N-type Zinc Research Articles

Hot-point probe measurements of N-type and P-type ZnO films

PurposeThis paper aims to develop a low-cost hot-point which can facilitate the conductivity type of N-type and P-type zinc oxide (ZnO) films. In this study, a diode was made out of the N-type and P-type ZnO films, and current-voltage (I-V) characteristic measurements were conducted.Design/methodology/approachA low-cost hot-point probe consists of a soldering iron station, digital multimeter and a pair of probes. The setup is adopted to identify N-type and P-type ZnO films. In particular, P-type films have been deployed for the first time.FindingsHot-point probe setup has been successfully developed. Measurements of N-type films give a positive voltage reading, whereas P-type films give a negative voltage reading. The measured voltage dominates at 1 per cent for N-type Ga and at 15 per cent for P-type Na. I-V characteristics of the fabricated diode showed a similar trend to the conventional diode.Research limitations/implicationsN-type has been often attempted. However, P-type has rarely been attempted because of the self-compensation effect in ZnO. There is a need to verify the conductivity type of ZnO films, especially P-type, as P-type films are not stable. The hot-point probe setup serves as a quick means to verify P-type ZnO films.Originality/valueTo the best of the authors’ understanding, this verification tool was developed and deployed to verify the N-type and P-type ZnO films. The P-type films are coated on top of the N-type films for diode I-V measurements.

Tuning the Seebeck effect in C60-based hybrid thermoelectric devices through temperature-dependent surface polarization and thermally-modulated interface dipoles.

Fullerene (C60) is an important n-type organic semiconductor with high electron mobility and low thermal conductivity. In this work, we report the experimental results on the tunable Seebeck effect of C60 hybrid thin-film devices by adopting different oxide layers. After inserting n-type high-dielectric constant titanium oxide (TiOx) and zinc oxide (ZnO) layers, we observed a significantly enhanced n-type Seebeck effect in oxide/C60 hybrid devices with Seebeck coefficients of -5.8 mV K-1 for TiOx/C60 and -2.08 mV K-1 for ZnO/C60 devices at 100 °C, compared with the value of -400 μV K-1 for the pristine C60 device. However, when a p-type nickel oxide (NiO) layer is inserted, the C60 hybrid devices show a p-type to n-type Seebeck effect transition when the temperature increases. The remarkable Seebeck effect and change in Seebeck coefficient in different oxide/C60 hybrid devices can be attributed to two reasons: the temperature-dependent surface polarization difference and thermally-dependent interface dipoles. Firstly, the surface polarization difference due to temperature-dependent electron-phonon coupling can be enhanced by inserting an oxide layer and functions as an additional driving force for the Seebeck effect development. Secondly, thermally-dependent interface dipoles formed at the electrode/oxide interface play an important role in modifying the density of interface states and affecting the charge diffusion in hybrid devices. The surface polarization difference and interface dipoles function in the same direction in hybrid devices with TiOx and ZnO dielectric layers, leading to enhanced n-type Seebeck effect, while the surface polarization difference and interface dipoles generate the opposite impact on electron diffusion in ITO/NiO/C60/Al, leading to a p-type to n-type transition in the Seebeck effect. Therefore, inserting different oxide layers could effectively modulate the Seebeck effect of C60-based hybrid devices through the surface polarization difference and thermally-dependent interface dipoles, which represents an effective approach to tune the vertical Seebeck effect in organic functional devices.

Random Dopant Fluctuation-Induced Threshold Voltage Variation-Immune Ge FinFET With Metal–Interlayer–Semiconductor Source/Drain

The impact of process-induced random dopant fluctuation (RDF)-induced threshold voltage ( $V_{\mathrm{ th}}$ ) variation on the performance of 7-nm n-type germanium (Ge) FinFETs with and without a metal–interlayer–semiconductor (MIS) source/drain (S/D) structure is investigated using 3-D TCAD simulations. In order to reduce the RDF-induced $V_{\mathrm{ th}}$ variation, an MIS S/D structure with a heavily doped n-type zinc oxide (ZnO) interlayer is used in the S/D region of the Ge FinFET. Thus, without performance degradation, the Ge FinFET with an MIS S/D structure achieves approximately threefold reduction in the RDF-induced $V_{\mathrm{ th}}$ variation (versus without an MIS S/D structure). The impact of various fin parameters (i.e., fin height and fin width) on the RDF-induced $V_{\mathrm{ th}}$ variation is also investigated. It is noteworthy that variation is suppressed as the fin height (fin width) increases (decreases).

