P-type Oxide Research Articles

Poisson ratio and bulk lattice constant of (Sr0.25La0.75)CrO3 from strained epitaxial thin films

About 30 nm thick (001)-oriented (Sr0.25La0.75)CrO3 (SLCO) epitaxial thin films were grown by solid-source oxide molecular beam epitaxy on four different single-crystalline cubic or pseudocubic (001)-oriented oxide substrates, LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, SrTiO3, and DyScO3, which result in lattice mismatch ranging from –2% to +1.7%. All the films are of high-quality, flat, and strained by the substrates. By assessing the evolution of the out-of-plane lattice parameter as a function of the in-plane lattice parameter of the samples, we determine both the Poisson ratio (ν = 0.32) and the bulk lattice constant (ab = 3.876 Å) of SLCO. The Poisson ratio significantly differs from LaCrO3 (ν = 0.23), and the (SrxLa1−x)CrO3 solid solution appears to obey structural Vegard's law. Since SLCO is the only one p-type transparent conductive oxide of perovskite structure and has promising thermoelectric properties, integrating SLCO in heterostructures and devices is, therefore, of paramount importance, which confers on our results their strong interest. Besides, the method used here can be straightforwardly applied to other complex oxides.

Polyol Reduction: A Low-Temperature Eco-Friendly Solution Process for p-Channel Copper Oxide-Based Transistors and Inverter Circuits.

An optimized polyol reduction method was proposed for p-type CuxO deposition using a spin-coating method at low temperatures. The film characterizations and the electrical properties of integrated thin-film transistors (TFTs) were investigated as a function of annealing temperature and polyol type. The CuxO TFTs derived from propylene glycol showed the optimal performance with an average field-effect hole mobility of 0.15 cm2 V-1 s-1, an on/off current ratio of ∼104, and a threshold voltage of -7 V at a low temperature of 220 °C. Considering few investigations on the operational/air stability of solution-processed p-type oxide TFTs, we carried out systematical studies and revealed different roles of O2 and H2O on the device performance. The low activation energy (0.16 eV) for hole transport and high voltage gain (37) of the composed complementary inverter highlight great potential for the construction of all oxide-based transparent flexible electronics and circuits.

The bipolar resistive switching and negative differential resistance of NiO films induced by the interface states

The Au/NiO/Pt structure was fabricated by magnetron sputtering on the TiOx/SiO2/Si substrates to investigate the bipolar resistive switching and negative differential resistance in details. The XRD results shows the NiO films have the (111) preferential orientation. XPS measurements shows the Ni3+ exists in NiO films, indicating that the p-type nonstoichiometric nickel oxide films forms. The I–V characteristic curves show that the bipolar resistive switching and negative differential resistance seriously depend on the scan mode of applied voltage. When the applied voltage scans from negative voltage to positive voltage and return to negative voltage, the negative differential resistance is obtained accompanied with the distinct resistive switching characteristic. However, the negative differential resistance characteristic disappears when the applied voltage swept from 0 V to positive voltage and returned to 0 V from negative voltage. This behavior is highly affected by the interface states, located at the interface of Au and p-NiO films, trap and release the holes. The schematic diagram of energy band structure and interface state can clearly depict the trap-and-release process, resulting the bipolar resistive switching accompanied with the negative differential resistance.

Influence of pressure assisted sintering and reaction sintering on microstructure and thermoelectric properties of bi-doped and undoped calcium cobaltite

