Showing papers on "Heterojunction published in 2006"
TL;DR: In this paper, the fabrication, properties, and solar energy applications of highly ordered TiO 2 nanotube arrays made by anodic oxidation of titanium in fluoride-based electrolytes are reviewed.
1,905 citations
TL;DR: In this article, the authors combined and summarized the experimental findings on this nanomorphology-efficiency relationship and proposed a bicontinuous interpenetrating phase structures within these blend films.
Abstract: Within the different organic photovoltaic devices the conjugated polymer/fullerene bulk heterojunction approach is one of the foci of today's research interest. These devices are highly dependent on the solid state nanoscale morphology of the two components (donor/acceptor) in the photoactive layer. The need for finely phase separated polymer–fullerene blends is expressed by the limited exciton diffusion length present in organic semiconductors. Typical distances that these photo-excitations can travel within a pristine material are around 10–20 nm. In an efficient bulk heterojunction the scale of phase separation is therefore closely related to the respective exciton diffusion lengths of the two materials involved. Once the excitons reach the donor/acceptor interface, the photoinduced charge transfer results in the charge separation. After the charges have been separated they require percolated pathways to the respective charge extracting electrodes in order to supply an external direct current. Thus also an effective charge transport relies on the development of a suitable nanomorphology i.e. bicontinuous interpenetrating phase structures within these blend films. The present feature article combines and summarizes the experimental findings on this nanomorphology–efficiency relationship.
1,390 citations
TL;DR: A large electric-field response of quasi–two-dimensional electron gases generated at interfaces in epitaxial heterostructures grown from insulating oxides is reported, indicating that the conductivity of the electron gases can be modulated through a quantum phase transition from an insulating to a metallic state.
Abstract: We report on a large electric-field response of quasi-two-dimensional electron gases generated at interfaces in epitaxial heterostructures grown from insulating oxides. These device structures are characterized by doping layers that are spatially separated from high-mobility quasi-two-dimensional electron gases and therefore present an oxide analog to semiconducting high-electron mobility transistors. By applying a gate voltage, the conductivity of the electron gases can be modulated through a quantum phase transition from an insulating to a metallic state.
1,356 citations
TL;DR: Co3O4/BiVO4 composite photocatalyst with a p-n heterojunction semiconductor structure has been synthesized by the impregnation method and exhibits enhanced photocatalytic activity for phenol degradation under visible light irradiation.
Abstract: Co3O4/BiVO4 composite photocatalyst with a p−n heterojunction semiconductor structure has been synthesized by the impregnation method. The physical and photophysical properties of the composite photocatalyst have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transimission electron microscopy (TEM), BET surface area, and UV−visible diffuse reflectance spectra. Co is present as p-type Co3O4 and disperses on the surface of n-type BiVO4 to constitute a heterojunction composite. The photocatalyst exhibits enhanced photocatalytic activity for phenol degradation under visible light irradiation. The highest efficiency is observed when calcined at 300 °C with 0.8 wt % cobalt content. On the basis of the calculated energy band positions and PL spectra, the mechanism of enhanced photocatalytic activity has been discussed.
820 citations
TL;DR: Inverted organic photovoltaic devices based on a blend of poly(3-hexylthiophene) and a fullerene have been developed by inserting a solution-processed ZnO interlayer between the indium tin oxide (ITO) electrode and the active layer using Ag as a hole-collecting back contact as discussed by the authors.
Abstract: Inverted organic photovoltaic devices based on a blend of poly(3-hexylthiophene) and a fullerene have been developed by inserting a solution-processed ZnO interlayer between the indium tin oxide (ITO) electrode and the active layer using Ag as a hole-collecting back contact. Efficient electron extraction through the ZnO and hole extraction through the Ag, with minimal loss in open-circuit potential, is observed with a certified power conversion efficiency of 2.58%. The inverted architecture removes the need for the use of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) as an ITO modifier and for the use of a low-work-function metal as the back contact in the device.
