N-type Thin Films Research Articles

Quantitative Assessment of Carrier Density by Cathodoluminescence. I. GaAs Thin Films and Modeling

Doping is a fundamental property of semiconductors and constitutes the basis of modern microelectronic and optoelectronic devices. Their miniaturization requires contactless characterization of doping with nanometer scale resolution. Here, we use low- and room-temperature cathodoluminescence (CL) measurements to analyze p-type and n-type GaAs thin films over a wide range of carrier densities ($2\times 10^{17}$ to $1\times 10^{19}$ cm$^{-3}$). The spectral shift and broadening of CL spectra induced by shallow dopant states and band filling are the signature doping. We fit the whole spectral lineshapes with the generalized Planck's law and refined absorption models to extract the bandgap narrowing (BGN) and the band tail for both doping types, and the electron Fermi level for n doping. This work provides a rigorous method for the quantitative assessment of p-type and n-type carrier density using CL. Taking advantage of the high spatial resolution of CL, it can be used to map the doping in GaAs nanostructures, and it could be extended to other semiconductor materials.

Modeling of two complementary ambipolar organic thin film transistors: application to organic inverter

In this paper, we have study two types of thin-film organic transistors and their application to release the organic inverter. For manufacturing p-type and n-type organic thin film transistors (OTFT), pentacene and N,N'-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13H27) have been used as organic semiconductors active layers. These organic thin film transistors have been shown excellent ambipolar operation. We proceeded initially to model and study these complementary organic transistors individually. Therefore we present the various electrical parameters resulting from the modeling of these two types of organic transistors (n-type and p-type) as well as the various parameters characterizing the organic inverter. Very good agreement is obtained between the experimental electrical characteristics of the two types of organic transistors and the characteristics obtained by the analytical model, as well as the experimental characteristics of the organic inverter thus produced.

Halogen bonding vs. π-stacking interactions in new bis(acenaphthylene)dione semiconductors

A series of new halogenated bis(acenaphthylene)dione (BAN) derivatives was synthesized, and the effect of halogen bonding on both molecular and crystal structure, and charge transport in n-type thin film transistors was investigated.

Disilane doping of semi-polar (11-22) n-GaN: The impact of terrace-like evolution toward the enhancement of the electrical properties

Semi-polar (11-22) n-type gallium nitride thin films with various disilane doping levels were deposited via metal-organic chemical vapor deposition. The impact of the dissimilar disilane doping levels on the crystal, morphological, strain, and electrical properties was extensively studied. An X-ray rocking curve analysis demonstrated an improved crystal quality with enhanced terrace-like features using 15 standard cubic centimeters per minute of disilane doping. A closely packed step terrace-like feature was exhibited, reducing the density of arrowhead-like features. This facilitated a smoother surface with a root mean square surface roughness of 5.7 nm. Raman spectroscopy revealed that using an intermediate disilane flux reduced the compressive strain. An electrical analysis also showed that a moderate disilane doping level improved the carrier concentration and mobility to 1.3 × 1018 cm−3 and 99.3 cm2. V−1. s−1, respectively.

Transport properties of n-type Cux-TiyCz thin film semiconductor at different Cu/TiC ratios

Cu-TiC thin films possess a unique combination of optical and electrical properties. In this work, Cux-TiyCz thin film is deposited on Si (1 0 0) substrate by DC magnetron sputtering process. The Hall results revealed n-type conductivity and carrier concentration in the order of 1018 m−3, when Cu/TiC atomic percentage ratio (r) is varied between 2.14 and 7.5. The optical band-gap varies between 2.67 and 1.97 eV at different values of r. The film exhibits minimum Hall mobility (240 cm2/Vs)) and electrical resistivity (9.3 Ω.m) at an optimum ratio (r ∼ 5) in room temperature. The increasing crystallite size as a function of the Cu/TiC ratio is observed in the polycrystalline films with Cu and TiC phases. The average particle size has also increased in nanometre dimensions at r ∼ 5. The stoichiometric value close to Cu-TiC3 has culminated in future coating and electronic design applications.

