Showing papers on "Depletion region published in 2012"

Metal--Semiconductor Schottky Barrier Junctions and Their Applications

Abstract: 1. Physics of Schottky Barrier Junctions.- 1. Introduction.- 2. Origins of Barrier Height.- 2.1. Schottky-Mott Theory of Ideal Metal-Semiconductor Contact.- 2.2. Modifications to Schottky Theory.- 2.3. Classifications of Metal-Semiconductor Interfaces.- 2.4. Contacts on Reactive Interfaces.- 2.5. Contacts with Surface States and an Insulating Interfacial Layer.- 2.6. Contacts on Vacuum Cleaved Surfaces.- 3. Measurement of Barrier Height.- 3.1. Capacitance-Voltage Measurement.- 3.2. Current-Voltage Measurement.- 3.3. Photoelectric Measurement.- 4. Results of Barrier Height Measurements.- 4.1. Chemically Prepared Surfaces.- 4.2. Vacuum Cleaved Surfaces.- 4.3. Concluding Remarks.- 5. Capacitance-Voltage Characteristics.- 5.1. Electric Field and Potential Distribution in the Depletion Region.- 5.2. Depletion Region Capacitance.- 5.2.1. Ideal Schottky Barrier.- 5.2.2. Effect of Minority Carriers.- 5.2.3. Effect of Interfacial Layer.- 5.2.4. Effect of Deep Traps.- 6. Current-Voltage Characteristics.- 6.1. Transport Mechanisms.- 6.1.1. Diffusion and Thermionic Emission over the Barrier.- 6.1.2. Tunneling through the Barrier.- 6.1.3. Carrier Generation and Recombination in the Junction Depletion Region.- 6.1.4. Minority Carrier Injection.- 6.2. Forward Characteristics.- 6.3. Reverse Characteristics.- 7. Transient Behavior.- 8. Low-Resistance Schottky Barrier Contacts.- References.- 2. Interface Chemistry and Structure of Schottky Barrier Formation.- 1. Introduction.- 2. Perspectives on Schottky Barrier Formation.- 2.1. Introduction.- 2.2. Brief Review of Phenomenological Schottky Barrier Data.- 3. The Chemistry and Structure of the Interfacial Layer.- 3.1. Synopsis of the Layer-by-Layer Evolution.- 3.2. Some Techniques for Studying the Stages of Interface Formation.- 4. Evolution of the Interfacial Layer.- 4.1. Stage 0: The Clean Semiconductor Surface.- 4.1.1. Silicon (100) and (111) Surfaces.- 4.1.2. GaAs (110) and GaAs (100) Surfaces.- 4.2. Stage 1: The Dilute Limit (< 1/2 Monolayer).- 4.3. Stage 2: Monolayer Formation-Metal Film Nucleation.- 4.4. Stage 3: Additional Monolayers and Interdiffusion.- 4.5. Some Specific Characteristics of the Interfacial Layers.- 5. Formation of Interface States.- 5.1. Intrinsic Interface States Derived from the Metal and Semiconductor.- 5.2. Localized Defect and Impurity Related States.- 5.3. Interface States and the Stages of Interface Formation.- 6. Case Studies of the Chemistry and Structure of Schottky Barrier Formation.- 6.1. Case Studies of Silicon Schottky Barriers.- 6.1.1. Al, Ag, Cu, and Au Schottky Barriers.- 6.1.2. Silicide-Silicon Interfaces.- 6.2. Case Studies of III-V and II-VI Compound Semiconductor Schottky Barriers.- 6.2.1. The Ga-Al-As System.- 6.2.2. The GaAlAs Ternary System with Au Schottky Barriers.- 6.2.3. InP.- 6.2.4. Some II-VI Examples.- 7. Summary.- References.- 3. Fabrication and Characterization of Metal-Semiconductor Schottky Barrier Junctions.- 1. Introduction.- 2. Selection of Semiconductor Materials.- 3. Metal-Semiconductor Systems.- 3.1. Metal-Silicon Systems.- 3.2. Metal-GaAs Systems.- 3.3. Multilayer Metallization Systems.- 4. Design Considerations.- 5. Fabrication Technology.- 5.1. Surface Processing.- 5.2. Dielectric Film Deposition.- 5.3. Ohmic Contact Formation.- 5.4. Metal Deposition.- 5.5. Other Steps.- 6. Characterization.- References.- 4. Schottky-Barrier-Type Optoelectronic Structures.- 1. Introduction.- 2. Barrier Formation in Schottky-Barrier-Type Junctions.- 3. Transport in Schottky-Barrier-Type Structures.- 3.1. MS and MIS Structures.- 3.2. SIS Structures.- 4. Schottky-Barrier-Type Optoelectronic Structures.- 4.1. Schottky-Barrier-Type Light-Emitting Structures.- 4.2. Schottky-Barrier-Type Photodiodes.- 4.3. Schottky-Barrier-Type Photovoltaic Devices.- 4.3.1. MS and MIS Photovoltaic Devices.- 4.3.2. SIS Photovoltaic Devices.- 3. Summary.- References.- 5. Schottky Barrier Photodiodes.- 1. Introduction.