Schottky Barrier Cells Research Articles

Theoretical study of a high-efficiency GaP–Si heterojunction betavoltaic cell compared with metal–Si Schottky barrier betavoltaic cell

In this work, energy converters, which contain a GaP–Si heterojunction and Si-based Schottky barrier diodes with Al, Ti, Ag, and W, are used to convert 2 μm-thick 63Ni radioactive source energy into electrical energy. First, energy deposition distributions of the 63Ni radioactive source in these converters are simulated by using the Monte Carlo method. Then, the electrical output properties of the 63Ni/GaP–Si cell and 63Ni/metal–Si cell are determined through the numerical calculation. For the 63Ni/GaP–Si cell, with the optimized thickness of the GaP layer and doping concentration of Si, the maximum output power density and the conversion efficiency are 0.189 µW cm−2 and 1.83%, respectively. For the Si-based Schottky barrier cells with Al, Ti, Ag, and W, the 63Ni/Al–Si cell has the best electrical output properties with the same thickness of the metal layer and doping concentration of Si. When the thickness of metal Al is 0.1 µm and the doping concentration Na is 1 × 1013 cm−3, the maximum output power density and the conversion efficiency are 0.121 µW cm−2 and 1.18%, respectively. The calculation results indicate that the 63Ni/GaP–Si battery has better electrical output properties than the 63Ni/Al–Si Schottky battery. These results are valuable for fabricating practical batteries.

Transverse Scaling of Schottky Barrier Charge-Trapping Cells for Energy-Efficient Applications

This work numerically elucidates the effects of transverse scaling on Schottky barrier charge-trapping cells for energy-efficient applications. Together with the scaled gate structures and charge-trapping dielectrics, variations in bias conditions on source-side injection are considered for properly operating Schottky barrier cells in low-power or high-efficiency applications. A gate voltage of 5 to 9 V with a drain voltage of 1 to 3 V was employed to program the Schottky barrier cells. Both the non-planar double-gate gate structure and scaled dielectric layers effectively improve the source-side programming. When the gate voltage of 5 V was operated, there were roughly two orders of magnitude greater injected gate currents observed in the ONO-scaled double-gate cells. Five successive programming-trapping iterations were employed to consider the coupling of trapped charges and Schottky barriers, examining the differences in physical mechanisms between different design options. The gate structures, dielectric layers, and gate/drain voltages are key factors in designing transverse scaled Schottky barrier charge-trapping cells for low-power and high-efficiency applications.

Effects of High Temperatures on Cell Reading, Programming, and Erasing of Schottky Barrier Charge-Trapping Memories

This paper examines the temperature effect of Schottky barrier source/drain charge-trapping memories. The current–voltage curves and programming/erasing characteristics are experimentally investigated at room temperature and higher 85 °C and 125 °C. 2-D device simulations were performed to elucidate the physical mechanisms of Schottky barrier cell devices at high temperatures. For Schottky barrier charge-trapping cells, two different mechanisms of ambipolar conduction are classified: 1) thermionic emission and 2) Schottky barrier tunneling. The thermionic emission is susceptible to variations of high temperatures, leading to considerable shifts in logarithmic scale off-state drain-currents at low gate voltages. However, at adequately large gate voltages, the Schottky barrier tunneling plays a key role in contributing drain currents. The Schottky barriers and associated tunneling are relatively insensitive to the variations of device temperatures, preserving favorable temperature-insensitive programming and erasing Schottky barrier charge-trapping cells for use in the high-temperature automotive industry.

Answer to comments on “Fabrication and photovoltaic conversion enhancement of graphene/n-Si Schottky barrier solar cells by electrophoretic deposition”

Here, we reply to comments by Valentic et al. on our paper published in Electrochimica Acta (2014, 130: 279). They commented that Au nanoparticles played the dominant role on the whole cell's performances in our improved graphene/Si solar cell. We argued that our devices are Au-doped graphene/n-Si Schottky barrier devices, not Au nanoparticles (film)/n-Si Schottky barrier devices. During the doping process, most of the Au nanopatricles covered the surfaces of the graphene. Schottky barriers between doped graphene and n-Si dominate the total cells properties. Through doping, by adjusting and tailoring the Fermi level of the graphene, the Fermi level of n-Si can be shifted down in the graphene/Si Schottky barrier cell. They also argued that the instability of our devices were related to variation in series resistance reduced at the beginning due to slightly lowered Fermi level and increased at the end by the self-compensation by deep in-diffusion of Au nanoparticles. But for our fabricated devices, we know that an oxide layer covered the Si surface, which makes it difficult for the Au ions to diffuse into the Si layer, due to the continuous growth of SiO layer on the Si surface which resulted in series resistance decreasing at first and increasing in the end.