Rational band engineering and structural manipulations inducing high thermoelectric performance in n-type CoSb3 thin films

Owing to the earth-abundancy, eco-friendliness and high thermoelectric performance, CoSb3 skutterudites have been employed in thermoelectric devices with a high energy conversion efficiency. However, the thermoelectric performance of CoSb3-based thin films is still relatively low within the medium temperature range. In this work, we report a record high ZT of ~0.65 at 623 K in the n-type Ag/In co-doped CoSb3 thin films, fabricated by a facile magnetron sputtering technique. Extensive characterizations and computational results indicate both Ag and In as fillers prefer to occupy the interstitial sites in the CoSb3 lattice. A 0.2% Ag doping induces impurity states in the band structure of CoSb3, boosts the density-of-states near the Fermi level and enhances the absolute Seebeck coefficient up to ~198 μV K−1. Simultaneously, a 4.2% In doping further tunes the bandgap, increases the electrical conductivity up to ~75 S cm−1, and contributes to an optimized power factor of ~2.94 μW cm−1 K−2 at 623 K. In addition, these interstitial dopants accompanying with dense grain boundaries contribute an ultra-low thermal conductivity of ~0.28 W m−1 K−1 at 623 K, leading to a high ZT in the film system. This work demonstrates that rational band engineering and structural manipulations can achieve high performance in n-type CoSb3-based thin films, which possess full potential for applying to miniature thermoelectric devices.

Organic thermoelectric thin films with large p-type and n-type power factor

P- and n-type thermoelectric (TE) materials were prepared by using a layer-by-layer method. Assembled nanocomposites displayed high TE properties. For the p-type nanocomposites, polyaniline (PANi)/graphene-poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/PANi/carbon nanotubes (CNT)-PEDOT:PSS quadlayers (QL) were assembled by immersing a substrate alternately to aqueous solutions of these charged materials. Various concentrations of three types of CNT (single-walled, double-walled (DWNT), and multi-walled) and two different surface areas of graphene (300 and 750 m2 g−1) were investigated. The best QL films, assembled with graphene and DWNT, exhibit a power factor (PF = S2 σ) of 3050 µW m−1 K−2 at room temperature, which is among the highest values for a fully organic material. In an effort to improve TE properties in n-type organic thin films, hydrazine is introduced to the films in which DWNT, stabilized by polyethylenimine (PEI), is alternately deposited with graphene, stabilized by polyvinylpyrrolidone (PVP). After doping these films for 5 min with hydrazine, electrical conductivity and Seebeck coefficient significantly increase. An 80 DWNT-PEI/graphene-PVP bilayer film achieves a PF as high as 380 µW m−1 K−2 at room temperature, exhibiting a twofold improvement relative to that of un-doped films. In light of the growing interest in organic thermoelectric nanocomposites, this study provides an effective means to achieve high performance that will allow these unique materials to replace inorganic semiconductors in some applications.

Fabrication and characterization of potassium-doped ZnO thin films

To develop a simple and effective method for fabricating a type of transparent p-type zinc oxide (ZnO) thin films, potassium-doped ZnO (K-ZnO) thin films were designed and prepared via molten-salt treatment (MST) in KNO3 for n-type ZnO thin film. The influence of filming temperature during sputtering and the followed MST on the crystalline structure, transmittance, bonding environment, surface morphology, and electrical property of the ZnO thin films has been investigated. The formed compound on quartz glass could be identified as wurtzite ZnO. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results show that the crystalline quality improves with raising the filming temperature. In addition, K 2p XPS spectra hint that the outside surface of ZnO thin films contains a certain amount of K, after MST for ZnO thin films. Compared with that of the followed MST, atomic force microscope (AFM) results also show that the filming temperature significantly affects surface morphology. More importantly, the ZnO thin films obtain p-type characteristics after MST for ZnO n-type thin films, with excellent transmittance and increased mobility.

Electrical and photocurrent properties of a polycrystalline Sn-doped β-Ga2O3 thin film

Polycrystalline n-type β-Ga2O3 thin films with a thickness of 100 nm are demonstrated via the sputtering process followed by the spin-on-glass Sn-doping technique. The thin films are used as an active layer for power electronics and ultraviolet optoelectronics. In the present study, they are implemented in back-gated metal-oxide-semiconductor field-effect transistors with a 300-nm thick SiO2 gate dielectric. The fabricated device shows typical power electronic properties with high breakdown voltages (as high as 216 V). The device also shows a clear photoresponse to the 254-nm light illuminations, indicating that the polycrystalline β-Ga2O3 thin film is also suitable for solar-blind photodetectors.