Calcium cobaltite (Ca3Co4O9) is considered as one of the most promising thermoelectric p-type oxides for energy harvesting applications at temperatures above 500 °C. It is challenging to sinter this material as its stability is limited to 920 °C. To facilitate a practicable and scalable production of Ca3Co4O9 for multilayer generators, a systematic study of the influence of powder calcination, Bi doping, reaction sintering, and pressure-assisted sintering (PAS) on microstructure and thermoelectric properties is presented. Batches of doped, undoped, calcined, and not calcined powders were prepared, tape-cast, and sintered with and without uniaxial pressure at 900 °C. The resulting phase compositions, microstructures, and thermoelectric properties were analyzed. It is shown that the beneficial effect of Bi doping observed on pressureless sintered samples cannot be transferred to PAS. Liquid phase formation induces distortions and abnormal grain growth. Although the Seebeck coefficient is increased to 139 μV/K by Bi doping, the power factor is low due to poor electrical conductivity. The best results were achieved by PAS of calcined powder. The dense and textured microstructure exhibits a high power factor of 326 μW/m K2 at 800 °C but adversely high thermal conductivity in the relevant direction. The figure of merit is higher than 0.08 at 700 °C.

Highly sensitive thermoelectric touch sensor based on p-type SnOx thin film

Here, the ability of using p-type tin oxide (SnOx) thin films as a thermal sensor has been investigated. Firstly, the thermoelectric performance was optimized by controlling the thickness of the SnOx film from 60 up to 160 nm. A high Seebeck coefficient of +263 μV K−1 and electrical conductivity of 4.1 × 102 (S m−1) were achieved in a 60 nm thick SnOx film, due to a compact nanostructured film and the absence of the Sn metallic phase, which was observed for the thicker SnOx film leading to a typical thermoelectric transport properties of a n-type Sn film. Moreover, x-ray photoelectron spectroscopy revealed the co-existence of SnO (79.7%) and SnO2 (20.3%) phases in the 60 nm thick SnOx film, while the optical measurements revealed an indirect gap of 1.8 eV and a direct gap of 2.7 eV, respectively. The 60 nm-SnOx thin film have been tested as a thermoelectric touch sensor, achieving a Vsignal/Vnoise ≈ 20, with a rise time <1 s. Therefore, this work provides an efficient way for developing highly efficient thermal sensors with potential use in display technologies.

Low temperature synthesis of α- and β-phase Bi2O3 thin film via B doping: tailoring optical band gap and n- to p-type Bi2O3

In this article, we fabricated p-type bismuth oxide (Bi2O3) thin films with tailoring optical band gap by boron (B) doping, for the first time. In addition, an effort is made to see the influence of B doping on the surface morphological, structural, optical and electrical transport properties of Bi2O3 thin films. Field Emission Scanning Electron Microscope (FESEM) images demonstrated that the film surface is covered by well-defined multigonal shaped particles and glassy surface. α-Bi2O3 (monoclinic) and β-Bi2O3 (tetragonal) phase structures are confirmed by X-ray diffraction (XRD) analysis. The average crystallite size is decreased from 46.62 to 23.57 nm with B doping concentration. Moreover, the average strain, stress and dislocation density values are calculated using XRD data. The optical band gaps have changed from 3.70 to 3.99 eV with the texture coefficient values of $$ \left( {11\bar{2}} \right) $$ orientation plane. A minimum refractive index and optical conductivity value are found to be 2.58 and 2.23 × 106 Ω−1 m−1 for 3 at.% B content. Electrical parameters, viz. resistivity, sheet resistance, charge carrier concentration, mobility and conductivity types are investigated using a van der Pauw Hall measurement system. Electrical measurements demonstrated that the resistivity values are found to vary in the range of 1.23–1.82, × 103 Ω-m with increasing B doping concentrations. A high-quality factor is obtained 5.52 × 10−6 Ω−1 for higher doping content at 550 nm wavelength. This work promotes a new vision into the fabrication of p-type Bi2O3 thin films and facilitates their application in the field of optoelectronic devices, viz. window layer coating, p–n junction and photovoltaic applications.

Large-Scale Computational Identification of p-Type Oxide Semiconductors by Hierarchical Screening

With potentials to outperform traditional semiconductors, oxide semiconductors are penetrating into a wide range of energy, environmental, and electronic applications. However, an insufficient libr...