814 citations
TL;DR: Star-shaped molecules based on a triphenylamine core derivatized with various combinations of thienylenevinylene conjugated branches and electron-withdrawing indanedione or dicyanovinyl groups have been synthesized, showing that the introduction of the electron-acceptor groups induces an intramolecular charge transfer that results in a shift of the absorption onset toward longer wavelengths and a quenching of photoluminescence.
Abstract: Star-shaped molecules based on a triphenylamine core derivatized with various combinations of thienylenevinylene conjugated branches and electron-withdrawing indanedione or dicyanovinyl groups have been synthesized. UV−vis absorption and fluorescence emission data show that the introduction of the electron-acceptor groups induces an intramolecular charge transfer that results in a shift of the absorption onset toward longer wavelengths and a quenching of photoluminescence. Cyclic voltammetry shows that all compounds present a reversible first oxidation process whose potential increases with the number of electron-withdrawing groups in the structure. Prototype bulk and bilayer heterojunction solar cells have been realized using fullerene C60 derivatives as acceptor material. The results obtained with both kinds of devices show that the introduction of electron-acceptor groups in the donor structure induces an extension of the photoresponse in the visible spectral region, an increase of the maximum external...
760 citations
TL;DR: In this article, the authors report on the fabrication of heterojunction solar cells made by deposition of transparent conducting oxide (TCO) films on Cu2O substrates, which have reached an open-circuit voltage of 0.595V, a short-ccurrent current density of 6.78mA∕cm2, a fill factor of 50%, and a conversion efficiency of 2% under simulated AM1.5G illumination.
Abstract: We report on the fabrication of heterojunction solar cells made by deposition of transparent conducting oxide (TCO) films on Cu2O substrates. The TCO films have been grown by ion beam sputtering on good quality Cu2O sheets prepared by oxidizing copper at a high temperature. The best solar cell has reached an open-circuit voltage of 0.595V, a short-circuit current density of 6.78mA∕cm2, a fill factor of 50%, and a conversion efficiency of 2% under simulated AM1.5G illumination, which is the highest efficiency value reported for this kind of heterojunction devices. These devices represent a good starting point for the development of very low cost solar cells.
506 citations
TL;DR: In this article, a polycrystalline thin films of tin sulphide have been synthesized using spray pyrolysis, which had resistivities ∼30 cm with an optical energy band gap (E g ) of 1.32 eV.
505 citations
TL;DR: The specific topics discussed here include the fine structure of the band-edge optical transitions and its effect on temperature-dependent single-exciton recombination dynamics, Auger recombination of multiexcitons in size- and shape-controlled nanocrystals with a specific emphasis on optical-gain properties of nanocrystalline materials.
Abstract: One consequence of strong spatial confinement of electronic wave functions in ultrasmall semiconductor nanocrystals is a great enhancement of carrier-carrier interactions, which has a dramatic effect on the spectral and dynamical properties of both single and multiexciton states. Strong carrier-carrier interactions open new nanocrystal-specific energy relaxation and recombination channels associated, e.g., with electron-hole energy transfer and ultrafast nonradiative Auger recombination. Further, they lead to extremely efficient direct photogeneration of multiple electron-hole pairs (excitons) by single photons known as carrier (or exciton) multiplication. This review focuses on the effect of Coulomb interactions on carrier recombination and photogeneration mechanisms in nanocrystals based on II-VI (e.g., CdSe) and IV-VI (e.g., PbSe) compounds. The specific topics discussed here include the fine structure of the band-edge optical transitions and its effect on temperature-dependent single-exciton recombination dynamics, Auger recombination of multiexcitons in size- and shape-controlled nanocrystals with a specific emphasis on optical-gain properties of nanocrystalline materials (including quantum rods and multicomponent core-shell heterostructures), and the direct generation of multiple excitons via carrier multiplication and its implications in photovoltaic technologies.
475 citations
TL;DR: In this paper, a GaN/ultrathin InGaN/GaN heterojunction was used to provide a backbarrier to the electrons in an AlGaN and GaN high-electron mobility transistor (HEMT).