Piezotronic effect on Rashba spin–orbit coupling based on MAPbI3/ZnO heterostructures

Rashba spin–orbit coupling (SOC) is a core issue in semiconductor spintronics, which allows the manipulation of electron spin through an electric field rather than an external magnetic field, revealing a bright prospect for advanced electronic devices with ultra-high speed and integration. Conversely, the emerging piezotronic effect is the born characteristic for many semiconductors that have a non-central symmetric structure, such as ZnO and GaN. Here, we design three heterostructure devices, based on piezoelectric p-type (CH3NH3)PbI3 single crystals and n-type wurtzite-structured ZnO thin films, to theoretically study how the piezotronic effect can effectively work on the Rashba spin–orbit coupling. Benefiting from large piezoelectric charges at the interface when a vertical strain is applied, a high concentration of two-dimensional electron gas is induced in the plane of the heterostructure, which can tune the built-in electric field at the interface and further manipulate the Rashba SOC. With the increase in pressure, both the Rashba parameter and spin splitting are found to first vanish and then increase linearly for ZnO with doping densities of 1015 and 1016 cm−3. This work provides insight for manipulating electron spins via the introduction of piezocharges, showing great application potential of the piezotronic effect in tuning spintronic devices.

Transparent flexible thin-film p\u2013n junction thermoelectric module

Transparent and flexible thermoelectrics has been highly sought after for future wearable devices. However, the main stumbling block to prevent its widespread adoption is the lack of p-type transparent thermoelectrics and the stringent criteria of electrical and thermal properties matching appropriately between p-legs and n-legs. This work demonstrates the fabrication of p-type PEDOT:PSS films whose optical properties, electrical conductivity, thermal conductivity, and Seebeck coefficient were engineered to perfectly match the n-type indium tin oxide (ITO) counterparts. The dense p-type PEDOT:PSS and n-type ITO thin films show a thermoelectric figure of merit of zT = 0.30 and 0.29 at 450 K, and a thermal conductivity of 0.22 and 0.32 W m−1 K−1, respectively. A flexible thermoelectric generator (TEG) module with a high transmittance of >81% in the visible wavelength range of 400–800 nm is fabricated using 10 pairs of p-type PEDOT:PSS and n-type ITO thin film legs. An ultra-high power density of 22.2 W m−2 at a temperature gradient of 80 K was observed, which is the highest power density reported for organic/hybrid-based flexible TEGs so far. Our transparent flexible thin-film p–n junction thermoelectric module with exceptionally high power generation may take a tremendous step forward towards multi-functional wearable devices.

Structure, Morphology, and Photoelectric Performances of Te-Sb2Se3 Thin Film Prepared via Magnetron Sputtering.

Antimony selenide (Sb2Se3) has been widely investigated as a promising absorber material for photovoltaic devices. However, low open-circuit voltage (Voc) limits the power conversion efficiency (PCE) of Sb2Se3-based cells, largely due to the low-charge carrier density. Herein, high-quality n-type (Tellurium) Te-doped Sb2Se3 thin films were successfully prepared using a homemade target via magnetron sputtering. The Te atoms were expected to be inserted in the spacing of (Sb4Se6)n ribbons based on increased lattice parameters in this study. Moreover, the thin film was found to possess a narrow and direct band gap of approximately 1.27 eV, appropriate for harvesting the solar energy. It was found that the photoelectric performance is related to not only the quality of films but also the preferred growth orientation. The Te-Sb2Se3 film annealed at 325 °C showed a maximum photocurrent density of 1.91 mA/cm2 with a light intensity of 10.5 mW/cm2 at a bias of 1.4 V. The fast response and recovery speed confirms the great potential of these films as excellent photodetectors.

Enhanced physical properties of ZEO thin films for device applications

Transparent conducting Eu doped ZnO thin films are deposited on glass substrates by spray pyrolysis technique. The effect of Eu doping on surface morphology, structural and electrical properties of ZnO thin films are studied. The structural analysis reveal that the films are crystallized in the wurtzite phase with preferred orientation along (0 0 2) plane. EDX and elemental mapping results establish the presence and distribution of Eu, Zn and O for the ZEO thin films. The Hall measurement results demonstrate that the Eu doped ZnO (ZEO) films have n-type conduction. The n-type ZEO thin films with comparatively low resistivity of 2.93 × 10 − 3 Ω cm and relatively high carrier concentration of 5.18 × 10 19 cm −3 are obtained at doping level of 2 at.%. The mobility values of ZEO thin films decrease from 28.4 cm 2 V − 1 s −1 to 1.02 cm 2 V − 1 s −1 with increase of dopant concentration.