High-Performance Amorphous Silicon Thin Film Solar Cells Prepared at 100 °C: Toward Flexible Building-Integrated Photovoltaics

For low-cost and lightweight polymer/plastic substrates in flexible building-integrated photovoltaic (BIPV) modules, low-temperature processing is essential. Amorphous silicon (a-Si:H) requires processing at a temperature of 200–250 °C by plasma-enhanced chemical vapor deposition to obtain satisfactory optoelectronic properties, which limits such substrates in terms of thermal budget. This study is focused on the fabrication of p–i–n-type a-Si:H solar cells at relatively low temperatures (100 °C). Intrinsic a-Si:H films with large optical gaps (1.83 eV) were prepared at 100 °C using a high hydrogen dilution ratio. In addition, p-type amorphous silicon oxide and n-type microcrystalline silicon oxide films with large optical gaps and suitable conductivities were prepared at 100 °C using a gas mixture containing the dopant B2H6 or PH3 and CO2. Finally, an a-Si:H p–i–n cell was fabricated at 100 °C; it exhibited an excellent power conversion efficiency of 9.0%, which was higher than those reported for a-Si:H thin film photovoltaics prepared at 100 °C. We believe that this study will open promising routes for the development of high-performance and flexible BIPVs.

Numerical Simulation of Crystalline Silicon Heterojunction Solar Cells with Different p-Type a-SiOx Window Layer

In this study, p-type amorphous silicon oxide (a-SiOx) films are deposited using a radio-frequency inductively-coupled plasma chemical vapor deposition system. Effects of the CO2 gas flow rate on film properties and crystalline silicon heterojunction (HJ) solar cell performance are investigated. The experimental results show that the band gap of the a-SiOx film can reach 2.1 eV at CO2 flow rate of 10 standard cubic centimeters per minute (sccm), but the conductivity of the film deteriorates. In the device simulation, the transparent conducting oxide and contact resistance are not taken into account. The electrodes are assumed to be perfectly conductive and transparent. The simulation result shows that there is a tradeoff between the increase in the band gap and the reduction in conductivity at increasing CO2 flow rate, and the balance occurs at the flow rate of six sccm, corresponding to a band gap of 1.95 eV, an oxygen content of 34%, and a conductivity of 3.3 S/cm. The best simulated conversion efficiency is 25.58%, with an open-circuit voltage of 741 mV, a short-circuit current density of 42.3 mA/cm2, and a fill factor of 0.816%.

Radiation-Tolerant p-Type SnO Thin-Film Transistors

This present work investigated the effects of proton-beam irradiation on SnO-based p-type oxide thin-film transistors (TFTs) for the first time. The experiments were performed using a 5-MeV proton beam with doses ranging from $10^{12}$ to $10^{14}\,\,\textsf {p}\cdot \textsf {cm}^{-2}$ . The experimental results showed that the transfer curves of the p-type SnO TFT rarely changed following the proton irradiation at every irradiation condition, indicating that the p-type SnO TFT could be potentially useful in implementing complementary-logic-based oxide TFT circuits operating in harsh environments. The insensitivity of current conduction paths to SnO lattice disorder was considered as a possible mechanism for the observed radiation tolerance of the p-type SnO TFTs.

A review on recent progress of p-type nickel oxide based gas sensors: Future perspectives

Recently, technological and industrial advances uninterruptedly cause the release of hazardous and toxic gases that are harmful to human life; as a result gas sensing devices that are highly sensitive and selective to such gases are in a high demand. Presently, gas sensors based on p-type NiO are pleasing more consideration, because of its excellent reproducibility, high specific surface areas, great sensitivity, low cost and environmental friendly. Herein, we reviewed the different synthesis methods on p-type NiO nanostructures and their application as gas sensors. The fundamental gas sensing mechanism related to the p-type NiO is briefly explained. The effects of noble metals, transition metals, and transition metal dichalcogenide and phosphors materials on the NiO gas sensing performance are also discussed in detail. Influence of 0D, 1D, 2D and 3D heterostructures on NiO gas sensing characteristics are also given. The arrangement of various semiconductor metal oxides to form heterostructures which further improve the selectivity and sensitivity of the sensing parameters is also discussed and we show that number of publications on heterostructures related to NiO increased drastically since the year 2010.