Abstract: A GaN/ultrathin InGaN/GaN heterojunction has been used to provide a back-barrier to the electrons in an AlGaN/GaN high-electron mobility transistor (HEMT). The polarization-induced electric fields in the InGaN layer raise the conduction band in the GaN buffer with respect to the GaN channel, increasing the confinement of the two-dimensional electron gas under high electric field conditions. The enhanced confinement is especially useful in deep-submicrometer devices where an important improvement in the pinchoff and 50% increase in the output resistance have been observed. These devices also showed excellent high-frequency performance, with a current gain cut-off frequency (f/sub T/) of 153 GHz and power gain cut-off frequency (f/sub max/) of 198 GHz for a gate length of 100 nm. At a different bias, a record f/sub max/ of 230 GHz was obtained.
384 citations
TL;DR: The performance of organic solar cells based on the blend of regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) is strongly influenced by blend composition and thermal annealing conditions.
TL;DR: In this paper, the deposition conditions of cuprous oxide (Cu2O) thin films on glass substrates and nitrogen doping into Cu2O were studied by using reactive radio-frequency magnetron sputtering method.
TL;DR: In this paper, the authors examined superlattices composed of the half-metallic ferromagnet La2/3Ca1/3MnO3 and the high-temperature superconductor YBa2Cu3O7 by absorption spectroscopy with circularly polarized X-rays and by off-specular neutron reflectometry.
Abstract: Carefully controlled interfaces between two materials can give rise to novel physical phenomena and functionalities not exhibited by either of the constituent materials alone. Modern synthesis methods have yielded high-quality heterostructures of oxide materials with competing order parameters. Although magnetic correlations at the interface are expected to be important in determining the macroscopic properties of such systems, a quantitative determination of the interfacial magnetization profile has thus far not been reported. Here we examine superlattices composed of the half-metallic ferromagnet La2/3Ca1/3MnO3 and the high-temperature superconductor YBa2Cu3O7 by absorption spectroscopy with circularly polarized X-rays and by off-specular neutron reflectometry. The resulting data yield microscopic insight into the interplay of spin and orbital degrees of freedom at the interface. The experiments also reveal an extensive rearrangement of the magnetic domain structure at the superconducting transition temperature. This methodology establishes an incisive probe of the interplay between competing electronic order parameters in oxide heterostructures.
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TSMC1
TL;DR: In this paper, the fabrication of monolithic lattice-mismatched semiconductor heterostructures with limited area regions having upper portions substantially exhausted of threading dislocations is discussed.
Abstract: Fabrication of monolithic lattice-mismatched semiconductor heterostructures with limited area regions having upper portions substantially exhausted of threading dislocations, as well as fabrication of semiconductor devices based on such lattice-mismatched heterostructures.
TL;DR: In this article, the currentvoltage and resistance switching mechanism of hole carrier injected space charge limited (SCL) conduction controlled by the interface traps exponentially distributed in energy were investigated.
Abstract: The current-voltage $(I\text{\ensuremath{-}}V)$ characteristics and resistance switching mechanism of $\mathrm{Ag}∕{\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}(\mathrm{LCMO})∕\mathrm{Pt}$ sandwiched films, which were deposited on $\mathrm{Pt}∕\mathrm{Ti}∕{\mathrm{SiO}}_{2}∕\mathrm{Si}$ substrates by pulse laser deposition, were investigated. The $I\text{\ensuremath{-}}V$ characteristics can be explained by hole carrier injected space charge limited (SCL) conduction controlled by $\mathrm{Ag}∕\mathrm{LCMO}$ interface traps exponentially distributed in energy. The hysteresis and asymmetry in the $I\text{\ensuremath{-}}V$ curves are due to trapping/detrapping process of hole carriers. The resistance changes under different voltage range are related to the carrier trapping levels induced by the positive voltage bias. Retention property of resistance is attributed to ordering/disordering transition, which is discussed on the basis of trap-assisted interface phase separation scenario. Therefore, the resistance switching induced by voltage pulses is attributed to the interface induced bulklike limited transport effect.