Carriers concentration tailoring and phonon scattering from n-type zinc oxide (ZnO) nanoinclusion in p- and n-type bismuth telluride (Bi2Te3): Leading to ultra low thermal conductivity and excellent thermoelectric properties

ZnO/Bi2Te3 (p- and n-type) nanocomposites with 5 vol% nanosized ZnO content are fabricated via ball milling mixing and spark plasma sintering. Herein, ZnO is an intrinsic n-type semiconductor with low thermal conductivity. In ZnO/Bi2Te3 (p- and n-type) composites, ZnO exits as nanoinculsions to more effectively inhabit the phonon transporting, and simultaneously tailor the carrier concentration of composite materials. Ultra low lattice thermal conductivity (0.22–0.3 W/mK2) is obtained in both materials. ZnO nanoinclusions can lead to higher carriers and high electronic conductivity of n-type Bi2Te2.7Se0.3 composite material. Since electronic thermal conductivity is dominant (75%) in thermal conductivity, more phonon scattering from defects and nanoinclusions does not effectively improve ZT values of n-type materials. In contrast, while ZnO addition can obviously reduce the carrier concentration and lead to the resistivity's large increase, ZnO nanoinclusions in p-type Bi1.5Sb0.5Te3 composite material would significantly decrease the lattice and total thermal conductivity. As a result, an enhancement (30%) of ZT values (∼1.3) can be achieved in composite material compared with p-type ingot.

The electrical properties of n-ZnO/p-SnO heterojunction diodes

In the present work, n-type zinc oxide (ZnO) and p-type tin monoxide (SnO) based heterostructure diodes were fabricated on an indium-tin-oxide glass using the radio frequency magnetron sputtering technique. The prepared ZnO/SnO diodes exhibited a typical rectifying behavior, with a forward to reverse current ratio about 500 ± 5 at 2 V and turn on voltage around 1.6 V. The built-in voltage of the diode was extracted to be 0.5 V based on the capacitance-voltage (C–V) measurement. The valence and conduction band offsets were deliberated through the band energy diagram of ZnO/SnO heterojunction, as 1.08 eV and 0.41 eV, respectively. The potential barrier-dependent carrier transportation mechanism across the space charge region was also investigated.

Effect of Oxide Intermediate Layers on Pyramidally Textured Cu2O/ZnO Solar Cells Prepared By Electrodeposition

