altering the temperature from 700°C to 1000°C. Systematic field emission scanning electron microscopy analysis demonstrates the impact of doping temperature on the morphological properties of SOD. The x-ray diffraction measurements reveal that the p-type ZnO thin films had (002) preferred crystal orientation. At the same time, x-ray photoelectron spectroscopy validated the formation of the PZn–2VZn complex, which was responsible for the acceptor behaviour of films. Moreover, the photoluminescence spectra tracked down that the origin of 3.35 and 3.31 eV emission peaks is due to the acceptor bound exciton and free-electron to acceptor level transitions, respectively. Finally, an elevated hole concentration of 2.09 × 1016 cm−3 is achieved with a resistivity of 1.14 Ω-cm at 800°C doping temperature. However, the film doped at 900°C and 1000°C showed n-type behaviour due to the generation of high concentration donor defects. Here, we successfully demonstrate that the SOD process has great potential to produce high-quality p-type ZnO thin films suitable for optoelectronic devices applications.

Electrical and ferromagnetic properties of p-type ZnO thin films with and without the addition of graphene prepared by the sol-gel method

This study determines the effect of the addition of graphene on the electrical and ferromagnetic properties of the ZnO thin films that are prepared by the sol-gel method. ZnO is a typically oxygen-deficient metal oxide and exhibits intrinsic n-type conductivity. ZnO thin films to which graphene is added and those to which it is not, which are annealed at 500 °C for 30 min in oxygen, exhibit p-type behavior. There is an increase in the hole concentration of the graphene-doped ZnO thin film because of competition between the densities of donor-like defects such as oxygen vacancies and acceptor-like defects such as oxygen interstitials (Oi) and the defect complex that is related to the substitution of carbon for zinc (CZn) and Oi. There is ferromagnetism in a ZnO thin film at room temperature because of the presence of Oi. The intensity of the ferromagnetic signal is increased because CZn and Oi are formed in a graphene-doped ZnO thin film.

The low temperature growth of stable p-type ZnO films in HiPIMS

In this study, the influence of substrate temperature on properties of Al-N co-doped p-type ZnO films is explored. Benefitting from the high ionization rate in high-power impulsed magnetron sputtering, the concentration of ionized nitrogen N+ and ionized zinc Zn+ were increased, which promoted the formation of ZnO films and lowered the necessary substrate temperature. After optimization, a co-doped p-type ZnO thin film with a resistivity lower than 0.35 Ω cm and a hole concentration higher than 5.34 × 1018 cm−3 is grown at 280 °C. X-ray diffraction results confirm that Al-N co-doping does not destruct the ZnO wurtzite structure. X-ray photoelectron spectroscopy demonstrates that the presence of Al promotes the formation of acceptor (No) defects in ZnO films, and ensures the role of Al in stabilizing p-type ZnO.

Self-compensation reduction as first step of p-type ZnO synthesis

Abstract In this work, we used a new strategy, based on the reduction of self-compensation, to synthesize p-type ZnO thin films. This new protocol is based on the control of intrinsic defects especially the vacancies and the interstitials of both zinc and oxygen networks. It consists of using zinc nitrate as a precursor and varying its concentration on the one hand, and the addition of acetic acid on the other. Hall Effect measurements have shown a decrease in electron concentration as the nitrate concentration increases. A concrete transition in the conductivity of ZnO from n-type to p-type has been observed for concentration around 0,4M. Thermal Analyses (DTA-TGA), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), UV–visible spectrophotometry were used to study the structural, morphological and optical properties of the synthesized layers. All these measures confirm the appearance of a change in behavior when nitrate concentration is approaching 0,4M. This transition in conductivity-type in ZnO layers has been linked to a significant increase in the oxygen content as confirmed by an EDX analysis during films growth. The growth of p-type ZnO films based on zinc nitrate can potentially lead to the development of new transparent devices applicable in optoelectronics and photovoltaic fields.