TL;DR: In this article, room temperature electron mobility of 1170cm2∕Vs is obtained in an undoped, lattice-matched, Al0.82In0.18N∕GaN field effect transistor heterostructure.
Abstract: Room temperature electron mobility of 1170cm2∕Vs is obtained in an undoped, lattice-matched, Al0.82In0.18N∕GaN field-effect transistor heterostructure, while keeping a high (2.6±0.3)×1013cm−2 electron gas density intrinsic to the Al0.82In0.18N∕GaN material system. This results in a two-dimensional sheet resistance of 210Ω∕◻. The high mobility of these layers, grown by metal-organic vapor phase epitaxy on sapphire substrate, is obtained thanks to the insertion of an optimized AlN interlayer, reducing the alloy related interface roughness scattering.
TL;DR: In this paper, a heterojunction of n-type zinc oxide (ZnO) nanowires and p-type silicon has been successfully constructed to demonstrate ultraviolet (UV) photodiodes.
Abstract: A heterojunction of n-type zinc oxide (ZnO) nanowires and p-type silicon has been successfully constructed to demonstrate ultraviolet (UV) photodiodes. The prototype device consists of naturally doped n-type ZnO nanowires grown on top of a (1 0 0) p-silicon substrate by the bottom-up growth process. The diameter of the nanowires is in the range of 70–120 nm, and the length is controlled by the growth time. The isolation is achieved by using spin-on glass (SOG) that also works as the foundation of the top electrode. The current–voltage (I–V) characteristics show the typical rectifying behavior of heterojunctions, and the photodiode exhibits response of ∼0.07 A/W for UV light (365 nm) under a 20 V reverse bias.
TL;DR: In this article, self-assembled monolayers (SAMs) of molecules with permanent dipole moments have been used to control the anode work function and device performance in molecular solar cells based on a CuPc:C60 (CuPc): copper phthalocyanine) heterojunction.
Abstract: Surface modification of indium tin oxide (ITO)-coated substrates through the use of self-assembled monolayers (SAMs) of molecules with permanent dipole moments has been used to control the anode work function and device performance in molecular solar cells based on a CuPc:C60 (CuPc: copper phthalocyanine) heterojunction. Use of SAMs increases both the short-circuit current density (Jsc) and fill factor, increasing the power-conversion efficiency by up to an order of magnitude. This improvement is attributed primarily to an enhanced interfacial charge transfer rate at the anode, due to both a decrease in the interfacial energy step between the anode work function and the highest occupied molecular orbital (HOMO) level of the organic layer, and a better compatibility of the SAM-modified electrodes with the initial CuPc layers, which leads to a higher density of active sites for charge transfer. An additional factor may be the influence of increasing electric field at the heterojunction on the exciton-dissociation efficiency. This is supported by calculations of the electric potential distribution for the structures. Work-function modification has virtually no effect on the open-circuit voltage (Voc), in accordance with the idea that Voc is controlled primarily by the energy levels of the donor and acceptor materials.
TL;DR: In this paper, the authors show that the visible electroluminescence (EL) at room temperature has been realized based on n-ZnO∕p-Si heterojunction, where the tunneling mechanism via deep-level states was the main conduction process at low forward bias, while space charge-limited current conduction dominated the carrier transport at higher bias.
Abstract: The distinct visible electroluminescence (EL) at room temperature has been realized based on n-ZnO∕p-Si heterojunction. The EL peak energy coincided well with the deep-level photoluminescence of ZnO, suggesting that the EL emission was originated from the radiative recombination via deep-level defects in n-ZnO layers. The transport mechanisms of the diodes have been discussed with the characteristics of current-voltage (I-V) and light-output–voltage (L-V), in terms of the energy band diagram of ZnO∕Si heterojunction. The tunneling mechanism via deep-level states was the main conduction process at low forward bias, while space-charge-limited current conduction dominated the carrier transport at higher bias. Light-output–current (L-I) characteristic of the diode followed a power law such as L∼Im, which showed a superlinear behavior at low injection current and became almost linear due to the saturation of nonradiative recombination centers at high current level.