Thin-film oxide solar cells composed of a pn heterojunction of p-type cuprous oxide (Cu2O) and n-type zinc oxide (ZnO) have attracted increasing attention as a promising candidate for a low-cost and environment-friendly photovoltaic device because the main constituent elements of copper, zinc, and oxygen are earth abundant and non toxic. In this solar cells, p-type Cu2O with a bandgap energy of 2.1 eV acts as a solar light absorber, and exhibits a theoretical conversion efficiency of ca. 18%. To date, many efforts have been devoted to develop the fabrication methods and improve the photovoltaic conversion efficiency of Cu2O/ZnO-based solar cells.1 We have reported that p-Cu2O/n-ZnO heterojunction can be formed using only electrodeposition in aqueous solutions (< 80°C), where no vacuum process and no post annealing were employed.2 This preparation method, therefore, potentially offers a simple and large scalable route to more low-cost and environment-friendly solar cells. To improve the conversion efficiency, we recently prepared pyramidally textured ZnO films by electrodeposition.3 Pyramidally textures are a well-known structure that exhibits a large light-scattering effect, making efficient solar-light absorption possible. Indeed, the obtained pyramidally textured ZnO films showed a high haze value of 52% in the visible region, and pyramidally textured Cu2O/ZnO solar cells showed a 1.3 times higher short circuit current density than that using a traditional planar ZnO.3 As another approach to improve the conversion efficiency, we demonstrated that electrodeposited highly resistive ZnO thin layers inserted between the Cu2O/ZnO interface can act as an effective intermediate layer.4 Oxide intermediate layers with a wide bandgap energy, such as gallium oxide (GaO x ) and zinc-magnesium oxide (ZnMgO x ), have also been reported to act as an effective interface buffer layer.1 In the present study, these oxide intermediate layers have been inserted between the pyramidally textured Cu2O/ZnO interface to further improve the conversion efficiency. The oxide intermediate layers were prepared using solution processes including electrodeposition and spin-coating techniques, and the photovoltaic performances were evaluated. In one case, for example, a ~1.7 times higher conversion efficiency was achieved by using a solution-processed GaO x intermediate layer, where both the short circuit current density and open circuit voltage increased significantly. Acknowledgement: This work was supported by JSPS KAKENHI, JAPAN.

Analysis of Schottky Contact Formation in Coplanar Au/ZnO/Al Nanogap Radio Frequency Diodes Processed from Solution at Low Temperature.

Much work has been carried out in recent years in fabricating and studying the Schottky contact formed between various metals and the n-type wide bandgap semiconductor zinc oxide (ZnO). In spite of significant progress, reliable formation of such technologically interesting contacts remains a challenge. Here, we report on solution-processed ZnO Schottky diodes based on a coplanar Al/ZnO/Au nanogap architecture and study the nature of the rectifying contact formed at the ZnO/Au interface. Resultant diodes exhibit excellent operating characteristics, including low-operating voltages (±2.5 V) and exceptionally high current rectification ratios of >10(6) that can be independently tuned via scaling of the nanogap's width. The barrier height for electron injection responsible for the rectifying behavior is studied using current-voltage-temperature and capacitance-voltage measurements (C-V) yielding values in the range of 0.54-0.89 eV. C-V measurements also show that electron traps present at the Au/ZnO interface appear to become less significant at higher frequencies, hence making the diodes particularly attractive for high-frequency applications. Finally, an alternative method for calculating the Richardson constant is presented yielding a value of 38.9 A cm(-2) K(-2), which is close to the theoretically predicted value of 32 A cm(-2) K(-2). The implications of the obtained results for the use of these coplanar Schottky diodes in radio frequency applications is discussed.

Relationship between microstructure and electronic properties of energetically deposited zinc tin oxide

Thin films of amorphous n-type zinc tin oxide have been energetically deposited from a filtered cathodic vacuum arc at moderate temperatures. The characteristics of these films span a range suitable for semiconductor devices and transparent conducting oxide interconnects with carrier concentration and mobility dependent on local bonding. X-ray photoelectron spectroscopy (XPS) and electron diffraction have revealed that acceptor-like Sn(II) bonding in the films decreased with increasing growth temperature, resulting in higher n-type carrier concentrations. XPS and in situ Ar plasma treatment showed that downward surface band bending resulted from OH attachment. Persistent photoconductivity was attributed to the photoionization of oxygen vacancies.

Solution-processible organic-inorganic hybrid bipolar field-effect transistors

Organic-inorganic hybrid bipolar field-effect transistors (HBFETs) comprising a layer of p-type organic poly(3-hexylthiophene) (P3HT) separated from a parallel layer of n-type inorganic zinc oxide (ZnO) were demonstrated by solution processing. In order to achieve balanced hole and electron mobilities, we initially optimized the hole-transporting P3HT channel by the addition of the polar non-solvent acetonitrile (AN) to P3HT solutions in chloroform, which induced a selfassembled nano-fibril morphology and an enhancement of hole mobilities. For the electron channel, a wet-chemically-prepared ZnO layer was optimized by thermal annealing. Unipolar P3HT FET with 5% AN exhibited the highest hole mobility of 7.20 × 10−2 cm2V−1s−1 while the highest electron mobility (3.64 × 10−2 cm2V−1s−1) was observed in unipolar ZnO FETs annealed at 200°C. The organic-inorganic HBFETs consisting of the P3HT layer with 5% AN and ZnO annealed at 200°C exhibited well-balanced hole and electron mobilities of 1.94 × 10−2 cm2V−1s−1 and 1.98 × 10−2 cm2V−1s−1, respectively.

