Showing papers on "Depletion region published in 1980"

Electrochemistry at Semiconductor and Oxidized Metal Electrodes

Abstract: 1. The Solid and the Solution.- 1.1. The Solid.- 1.1.1. Donors, Acceptors, and Traps.- 1.1.2. Energy Levels at the Surface.- 1.1.3. Conductance in Solids.- 1.2. The Solution.- 1.2.1. Introduction.- 1.2.2. The Electrode Fermi Energy as a Function of the Redox Couples in Solution.- 1.2.3. The Relation between the Hydrogen and the Vacuum Scales of Energy.- 1.2.4. Fluctuating Energy Levels in Solution.- 1.2.5. The Energy Levels Associated with Two-Equivalent Ions.- 1.2.6. Conductance in Liquids.- 2. The Solid/Liquid Interface.- 2.1. Surface Ions and Their Energy Levels.- 2.1.1. Adsorption.- 2.1.2. Surface States at the Solid/Liquid Interface.- 2.2. Double Layers at the Solid/Liquid Interface.- 2.2.1. General.- 2.2.2. The Gouy Layer.- 2.2.3. The Helmholtz Double Layer.- 2.2.4. The Space Charge Double Layer in the Semiconductor.- 2.3. Theoretical Predictions of the Energy Levels of Band Edges.- 2.4. The Band Model of the Solid/Solution Interface.- 3. Theory of Electron and Hole Transfer.- 3.1. Introduction.- 3.1.1. General.- 3.1.2. The Activation Energy in Electrode Reactions.- 3.2. Classical Model.- 3.3. The Energy Level Model of Charge Transfer.- 3.3.1. General.- 3.3.2. The Metal Electrode.- 3.3.3. The Semiconductor Electrode.- 3.4. Qualitative Description of Electrode Processes Using the Band Model.- 3.4.1. The Behavior of the Metal Electrode.- 3.4.2. The Behavior of the Semiconductor Electrode.- 3.4.3. The Transition between Semiconductor and Metallic Behavior.- 4. Measurement Techniques.- 4.1. Capacity Measurements.- 4.1.1. Introduction.- 4.1.2. Measurement Theory.- 4.1.3. Analysis.- 4.1.4. Complex Mott-Schottky Plots.- 4.1.5. Determination of Band Edges.- 4.2. Measurements of the Current/Voltage Characteristics.- 4.2.1. General Techniques Voltammetry.- 4.2.2. Rotating Electrodes.- 4.2.3. Illumination.- 4.3. Other Techniques.- 4.3.1. Techniques for Vs Measurement.- 4.3.2. Techniques to Determine Surface Species or Phases.- 4.3.3. Techniques to Study Electrode Reactions.- 5. The Properties of the Electrode and Their Effect on Electrochemical Measurements.- 5.1. The Behavior of the Perfect Crystal.- 5.1.1. The Helmholtz Double Layer: The Surface Charges on the Electrode.- 5.1.2. The Space Charge Region of the Perfect Crystal.- 5.2. The Behavior of Electrode Defects.- 5.2.1. Introduction.- 5.2.2. Deviations of Mott-Schottky Plots Due to Bulk Flaws.- 5.2.3. Current Flow Associated with Bulk Flaws.- 5.3. Observed Flat Band Potentials for Various Semiconductors.- 6. Observations of Charge Transfer at an Inert Semiconductor Electrode.- 6.1. Introduction.- 6.2. Majority Carrier Capture.- 6.2.1. Direct Carrier Transfer to Ions in Solution.- 6.2.2. Indirect Electron Transfer to Ions in Solution.- 6.3. Minority Carrier Capture.- 6.3.1. Minority Carrier Capture on Two-Equivalent Species: Radical Formation and Current Doubling.- 6.3.2. Minority Carrier Capture by One-Equivalent Ions.- 6.3.3. Photocatalysis.- 6.4. Intrinsic Surface States and Recombination Centers.- 6.4.1. Intrinsic Surface States as Carrier Transfer Centers.- 6.4.2. Intrinsic Surface States and Ions in Solution as Recombination Centers.- 6.5. Carrier Injection.- 6.5.1. Direct Electron and Hole Injection.- 6.5.2. Injection by Tunneling.- 6.5.3. Injection by Optically Excited Ions: Dye Injection.- 6.6. High-Current, High-Voltage Processes.- 6.6.1. Introduction.- 6.6.2. High Currents with Accumulation Layers.- 6.6.3. Tunneling and Breakdown on Non-Transition-Metal Semiconductors.- 6.6.4. Practical Electrodes.- 6.7. Analysis of Complicated Electrode Reactions using the Tools of Semiconductor Electrochemistry.- 6.7.1. The Photocatalytic Oxidation of Formic Acid.- 6.7.2. Analysis of the Energy Levels of Two-Equivalent Species.- 6.7.3. The Reduction of Iodine on CdS.- 7. Chemical Transformation in the Electrode Reaction.- 7.1. Introduction.- 7.2. Inner Sphere Changes during Redox Reactions at an Inert Electrode.- 7.3. Adsorption onto and Absorption into the Electrode.- 7.3.1. Adsorption of Water, Hydrogen, and Oxygen.- 7.3.2. Adsorption of Electrolyte Ions.- 7.3.3. Action of Deposited Species.- 7.3.4. Movement of Impurities and Defects into the Electrode.- 7.4. Corrosion.- 7.4.1. Introduction.- 7.4.2. Theory and Observations of Semiconductor Corrosion.- 7.4.3. Stabilizing Agents to Prevent Corrosion.- 8. Coated Electrodes.- 8.1. Introduction.- 8.1.1. The Band Model for Oxide Films.- 8.1.2. Thin Films.- 8.1.3. The Structure of Thick Films.- 8.2. Current Transport through Oxide Films.- 8.2.1. Thin Oxide Layers.- 8.2.2. Model of Electronic Conduction through Thick Coherent Layers.- 8.2.3. Semiconducting Oxide Layers on Metal Electrodes.- 8.2.4. Insulating Layers on Metal and Semiconductor Electrodes.- 8.3. Deposition of Reaction Products on Semiconductor Electrodes.- 9. Applications of Semiconductor Electrodes.- 9.1. Solar Energy Conversion.- 9.1.1. Introduction.- 9.1.2. Photovoltaic Cells.- 9.1.3. Conversion of Optical to Chemical Energy.- 9.1.4. Corrosion of PEC Cells.- 9.1.5. The Future Potential of PEC Solar Cells.- 9.2. Electrocatalysis on Semiconductors.- 9.2.1. General.- 9.2.2. Surface State Additives and Narrow Bands in Electrocatalysis.- 9.3. New Devices.- 9.4. Electropolishing of Semiconductors.- References.- References to Review Articles and Books.- Author Index.