Coupling of carriers injection and charges distribution in Schottky barrier charge-trapping memories using source-side electrons programming

This study elucidates the coupling of Schottky barriers and trapped charges involved in the source-side electrons programming and two-bit/cell reading of the Schottky barrier charge-trapping cells. Two-dimensional numerical iterations were employed to examine the distribution of electron injections and trapped charges, and to discuss the differences of physical mechanisms between the Schottky barrier and conventional cells. In the Schottky barrier cells, both the conduction and injection of electron carriers depend on the Schottky source barrier lowering. The source-side trapped charges alter the source-side lateral field distribution, reducing the maximum of the lateral electric field, and moving the subsequent injections away from the source edge. The distribution of total trapped-charges is considerably wider than that of the initial injection. However, because of source-side conduction, the excellent screening of second-bit effect is beneficial to operate the NOR-type multibit/cell charge-trapping memories.

Effects of Dopant-Segregated Profiles on Schottky Barrier Charge-Trapping Flash Memories

This paper numerically elucidates the effects of dopant-segregated (DS) profiles on the cell operations for Schottky barrier charge-trapping Flash memories. Various DS profiles were employed to examine the cell conduction, programming, and erasing. The DS profile has a key function in determining the injected mechanisms and locations of cell programming and erasing. The heavy DS layer, concentration of 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , induces the DS Schottky barrier cell to become a conventional-like drain-side injection cell, thereby producing similar programming and erasing characteristics as those of a traditional doped source/drain cell. The light DS profile, concentration lower than 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , retains the DS-structured cell as an intrinsic Schottky barrier-like source-side injection cell. Because the intrinsic Schottky barrier cells generate most of the efficient programming/erasing injections with minimized short-channel effects, it is dispensable to incorporate the DS profiles in Schottky barrier charge-trapping cells.

Reading Operation and Cell Scalability of Nonvolatile Schottky barrier Multibit Charge-Trapping Memory Cells

Using unique ambipolar conduction, a Schottky barrier multibit cell can be programmed using source-side electron injection and can be erased reversely using drain-side hole compensation. This paper numerically discusses the particular reading operation and cell scalability of the Schottky barrier multibit cell resulting from the presence of Schottky source/drain barriers. Forward and reverse reading schemes were examined to determine the multibit-cell state. Critical cell factors, such as channel length, Schottky barrier height, and electrode voltage, were examined to select appropriate structural parameters and operational conditions. Because of the unique Schottky source/drain barriers, the scaled Schottky barrier cell exhibits excellent short-channel immunity and retains the nature of cell reading, source-side programming, and drain-side erasing in a nanoscale regime. Preserving a compact stack-gate architecture and a thorough CMOS process, the Schottky barrier multibit cell serves as a promising candidate for use in nonvolatile embedded and commodity memory devices.

Design Considerations of Nanoscale Schottky Barrier Flash Memory with Source-Side Injection Programming

This work numerically elucidates the considerations and optimizations of nanoscale Schottky barrier Flash cells with source-side injection programming. Due to the unique Schottky barrier junction and particular source-side injection programming, the considerations of device parameters in Schottky barriers Flash cells are dissimilar from those in traditional drain-side channel hot-electron cells. Dependences of design parameters, such as Schottky barrier height, tunnel-oxide thickness, substrate concentration, junction depth, and channel length, on the source-side injection programming are clarified to optimize nanoscale Schottky barrier Flash memory. A feasible design of 50 nm Schottky barrier cell is illustrated to have high injection efficiency at low programming voltage.

Nonvolatile Schottky Barrier Multibit Cell With Source-Side Injected Programming and Reverse Drain-Side Hole Erasing

This paper presents a novel Schottky barrier multibit cell with source-side injected programming and reverse drain-side hole erasing. Based on the unique ambipolar conduction of Schottky barrier devices, the source Schottky barrier promotes the amounts of hot electrons at a positive gate voltage to perform source-side injected programming, whereas the drain Schottky barrier enhances the generations of hot holes at a negative gate voltage to carry out reverse drain-side erasing. The proposed Schottky barrier charge-trapping cells are numerically demonstrated to exhibit low-voltage and high-efficiency programming/erasing without the presence of any gate versus source/drain bias tradeoff. The tight and matched distributions of injected carriers make this Schottky barrier cell excellent in future multibit-cell applications.

Highly Ordered Molecular Orientation in a Phthalocyanine Film Deposited on a Well-Polished Indium–Tin Oxide Substrate

Metal-free phthalocyanine (H2Pc) was deposited on an indium–tin oxide (ITO) substrate with a pentacene buffer layer, and the effect of polishing of the ITO surface on the molecular orientation of H2Pc was studied. By rubbing the ITO surface 10,000 times with a plastic eraser, the average surface roughness of ITO was decreased to 1.0 nm from its initial value of 2.0 nm, and the (313) X-ray diffraction peak of α-form H2Pc became significantly large. Rocking curves and optical absorption spectra indicated that, by polishing the ITO surface, the disorder in the orientation of the stacking axis (b-axis) of H2Pc was reduced. A Schottky barrier cell of H2Pc with a highly ordered molecular orientation showed a lower photovoltaic performance than that with a disordered orientation.