- 2. General Parameters of Photodiodes.- 2.1. Signal-to-Noise Ratio (S/N).- 2.2. Noise Equivalent Power (NEP).- 2.3. Detectivity (D).- 2.4. Normalized Detectivity (D*).- 2.5. Detectivity Normalized Also with Respect to the Field of View(D**).- 2.6. Resistance Area Product.- 2.7. Response Time.- 3. Selection of Materials.- 3.1. Metal Systems.- 3.2. Semiconducting Materials.- 4. Fabrication Technology.- 5. Techniques for Evaluating Device Parameters.- 5.1. Current-Voltage Characteristics.- 5.2. Capacitance-Voltage Characteristics.- 5.3. Photoelectric Measurements.- 5.4. Electron Beam Induced Current Technique.- 6. Applications.- 7. Conclusions.- References.- 6. Microwave Schottky Barrier Diodes.- 1. Introduction.- 2. Diode Design Considerations.- 2.1. Equivalent Circuit.- 2.2. Frequency Conversion.- 2.3. Basic Mixer Diode RF Parameters.- 2.3.1. Conversion Loss Theory.- 2.3.2. Noise-Temperature Ratio.- 2.3.3. Overall Receiver Noise Figure.- 2.3.4. Mixer Noise Temperature.- 2.3.5. RF Impedance.- 2.3.6. IF Impedance.- 2.3.7. Receiver Sensitivity.- 2.3.8. Doppler Shift.- 2.3.9. Typical Doppler Radar System.- 2.4. Basic Detector RF Parameters.- 2.4.1. Video Resistance (Rv).- 2.4.2. Voltage Sensitivity.- 2.4.3. Current Sensitivity ?.- 2.4.4. Minimum Detectable Signal (MDS).- 2.4.5. Tangential Signal Sensitivity (TSS).- 2.4.6. Nominal Detectable Signal (NDS).- 2.4.7. Noise Equivalent Power (NEP).- 2.4.8. Video Bandwidth.- 2.4.9. Superheterodyne vs. Single Detection.- 2.5. Mixer Configurations.- 2.5.1. Single-Ended Mixer.- 2.5.2. Single-Balanced Mixer.- 2.5.3. Double-Balanced Mixer.- 2.5.4. Image Rejection Mixer.- 2.5.5. Image Enhanced or Image Recovery Mixer.- 3. Properties of Schottky Barrier Diodes.- 3.1. Diode Theory.- 3.2. DC Parameters.- 3.2.1. Junction Capacitance.- 3.2.2. Overlay Capacitance.- 3.2.3. Series Resistance.- 3.2.4. Figure of Merit.- 3.3. Semiconductor Materials.- 3.4. Epitaxial GaAs.- 3.5. Barrier Height Lowering.- 3.6. Fabrication.- 4. Microwave Performance.- 4.1. Mixer Diodes.- 4.2. Detector Diodes.- 5. RF Pulse and CW Burnout.- 5.1. Introduction.- 5.2. Factors Affecting RF Burnout.- 5.3. Experimental Results.- 5.4. Physical Analysis of RF Pulsed Silicon Schottky Barrier Failed Diodes.- 5.5. Physical Analysis of RF Pulsed Millimeter GaAs Schottky Barrier Failed Diodes.- 5.6. Electrostatic Failure of Silicon Schottky Barrier Diodes.- 6. Conclusions.- References.- 7. Metal-Semiconductor Field Effect Transistors.- 1. Introduction.- 2. Small-Signal FET Theory.- 3. Design Parameters of a Low-Noise Device.- 4. Practical Small-Signal FET Fabrication Techniques.- 4.1. Material Growth Techniques.- 4.2. FET Fabrication Technology.- 5. GaAs Power Field Effect Transistors.- 5.1. Principle of Power FET Operation.- 5.2. Thermal Impedance.- 5.3. Power FET Technology.- 6. Conclusions.- References.- 8. Schottky Barrier Gate Charge-Coupled Devices.- 1. Introduction.- 2. Schottky Gate CCDs.- 3. Potential-Charge Relationships.- 3.1. Surface Channel CCD.- 3.2. Bulk Channel CCD.- 3.3. Schottky Gate CCD.- 4. Charge Storage Capacity.- 4.1. Surface Channel CCD.- 4.2. Bulk Channel CCD.- 4.3. Schottky Gate CCD.- 5. Charge Transfer.- 5.1. Charge Transfer Efficiency.- 5.2. Charge Transfer Mechanisms.- 5.2.1. Surface Channel CCD.- 5.2.2. Bulk Channel CCD.- 5.2.3. Schottky Gate CCD.- 6. Input-Output Circuits.- 7. Schottky Gate Heterojunction CCDs.- 8. Experimental Results.- 8.1. High-Frequency Devices.- 8.2. Heterojunction Devices.- 9. Applications.- References.- 9. Schottky Barriers on Amorphous Si and their Applications.- 1. Introduction.- 2. Properties of Amorphous Si.- 2.1. Deposition Methods.- 2.2. Structural Properties.- 2.3. Electronic Properties.- 2.4. Surfaces.- 3. The Schottky Barrier on ?-Si:H.- 3.1. Current-Voltage Measurements.- 3.2. Capacitance Measurements.- 3.3 Internal Photoemission.- 4. Interface Kinetics and Its Effect on the Schottky Barrier.- 5. Applications.- 5.1. Drift Mobility.- 5.2. Deep Level Transient Spectroscopy.- 5.3. Solar Cells.- 5.4. Thin Film Transistors.- 6. Concluding Remarks.- References.