Hot carrier injection at semiconductor‐electrolyte junctions

Abstract: It is shown that the energy of electronic minority charge carriers injected into an electrolyte from an illuminated semiconductor electrode may be significantly greater than that predicted by previous models. The time constants for tunneling from the semiconductor states in the depletion region are evaluated by two methods: approximating the final states as a continuum resulting from strong electron‐vibration interaction in the electrolyte, and calculating the oscillation time between semiconductor states and the discrete electrolyte states before vibrational relaxation. Comparisons are made with the time constants for intraband electronic relaxation in the semiconductor, including the effects of quantization due to confinement in the depletion region, and with those for the vibrational relaxation in the electrolyte. The general conditions for the injection of hot carriers from semiconductors into electrolytes are specified.

High Speed Photoresponse Mechanism of a GaAs-MESFET

Abstract: The high speed photoresponse of a GaAs-MESFET has been demonstrated using a light pulse of about 100 ps duration with a 2 GHz repetition rate generated by a GaAlAs-DH laser diode. The measured current pulse heights through the gate and through the drain as a function of the gate bias voltage confirmed a theory that the photoresponse in MESFETs is caused by the sweepout effect of photogenerated carriers in the depletion layer extending from the gate to the drain, just as in photodiodes with subsequent ordinal FET amplification.

Anomalous low-frequency grain-boundary capacitance in silicon

Abstract: The admittance of silicon bicrystals has been measured as a function of temperature, frequency, and dc voltage. In some cases the low‐frequency capacitance is anomalously large. The ac response of a simple double depletion layer structure is calculated. The anomalous capacitive currents are due to an out‐of‐phase modulation of the barrier height caused by charge injected into grain‐boundary traps.

The superposition principle for homojunction solar cells

Abstract: The superposition principle for solar cells states that the current flowing in an illuminated cell subject to a forward bias V is given by the algebraic sum of the short-circuit photocurrent and the current which would flow at bias V in the dark. Several authors have published arguments establishing the validity of this principle for homojunction cells operated so that the minority-carrier concentrations in the quasi-neutral regions do not exceed low injection levels. All these arguments depend on the assumption that the quasi-Fermi levels are constant across the depletion region of a forward-biased, illuminated cell. The accuracy of this assumption is examined in detail in the present paper. It is found that the quasi-Fermi levels do, in fact, vary significantly across the depletion region of an illuminated cell operated at short-circuit or low forward bias. However, it is shown that if the carrier mobilities are reasonably high and the carrier lifetimes reasonably long, the superposition principle still provides an excellent description of the cell characteristics at all bias levels. The superposition principle may seriously overestimate the efficiency of cells fabricated on poor-quality substrates with very short lifetimes and low mobilities.