Effect of doping concentration on optical and electrical properties of intrinsic n-type ZnO (i-ZnO) and (Cu, Na and K) doped p-type ZnO thin films grown by chemical bath deposition method

Effect of doping concentration on optical and electrical properties of intrinsic n-type ZnO (i-ZnO) and (Cu, Na and K) doped p-type ZnO thin films grown by chemical bath deposition method

Non-axial NO-VZn shallow acceptor complexes in nitrogen implanted p-type ZnO thin films

Over the past two decades, there have been numerous reports about the p-type behavior of N-doped ZnO. To date, however, its origin still remains mysterious, especially, N ion-implanted ZnO system. Herein, ZnO films were implanted with 70 keV N ions to a fluence of 1 × 1017 cm−2 at room temperature, followed by annealing in the range of 750–950 °C. The obtained p-type ZnO films have a widely hole concentration of 2.87 × 1015 ~ 2.64 × 1016 cm−3, a mobility of 1.37 ~ 7.27 cm2V-1s−1 and a resistivity of 148.3 ~ 299.4 Ω.cm. The thermal evolution of point defects and the possible shallow acceptors in N-implanted ZnO films were further investigated by means of Raman scattering, Photoluminescence (PL) and Electron paramagnetic resonance (EPR). The results show that abundant intrinsic-related defects including zinc interstitials (Zni), oxygen vacancies (VO) and zinc vacancies (VZn) were introduced during ion implantation. It is demonstrated that appropriate post-annealing can not only reduce the compensation of donor defects, but also facilitate the formation of N-related shallow acceptor complexes, both of which contribute to the p-type conduction transition of N-implanted ZnO films. The non-axial NO-VZn complexes are proposed to be a kind of potential and stable acceptors in N ion-implanted ZnO films.

A simple and effective approach to fabricate transparent p-n homojunction KZO/ZnO thin films

Transparent p-type potassium-doped ZnO (KZO) thin films are fabricated by a simple and effective approach of molten-salt treatment (MST) in KNO3 for ZnO thin films, to further fabricating p-n homojunction KZO/ZnO thin films with one-step method. XRD and PL results show the influence of MST on ZnO crystal, especially on the grain size. The transmittance of KZO/ZnO thin films has been slightly improved in visible-light region. Notably, after MST at 400 °C, hall-effect test reveals that the carrier type successfully transfers to p-type, and I-V curve hints that the p-n homojunction KZO/ZnO could be considered formed. Meanwhile, TEM, SIMS and XPS results reveal that K has doped into KZO thin films, resulting in the generated p-type carriers.

Effects of oxygen partial pressure on the structural and electrical properties of Al and Sb co-doped p-type ZnO thin films grown by pulsed laser deposition

ZnO:Al0.01Sb0.02 thin films were grown on the c-plane sapphire via pulsed laser deposition at 500 °C under different oxygen partial pressures (0.13–66.66 Pa) and their structural and electrical properties were investigated. The thin films deposited under low oxygen partial pressures (0.13–7.99 Pa) grew with a c-axis preferred orientation and a 30° rotated one. At higher oxygen partial pressures (13.33–66.66 Pa), in addition to the main c-axis-oriented domains, partial domains with 32°- and 90°-tilted c-axes were observed. The ZnO:Al0.01Sb0.02 thin films deposited at low oxygen partial pressure and high oxygen partial pressure exhibited n-type and p-type conduction, respectively. The X-ray photoelectron spectroscopy analysis exhibited that the thin films contained more Sb5+ than Sb3+; therefore, the p-type conduction was owing to the Sb5+ ions, which formed the SbZn–2VZn complex.

Study on material properties of Sn- and Cu-doped ZnO thin films as n- and p-type thermoelectric materials based on wet solution synthesis

Sn-doped n-type and Cu-doped p-type ZnO films were fabricated by depositing solutions derrived by sol–gel route on glass substrates through dip-coating cycles. The X-ray diffractometry demonstrates the typical crystalline structure of hexagonal wurzite of ZnO. The surface morphology was made through scanning electronmicroscopy showing the density and shape of films’ grains of which size was determined between 40 and 55 µm. The results of Hall measurement indicate clearly the material nature of fabricated films at room temperature. The best electrical property of Sn-doped n-type ZnO films is corresponding to Sn content of 2 at.% with carrier concentration of 3.0 × 1018 cm−3. The formation of p-type ZnO thin films was elucidated by the manner of solution synthesis that glucose was added into the solube mixer of zinc acetate and copper(II) nitrate trihydrate and the way of thermal treatment for films in vacuum with pretty good hole concentration of about 1015 cm−3. The electrical transport properties characterizing thermoelectric (TE) behavior of all films were investigated between room temperature to 400 °C (or from 300 to 673 K). The obtained results of electrical conductivity, Seebeck coefficient and power factor revealed that Sn-doped n-type ZnO films have the quality and properties similar to Al-doped ones and Cu-doped ZnO films can be promising p-type materials for TE applications.