Fermi level shift and doping efficiency in p -doped small molecule organic semiconductors: A photoelectron spectroscopy and theoretical study

Abstract: We study the mechanism of molecular doping of the organic small molecule N,N,N${}^{\ensuremath{'}}$,N${}^{\ensuremath{'}}$-tetrakis(4-methoxyphenyl)-benzidine (MeO-TPD) doped with the fluorinated fullerene ${\mathrm{C}}_{60}{\mathrm{F}}_{36}$ or the acceptor molecule 2,2${}^{\ensuremath{'}}$-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (F6-TCNNQ). Varying the doping concentration, photoemission spectroscopy measurements show a comparable Fermi level shift for both dopants. The doping efficiency, defined as the ratio of free charge carriers (holes) to acceptors, is estimated from the depletion layer thickness in metal/intrinsic/$p$-doped structures. For low concentrations, we observe rather high doping efficiencies of up to 36$%$ for ${\mathrm{C}}_{60}{\mathrm{F}}_{36}$, whereas for both dopants the doping efficiency strongly decreases with increasing doping concentration down to less than 10$%$. By numerically solving the charge neutrality equation using a classical semiconductor physics approach and comparing the results to the ultraviolet photoelectron spectroscopy data, we show that for very low concentrations doping is hindered by deep intragap states. In particular, the calculations can statistically explain the strong decrease of the doping efficiency for high doping concentrations.

Incompatible Length Scales in Nanostructured Cu2O Solar Cells

Abstract: Electrodeposited Cu2O-ZnO heterojunctions are promising low-cost solar cells. While nanostructured architectures improve charge collection in these devices, low open-circuit voltages result. Bilayer and nanowire Cu2O-ZnO heterojunction architectures are systematically studied as a function of the Cu2O layer thickness, ZnO nanowire length, and nanowire seed layer. It is shown that a thick depletion layer exists in the Cu2O layer of bilayer devices, owing to the low carrier density of electrodeposited Cu2O, such that the predominant charge transport mechanisms in the Cu2O and ZnO are drift and diffusion, respectively. This suggests that the low open-circuit voltage of the nanowire cells is due to an incompatibility between the nanostructure spacing required for good charge collection ( 2 μm). The work shows the way to improve low-cost Cu2O cells: increasing the carrier concentration or mobility in Cu2O synthesized at low temperatures.