Epitaxial Growth of Bendable Cubic NiO and In2O3 Thin Films on Synthetic Mica for p- and n-type Wide-Bandgap Semiconductor Oxides

AbstractBendable p-type NiO and n-type In2O3 thin films were epitaxially grown on synthetic mica using mist chemical vapor deposition. It was found that at a growth temperature of 400 °C, epitaxially grown cubic (111) NiO thin films developed twin rotational domains, and the epitaxial relationship between each domain and the substrate was (111) NiO [1-10] or [10-1] || (001) synthetic mica [100]. In the visible light region, the epitaxial NiO thin films showed high transparencies, and their cut-offs appeared in the UV region. Additionally, at a growth temperature of 500 °C, cubic (111) In2O3 thin films with and without Sn doping were epitaxially grown on synthetic mica. As a result of the plasma oscillation of free carriers, Sn-doped In2O3 thin films exhibited reflection characteristics in the infrared region, while maintaining their visible light transmission characteristics. Furthermore, compared with non-doped In2O3, Sn doping decreased the sheet resistance by two digits.

Low voltage, high gain inverters based on amorphous zinc tin oxide on flexible substrates

Deposition of semiconductors on bendable substrates is a crucial step toward flexible circuitry and deposition by a roll-to-roll process. Since most bendable substrates have limited temperature stability (normally degradation starts between 150 °C and 300 °C), processing temperatures are typically below that of rigid substrates. Amorphous oxide semiconductors (AOSs) such as indium gallium zinc oxide (IGZO) can be fabricated at room temperature (RT) and exhibit electron mobilities >10 cm2 V−1 s−1 being a pre-requisite for application in backplanes of displays. While IGZO is already commercially exploited, the search for alternative materials is highly relevant because indium and gallium are rare and expensive. Zinc tin oxide (ZTO) is a promising AOS since zinc and tin are highly abundant and cheap. In this letter, we discuss RT-fabricated n-type ZTO thin films used as the channel material in flexible inverter circuits based on junction field-effect transistors. RT-fabricated nickel oxide is used as a semitransparent p-type gate material. The devices are fabricated on flexible polyimide and exhibit an excellent peak gain magnitude of 464 and uncertainty level as low as 130 mV at a supply voltage of only 3 V. They are characterized before and after bending at various radii. Even after bending at 2 mm radius, the inverters behave still very well.

Influence of Nb-doping on the local structure and thermoelectric properties of transparent TiO2:Nb thin films

Abstract Transparent n-type niobium-doped titanium dioxide thin films (TiO2:1.5 at.%Nb) with pronounced thermoelectric properties were produced from a composite Ti:Nb target by reactive magnetron sputtering. The thin films were comprehensively characterized by X-ray diffraction, X-ray photoelectron spectroscopy, optical spectroscopy, electrical conductivity, and thermoelectric measurement techniques. The local structure of the thin films was investigated in detail by X-ray absorption spectroscopy at the Ti and Nb K-edges. A set of radial distribution functions were extracted from the simultaneous analysis of EXAFS data at two absorption edges using the reverse Monte Carlo method. It was found that Nb dopant atoms modify the local environment of the films, but their average structure remains close to that of the anatase phase. This conclusion is also supported by the ab initio simulations of XANES. A very high absolute Seebeck coefficient (S = 155 μV/K) for n-type TiO2 was achieved with Nb doping, yielding a maximum power factor and thermoelectric figure of merit of 0.5 mW m−1 K−2 and 0.18 at a temperature of 300 K, respectively, for a 150 nm thick film. From frequency-domain thermoreflectance experiments, a thermal conductivity value of 1.3 W m−1 K−1 was obtained for the optimized TiO2:Nb film.