Optical and Electrical Characterization of Stable p-Type ZnO Thin Films Obtained by Bismuth Doping.

We report the growth of stable p-type ZnO thin films obtained by doping bismuth (Bi) in ZnO and deposited over ITO coated glass substrate. The Bi doped ZnO thin films have been deposited by a sol-gel spin coating method using zinc acetate and bismuth nitrate as main precursors. The structural, optical and electrical properties of annealed Bi doped thin films have been studied in detail using X-ray diffraction (XRD), Atomic force microscopy (AFM), ellipsometry, hot probe system and Hall measurement. The presence of strong diffraction peak along (101) obtained from the XRD spectra shows that the high-quality Bi doped ZnO nanostructures grow along (101) orientation. A number of important micro-structural parameters for the thin films such as grain size, lattice parameters, stress and texture coefficient have been calculated, in order to show the effect of Bi incorporation in ZnO thin film. Further, transmittance has been calculated over the range of 350- 800 nm wavelength regions. The optical band gap of Bi doped ZnO films have also been calculated for different concentrations of Bi using the data taken by an ellipsometer. Hot probe characterization method has been used to ascertain the type of semiconductor thin film and it was observed that films doped with the concentration of 10 mol% Bi show p-type nature that was found to be stable over the period of eight months. Further, in order to calculate the resistivity, hole concentration, and mobility of p-type Bi doped ZnO thin film Hall measurement have been performed.

Effect of surface carbon contamination on the chemical states of N-doped ZnO thin films

Nitrogen-doped ZnO thin films [ZnO:N] and intentional surface carbon-contaminated ZnO:N thin films [ZnO:N@C] were grown on quartz substrates by radio frequency magnetron sputtering deposition method. The structural, electrical and optical properties as well as chemical states of elements were investigated by means of X-ray diffraction (XRD), Hall effect measurement (Hall), UV–Vis–Near infrared spectrophotometer and X-ray photoelectron spectroscopy (XPS). The results indicate that surface carbon contamination almost does not affect the band gap of ZnO:N thin films but has a strong impact on the crystal quality of ZnO:N thin film surface and results in a significant increase in tensile stress. The XPS analysis shows that the effect of surface carbon contamination treatment on the chemical states of ZnO:N thin films is remarkable. Because the stability of Zn–N bonds in N-rich local environments is nowhere near that of those in O-rich local environments, the N atoms in N-rich local environments easily bond with surface carbon atoms to form undesirable C–N bonds, thus resulting in a decrease of NO acceptors in N-rich local environments. Obviously, it is unfavorable to subsequently prepare high stability of N-doped p-type ZnO thin films.

Role of N 2p vacancy in p-type ZnO thin films

Role of N 2<i>p</i> vacancy in <i>p</i>-type ZnO thin films

Analysis of structural, optical and electrical properties of metal/p-ZnO-based Schottky diode

A systematic study of the behaviour of Pd/p-ZnO thin film Schottky diode has been reported. The p-type ZnO thin film with improved stability has been grown on n-type Si by doping ZnO with copper. Seebeck measurement confirmed the p-type nature of Cu-doped ZnO thin film. The X-ray diffraction spectra of the deposited film revealed polycrystalline nature with preferred growth orientation of (101) of ZnO film. The surface morphological study demonstrated the conformal deposition of a thin film over n-Si wafer. The estimated bandgap of Cu-doped p-type ZnO thin film from ellipsometric measurement turns out to be 3.14 eV at 300 K. The measured electrical parameters of the proposed Pd/p-ZnO Schottky diode have also been validated by the results of numerical simulation obtained by using ATLASTM device simulator.