TL;DR: Spectrally resolved photocurrent measurements on single self-assembled nanowire heterostructures believe that these wires form promising candidates as nanoscale infrared polarization-sensitive photodetectors.
Abstract: We report on spectrally resolved photocurrent measurements on single self-assembled nanowire heterostructures. The wires, typically 3 microm long with an average diameter of 85 nm, consist of InAs with a 1 microm central part of InAsP. Two different sets of wires were prepared with phosphorus contents of 15+/-3% and 35+/-3%, respectively, as determined by energy-dispersive spectroscopy measurements made in transmission electron microscopy. Ohmic contacts are fabricated to the InAs ends of the wire using e-beam lithography. The conduction band offset between the InAs and InAsP regions virtually removes the dark current through the wires at low temperature. In the optical experiments, interband excitation in the phosphorus-rich part of the wires results in a photocurrent with threshold energies of about 0.65 and 0.82 eV, respectively, in qualitative agreement with the expected band gap of the two compositions. Furthermore, a strong polarization dependence is observed with an order of magnitude larger photocurrent for light polarized parallel to the wire than for light polarized perpendicular to the wire. We believe that these wires form promising candidates as nanoscale infrared polarization-sensitive photodetectors.
TL;DR: In this article, a two-component layered structure of organic light-emitting transistors (OLETs) with balanced ambipolar transport and mobility as large as 3 × 10 cm V s is presented.
Abstract: Today organic materials are routinely employed for the fabrication of light-emitting devices (OLEDs) and thin-film transistors (OTFTs), with the first technological realizations already having reached the market. Moreover, OTFTs with unipolar mobility values comparable to those of amorphous silicon (1 cm V s) have now been demonstrated. Applications impacting display technologies and those sectors where low cost is a key factor and low performance is acceptable include electronic paper and radio-frequency identification (RF-ID) products. In a recent development, OTFTs also exhibiting electroluminescence (EL) have been successfully demonstrated. Organic light-emitting transistors (OLETs) represent a significant technological advance by combining two functionalities, electrical switching and light emission, in a single device, thus significantly increasing the potential applications of organic semiconductors. In particular, if appropriate materials can be introduced, OLETs offer an ideal structure for improving the lifetime and efficiency of organic light-emitting heterostructures due to the intrinsically different driving conditions and charge-carrier balance compared to conventional OLEDs. Potential applications of OLETs include flat-panel display technologies, lighting, and, ultimately, easily fabricated organic lasers. The first OLET prototypes were unipolar transport devices, and recombination was expected to take place in close proximity to the metallic drain electrode where efficiency-depleting exciton quenching is also likely to occur. To avoid this significant device deficiency and to instead generate EL nearer the center of the channel, OLETs with ambipolar charge transport would be highly desirable. Furthermore, balanced ambipolar conduction is crucial for maximizing exciton recombination through efficient electron–hole balancing. Up to now various solutions have been proposed: single ambipolar materials and two-component coevaporated or layered structures. In coevaporated films, two materials are simultaneously sublimed to form bulk heterojunctions. However, carrier transport is unbalanced and the mobility values are below 10 cm V s. Devices employing a polymer film showing intrinsic ambipolar transport have also been reported but with mobility values for both charge carriers around 10 cm V s. In this paper we report OLETs based on two-component layered structures that have balanced ambipolar transport and mobility values as large as 3 × 10 cm V s. These devices are realized by sequentially depositing p-type (a,x-dihexyl-quaterthiophene, DH4T) and n-type films (N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide, PTCDIC13H27, P13). The combination with the highest mobility and most-balanced transport is obtained with DH4T grown in direct contact with the dielectric. For comparison, we have also employed pentacene in place of DH4T as the p-type material and showed that unbalanced