Investigation on the p-type formation mechanism of nitrogen ion implanted ZnO thin films induced by rapid thermal annealing

N-doped p-type zinc oxide (ZnO) thin films were prepared by rapid thermal annealing (RTA) of nitrogen ion implanted high quality ZnO epitaxial layers. Annealing at 900 °C in a nitrogen atmosphere leads to the conversion of conductivity from n to p-type with a hole concentration of 9.60×1017 cm-3, which is reflected in photoluminescence spectra. To reveal the thermal activation and doping mechanism of this film, the samples were also analyzed by Raman scattering and X-ray photoelectron spectroscopy. The results indicate that elimination of the Zni related shallow donors and the formation of shallow acceptor complex No-VZn account for the stable p-type conductivity of N-doped ZnO. The shallow acceptor state is calculated at 0.161 eV above the valence band edge.

Fast rate oxidation to Cu2O, at room temperature, of metallic copper films produced by the argon-plasma bombardment of CuO films

Using a powerful argon plasma equipment, 400 °C sintered CuO thin films were rapidly reduced to metallic copper for treatment times less than 35 s. The transformation caused the crystallographic plane of Cu to appear at the expense of the CuO ones. Likewise, transmittance spectra showed a rapid decline while reflectance spectra exhibited a fast increase towards the infrared region. The last effect was caused by the production of free electrons of metallic copper, which was also evidenced by a low electrical resistivity of 30 μΩ∙cm. The plasma-produced Cu samples displayed a fast oxidation rate at room temperature and atmospheric conditions, which has been rarely mentioned in literature. Interestingly, instead of CuO, the oxidation produced Cu2O films, which is a p-type semiconductor oxide with high potential for several applications. Even though it only requires some hours, the oxidation was allowed to take place for one week. X-ray diffraction, X-ray photoelectron spectroscopy, transmittance-reflectance, and resistivity measurements demonstrated the oxidation of Cu to Cu2O. Similar phenomena were confirmed for lower sintering temperatures of the CuO films. Nevertheless, the oxidation tendency of plasma-obtained Cu films showed a dependence on CuO sintering temperature and on plasma processing time. A stable form of metallic copper, that does not oxidize, was produced at lower sintering temperatures and longer plasma processing times. At other conditions, a metastable form of metallic copper was obtained, which readily transformed to Cu2O. Based on the results, a transformation pathway scheme was elaborated. The scheme can provide with a route to rapidly produce high quality Cu2O films on glass with tunable electrical and optical properties.

Plasmonic Ag nanoparticles arbitrated enhanced photodetection in p-NiO/n-rGO heterojunction for future self-powered UV photodetectors

We report on the low cost and low temperature chemical synthesis of p-type nickel oxide (NiO) and n-type reduced graphene oxide (rGO) and their integration onto ITO/glass substrate to form p-NiO/n-rGO heterojunction for possible self-powered ultraviolet (UV) photodetector applications. Different spectroscopies and microscopes were employed to study their microstructural and surface properties. Whereas, the electrical characterizations have been performed on the devices to ascertain the responsivity, detectivity, external quantum efficiency and temporal responses under dark and UV illumination. It is noteworthy that rGO has not only been used as an n-type semiconductor, but also acted as an electron transport layer, which satisfactorily separates out the electrons from the generated carrier pairs, leading to enhanced photoresponse. Furthermore, efforts were also consecrated to synthesize Ag nanoparticles (NPs) of ∼5 nm radius. The integration of Ag NPs on the conventional NiO/rGO heterojunction facilitates an improved UV light absorption property. It was understood that the performance improvement was owed to the local surface plasmon resonance of Ag NPs within the active layer of NiO. Surprisingly, both the devices (with and without Ag NPs) exhibit photovoltaic behavior which shows its potential for self-powered device application. When the Ag NPs embedded device is concerned, it showed better on/off ratio (6.3 × 103), high responsivity (72 mAW−1), large detectivity (3.95 × 1012 Jones), and high efficiency (24.46%) as compared to the conventional NiO/rGO heterojunction one (without Ag NPs). The variation in the photoresponse and improved charge transport was explained through a band-diagram, which also showcases a comprehensive understanding on the operational principle of the fabricated self-powered devices. Thus, this self-powered photodetector driven by built in electric field is operated independently and can be attached with any other electronic gadgets for internet of things applications.