Single crystalline ZnO radial homojunction light-emitting diodes fabricated by metalorganic chemical vapour deposition

ZnO radial p–n junction architecture has the potential for forward-leap of light-emitting diode (LED) technology in terms of higher efficacy and economical production. We report on ZnO radial p–n junction-based light emitting diodes prepared by full metalorganic chemical vapour deposition (MOCVD) with hydrogen-assisted p-type doping approach. The p-type ZnO(P) thin films were prepared by MOCVD with the precursors of dimethylzinc, tert-butanol, and tertiarybutylphosphine. Controlling the precursor flow for dopant results in the systematic change of doping concentration, Hall mobility, and electrical conductivity. Moreover, the approach of hydrogen-assisted phosphorous doping in ZnO expands the understanding of doping behaviour in ZnO. Ultraviolet and visible electroluminescence of ZnO radial p–n junction was demonstrated through a combination of position-controlled nano/microwire and crystalline p-type ZnO(P) radial shell growth on the wires. The reported research opens a pathway of realisation of production-compatible ZnO p–n junction LEDs.

Investigation of formation mechanism of Li-P dual-acceptor doped p-type ZnO

In this work, the dual-acceptor doping method has been used to produce low resistive and stable p-type ZnO thin films. The ZnO:(Li, P) films were deposited on n-type Si substrates by dual ion beam sputtering. The p-type conduction was achieved by thermal annealing at 800 °C for 20 min in N2 ambient. The lowest resistivity of 0.016 Ω cm with a hole concentration and a Hall mobility of 2.31 × 1020 cm−3 and 1.6 cm2/V s, respectively, were obtained at an optimal deposition temperature of 300 °C. X-ray photoelectron spectroscopic analysis confirmed the formation of LiZn and PZn-2VZn acceptor complexes along with a trace of PO defects resulting in a high hole concentration.

Fabrication of Sb-doped p-type ZnO Thin Films by Pulsed Laser Deposition

In this work, antimony (Sb)-doped p-type ZnO thin films on c-plane sapphire substrates have been fabricated by pulsed laser deposition, with Sb2O3 used as the dopant source. The effects of ambient gas or growth temperature on the fabrication process were investigated. The nitrogen ambient was found to be essential to achieve the p-type conduction. The Hall-effect measurements at room temperature indicated that the ZnO thin films doped with 3 at.% Sb and grown at 600 °C under N2 atmosphere exhibited p-type behavior with a hole concentration of 1.17×1017 cm−3, hole mobility of 0.63 cm2/V·s, and resistivity of 84.51 Ω·cm. X-ray diffraction and scanning electron microscopy revealed good crystallization and homogenous surface morphology of the ZnO:Sb thin films. The optical transmission spectrum of the ZnO:Sb thin films indicated that the energy band gap value was around 2.9 eV. Post-growth annealing at 650 oC converted the p-type conduction to n-type. This result implied that Sb-doping and annealing treatment were dominant factors determining native and extrinsic defects in the ZnO thin films, and thus controlling their electrical conductivity properties.

Hydrogen incorporation effect in phosphorus-doped p-type ZnO thin films grown by radio-frequency magnetron sputtering

We report on the influence of hydrogen incorporation on the conductivity of phosphorous (P) doped ZnO thin films grown by using radio-frequency (RF) magnetron sputtering.

Formation of p-type ZnO thin film through co-implantation

We present a study on the formation of p-type ZnO thin film through ion implantation. Group V dopants (N, P) with different ionic radii are implanted into chemical vapor deposition grown ZnO thin film on GaN/sapphire substrates prior to thermal activation. It is found that mono-doped ZnO by N+ implantation results in n-type conductivity under thermal activation. Dual-doped ZnO film with a N:P ion implantation dose ratio of 4:1 is found to be p-type under certain thermal activation conditions. Higher p-type activation levels (1019 cm−3) under a wider thermal activation range are found for the N/P dual-doped ZnO film co-implanted by additional oxygen ions. From high resolution x-ray diffraction and x-ray photoelectron spectroscopy it is concluded that the observed p-type conductivities are a result of the promoted formation of PZn–4NO complex defects via the concurrent substitution of nitrogen at oxygen sites and phosphorus at zinc sites. The enhanced solubility and stability of acceptor defects in oxygen co-implanted dual-doped ZnO film are related to the reduction of oxygen vacancy defects at the surface. Our study demonstrates the prospect of the formation of stable p-type ZnO film through co-implantation.