Nanowire Piezo-Phototronic Photodetector: Theory and Experimental Design

Abstract: one-dimensional structures of these materials are ideal for fabricating strain-controlled piezo-phototronic devices. The strain applied to cause the deformation of the nanowires is mainly through shape change of the fl exible substrate that supports the device. Such devices can be the basis for active fl exible electronics, which uses the mechanical actuation from the substrate for inducing new electronic/optoelectronic effects. As the piezopotential is controlled by externally applied mechanical deformation with different orientation and magnitude, the piezo-phototronics effect can be combined with fl exible optoelectronics to promote new device functions. Previously, we have demonstrated the enhancement of the sensitivity of UV photodetector, [ 6 ] the response of photocells, [ 7 ] and the emission effi ciency of light emitting diodes. [ 8 ] In these reports, the coupling between piezoelectric effect and photoexcitation has been investigated experimentally. Theoretical calculation of the piezopotential along ZnO nanowires under different strain has been carried out, [ 9‐11 ] and a theoretical framework has been built for the two-way coupling between the piezoelectric effect and semiconductor transport properties. [ 12 ] Theoretical study for the three-way coupling in piezophototronics remains to be investigated. Constructing such a model will not only provide an in-depth understanding about the experimental results, but also explore the core phenomena and build high performance devices. Besides piezo-phototronic effect, other factors such as piezoresistance effect and change of contact area or contact condition can also affect the device performance. It is important to distinguish the contribution made by the piezo-phototronics effect from these other factors through theoretical analysis. In this paper, we have constructed a theoretical model and fabricated corresponding experimental devices to study the piezo-phototronic photodetectors based on single-Schottky and double-Schottky contacted metal‐semiconductor‐metal (MSM) structures. We have coupled the photoexcitation and piezoelectric terms into basic current equations to study their infl uence on the fi nal device performance. Theoretically predicted results have been quantitatively verifi ed by photodetectors based on CdS nanowires for visible light and ZnO nanowires for UV light. Our experimental results show that the piezo-phototronic effect dominates the performance of the photodetector rather than other experimental factors. It is shown that the piezophototronic effect is signifi cantly pronounced at low light intensities, which is important for extending the sensitivity and application range of the photodetector. The conclusions drawn on Schottky contacts present the core properties of the effect and can easily be extrapolated to other structures like p-n junctions. Finally, based on the theoretical model and experimental results, we have proposed three criteria for describing the contribution made by the piezo-phototronic effect to the performance of the photodetectors, which are useful for distinguishing this effect from other factors in governing the performance of the photodetector. The theoretical model for two-way coupling in piezotronics has been developed in a previous report. [ 12 ] Here we adopt the same assumptions and follow similar methods, as schematically shown in Figure 1 . The depletion approximation is assumed for the Schottky contact. Piezoelectric polarization is induced in a semiconductor nanowire when it is subjects to strain, it is reasonable to assume that the piezo charges are distributed in a layer in the depletion zone, which tune the Schottky barrier height. The formation of an inner potential will drive the free charge carriers to redistribute. If there is no external bias, the inner electric fi eld and net charges should only exist in the depletion zone at static or quasi-static state. The Schottky contact current equation will be used as the basic starting point. The infl uence of photoexcitation and piezo-charges on the material band structure will be discussed, and the fi nal coupled term will be integrated into the current transport equation. To give more intuitive perspective of the piezo-phototronic effect, we have also carried out numerical simulations. A one-dimensional model and other simplifi cations are adopted for easy understanding. The core equations and conclusions are shown in the anayltical model below. Current Density for a Forward Schottky Contact : For a piezophototronic photodetector, a measurement of the photoninduced current is an indication of photon intensity. The coupling effect of piezoelectricity and photon excitation is also

Highly enhanced charge injection in thienoacene-based organic field-effect transistors with chemically doped contact

Abstract: We describe the mechanism of contact resistance reduction and improvement in device performance of organic field-effect transistors by chemical doping at the contact interface. Insertion of iron(III)trichloride into the contact interface significantly reduced the contact resistance from 200 to 8.8 kΩ cm at a gate voltage of −40 V, and a field-effect mobility of 7.0 cm2/V s was achieved in devices based on dioctylbenzothienobenzothiophene. The improved charge injection is attributable to a reduction in the depletion layer thickness at the contact interface and occupation of trap states in the access region due to the generation of charge carriers by contact doping.

The Transitional Heterojunction Behavior of PbS/ZnO Colloidal Quantum Dot Solar Cells

Abstract: The nature of charge separation at the heterojunction interface of solution processed lead sulphide-zinc oxide colloidal quantum dot solar cells is investigated using impedance spectroscopy and external quantum efficiency measurements to examine the effect of varying the zinc oxide doping density. Without doping, the device behaves excitonically with no depletion region in the PbS layer such that only charge carriers generated within a diffusion length of the PbS/ZnO interface have a good probability of being harvested. After the ZnO is photodoped such that the doping density is near or greater than that of the PbS, a significant portion of the depletion region is found to lie within the PbS layer increasing charge extraction (p–n operation).