P-n-Sensitized Heterostructure Co3O4/Fullerene with Highly Efficient Photoelectrochemical Performance for Ultrasensitive DNA Detection.

Significantly sensitized architectures meeting the requirements of high photoelectric conversion efficiency and promising photocurrent intensity are extremely desirable, but challenges in sensitizer development and efficiency in photoelectrochemical (PEC) fields remain. In this paper, the p-type metal oxide semiconductor Co3O4 was attached as an effective photosensitizer to n-type fullerene C60 in view of appropriately matched energy band levels to form the highlighted p-n-sensitized heterostructure Co3O4/fullerene, with facilitated charge separation and accelerated carrier mobility. Compared with traditional p-n heterostructure, the p-n-sensitized heterostructure Co3O4/fullerene illustrated a wider range for light absorption with further enhanced light-harvesting capability, thereby leading to more exceptional PEC performance containing remarkably promoted photoelectric conversion efficiency and improved photocurrent intensity. Impressively, the photocurrent intensity obtained by Co3O4/fullerene was about sixfold higher than that of fullerene alone, and this achievement was quite favored compared to the reported works for fullerene sensitization, which could be responsible for the advancement of detection sensitivity for the subsequently constructed biosensor. Unambiguously, given the p-n-sensitized heterostructure Co3O4/fullerene of high PEC activity, the well-fabricated three-dimensional DNA walker applied as a target-cascade signal amplification strategy, and the Au layer employed as the specific linker between the photoactive material and the signal amplification product, a smart PEC biosensor was successfully enabled for ultrasensitive investigation of the model DNA (a fragment of the p53 gene), showing a wide linear range of 60 to 1 × 105 aM and a detection limit of 20 aM. This proposed PEC biosensor provided acceptable insights into the clinic analysis, disease therapies, and other relevant subjects.

Selective carbon monoxide sensing properties of bismuth iron oxide

Among nitrogen oxide (NO2), methane (CH4), isobutane (i-C4H10) and carbon monoxide (CO) gases; selective CO sensing has been reported for perovskite p-type bismuth iron oxide (BFO) gas sensor at 200 °C. We have adopted glycine based auto-combustion route to synthesize phase pure BFO powders. For 100 ppm of CO, response% is reported to be 60% with response and recovery times of 85 s and 102 s respectively. BFO sensor yields high sensitivity (n∼ 1.27) and high selectivity with respect to NO2 (selectivity coefficient, κ ∼217.5), CH4 (κ∼994.2) and i-C4H10 (κ∼8.4). The sensor also exhibits excellent repeatability and long-term stability. The selective CO sensing characteristics of BFO sensor has been attributed to the catalytic nature of BFO surface towards efficient CO oxidation. Lower metal-oxygen binding energy, favorable ‘d’ orbital electron configuration of surface iron cations and nature of the surface adsorbed species are demonstrated to be the three dominant parameters in yielding superior catalytic activity towards CO oxidation in order to promote selective CO sensing.