Depletion layer studies in organic films: Temperature dependence studies of low frequency capacitance measurements in tetracene and magnesium phthalocyanine

Abstract: The voltage dependence of capacitance in two photovoltaic sandwich cells, (Al ‖ tetracene ‖ Nesatron) and (Al ‖ magnesium phthalocyanine ‖ Nesatron), is reported as a function of temperature. The tetracene cell shows a voltage independent (geometric) capacitance at room temperature which upon heating to 120 °C changes to a depletion layer type capacitance at 10−1 Hz. Values for depletion width, carrier concentration, and barrier voltage are consistent with those reported in a previous publication where carriers in tetracene were mobilized by light. Magnesium phthalocyanine cells, on the other hand, show a depletion layer capacitance at room temperature and upon cooling revert to a geometric capacitance at some lower temperature depending on the frequency of the measurement. A theoretical treatment is presented which describes the frequency and temperature dependence of the depletion layer capacitance. From this analysis a method for measuring activation energies and rate constants for detrapping is obtain...

Semiconductor device having a reduced surface field strength

Abstract: A semiconductor device of the "RESURF" type has a substrate region and a superimposed semiconductor layer which forms a p-n junction with the substrate region. The semiconductor layer has an island-shaped region which is depleted at least locally up to the surface at a reverse voltage applied across the p-n junction which is well below the breakdown voltage of the p-n junction. According to the invention the island-shaped part of the semiconductor layer over at least a part of its area has a doping profile in the vertical direction with at least two overlying layer portions with different average net doping concentrations and of the same or opposite conductivity type, so as to increase the current-carrying capacity of the semiconductor layer.

Capture from free‐carrier tails in the depletion region of junction barriers

Abstract: Junction experiments have been proposed in which measurements of depletion capacitance as a function of decreasing reverse bias are used to determine the energy level of a deep trap. Since deep levels in the depletion layer are filled from the free‐carrier tail extending from the bulk, this process is slow to reach equilibrium. Calculation and experiment demonstrate this effect and it is emphasized that its neglect leads to serious misinterpretation.

The barrier height change and current transport phenomena with the presence of interfacial layer in MIS Schottky barrier solar cells

Abstract: In this comprehensive study, several interesting results which are different from those previous are reported. We find the barrier height decreases for n -type and increases for p -type when positive ions are introduced into the insulating layer. The increase of open circuit voltage can be traced to the suppression of the dark saturation current by the depletion field induced by the positive charge, and to the diminution of the majority tunneling current by the oxide potential barrier. The tunneling probabilities for majority and minority carriers are different; there are only a finite amount of majority carriers with thermionic energy greater than q ( V bi − V s ) which can surmount the depletion potential and tunnel into the metal, whereas the photogenerated minority carriers derive kinetic energy in the depletion layer making tunneling easier. Transport coefficients for electrons to transmit from metal to semiconductor and from semiconductor to metal are different for the departure of built in potentials during illumination.

Recombination in the space-charge region of Schottky barrier solar cells

Abstract: The expression for the recombination rate as a function of voltage, of illumination level, and of position in the space-charge region of the semiconductor is derived analytically. The recombination current density is derived by numerical integration of the above expression. The results show good agreement with experiment for the typical Au- n -type Si near-ideal Schottky barrier solar cells, and the comparison provides information on the uncovering of deep recombination centers by the hole quasi-Fermi level under increasing illumination. It is found that the principal effect of recombination under illumination is the reduction of the photocurrent. A rather surprising but gratifying result is that, once the above effect is taken into account by using short-circuit currents rather than photocurrents, the remaining (voltage dependent) effect of recombination is extremely close to the one in the dark, provided the increase in “uncovered” recombination centers with illumination is taken into account.

Hybrid Quantum Oscillations in a Surface Space-Charge Layer

Abstract: The transconductance of an accumulation layer on $n$-type InAs is studied in a magnetic field $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$ parallel to the layer. Structures are observed, nonperiodic in $\frac{1}{H}$, corresponding to mixed electric and magnetic subbands. The effect promises a simple, sensitive method of probing the shape of the self-consistent potential in surface space-charge layers with multiply occupied subbands.