310 GHz gain-bandwidth product Ge/Si avalanche photodetector for 1550 nm light detection.

Abstract: We report a normal incidence Ge/Si avalanche photodiode with separate-absorption-charge-multiplication (SACM) structure by selective epitaxial growth. By proper design of charge and multiplication layers and by optimizing the electric field distribution in the depletion region to eliminate germanium impact-ionization at high gain, a high responsivity of 12 A/W and a large gain-bandwidth product of 310 GHz have been achieved at 1550 nm.

Nonvolatile memory and electronic apparatus

Abstract: An active region, a source region, and a drain region are formed on a single crystal semiconductor substrate or a single crystal semiconductor thin film. Impurity regions called pinning regions are formed in striped form in the active region so as to reach both of the source region and the drain region. Regions interposed between the pinning regions serve as channel forming regions. A tunnel oxide film, a floating gate, a control gate, etc. are formed on the above structure. The impurity regions prevent a depletion layer from expanding from the source region toward the drain region.

Cu2ZnSnS4 (CZTS) nanoparticle based nontoxic and earth-abundant hybrid pn-junction solar cells.

Abstract: A heterojunction between a layer of CZTS nanoparticles and a layer of fullerene derivatives forms a pn-junction. We have used such an inorganic–organic hybrid pn-junction device for solar cell applications. As routes to optimize device performance, interdot separation has been reduced by replacing long-chain ligands of the quantum dots with short-chain ligands and thickness of the CZTS layer has been varied. We have shown that the CZTS–fullerene interface could dissociate photogenerated excitons due to the depletion region formed at the pn-junction. From capacitance–voltage characteristics, we have determined the width of the depletion region, and compared it with the parameters of devices based on the components of the heterojunction. The results demonstrate solar cell applications based on nontoxic and earth-abundant materials.

Analysis of the forward and reverse bias I-V and C-V characteristics on Al/PVA:n-PbSe polymer nanocomposites Schottky diode

Abstract: This paper presents the fabrication and characterization of the Al/PVA:n-PbSe Schottky diode I-V characteristics have been measured at different temperatures in the forward bias The behavior study of the series resistance (RS), the ideality factor (n), the effective barrier height (Φb), the Richardson constant (A*), and the leakage current with the temperature have emphasized an inhomogeneity of the barrier height and a tunneling mechanism assisted by traps in the SBD In C-V measurements, in the reverse bias, the Al/PVA:n-PbSe has been performed as a function of temperature and frequency The values of barrier height (ΦC-V), the built-in–voltage (Vbi) and carrier concentration (ND) and depletion layer width (W) have been calculated at different temperatures in reverse bias The barrier inhomogeneities of the Al/PVA:n-PbSe contact has been explained on an assumption of a Gaussian distribution of barrier heights by using the potential fluctuation model

Systematic optimization of quantum junction colloidal quantum dot solar cells

Abstract: The recently reported quantum junction architecture represents a promising approach to building a rectifying photovoltaic device that employs colloidal quantum dot layers on each side of the p-n junction. Here, we report an optimized quantum junction solar cell that leverages an improved aluminum zinc oxide electrode for a stable contact to the n-side of the quantum junction and silver doping of the p-layer that greatly enhances the photocurrent by expanding the depletion region in the n-side of the device. These improvements result in greater stability and a power conversion efficiency of 6.1% under AM1.5 simulated solar illumination.

Surface depletion induced quantum confinement in CdS nanobelts.

Abstract: We investigate the surface depletion induced quantum confinement in CdS nanobelts beyond the quantum confinement regime, where the thickness is much larger than the bulk exciton Bohr radius. From room temperature to 77 K, the emission energy of free exciton A scales linearly versus 1/L2 when the thickness L is less than 100 nm, while a deviation occurs for those belts thicker than 100 nm due to the reabsorption effect. The 1/L2 dependence can be explained by the surface depletion induced quantum confinement, which modifies the confinement potential leading to a quasi-square potential well smaller than the geometric thickness of nanobelts, giving rise to the confinement effect to exciton emission beyond the quantum confinement regime. The surface depletion is sensitive to carrier concentration and surface states. As the temperature decreases, the decrease of the electrostatic potential drop in the surface depletion region leads to a weaker confinement due to the decrease of carrier concentration. With a la...

