A B C D E F G H I J K L M N O P Q R S
SAFETY ASSESSMENT SAFFMAN LENGTH SALINE WATER RECLAMATION SALT SALT DILUTION METHOD FOR FILM FLOW RATE MEASUREMENT SALTATION SALTING OUT SAMPLING SAMPLING METHODS, FOR DROPSIZE MEASUREMENT SAND BLASTING SANDIA NATIONAL LABORATORY, SNL Satellite remote sensing SATELLITES SATURATED FLUID PROPERTIES SATURATED SURFACES SATURATED VOLUME SATURATION PRESSURE SATURATION TEMPERATURE SAUTER MEAN DIAMETER SCALE-UP OF PERFORATION PROCESS SCALES OF TURBULENCE SCALING SCATTERING SCATTERING AMPLITUDE SCATTERING EFFICIENCY SCATTERING INDICATRIX SCATTERING OF RADIATION Scattering problem for cylindrical particles SCHEIBEL EQUATION FOR DIFFUSION IN LIQUIDS SCHLIEREN INTERFEROMETRY SCHLIEREN TECHNIQUE SCHMIDT NUMBER SCHMIDT, ERNST (1892-1975) SCHUSTER-HAMAKER MODEL SCHUSTER-SCHWARZCHILD APPROXIMATION, FOR COMBINED RADIATION AND CONDUCTION SCRAPED SURFACE HEAT EXCHANGERS SCREEN SEPARATORS SCREENS SCREW ROTARY COMPRESSOR SCREWS, PLASTICATING SCROLL DISCHARGE CENTRIFUGE SCRUBBERS SEA WATER COMPOSITION SECOND LAW OF THERMODYNAMICS SECOND NORMAL STRESS DIFFERENCE COEFFICIENT Secondary Flows Secondary quantity SECONDARY RECOVERY PROCESSES SEDIMENTATION SEDIMENTING CENTRIFUGES SEEPAGE SEGMENTAL BAFFLES SEGREGATION SEIDER-TATE CORRELATION SELECTIVE FROTH FLOTATION SELF ORGANIZATION SELF-SIMILAR HARDENING BEHAVIOR SELF-SIMILARITY SEMI-CONDUCTOR THERMOMETERS SEMI-SLUG FLOWS Semi-transparent media containing bubbles SEMIANNULAR FLOW SEMICONDUCTOR DIODE LASERS SEMICONDUCTORS SEMITRANSPARENT MEDIA SENSIBLE HEAT STORAGE SEPARATED FLOW MODELS SEPARATED LIQUID FLOWS SEPARATION OF BOUNDARY LAYERS SEPARATION OF EMULSIONS SEPARATION OF FLUID MIXTURES SEPARATION OF GAS AND SOLIDS SEPARATION OF LIQUIDS SEPARATION OF LIQUIDS AND SOLIDS SEPARATION OF PHASES IN GAS-LIQUID FLOWS SEPARATION PROCESSES SEPARATION, LIQUID/LIQUID SEPARATION, PARTICLES/LIQUID SERIES EXPANSIONS SESSILE DROPS AND BUBBLES SETTLING SLURRIES SEVERE ACCIDENTS, IN NUCLEAR REACTORS, CONTAINMENT OF SHADOWGRAPH TECHNIQUE SHAPE MEMORY SHAPE OF VAPOR FORMATIONS IN EXPLOSIVE BOILING SHAPE SELECTIVE CATALYSIS SHEAR FLOW Shear Layer SHEAR MODULUS Shear Stress SHEAR STRESS MEASUREMENT SHEAR STRESS VELOCITY SHEAR THICKENING SHEAR THICKENING FLUIDS SHEAR THINNING FLUIDS SHEAR VISCOSITY SHEARING INTERFEROGRAM SHEATH CHARACTERISTICS SHEET SPLITTING, IN DROP FORMATION SHELL AND TUBE CONDENSERS SHELL AND TUBE HEAT EXCHANGERS SHELL BOILER SHELL PROGRESSIVE MODEL SHELL-SIDE REFRIGERATION CHILLERS SHELLS SHERWOOD NUMBER SHERWOOD, THOMAS KILGORE (1903-1976) SHOCK TUBES SHOCK WAVE PROPAGATION SHOCK WAVES SHOCK WAVES, CONICAL SHORT ROUGHNESS STRIP SHORT TIME LAPSE PHOTOGRAPHY SHORT-TUBE VERTICAL EVAPORATOR SHOT TOWERS SHRINKING CORE MODEL SI UNITS SIDERITES SIEVE, TRAY COLUMN Silica based nanoporous composite materials SILICA GEL SILICON SILICON CARBIDE SILICON SOLAR CELLS SILOS, GRANULAR FLOW FROM SILVER SILVER METHOD SIMILARITY CONDITIONS SIMILARITY, THEORY OF SIMILITUDE Simplest approximations of double spherical harmonics SIMPLEX ATOMIZER SIMPLIFIED BOILING WATER REACTOR, SBWR SIMULATING SUBSURFACE TEMPERATURE SINCLAIR-LA MER AEROSOL GENERATOR Single-phase medium SINGLET STATE SINGLET STATE LIFETIME Singularities SINGULARITIES, HYDRAULIC RESISTANCE IN SINTERING SINUOUS JETS SIPHON CENTRIFUGE SKIMMER PIPE AND KNIFE CENTRIFUGES SKIN EFFECT SKIN FRICTION SLAG FORMATION SLIGHTLY DEFORMED