Chemically sensitive JFET transducer devices utilizing a blocking interface

Abstract: A chemically sensitive junction field effect transistor transducer capable of selectively detecting and measuring chemical properties of substances to which the transducer is exposed. The transducer includes a substrate material, a semiconductor layer having a doping polarity laid over the surface of the substrate, a "source" contact connected to one part of the semiconductor layer, a "drain" contact connected to another part, and a chemically sensitive blocking interface gate structure overlying the upper surface of that portion of the semiconductor layer between the source and drain contacts. The gate structure is adapted to interact with selected chemical substances in the substance being tested and to produce an electric field in relation to the presence, concentration, or activity thereof. This electric field, in turn, causes a modulation of the depletion region in the semiconductor layer that affects the conductivity thereof, and hence the amount of source-drain current that can flow through the transducer. The gate structure also serves as a blocking interface and prevents current from flowing through the gate structure. The chemically sensitive blocking interface gate structure may include numerous configurations and materials adapted for sensing various chemical or biochemical properties.

Current‐voltage characteristics of amorphous silicon P‐N junctions

Abstract: The forward and reverse current‐voltage characteristics of amorphous silicon p‐n junction diodes are presented as a function of doping level. A study of the forward characteristics with temperature show that at high doping levels the current is limited by tunnelling through the depletion region via gap states. At the lowest doping levels the diode current is determined by generation‐recombination in the depletion region. A similar interpretation is applied to the reverse characteristics. These results are relevant to the use of these diodes both as nonlinear elements in matrix‐addressed large‐area liquid‐crystal displays and thin‐film solar cells.

Capacitance studies of the depletion region in hydrogenated a-Si Schottky barrier solar cells

Abstract: The frequency dependence of the capacitance of a-SiH x Schottky barrier solar cells, in the frequency range 1–10 5 Hz, is interpreted in terms of a simple model based on the spatial variation of the resistivity in the junction region. This interpretation is found to be consistent with the dependence of the capacitance on temperature, illumination and bias. From the capacitance measurements, we are able to derive the potential profile in the space charge region and the density of states in the gap.

Analytical solutions for the breakdown voltages of punched-through diodes having curved junction boundaries at the edges

Abstract: Analytical expressions are derived for the breakdown voltages of punched-through diodes having a plane structure terminated with cylindrical and spherical curved boundaries at the edges, through the use of suitable approximations for the electric field in the depletion layer. The expressions derived include both p+-i-n+and p+-p-n+(or p+-n-n+) types and are given in terms of the middle-region (i-layer or p-layer) width, the radius of curvature of the junction edge, the punch-through voltage, and the plane parallel breakdown voltage of p+-i-n+diodes. The results obtained include a correlation between the middle-region (p-layer) width and the width of the depletion layer in the curved portions of the junction when the applied reverse bias across the diode is just sufficient so that punchthrough takes in the portions where the junction is plane parallel. These results are made use of in the breakdown voltage calculations.

Amorphous silicon solar battery

Abstract: A semicomductor device comprises a body of amorphous silicon fabricated by a glow discharge in silane, and a metallic region on a surface of said body providing a surface barrier junction at the interface of said metallic region and said body which is capable of generating a space charge region in said body

Influence of the surface on photoluminescence from indium phosphide crystals

Abstract: The photoluminescence of indium phosphide has been measured on crystals in ultrahigh vacuum and subsequently oxidized in a controlled manner The luminescence intensity can vary by more than an order of magnitude and shows a close correspondence to the known shift of the Fermi level at the surface under oxidation We conclude that the oxidation‐induced surface space charge layer is nonradiative due to the presence of the electric field The band bending and surface charge variation can be estimated quantitatively from the data The influence of surface contamination on Schottky barrier formation is also reported

Surface-acoustic-wave device

Abstract: A surface-acoustic-wave device has a laminate formed of a semiconductor and a piezoelectric layer and a depletion layer control means locally provided at an interface portion of the semiconductor and said piezoelectric layer, wherein a parametric interaction is caused at a region other than an area where the depletion layer control means is provided and a depletion layer capacitance is controlled by applying a DC bias voltage and a pumping voltage to the depletion layer control means.

Method of fabricating polysilicon/silicon junction field effect transistors

Abstract: A junction field effect transistor is fabricated in crystalline silicon by using oppositely doped polysilicon as the gate (POSFET). The depletion region of the pn (or np) junction formed at the polysilicon/silicon interface is used as the gate electrode to modulate the current path through the silicon channel from source to drain, the source and drain contacts may either be conventional metal or polysilicon heavily doped of the same conductivity type as the single crystal silicon substrate.