ambipolarity is obtained. Morphological analysis of the outermost and buried layers, performed by laser scanning confocal microscopy (LSCM), allows selective imaging of materials with energetically separated photoluminescence (PL) spectra. Importantly, it is shown that ‘growth compatibility’ between the nand p-type materials is essential in forming a continuous interface and thereby controlling the resulting OLET optoelectronic-response properties. Each OLET material was first evaluated in a single layer in a top source–drain contact OTFT. As substrates we employed heavily doped silicon wafers with thermally grown oxides. Surface treatments such as octadecyltrichlorosilane or hexamethyldisilazane did not result in substantial improvement in the device performance. Parameters such as substrate temperature (Tsub) and evaporation rate were varied to optimize electrical characteristics. The optimum growth conditions were found to be: Tsub = 90 °C and rate = 0.1 A s –1 for DH4T, and Tsub = 25 °C and rate = 0.1 A s –1 for P13. In Table 1, the mobility (l) and threshold-voltage (Vth) values obtained are summarized. These are comparable to the highest values reported in the literature. The DH4T devices were stable even C O M M U N IC A TI O N S
TL;DR: In this paper, printed bulk heterojunction solar cells from poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) with power efficiencies of over 4
Abstract: In this paper we report on printed bulk heterojunction solar cells from poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) with power efficiencies of over 4 % Devices have been produced by doctor blading, which is a reel-to-reel compatible large-area coating technique Devices exhibit a short-circuit current of over 115 mA cm–2, a fill factor of 58 %, and an open-circuit voltage of 615 mV, resulting in an AM15 power efficiency of over 40 % at 25 °C and under 100 mW cm–2 The mismatch factor of the solar simulator is cross-calibrated by determining the spectral quantum efficiency of organic devices as well as of a calibrated Si device, and by the combination of outdoor tests; these efficiencies are precise within less than 3 % relative variation Although the devices are regarded as fairly optimized, analysis in terms of a one-diode equivalent circuit reveals residual losses and loss mechanisms Most interestingly, the analysis points out the different properties of spin-coated versus bladed devices Based on this analysis, the future efficiency potential of P3HT–PCBM solar cells is analyzed
TL;DR: In this article, a wideband gap oxide alloy, BeZnO, was proposed and studied, which can be used for fabricating films and heterostructures of ZnO-based electronic and photonic devices and for other applications.
Abstract: A wide-band gap oxide alloy, BeZnO, is proposed and studied in this letter The BeZnO films were deposited on sapphire substrates by our hybrid beam deposition growth method The value of the energy band gap of BeZnO can be efficiently engineered to vary from the ZnO band gap (34 eV) to that of BeO (106 eV) BeZnO can be used for fabricating films and heterostructures of ZnO-based electronic and photonic devices and for other applications Changes in the measured energy band gap and lattice constant values with Be content are described for BeZnO alloys
TL;DR: In this article, a heterojunction diode was thermal treated in hydrogen ambient to increase the electron injection rate from the n-ZnO films into the ZnO nanowires.
Abstract: ZnO nanowire-array-embedded n-ZnO∕p-GaN heterojunction light-emitting diodes were fabricated by growing Mg-doped p-GaN films, ZnO nanowire arrays, and polycrystalline n-ZnO films consecutively. Electroluminescence emission having the wavelength of 386nm was observed under forward bias in the heterojunction diodes and the UV-violet light was emerged from the ZnO nanowires. The heterojunction diode was thermal treated in hydrogen ambient to increase the electron injection rate from the n-ZnO films into the ZnO nanowires. High concentration of electrons supplied from the n-ZnO films activated the radiative recombination in the ZnO nanowires, i.e., increased the light-emitting efficiency of the heterojunction diode.
TL;DR: In this article, the influence of thermal annealing on nano-structural and optical properties of thin spin-coated P3HT/PCBM-films was studied.
01 Jan 2006
TL;DR: In this paper, the authors investigated the properties of wide gap Chalcopyrite in thin-film solar cells and found that the wide gap properties of the Chalcopyrite can affect the performance of the solar cells.