Study of barrier inhomogeneities in I–V-T and C-V-T characteristics of Al/Al2O3/PVA:n-ZnSe metal–oxide–semiconductor diode

Abstract: This paper presents detailed analysis of forward and reverse bias I-V and C-V characteristics of Al/Al2O3/PVA:n-ZnSe metal-oxide-semiconductor diode. PVA:n-ZnSe nanocomposites are prepared by chemical bath deposition technique. The alumina layer is deposited on Al substrate by electrolytic anodization method. The temperature dependence I-V parameters such as series resistance (RS), the ideality factor (n), the barrier height (φb), the Richardson constant (A*), mean barrier height, and the leakage current (Ileakage) have been explained on the basis of inhomogeneity. The series resistance obtained from Chenug’s method and Norde’s method shows close agreement with each other. In C-V measurements, in the reverse bias of Al/Al2O3/PVA:n-ZnSe metal-oxide-semiconductor diode has been performed as a function of temperature. The temperature dependence C-V parameters barrier height φ(C−V), the built-in-voltage (Vbi), carrier concentration (ND), Fermi energy (EF), and depletion layer width (W) have been calculated at...

Dark Current in Silicon Photomultiplier Pixels: Data and Model

Abstract: The dark current behavior of the pixels forming the Si photomultiplier as a function of the applied overvoltage and operation temperature is studied. The data are modeled by assuming that dark current is caused by current pulses triggered by events of diffusion of single minority carriers injected from the peripheral boundaries of the active area depletion layer and by thermal emission of carriers from Shockley–Read–Hall defects in the active area depletion layer.

Flexible and Transparent Paper-Based Ionic Diode Fabricated from Oppositely Charged Microfibrillated Cellulose

Abstract: Recently, organic diodes have attracted great research interest because of their unique applications in flexible electronics. Electronic paper is one of the most attractive organic electronic devices. Hereby, we report a transparent, flexible, ionic diode paper made of two oppositely charged microfibrillated cellulose (MFC) sublayers. The current rectification ratio is around 15 at ±5 V and exhibits good repeatability at room temperature. Instead of forming a depletion region to rectify current, this paper diode uses asymmetric charge distribution to selectively control the ion diffusion direction. The asymmetric charge distribution inside the diode paper can selectively transport cations and anions under positive and negative bias, to allow an electric current to pass in one direction while being blocked in the opposite direction. Although the mechanism is quite different from semiconductor-based p–n junction, the phenomenon turns out to be very similar. It was found that the moisture content, thickness ...

Effect of Quantum Dot Deposition on the Interfacial Flatband Potential, Depletion Layer in TiO2 Nanotube Electrodes, and Resulting H2 Generation Rates

Abstract: CdS QD-modified TiO2 nanotube arrays were fabricated using an anodic oxidation-sequential chemical bath deposition process. By means of FESEM, EDS, XRD and XPS, it could be confirmed that the use of an ultrasonication-assisted deposition approach improved the distribution of CdS QDs on the tube walls. The as-prepared CdS-modified TiO2 nanotube arrays exhibited enhanced photoelectrochemical properties and hydrogen production activity, which benefitted from the extended light absorption and the improved interfacial charge-transfer properties of TiO2 nanotube arrays. By analyzing the interfacial properties, the flatband potential, the depletion layer, the capacitance, and the impedance of the CdS/TiO2 photoelectrode, it can be concluded that compared with pure TiO2 nanotube arrays the CdS QD-modified arrays exhibited a more negative flat band potential and a lower energy barrier for interfacial electron transfer. The calculated depletion layer width (dSC) of the sensitized TiO2 nanotube arrays was larger, wh...

Waveguide-integrated near-infrared detector with self-assembled metal silicide nanoparticles embedded in a silicon p-n junction

Abstract: An all-silicon photodetector integrated in a silicon-on-insulator waveguide for the telecom regime is proposed. The device is based on internal photoemission from electrically floating metal silicide nanoparticles (NPs) embedded in the space charge region of a Si p-n junction. Numerical simulation indicates that the light absorption could be enhanced if localized surface plasmon resonances are excited on the metal silicide nanoparticles, thus enabling to shrink the detector’s footprint to a submicron scale. A proof-of-concept detector fabricated using standard silicon complementary metal-oxide-semiconductor technology exhibits a peak responsivity of ∼30 mA/W at 5-V reverse bias and a 3-dB bandwidth of ∼6 GHz. It is expected that the overall performance would be significantly improved by optimization of both the detector’s configuration and the fabrication parameters.