POROUS CIRCULAR CYLINDER SLIGHTLY INCLINED SURFACE-MOUNTED PRISMS Slip ratio SLIT FLOW METERS SLIT FLOWS SLOT-PERFORATED FLAT FINS SLOW MOTION PHOTOGRAPHY Slug flow SLUG FLOW, SOLID SUSPENSIONS SLUG FREQUENCY SLUG LENGTH SLURRIES SMALL ANCLE SCATTERING METHOD, FOR DROPSIZE MEASUREMENT SMELTING SMOKE, AS AN AIR POLLUTANT SMOKES SNELL REFRACTION LAW SNL SOAVE EQUATION SODA ASH SODIUM SODIUM CARBONATE SODIUM CHLORIDE SODIUM COOLED NUCLEAR REACTOR SODIUM HYDROXIDE SOFTENING OF WATER SOFTWARE ENGINEERING SOIL, THERMAL PROPERTIES SOL SOLAR AIR HEATERS SOLAR CELLS SOLAR COOKERS SOLAR DRYING SOLAR ENERGY SOLAR ENERGY THERMAL CONVERSION SOLAR PONDS SOLAR RADIATION SOLAR RADIATION SPECTRUM SOLAR REFRIGERATION SOLAR SELECTIVE SURFACES SOLAR SODIUM EVAPORATOR SOLAR STILLS SOLAR WATER HEATERS SOLENOIDAL FLOW SOLID FUELS SOLID HOLDUP SOLID PROPELLANT SOLID STATE LASERS SOLID-LIQUID-LIQUID FLOWS SOLIDIFICATION SOLIDIFICATION CONSTANT SOLIDOSITY SOLIDS CONCENTRATION SOLIDS IN LIQUIDS, BOILING HEAT TRANSFER SOLIDS SEPARATION SOLIDS, THERMAL CONDUCTIVITY OF SOLITARY WAVE SOLITON SOLUBILITY SOLUBILITY OF GASES IN LIQUIDS SOLUBILITY OF SOLIDS IN LIQUIDS SOLUTE SOLUTE DIFFUSION SOLUTE FUNCTIONALITY Solution algorithm SOLUTIONS Solutions for one-dimensional problems Solutions for One-Dimensional Radiative Transfer Problems SOLVENT SOLVENT EXTRACTION Some applications: electrical arcs and atmospheric re-entry Some applied problems of combined heat transfer Some methods for detailed numerical simulation of radiative transfer Some validity studies SONIC OSCILLATOR SONIC VELOCITY SONOCAPILLARY EFFECT SOOT SORET AND DUFOUR EFFECTS ON FREE CONVECTION SORET EFFECT SORPTION HEAT PUMPS SOUND ABSORPTION SOUND GENERATION SOUND PROPAGATION SOUR GASES SOUTTER-ION PUMP SPACE HEATING SPACERS SPACERS, EFFECT ON CHF SPARK-IGNITION ENGINES SPARSELY PACKED POROUS MEDIUM Spatial discretization schemes SPATIAL-TEMPORAL CORRELATION SPECIFIC HEAT CAPACITY SPECIFIC WORK, IN TURBINES SPECKLE METHOD SPECKLE PHOTOGRAPHY SPECTRA, EMISSION AND ABSORPTION SPECTRAL ANALYSIS SPECTRAL DENSITY FUNCTION SPECTRAL EMISSIVITY SPECTRAL EXTINCTION METHOD Spectral radiative properties of diesel fuel droplets Spectral radiative properties of disperse systems: theoretical modeling and experimental characterization Spectral radiative properties of gases and plasma: theoretical models and experimental data Spectral radiative properties of some important materials: experimental data and theoretical models SPECTROFLUORIMETRY Spectroscopic databases SPECTROSCOPY SPECULAR REFLECTION SPEED OF LIGHT SPEED OF SOUND SPENT FUEL SPHERE, DRAG COEFFICIENT FOR SPHERES, CONVECTIVE HEAT AND MASS TRANSFER SPHERES, DRAG AND LIFT SPHERES, SOLID, DRAG ON Spherical particles SPHERICITY SPIRAL CLASSIFIER SPIRAL HEAT EXCHANGERS SPIRAL TUBES, USE IN BENSON BOILERS SPIROPYRAN SPLATTERING, EFFECT ON JET IMPINGEMENT SPONTANEOUS CONDENSATION SPRAY CHARACTERISTICS SPRAY COLUMNS SPRAY CONDENSERS SPRAY COOLING SPRAY DRYER SPRAY DRYING SPRAY EQUATION SPRAY EVAPORATORS SPRAY FLOWS SPRAY FORMATION SPRAY NOZZLES SPRAY TOWERS SPRAYERS SPRAYING SPRAYS SPREADING OF LIQUIDS ON LIQUIDS SPUTTERING STABILITY STABILITY CRITERIA STABILITY OF EMULSIONS STABILITY OF FLOATING BODIES STACKS, POLLUTION FROM STAGGERED TUBE BANKS STAGNANT FILM MODEL STAGNATION POINT STAGNATION PRESSURE STAGNATION TEMPERATURE STANDARD CONDITIONS STANTON GAUGE