Abstract: Cu-Chalcopyrites-Unique Materials for Thin-Film Solar Cells- Band-Structure Lineup at I-III-VI2 Schottky Contacts and Heterostructures- Defects and Self-Compensation in Semiconductors- Confine Cu to Increase Cu-Chalcopyrite Solar Cell Voltage- Photocapacitance Spectroscopy in Copper Indium Diselenide Alloys- Recombination Mechanisms in Cu(In,Ga)(Se,S)2 Solar Cells- Shallow Defects in the Wide Gap Chalcopyrite CuGaSe2- Spatial Inhomogeneities of Cu(InGa)Se2 in the Mesoscopic Scale- Electro-Optical Properties of the Microstructure in Chalcopyrite Thin Films- Electronic Properties of Surfaces and Interfaces in Widegap Chalcopyrites- Interfaces of Cu-Chalcopyrites- Bandgap Variations for Large Area Cu(In,Ga)Se2 Module Production
TL;DR: In this article, high crystal quality and good surface morphology were confirmed by x-ray diffraction and scanning electron microscopy.n-ZnO∕p-GaN:Mg heterojunction light emitting diode (LED) mesas were fabricated on c-Al2O3 substrates using pulsed laser deposition for ZnO and metal organic chemical vapor deposition for the GaN:mg.
Abstract: n-ZnO∕p-GaN:Mg heterojunction light emitting diode (LED) mesas were fabricated on c-Al2O3 substrates using pulsed laser deposition for the ZnO and metal organic chemical vapor deposition for the GaN:Mg. High crystal quality and good surface morphology were confirmed by x-ray diffraction and scanning electron microscopy. Room temperature (RT) photoluminescence (PL) showed an intense main peak at 375nm and a negligibly low green emission indicative of a near band edge excitonic emission from a ZnO layer with low dislocation/defect density. The LEDs showed I-V characteristics confirming a rectifying diode behavior and a RT electroluminescence (EL) peaked at about 375nm. A good correlation between the wavelength maxima for the EL and PL suggests that recombination occurs in the ZnO layer and that it may be excitonic in origin. This also indicates that there is significant hole injection from the GaN:Mg into the ZnO.
TL;DR: In this article, the energy-band gap of the Al2O3-InGaAs interface was determined to be 3.83±0.05eV by x-ray photoelectron spectroscopy.
Abstract: The valence-band offset has been determined to be 3.83±0.05eV at the atomic-layer-deposition Al2O3∕InGaAs interface by x-ray photoelectron spectroscopy. The Au–Al2O3∕InGaAs metal-oxide-semiconductor diode exhibits current-voltage characteristics dominated by Fowler-Nordheim tunneling. From the current-voltage data at forward and reverse biases, a conduction-band offset of 1.6±0.1eV at the Al2O3–InGaAs interface and an electron effective mass ∼0.28±0.04m0 of the Al2O3 layer have been extracted. Consequently, combining the valence-band offset, the conduction-band offset, and the energy-band gap of the InGaAs, the energy-band gap of the atomic-layer-deposited Al2O3 is 6.65±0.11eV.
TL;DR: In this article, the electrical properties and optical absorption spectra of undoped BaSi 2 films grown by molecular beam epitaxy were investigated and the electron density and mobility of BaSi2 grown epitaxially on Si(111) were 5 × 10 15 cm − 3 and 820 cm 2 /V·s at room temperature, respectively.
TL;DR: In this paper, a core-multishell nanowires were designed to accommodate a strained InAs quantum well layer in a higher band gap InP nanowire, which enabled the successful fabrication of the nanostructure in which three layers were epitaxially grown without the assistance of any catalyst.
Abstract: We report the growth of InP∕InAs∕InP core-multishell nanowire arrays by selective area metalorganic vapor phase epitaxy. The core-multishell nanowires were designed to accommodate a strained InAs quantum well layer in a higher band gap InP nanowire. The precise control over nanowire growth direction and heterojunction formation enabled the successful fabrication of the nanostructure in which all three layers were epitaxially grown without the assistance of any catalyst. The grown nanowires were highly uniform, vertically oriented, and periodically aligned with controllable dimensions. 4K photoluminescence measurements confirmed the formation of strained InAs quantum well on InP (110) sidewalls and the well widths corresponding to the photoluminescence peaks were in good agreement with calculated values.