Rectifying and Nitrogen Monoxide Gas Sensing Properties of a Spin-Coated ZnO/CuO Heterojunction

We present the rectifying and nitrogen monoxide (NO) gas sensing properties of an oxide semiconductor heterostructure composed of n-type zinc oxide (ZnO) and p-type copper oxide thin layers. A CuO thin layer was first formed on an indium-tin-oxide-coated glass substrate by sol-gel spin coating method using copper acetate monohydrate and diethanolamine as precursors; then, to form a p-n oxide heterostructure, a ZnO thin layer was spin-coated on the CuO layer using copper zinc dihydrate and diethanolamine. The crystalline structures and microstructures of the heterojunction materials were examined using X-ray diffraction and scanning electron microscopy. The observed current-voltage characteristics of the p-n oxide heterostructure showed a non-linear diode-like rectifying behavior at various temperatures ranging from room temperature to 200 o C. When the spin-coated ZnO/CuO heterojunction was exposed to the acceptor gas NO in dry air, a significant increase in the forward diode current of the p-n junction was observed. It was found that the NO gas response of the ZnO/CuO heterostructure exhibited a maximum value at an operating temperature as low as 100 o C and increased gradually with increasing of the NO gas concentration up to 30 ppm. The experimental results indicate that the spin-coated ZnO/CuO heterojunction structure has significant potential applications for gas sensors and other oxide electronics.

Formation of a hybrid pn junction via p-type aluminium induced crystallized polycrystalline silicon on hydrothermally grown n-type zinc oxide nanowires

p-Type silicon coated zinc oxide (ZnO) nanowire heterojunction was fabricated using a combination of aluminium induced crystallization (AIC) and hydrothermal growth. The p-type AIC Si/n-type ZnO nanowires stacked layers were extensively characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), UV–vis spectroscopy, XRD, photoluminescence emission spectroscopy and electrical measurements. Photovoltaic measurements indicate that the device is light-sensitive and maybe of potential in sensor applications.

A facile method to oxidize p-type Zinc Selenide nanowires into n-type Zinc Oxide nanowires

A facile method was used to oxidize p-type Zinc Selenide (ZnSe) nanowires into n-type Zinc Oxide (ZnO) through a 700 °C annealing process in air. Single crystal ZnSe nanowires, with a hole concentration of 0.805 × 1018 cm−3 and a negative photoconductivity, were oxidized into polycrystalline ZnO nanowires with an electron concentration of 4.88 × 1018 cm−3 and a positive photoconductivity. Additionally, both the as-synthesized ZnSe nanowires and the post-oxidized ZnO nanowires presented excellent optoelectronic properties. This method can be used to construct radial p–n junctions or other nano-devices based on a single NW through a regioselective oxidation process.

Layer-by-Layer Assembled 2D Montmorillonite Dielectrics for Solution-Processed Electronics.

Layer-by-layer assembled 2D montmorillonite nanosheets are shown to be high-performance, solution-processed dielectrics. These scalable and spatially uniform sub-10 nm thick dielectrics yield high areal capacitances of ≈600 nF cm(-2) and low leakage currents down to 6 × 10(-9) A cm(-2) that enable low voltage operation of p-type semiconducting single-walled carbon nanotube and n-type indium gallium zinc oxide field-effect transistors.

Highly spectrum-selective ultraviolet photodetector based on p-NiO/n-IGZO thin film heterojunction structure.