Bi2Te3 / Si Thermophotovoltaic Cells Converting Low-Temperature Radiation into Electricity

The thermophotovoltaic cells which can convert the infrared radiation from room-temperature surroundings into electricity are of significance due to their potential applications in many fields. In this work, narrow bandgap Bi2Te3/Sb2Te3 thin film thermophotovoltaic cells were fabricated, and the formation mechanism of Bi2Te3/Sb2Te3 p-n heterojunctions was investigated. During the formation of the heterojunctions at room temperature, both electrons and holes diffuse in the same direction from n-type Bi2Te3 thin films to p-type Sb2Te3 thin films rather than conventional bi-directional diffusion. Because the strong intrinsic excitation generates a large number of intrinsic carriers which weaken the built-in electric field of the heterojunctions, their I-V curves become similar to straight lines. It is also demonstrated that Bi2Te3/Sb2Te3 thermophotovoltaic cells can output electrical power under the infrared radiation from a room-temperature heat source. This work proves that it is possible to convert the infrared radiation from dark and room-temperature surroundings into electricity through narrow bandgap thermophotovoltaic cells.

Study of a Platinum (Pt) Nanoparticle (NP)/Vanadium Pentoxide (V2O5) Thin Film-Based Ammonia Gas Sensor

A new and interesting ammonia (NH3) gas sensor, based on incorporating a radio frequency (RF) sputtered vanadium pentoxide (V2O5) thin film and thermal evaporated platinum (Pt) nanoparticles (NPs), is fabricated and studied herein. The studied Pt NP/V2O5 device demonstrates abnormal p-type conductive behavior, presumably caused by the presence of an inversion (hole) layer on the surface of the n-type V2O5 thin film. The employment of Pt NPs effectively enhances the specific surface area, catalytic activity, and related ammonia sensing properties. Experimentally, a high sensing response ratio for ${S}_{R}$ of 83.2% under 1000 ppm NH3/air gas and a very low detecting level of 100 ppb NH3/air with a relatively fast sensing speed are obtained at the optimum temperature of 300 °C. The studied device also shows the advantages of a simple structure, good selectivity, easy fabrication, and stable and reversible sensing performance. Therefore, the studied Pt NP/V2O5 thin film structure provides potential for high-performance ammonia sensing applications.

ScAlN/3C-SiC/Si platform for monolithic integration of highly sensitive piezoelectric and piezoresistive devices

This paper reports on a platform for monolithic integration of piezoelectric and piezoresistive devices on a single chip using the ScAlN/3C-SiC/Si heterostructure. Surface acoustic wave devices with an electromechanical coupling of 3.2% and an out-of-band rejection as high as 18 dB are demonstrated using the excellent piezoelectric properties of ScAlN and low acoustic loss of 3C-SiC. Additionally, a large piezoresistive effect in the low-doped n-type 3C-SiC(100) thin film has been observed, which exceeds the previously reported values in any SiC thin films. The growth of the n-type 3C-SiC thin film was performed using the low pressure chemical vapor deposition technique at 1250 °C and the standard micro-electro-mechanical systems process is used for the fabrication of 3C-SiC piezoresistors. The piezoresistive effect was measured using the bending beam method in different crystallographic orientations. The maximum gauge factor is –47 for the longitudinal [100] orientation. Using the longitudinal and transverse gauge factors for different crystallographic orientations, the fundamental piezoresistive coefficients of the low-doped n-type 3C-SiC thin film are measured to be π11=(−14.5±1.3)×10−11 Pa−1, π12=(5.5±0.5)×10−11 Pa−1, and π44=(−1.7±0.7)×10−11 Pa−1.

Experimental and Computational Analyses of Temperature Distributions in Slope-Type Thin-Film Thermoelectric Generators at Different Slope Angles and Evaluation of Their Thermoelectric Performance

Thin-film thermoelectric generators are not widely used mainly because it is difficult to provide a temperature difference (ΔT) within the generators. To solve this problem, in our previous study, we prepared slope-type thin-film thermoelectric generators (STTEGs) using electrodeposition and transferred processes. A thin-film generator including n-type Bi2Te3 and p-type Sb2Te3 thin films was attached on slope blocks made of polydimethylsiloxane. In this study, the slope angle of STTEGs was optimized based on experimental results and computational analyses using computational fluid dynamics (CFD). With the increase in the slope angle, the ΔT began increasing and became saturated at a slope angle of 58°, and this trend was also confirmed by experimental measurements. When the heat source temperature was set at 65 °C, the ΔT computationally reached 26 K at a slope angle of 58°, and the maximum output power was 46.1 nW. Therefore, we demonstrated that the highest performance of STTEGs with an optimal slope angle can be estimated by combining the experimental results and computational analyses.