Organic thin-film solar cells with a Cu anode: Improvement of the photovoltaic properties on aging in air

The photovoltaic properties of a Ga-doped ZnO (GZO)/3,4,9,10-perylene-tetracarboxyl-bis-benzimidazole (PTCBI)/Zn-phthalocyanine (ZnPc)/Cu heterojunction cell (cell A) and a GZO/ZnPc/Cu Schottky-barrier cell (cell B) were investigated. The energy conversion efficiency η of cell A was only 0.02% immediately after the device preparation but improved to 0.46% after aging for 24 days in air. To elucidate the mechanism of this aging effect, photocurrent action and electro-absorption spectra were measured for cell B. The results reveal that a Schottky barrier exists at the ZnPc/Cu interface which blocks the transport of photogenerated holes to the Cu electrode, and the barrier height is reduced by a white-light illumination of the device after aging. The change in barrier height is attributed to the formation of electron traps at the surface of the ZnPc layer on aging that trap photogenerated electrons.

Vertically Aligned ZnO Nanorod Arrays Sentisized with Gold Nanoparticles for Schottky Barrier Photovoltaic Cells

Vertically aligned zinc oxide (ZnO) nanorod arrays coated with gold nanoparticles have been used in Schottky barrier solar cells. The nanoparticles enhance the optical absorption in the range of visible light due to the surface plasmon resonance. In charge separations, photoexcited electrons are transferred from gold nanoparticles to the ZnO conduction band while electrons from donor (I−) in the electrolyte compensate the holes left on the gold nanoparticles. The fill factors of the dye-free Schottky barrier cell reach a value of ∼0.50. However, after incorporation of N719 sensitizing dye, the open circuit voltage increases to 0.63 V from 0.5 V being measured for dye-sensitized solar cells based on the bare ZnO nanorods. The Schottky barrier at the ZnO/Au interface blocks the electron transfer back from ZnO to the dye and electrolyte, and thus increases the electron density at the ZnO conduction band. The efficiency of the gold-coated ZnO nanorod dye-sensitized solar cells is thus increased from 0.7% to 1.2%.

Correlation between Inner Electric Field and Photocurrent of Zn-Phthalocyanine Schottky-Barrier Cells

An electroabsorption (EA) study is carried out at an electric-field modulation frequency ωm/(2π) of 1 Hz for two types of typical organic Schottky-barrier cell, namely, Au/Zn-phthalocyanine (ZnPc)/Al and Au/ZnPc/In/Al, in order to elucidate the role of the inner electric field in photocurrent (Iphoto) generation. From the bias dependence of the 1F- and 2F-EA intensities measured at the frequencies of ωm and 2ωm, respectively, it is shown that the inner electric field E0 as well as the modulation electric field Em is quenched in the ZnPc layer with a forward bias larger than ∼1 V. For Au/ZnPc/Al, a good correlation is observed between E0 and Iphoto, which indicates that Iphoto is generated by E0. For Au/ZnPc/In/Al, on the other hand, no correlation is observed between E0 and Iphoto. An interpretation of the latter is that Iphoto is caused by an increase in charge-injection probability at the ZnPc/In interface as a result of the trapping of photogenerated charges in the interface region. For both systems, the depletion layer is detected by capacitance-voltage measurement at 0.2 Hz.

DC electric and photoelectric measurements of CdTe thin films in Schottky-barrier cells

Measurements of the temperature dependence of ohmic and space-charge-limited (SCL) currents on thin films of polycrystalline particles of cadmium telluride in Schottky-junction cells have been carried out in air ambient. These cells showed rectification where p-CdTe material was flanked between an ohmic contact (Au) and a blocking contact (Al). At low voltages, the dark current in the forward direction which corresponds to negative potential at the Al electrode varies exponentially with voltage. At higher voltages, two distinct regions of ohmic and SCL conduction limited by a discrete trapping level are determined. Traps with a density of 3.85×10 22 m −3 located at 0.58 eV above the valence band edge have been observed. The thickness dependence in the square-law region has been found to confirm the d −3 law. Values of conversion efficiency as high as 11.3% and open-circuit voltage of 0.77 V have been evaluated from the photo-measurements of J– V characteristic at input power density of 100 mW cm −2. Space-charge concentrations and barrier heights have been estimated from the capacitance–voltage ( C– V) measurements both in dark and under constant illumination. The linearity of the C −2– V dependence is associated with a homogenous distribution of the impurities inside the space-charge region.