Ultraviolet photodetector with p-n heterojunction is fabricated by magnetron sputtering deposition of n-type indium gallium zinc oxide (n-IGZO) and p-type nickel oxide (p-NiO) thin films on ITO glass. The performance of the photodetector is largely affected by the conductivity of the p-NiO thin film, which can be controlled by varying the oxygen partial pressure during the deposition of the p-NiO thin film. A highly spectrum-selective ultraviolet photodetector has been achieved with the p-NiO layer with a high conductivity. The results can be explained in terms of the "optically-filtering" function of the NiO layer.

Fabrication and Characterization of N-Type Zinc Oxide/P-Type Boron Doped Diamond Heterojunction

Abstract Diamond and ZnO are very promising wide-bandgap materials for electronic, photovoltaic and sensor applications because of their excellent electrical, optical, physical and electrochemical properties and biocompatibility. In this contribution we show that the combination of these two materials opens up the potential for fabrication of bipolar heterojunctions. Semiconducting boron doped diamond (BDD) thin films were grown on Si and UV grade silica glass substrates by HFCVD method with various boron concentration in the gas mixture. Doped zinc oxide (ZnO:Al, ZnO:Ge) thin layers were deposited by diode sputtering and pulsed lased deposition as the second semiconducting layer on the diamond films. The amount of dopants within the films was varied to obtain optimal semiconducting properties to form a bipolar p-n junction. Finally, different ZnO/BDD heterostructures were prepared and analyzed. Raman spectroscopy, SEM, Hall constant and I-V measurements were used to investigate the quality, structural and electrical properties of deposited heterostructures, respectively. I-V measurements of ZnO/BDD diodes show a rectifying ratio of 55 at ±4 V. We found that only very low dopant concentrations for both semiconducting materials enabled us to fabricate a functional p-n junction. Obtained results are promising for fabrication of optically transparent ZnO/BDD bipolar heterojunction.

Light-Emitting n-ZnO Nanotube/n&lt;sup&gt;&amp;#x002B;&lt;/sup&gt;-GaAs Heterostructures Processed at Low Temperatures

In this letter, a light-emitting heterostructure is designed and manufactured using vertically aligned n-type zinc oxide nanorods (ZnO NRs) on n + -GaAs wafers. The chemically grown ZnO NRs were also converted to nanotubes (NTs) using 2 molar KCl solution and the device fabrication was repeated using them. Both types exhibited a significant visible light at a forward bias of 1 V but with different brightness. Photoluminescence ~390 nm from NRs and NTs was obtained and the current injection in these devices is explained by a tunneling phenomenon.

Large scale integration of flexible non-volatile, re-addressable memories using P(VDF-TrFE) and amorphous oxide transistors

Ferroelectric polymers and amorphous metal oxide semiconductors have emerged as important materials for re-programmable non-volatile memories and high-performance, flexible thin-film transistors, respectively. However, realizing sophisticated transistor memory arrays has proven to be a challenge, and demonstrating reliable writing to and reading from such a large scale memory has thus far not been demonstrated. Here, we report an integration of ferroelectric, P(VDF-TrFE), transistor memory arrays with thin-film circuitry that can address each individual memory element in that array. n-type indium gallium zinc oxide is used as the active channel material in both the memory and logic thin-film transistors. The maximum process temperature is 200 °C, allowing plastic films to be used as substrate material. The technology was scaled up to 150 mm wafer size, and offers good reproducibility, high device yield and low device variation. This forms the basis for successful demonstration of memory arrays, read and write circuitry, and the integration of these.