STANTON NUMBER STANTON, SIR THOMAS EDWARD (1865-1931) STARK BROADENING STARK NUMBER STARS, FUSION REACTIONS IN Static Head STATIC INSTABILITIES IN TWO-PHASE SYSTEMS STATIC MIXERS STATIC REGENERATORS STATIONARY PHASE, SP, CHROMATOGRAPHY Statistical band models STATISTICAL MECHANICS STATISTICAL THEORY, OF TURBULENT FLOW STATISTICAL THERMODYNAMICS STEAM ENGINES STEAM GAS TURBINE UNITS STEAM GENERATORS, NUCLEAR STEAM JET EJECTORS STEAM JET REFRIGERATION STEAM TABLES STEAM TURBINE STEAM-WATER SEPARATION STEEL AND TUBE CONDENSERS STEELS STEFAN'S LAW STEFAN, JOSEF (1835-1893) STEFAN-BOLTZMANN CONSTANT STEFAN-BOLTZMANN LAW STEFAN-MAXWELL EQUATIONS STEPWISE HEAT RELEASE STEREOSCOPIC IMAGING Stewart number Stewart number STEWARTSON TYPE FLOW STIELTJES' INTEGRAL STIRRED TANK REACTOR STIRRED TANKS STIRRED VESSEL PHASE INVERSION STOCHASTIC DIFFERENTIAL EQUATIONS STOCHASTIC PROCESS STOICHIOMETRIC COMBUSTION STOKES EQUATION STOKES FLOW STOKES LENGTH STOKES PARADOX STOKES PROBLEM STOKES SHIFT STOKES STREAM FUNCTION STOKES' LAW FOR SOLID SPHERES AND SPHERICAL BUBBLES STOKES-EINSTEIN EQUATION STOKES-EINSTEIN EQUATION, FOR DIFFERENTIAL COEFFICIENTS IN LIQUIDS STOMATAL CONTROL OF WATER LOSS FROM PLANTS STOPPING DISTANCE STORE'S FORMULA STRAIN STRAIN GAUGES STRAIN RATE STRANGE ATTRACTORS STRATIFICATION, UNSTABLE AND STABLE Stratified Gas-Liquid Flow STRATIFIED WAVY FLOW STRATOSPHERE STREAM ANALYSIS METHOD STREAM AVAILABILITY Stream Function Streamline Streamline Flow STREAMLINED BODIES, FLOW OVER STREAMLINES STREAMLINES, VISUALIZATION STREAMTUBE STRESS Stress in Fluids STRESS IN SOLID MATERIALS STRESS TENSOR STRESS VECTOR STRESS, NORMAL STRESS, SHEAR STRETCHING SHEET STRETCHING SURFACE STRETCHING/STABILIZING EFFLUX FLUID FILMS STROUHAL NUMBER Structure of plasma spectra STRUCTURED SURFACE STUART NUMBER SUBCHANNEL ANALYSIS SUBCHANNEL MIXING SUBCOOLED TWISTED FLOW SUBCOOLING SUBCOOLING EFFECTS ON POOL BOILING SUBLAYER FENCE SUBLIMATION SUBMERGED COMBUSTION SUBMERGED COMBUSTION EVAPORATORS SUBMERGED JETS SUBROUTINES SUBSTITUTE NATURAL GAS (SNG) SUBSURFACE BARRIER SUBUNDAL FLOW SUCTION SUCTION EFFECTS SULFUR SULFUR DIOXIDE SULFUR HEXAFLUORIDE SULFUR POLLUTION SULFURIC ACID SUN, HEAT TRANSFER IN SUPER-PHENIX SUPERCAVITATION SUPERCOMPUTING SUPERCONDUCTING MAGNETS SUPERCONDUCTORS SUPERCRITICAL HEAT TRANSFER SUPERFICIAL VELOCITY SUPERHEATING SUPERSATURATION SUPERSONIC EXTERNAL FLOW SUPERSONIC FLOW SUPERSONIC FLOW, IN NOZZLES SUPERSONIC HETEROGENEOUS FLOW SUPERSONIC JET SUPERUNDAL FLOW SUPPRESSION OF NUCLEATE BOILING SURFACE ACTIVE SUBSTANCES SURFACE ALLOYING OF METALS Surface and interfacial tension SURFACE CONDENSERS SURFACE DIFFUSION SURFACE DIMPLES SURFACE EFFECTS ON BOILING SURFACE EFFICIENCY SURFACE ENERGY SURFACE EXTENSIONS SURFACE FLOW VISUALIZATION SURFACE ROUGHNESS SURFACE TENSION SURFACE TENSION DEVICES SURFACE TREATMENT SURFACE, CIRCULAR SURFACE, PERMEABLE SURFACTANT COLLECTORS SURFACTANTS SURGE TANKS SUSPENSION OF PARTICLES IN LIQUID SUTHERLAND COEFFICIENT SWEATING SWEETENING OF GASES SWIRL BURNERS SWIRL FLOW DEVICES SWIRLING FLOW SWIRLING TAPES, FOR INCREASING BURNOUT FLUX SYMMETRIC TENSOR SYMMETRY ANALYSIS OF SECOND-GRADE FLOW SYNCHROTON RADIATION SYNOPTIC SCALE CIRCULATION, OF ATMOSPHERE SYNTHETIC ZEOLITES System of units
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SEMICONDUCTORS