Modeling the influence of doping on the performance of bulk heterojunction organic solar cells: One-dimensional effective semiconductor versus two-dimensional donor/acceptor model

Abstract: This work reports on two different approaches to simulate bulk-heterojunction organic solar cells (BHJ OSCs). The first is a one-dimensional (1D) description which is based on one effective semiconductor and the second is a two-dimensional model (2D) explicitly taking into account both the donor and the acceptor phase. A comparison between the two models is drawn and the influence of either $p$ or $n$ doping on the photovoltaic performance is investigated in detail. Slight differences in the results of the two models are explained with the underlying geometry and it is shown that many features can already be well described with the 1D effective semiconductor model. The influence of doping donor and acceptor phase independently can only be described with the 2D donor/acceptor model. The results indicate that this can be very beneficial for BHJ OSCs. The reason is that upon doping both phases the depletion zone is centered around the donor/acceptor interface and regions of high conductivity are formed in the bulk of the phases, i.e., farthest away from the donor/acceptor interface where charge carriers can recombine. This leads to a reduction of the transport resistance and thus to a significant increase in fill factor. This effect does not occur in a solar cell made of one material only. It is based on the fact that a BHJ OSC is a majority carrier device.

Optimization design of GaN betavoltaic microbattery

Abstract: Betavoltaic radioisotope microbatteries have gradually become the research direction of micro-power sources because of their several advantages, including small scale, stable output performance, long service life, high energy density, strong anti-jamming capability, and so on. Based on the theory of semiconductor physics, the current paper presented a design scheme of isotope microbattery with wide-gap semiconductor material GaN and isotope 147Pm. In consideration of the isotope’s self-absorption effect, the current paper studied and analyzed the optimization thickness of semiconductor and isotope source, junction depth, depletion region thickness, doping concentration, and the generation and collection of electron hole pairs with simulation of transport process of beta particles in semiconductor material using Monte Carlo simulation program MCNP. In the proposed design scheme, for a single decay, an average energy of 28.2 keV was deposited in the GaN, and the short circuit current density, open circuit voltage, and efficiency of a single device were 1.636 μA/cm2, 3.16 V, and 13.4%, respectively.

Enrichment of cations via bipolar electrode focusing.

Abstract: We have previously demonstrated up to 5 × 105-fold enrichment of anionic analytes in a microchannel using a technique called bipolar electrode focusing (BEF). Here, we demonstrate that BEF can also be used to enrich a cationic fluorescent tracer. The important point is that chemical modification of the microchannel walls enables reversal of the electroosmotic flow (EOF), enabling cations, instead of anions, to be enriched via an electric field gradient focusing mechanism. Reversal of the EOF has significant consequences on the formation and shape of the region of the buffer solution depleted of charge carriers (depletion zone). Electric field measurements and numerical simulations are used to elucidate the factors influencing the depletion zone. This information is used to understand and control the location and shape of the depletion zone, which in turn influences the stability and concentration of the enriched band.

Electrical properties of lateral p–n junction diodes fabricated by selective growth of n+ diamond

Abstract: We fabricated diamond lateral p–n junction diodes by selective growth of n+-type diamond and evaluated their structural and electrical properties. The phosphorus-doped n+ diamond was selectively grown by microwave chemical vapor deposition at the side of a boron-doped p-type layer to form lateral p–n junction diodes. No distinct defects are observed at the interface of the p–n junction diode by cross-sectional transmission electron microscopy, implying the good homoepitaxial growth of the n-type diamond. Electron beam induced-current measurements directly confirmed the existence of the depletion layer in p–n junction diode. The electrical properties of the lateral p–n junction diodes were investigated at room temperature to 773 K. The devices show normal diode characteristics at all temperatures. A very low leakage current <10−14 A in the reverse bias was obtained at room temperature, resulting in a high rectification ratio of 108. Although the rectification ratio decreases with increasing temperature, it possesses 106 even at 573 K. A breakdown voltage was examined to be more than 100 V.

Controlled formation of charge depletion zones by molecular doping in organic pin-diodes and its description by the Mott-Schottky relation

Abstract: Molecular doping of organic semiconductors is a key technology for highly efficient organic light-emitting diodes. Nevertheless, the underlying fundamental mechanisms are under discussion. This is because of the complex situation of structural disorder and strong polaronic coupling in such systems. We provide for the first time a systematic study of the formation of charge depletion zones in organic pin-diodes comprising molecular doped hole and electron transport layers. Impedance spectroscopy is employed to study the capacitance of these depletion zones. In particular, we show that the voltage dependent capacitance function obeys the Mott-Schottky relation concerning the influence of doping and the effect of an additional depletion zone given by the intrinsic interlayer. From temperature dependent measurements of the depletion capacitance, we can deduce the amount of active dopant states, their activation energy, and the spatial field distribution within the junction. The measured activation energy of t...