Opto-electronic properties of Co-Zn-Ni-O films deposited by RF-sputtering at ambient-temperature

Co-Zn-Ni-O thin films were grown on glass at ambient temperature (TS < 65 °C) by co-sputtering from Co3O4, ZnO, and NiO targets to determine the structural and opto-electronic properties across the ternary composition space. Compositional domains with spinel, wurtzite, rock-salt, and mixed phases were observed, albeit with very weak X-ray diffraction peaks, overall suggesting the likely presence of a co-existent amorphous component. The electrical conductivity had a maximum value of ∼35 S/cm that occurs where the optical absorption is also the strongest. The work functions range from 5.0 to 5.8 eV for all samples, but with no clear composition-based trends. Overall, it appears that the optoelectronic properties of the Co-Zn-Ni-O materials are much less sensitive to substrate temperature compared to other p-type oxide semiconductors, resulting in technologically-relevant ambient-temperature-deposited thin films.

Influence of oxide density on O2 diffusivity in thermally grown SiO2 on Si and SiGe and on oxidation kinetics

Ultrathin compressively strained SiGe layers is one of the most promising materials for high mobility channels of p-type metal oxide semiconductor field effect transistors (pMOSFETs). Fabrication of such layers by SiGe thermal oxidation processes need to be well controlled, which then require well-controlled oxidation kinetics and oxide properties for use in an industrial environment. In the present paper, we address oxidation kinetics of Si, Si0.9Ge0.1 and Si0.7Ge0.3 by means of dry furnace oxidation and dry rapid thermal oxidation (RTO). We showed in a previous paper that oxidation of SiGe by means of either dry furnace oxidation or dry RTO is limited by diffusion of the oxidizing species through the growing oxide and that the oxidation rate of SiGe is significantly higher than the one of Si. In the present paper we focus on the influence of the oxide density measured by Soft x-ray Reflectivity on oxidation kinetics. It is shown that the lower the density of the oxide is, the higher the oxidation rate is, in agreement with an oxidation regime that is governed by diffusion of O2 through the growing oxide. Finally, we propose a model of O2 diffusivity that depends on the oxide density through the modulation of the diffusion barrier. The modulation of the diffusion barrier is found to be linearly dependent on the oxide density.

Transparent nanoporous P-type NiO films grown directly on non-native substrates by anodization

While electrochemical anodization has been used to form a number of nanostructured n-type semiconducting metal oxides for optoelectronic device applications, there exists a dearth of p-type metal oxide films that are solution processable. Herein, we formed p-type semiconducting NiO films by vacuum depositing Ni thin films on non-native substrates (transparent conductive oxide (TCO)-coated glass substrates and silicon wafers) using magnetron sputtering, and subsequently anodizing and annealing the Ni films. The Ni films were subjected to electrochemical anodization in diethylene glycol based organic electrolytes and subsequently annealed at 600 °C to form nanoporous NiO films with a pore size of ~ 20 nm. Runaway etching is a key issue in Ni anodization which was mitigated through the use of ice bath cooling and galvanostatic anodization. The choice of substrate is found to be critical to the resulting morphology owing to the differing surface roughness. Crystalline NiO is found to have formed from Ni(OH)2 and NiOOH during annealing, and an additional NiSi layer is noted for NiO films on Si wafers. The bandgap of the NiO was estimated to be 3.5 eV. Electrochemical impedance spectroscopy and Mott–Schottky analysis confirmed p-type semiconducting behaviour, and enabled measurement of an acceptor density (NA) of 2.85 × 1018 cm−3 and a flatband potential (VFB) of 0.687 V versus Ag/AgCl.

Transparent Inorganic Copper Bromide (CuBr) p-Channel Transistors Synthesized From Solution at Room Temperature

Transparent polycrystalline p-channel copper bromide (CuBr) thin-film transistors (TFTs) are fabricated using a simple one-step spin coating at room temperature. Optimized CuBr TFTs operate in depletion mode with an on-voltage of 35 V and exhibit a hole mobility of 0.15 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , high on/off current ratio ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> and cycling bias sweep/air stabilities. The performance is superior to that of most solution-processed p-type oxide TFTs, highlighting CuBr as a promising p-type candidate for nextgeneration printable transparent electronics.