Depletion region

About: Depletion region is a(n) research topic. Over the lifetime, 9393 publication(s) have been published within this topic receiving 145633 citation(s).

Carrier Generation and Recombination in P-N Junctions and P-N Junction Characteristics

Abstract: For certain p-n junctions, it has been observed that the measured current-voltage characteristics deviate from the ideal case of the diffusion model. It is the purpose of this paper to show that the current due to generation and recombination of carriers from generation-recombination centers in the space charge region of a p-n junction accounts for the observed characteristics. This phenomenon dominates in semiconductors with large energy gap, low lifetimes, and low resistivity. This model not only accounts for the nonsaturable reverse current, but also predicts an apparent exp (qV/nkT) dependence of the forward current in a p-n junction. The relative importance of the diffusion current outside the space charge layer and the recombination current inside the space charge layer also explains the increase of the emitter efficiency of silicon transistors with emitter current. A correlation of the theory with experiment indicates that the energy level of the centers is a few kT from the intrinsic Fermi level.

Atomically thin p–n junctions with van der Waals heterointerfaces

Abstract: In heterostructures of the transition metal dichalcogenides MoS2 and WSe2, atomically thin p–n junctions are created that show gate-tunable rectifying and photovoltaic behaviour mediated by tunnelling-assisted interlayer recombination. Semiconductor p–n junctions are essential building blocks for electronic and optoelectronic devices1,2. In conventional p–n junctions, regions depleted of free charge carriers form on either side of the junction, generating built-in potentials associated with uncompensated dopant atoms. Carrier transport across the junction occurs by diffusion and drift processes influenced by the spatial extent of this depletion region. With the advent of atomically thin van der Waals materials and their heterostructures, it is now possible to realize a p–n junction at the ultimate thickness limit3,4,5,6,7,8,9,10. Van der Waals junctions composed of p- and n-type semiconductors—each just one unit cell thick—are predicted to exhibit completely different charge transport characteristics than bulk heterojunctions10,11,12. Here, we report the characterization of the electronic and optoelectronic properties of atomically thin p–n heterojunctions fabricated using van der Waals assembly of transition-metal dichalcogenides. We observe gate-tunable diode-like current rectification and a photovoltaic response across the p–n interface. We find that the tunnelling-assisted interlayer recombination of the majority carriers is responsible for the tunability of the electronic and optoelectronic processes. Sandwiching an atomic p–n junction between graphene layers enhances the collection of the photoexcited carriers. The atomically scaled van der Waals p–n heterostructures presented here constitute the ultimate functional unit for nanoscale electronic and optoelectronic devices.

The si-sio, interface – electrical properties as determined by the metal-insulator-silicon conductance technique

Abstract: Measurements of the equivalent parallel conductance of metal-insulator-semiconductor (MIS) capacitors are shown to give more detailed and accurate information about interface states than capacitance measurements. Experimental techniques and methods of analysis are described. From the results of the conductance technique, a realistic characterization of the Si–SiO 2 interface is developed. Salient features are: A continuum of states is found across the band gap of the silicon. Capture cross sections for holes and electrons are independent of energy over large portions of the band gap. The surface potential is subject to statistical fluctuations arising from various sources. The dominant contribution in the samples measured arises from a random distribution of surface charge. The fluctuating surface potential causes a dispersion of interface state time constants in the depletion region. In the weak inversion region the dispersion is eliminated by interaction between interface states and the minority carrier band. A single time constant results. From the experimentally established facts, equivalent circuits accurately describing the measurements are constructed.

Comparison of the device physics principles of planar and radial p-n junction nanorod solar cells

Abstract: A device physics model has been developed for radial p-n junction nanorod solar cells, in which densely packed nanorods, each having a p-n junction in the radial direction, are oriented with the rod axis parallel to the incident light direction. High-aspect-ratio (length/diameter) nanorods allow the use of a sufficient thickness of material to obtain good optical absorption while simultaneously providing short collection lengths for excited carriers in a direction normal to the light absorption. The short collection lengths facilitate the efficient collection of photogenerated carriers in materials with low minority-carrier diffusion lengths. The modeling indicates that the design of the radial p-n junction nanorod device should provide large improvements in efficiency relative to a conventional planar geometry p-n junction solar cell, provided that two conditions are satisfied: (1) In a planar solar cell made from the same absorber material, the diffusion length of minority carriers must be too low to allow for extraction of most of the light-generated carriers in the absorber thickness needed to obtain full light absorption. (2) The rate of carrier recombination in the depletion region must not be too large (for silicon this means that the carrier lifetimes in the depletion region must be longer than ~10 ns). If only condition (1) is satisfied, the modeling indicates that the radial cell design will offer only modest improvements in efficiency relative to a conventional planar cell design. Application to Si and GaAs nanorod solar cells is also discussed in detail.

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.