Investigation of Reverse Leakage Characteristics of InGaN/GaN Light-Emitting Diodes on Silicon

Abstract: We investigate the reverse leakage characteristics of InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) grown on Si (111) substrate by metal-organic chemical vapor deposition. The reverse leakage characteristics of InGaN/GaN LED on silicon are measured as low as ~10 nA at -5 V and -10 μA at -15 V. Temperature-dependent current-voltage (I-V) measurements of LED devices reveal that the reverse leakage current mechanism is mainly attributed to the field-enhanced thermionic emission, also known as Poole-Frenkel emission, of carriers from deep centers within the space charge region up to ~ -18 V. The analysis of T-I -V curve yields the calculation of the coefficient of the Poole-Frenkel effect (1.12 × 10-4 eV·V-1/2·cm1/2) and activation energies of carriers (~214 meV at -5 V). With further increase of reverse bias, up to -40 V, LED devices exhibit the onset of space-charge-limited leakage current mechanism without any local breakdown.

High operating temperature XBn-InAsSb bariode detectors

Abstract: A bariode is a new type of "diode-like" semiconductor photonic device, in which the transport of majority carriers is blocked by a barrier in the depletion layer, while minority carriers, created thermally or by the absorption of light, are allowed to pass freely across the device. In an n-type bariode, also known as an XBnn structure, both the active photon absorbing layer and the barrier layer are doped with electron donors, while in a p-type bariode, or XBpp structure, they are both doped with electron acceptors. An important advantage of bariode devices is that their dark current is essentially diffusion limited, so that high detector operating temperatures can be achieved. In this paper we report on MWIR n-type bariode detectors with an InAsSb active layer and an AlSbAs barrier layer, grown on either GaSb or GaAs substrates. For both substrate types, the bariodes exhibit a bandgap wavelength of ~ 4.1 μm and operate with Background Limited Performance (BLIP) up to at least 160K at F/3. Different members of the XBnn device family are investigated, in which the contact layer material, "X", is changed between n-InAsSb and p-GaSb. In all cases, the electro-optical properties of the devices are similar, showing clearly the generic nature of the bariode device architecture. Focal Plane Array detectors have been made with a pitch of 15 or 30μm. We present radiometric performance data and images from our Blue Fairy (320×256) and Pelican (640×512) detectors, operating at temperatures up to 180K. We demonstrate for both GaSb and GaAs substrates that detector performance can be achieved which is close to "Rule 07", the benchmark for high quality, diffusion limited, Mercury Cadmium Telluride (MCT) devices.

IGBT and diode

Abstract: In an IGBT, defects generated by ion implantation for introduction of the P-type collector region or N-type buffer region into the N − -type drift region near the N-type buffer region remain to improve the switching speed, however the leak current increases by bringing a depletion layer into contact with the crystal defects at the off time. To avoid this, an IGBT is provided which includes an N-type buffer region having a higher concentration than that of an N − -type drift region and being in contact with a P-type on its backside, and a defect remaining region provided near the boundary between the N-type buffer region and the N − -type drift region. The N − -type drift region located on the front surface side with respect to the defect remaining region is provided with an N-type field stopping region having a higher concentration than that of the N − -type drift region.

Characterization of dark current in Ge-on-Si photodiodes

Abstract: Ge-on-Si photodiodes were fabricated from germanium films grown using low-pressure chemical vapor deposition. The mechanisms responsible for the dark current in these devices are studied using geometric analysis, temperature-dependent current-voltage characterization, deep level transient spectroscopy, and device modeling. It is found that an important source of leakage current is associated with the surface depletion region, which is impacted by the nature of the fixed charge at the Ge/dielectric interface. This source of leakage especially affects devices with smaller area, on the order of 10 × 10 μm2. Through a post-metallization anneal (PMA), the dark current of these devices can be reduced by ∼1000X. A similar reduction can be obtained by intentionally doping the top of the germanium film p-type. After the PMA, it is found that the dark current density of large devices is ∼1 mA/cm2, due mainly to generation of minority carriers in the depletion region of the device. The effect of reducing the threading dislocation density is also discussed.

Memory and photovoltaic elements in organic field effect transistors with donor/acceptor planar-hetero junction interfaces

Abstract: Interfacial charge transfer at organic/organic planar-hetero junctions allows access to device structures that create new opportunities for flexible electronic devices. Fundamental characteristics ...