The influences of traps on the generation-recombination current in silicon diodes

Abstract: The recombination current in the space charge region of an abrupt Si P - N junction is calculated under the assumption that the electrochemical potentials or quasi-Fermi levels for the majority carriers are constant throughout the bulk and space-charge regions, and that the Hall-Shockley-Read centers are distributed uniformly with respect to position in the space-charge region, but can be either a single, discrete level or a continuous and uniform distribution with respect to energy. The results for the single level show that the slope can have constant value over a wide range of applied forward bias. These values are mainly dependent on the trap level position and are nearly independent of the minority carrier lifetime at a given doping concentration. They are also dependent on the lower doping concentration. Furthermore, very good linearity in the characteristic curve can be obtained if we assume that the recombination centers are uniformly distributed in energy throughout the energy gap.

Deep hole traps in high efficiency Shottky barrier solar cells on sputtered amorphous silicon as evidenced by spectral response and thermally stimulated current measurements

Abstract: Electrical and optical measurements are carried out on sputtered Schottky diodes the efficiency of which reaches 2.6% under AMl illumination without A.R. coating. From the spectral response, we deduce the Schottky barrier height. From the quantum efficiency at λ = 0.4765 μm. versus the incident photon flux, we can say that the space charge region is rapidly disturbed. From photocurrent versus wavelength and reverse voltage measurements, we deduce an evaluation of the “collecting region” width (650 A), fully compatible with the hole drift mobility (10−5 cm2 V−1 s−1). In addition, thermally stimulated currents allow us to conclude: 1. - The low mobility is due to a high density of hole deep trans. 2. - The Staebler-Wronski effect arises from the creation of electron traps.

Schottky barrier profiles in amorphous silicon-based materials

Abstract: The localized state density for a-Si:H and a-Si:H:F can be reasonably approximated by a hyperbolic function. Solution of Poisson's equation leads to potential profiles in the depletion region. The predicted width of the depletion region is in reasonable agreement with the results obtained from C-V experiments.

Effects on the open-circuit voltage of grain boundaries within the junction space-charge region of polycrystalline solar cells

Abstract: A physical explanation is given for the observed dependence of open-circuit voltage on grain size in polycrystalline solar cells when no such dependence is seen for short-circuit current This explanation identifies carrier recombination through grain-boundary surface states within the junction space-charge region as a primary mechanism underlying these dependencies Experimental data that support this explanation are discussed, and possible ways of improving the conversion efficiency of polycrystalline solar cells are indicated

Potential fluctuations in doped semiconductors with random impurity distribution

Abstract: The potential fluctuations in doped semiconductors which arise from a random spatial distribution of the impurities are estimated, taking the electronic screening into account. For a 99% compensated bulk material with an impurity concentration of 1018 cm−3, a mean-square fluctuation of the order of 0.1 V is obtained. For the depletion layer in a Schottky-gate n-p structure, potential fluctuations with an amplitude of 20-30 mV are predicted to occur under experimentally accessible conditions.

Chemical reactions of oxide layers on GaAs

Abstract: The interface of GaAs and its native oxide is shown to exhibit a region of excess As. The amount of this excess is increased by laser annealing of the oxide layers with a corresponding change of the depletion layer capacitance being observed. The migration of As out of the surface of GaAs is clearly observed when Al is deposited on GaAs but not when Ga is deposited. MOS structures, formed by a series of new processing steps, avoid the formation of excess As in the insulator region and As vacancy related traps in the semiconductor region of the interface. The C–V characteristics of these structures show improvements over those produced by conventional oxidation methods.

Interaction of IGFET field design with narrow channel device operation

Abstract: The effects of decreasing FET channel width as reported by previous workers reveal three basic mechanisms: Increase in current drive due to voltage gradients at channel width edge tapers; increase in threshold voltage due to the two dimensional aspects of the transition of channel depletion region to field oxide region; and the effect of field doping encroachment at channel edges. An independent investigation reported in this paper shows that for high resistivity substrate poly-gate FET technologies, the last mechanism has a strong dependence on the device's effective width, which varies not only with the gate-to-source bias but also with substrate back bias. Junction edge capacitance and breakdown voltages are also affected. To dimensional simulations qualitatively substantiate these observed effects. It is concluded that the cause of these effects and its variability can be attributed to both photo and hot process steps. The resultant trade-off between density and device performance is discussed in regard to its implications for present and future FET technologies.