(Invited) Anti-Ambipolar, Gate-Tunable p-n Heterojunctions

The recent emergence of two-dimensional (2D) materials has enabled the realization of atomically thin heterostructure devices [1]. Of particular interest are heterojunctions based on p-type and n-type semiconductors since these devices possess non-linear, gate-tunable transport characteristics. Here, we demonstrate a gate-tunable p-n heterojunction diode using thin films of semiconducting single-walled carbon nanotubes (s-SWCNTs) and single-layer molybdenum disulfide (SL-MoS2) as p-type and n-type semiconductors, respectively [2]. The vertical stacking of these two direct band gap semiconductors forms a heterojunction with electrical characteristics that can be tuned with an applied gate bias over a wide range of charge transport behavior ranging from insulating to rectifying with forward-to-reverse bias current ratios exceeding 104. The transfer characteristic of this p-n heterojunction shows a unique 'anti-ambipolar' behavior with two off-states at either extreme of the gate voltage range and a current maximum in the middle. The continuous transition from positive to negative transconductance in an anti-ambipolar characteristic enables operation of analog communication circuits with a reduced number of circuit components compared to unipolar transistors. Anti-ambipolarity can be widely generalized to heterojunctions of other materials such as s-SWCNTs and n-type amorphous indium gallium zinc oxide (a-IGZO), ultimately leading to all solution processed p-n heterojunctions at the wafer scale [3]. [1] D. Jariwala, V. K. Sangwan, L. J. Lauhon, T. J. Marks, and M. C. Hersam, "Emerging device applications for semiconducting two-dimensional transition metal dichalcogenides," ACS Nano, 8, 1102 (2014). [2] D. Jariwala, V. K. Sangwan, C.-C. Wu, P. L. Prabhumirashi, M. L. Geier, T. J. Marks, L. J. Lauhon, and M. C. Hersam, "Gate-tunable carbon nanotube-MoS2 heterojunction p-n diode," Proc. Nat. Acad. Sci. USA, 110, 18076 (2013). [3] D. Jariwala, V. K. Sangwan, J.-W. T. Seo, W. Xu, J. Smith, C. H. Kim, L. J. Lauhon, T. J. Marks, and M. C. Hersam, "Large-area, low-voltage, anti-ambipolar heterojunctions from solution-processed semiconductors," submitted, 2014.

High-performance Ge quantum dot decorated graphene/zinc-oxide heterostructure infrared photodetector.

A novel size-controllable germanium quantum dot (Ge QD) is synthesized and decorated onto reduced graphene oxide (RGO) fragments to overcome the low infrared (IR) photoresponses (∼0.1 A/W)13,14 of pristine graphene. With the integration of flexible substrate, monolayer graphene (MLG) electrode and n-type zinc oxide (ZnO), a high-performance QD-decorated-RGO/ZnO heterostructure infrared photodetector is reported in this study. The Ge QD-decorated-RGO hybrid photosensitive composite improves the responsivity (∼9.7 A/W, 1400 nm) in IR waveband without sacrificing the response speed (∼40 μs rise time and 90 μs recovery time). In addition, the effective barrier formed between graphene and ZnO interface restricts the dark current (∼1.4 nA, -3 V) to guarantee the relatively excellent rectifying behavior and high on/off ratio (∼10(3)) for this IR photodetector. With these superior inherent properties and micron-sized sensing active area, this photodetector manifests great potential in the future application of graphene-based IR photodetector.

Organic/inorganic heterojunction based on conducting polymer and pulse-laser-deposited (PLD) ZnO

ABSTRACTOrganic/inorganic heterojunctions have been fabricated by spin coating p-type poly (3, 4 ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) onto n-type zinc oxide (ZnO) films. The ZnO films were deposited onto indium tin oxide (ITO) coated glass by pulse laser deposition (PLD) technique. The current density-voltage (J-V) characteristics of the PLD-ZnO/PEDOT:PSS junction based on as-deposited PLD-ZnO film shows a good rectifying behavior with a rectification ratio of 156 at ±1 V, indicating the formation of a diode between ZnO and PEDOT:PSS. Using thermionic emission model, the ideality factor (n=2.1) and barrier height (0.66 eV) of the heterojunction were obtained. Those diode parameters are better than those of the chemical vapor deposited ZnO/PEDOT:PSS heterojunction reported elsewhere, indicating that PLD may be a promising technique on fabricating high quality ZnO/polymer heterojunctions.