Characterization of CdSexTe1−x sintered films

Abstract CdSe x Te 1− x is a promising ternary material which has received considerable attention due to its applications in the fabrication of large area economic solar cell, semiconductor-metal Schottky barrier cell, etc. This material possesses various advantages, principally the high absorption coefficient, optimum band gap and chemical stability, which make it attractive for this kind of devices. CdSe x Te 1− x films with variable concentration ( x =0 to 1) have been deposited onto ultra clean glass substrates by screen printing and then sintered. The optical, electrical and structural properties of CdSe x Te 1− x alloys have been studied, which were found applicable in photovoltaics. The optical band gap of these films were determined by reflectance measurements in the wavelength range of 700–880 nm. The modification of band gap of intermixed CdSe x Te 1− x system has been described and was found suitable for efficient absorption in the visible region of the spectrum. Schottky barrier height and ideality factor for Al/CdTe and Al/CdSe junctions were determined by current–voltage characteristics. X-ray diffraction patterns of these films were reported. The films were of polycrystalline texture over the whole range studied and exhibit predominant cubic zinc blende structure. Sintering is very simple and viable compared to other costly methods. It is a technique less time-consuming, of maximum material utility and less pollutant and offers a suitable method for preparing films on large area substrates.

Sensitization Effect of Porphyrin Dye on the Photocurrent of Al/Polythiophene Schottky-Barrier Cells

An enhanced photocurrent was obtained in an Al/porphyrin-sensitized regioregular polythiophene (PTh) Schottky-barrier cell when the top energy level of the valence band of PTh solid was more negative than the HOMO energy level of porphyrin. However, when ortho-substituted meso-phenylporphyrins were employed, the photocurrent enhancement decreased to about half compared to the case when nonsubstituted meso-phenylporphyrins were used. We conclude from these results that both a larger thermodynamic driving force for a photoinduced hole transfer from porphyrin to PTh and a closer distance between the two conjugating planes of porphyrin and PTh are necessary to obtain a larger photocurrent.

Admittance Study of a Pt/C60/In/Al Schottky-Barrier Cell

Electrical properties of a Pt/C60/In/Al Schottky-barrier cell have been studied by an admittance measurement carried out in the frequency range between f=0.2 Hz and 100 kHz, and also by a current density–voltage (J–V) measurement. The J–V measurement shows that the rectification is caused due to the asymmetry of electron injection efficiencies from the electrodes. The conductance Gp and capacitance Cp are significantly affected by the localized charges produced by the injection from the electrodes or by illumination. From the frequency dependence of Gp and Cp, it is estimated that the dielectric relaxation time of the localized charges is ∼0.3 s and the value of NLξ2 at zero bias in the dark is of the order of 106 m-1, where NL is the density of the localized charges in the C60 layer and ξ is the distance which determines the electric dipole moment µ of a localized charge by the relationship µ=eξ. NLξ2 increases significantly by the application of a forward bias or by illumination.

Enhanced photocurrent by Schottky-barrier solar cell composed of regioregular polythiophene with merocyanine dye

When electron-transfer from poly(3-hexylthiophene-2, 5-diyl) (PTh6) to merocyanine dye (MC) occurred in the mixed solid under illumination, the photocurrent of Al/MC+PTh6 mixed solid Schottky-barrier cell was enhanced compared to that of pure MC or pure PTh6 cell. This is because discrete pairs of electron and hole created by the photoinduced electron-transfer are effectively separated in the electric field formed at the Al/organic solid interface.

Organic solid-state solar cells with a mixture of monomeric porphyrins for light-harvesting and regioregular polythiophene for charge transport

An enhanced photocurrent was observed for a Schottky-barrier cell with a mixed solid consisting of metal-free porphyrin (H 2tpp) and regioregular polythiophene (PTh) compared to similar cells with pure metal-free porphyrin or pure PTh. This is because produced holes efficiently transport in the high-mobility PTh solid soon after a photoinduced electron-transfer from the PTh molecule to the photon harvesting H 2tpp molecule.

Photovoltaic cells based on chemically deposited p-type SnS

The aim of this work is to attract the attention of the scientific workers in the field of PV conversion of solar energy to SnS polycrystalline thin film as a candidate for construction of cheap solar cells, since it posseses similar photoelectric properties as polycrystalline silicon, but it can be produced on any kind of substrate, by simple, economic and environmentally approved technique. By the use of the method of chemical deposition from two separate solutions, complete preparation of three types of cells was done. All of them use SnS as base absorbing layer, with a difference in the window layer electrode. The first one has CdO, the second one has Cd 2SnO 4 thin film window electrode, both prepared by the chemical deposition method. The third cell was purely Schottky barrier cell in which the window electrode was SnO 2:F, prepared by spray pyrolysis. The I– V, C– V and spectral characteristics were registered and the conclusion was drawn that the best performances has shown the cells with Cd 2SnO 4 film as a window electrode.