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A typical semiconductor is a crystalline solid material with an Electrical Conductivity that is highly dependent on temperature. At low absolute temperatures a pure semiconductor will appear to be a good insulator, however, its conductivity rises dramatically as the temperature increases. Semiconductors like silicon are the basis of modern electronics and integrated circuit technology.

The electrical conductivity of a solid depends on two factors. Firstly, the number of mobile charge carriers present and secondly, the mobility or speed at which the carriers move under the influence of an electric field. It is the first consideration, usually called carrier concentration, that determines whether a material is a good conductor like a metal or an insulator such as diamond.

In a typical metal each atom contributes one or more of its outer electrons to a common sea of conduction electrons that permeates the solid, yielding a very large number of conduction electrons. This sea of electrons or electron gas will readily support a transport current in the presence of an electric field. By comparison, a good insulator has strongly localized electrons. A considerable amount of energy is required to break away the electrons from their current atom sites, making transport currents through the material impossible unless work is done initially to free a significant number of electrons.

Semiconductors have resistance properties in between the above two extremes, however, they are not simply poor insulators (or bad conductors). The name is used for those materials that exhibit insulator like properties at very low temperatures, because all the outer electrons called valence electrons are localized, but begin to conduct as the temperature is raised. This is because the thermal energy is sufficient to break away electrons from their local bonds and promote them into the role of conduction electrons. Thus at higher temperatures a semiconductor exhibits properties closer to those of metals. It is the dramatic change in conductivity due to the excitation of valence electrons into the conduction state as the ambient temperature is increased that is the characteristic feature of a semiconductor. The conductivity of a pure semiconductor would, theoretically, increase almost exponentially with absolute temperature. Conduction in a semiconductor takes place both via the conduction electrons and also the valence electrons that are now able move to neighboring atoms that have lost valence electrons. The vacancy travelling in the opposite direction to the valence electrons is called a hole. For convenience holes are regarded as positive charge carriers. Detailed descriptions of conduction processes in semiconductors can be found in Streetman (1990).

The most commonly used semiconductor material is Silicon, which is tetravalent and forms a diamond type crystal structure. The minimum energy required to promote an electron from the valence state (or band) to the conduction band in silicon is only about 1.1 eV (the energy gap). Hence, the ambient thermal energy at room temperature is sufficient to produce a low but significant number of conduction electrons. Even though the mean thermal energy of the electrons is less than the energy gap there are always some individual electrons with greater energies due to the statistical distribution in the electron energies.

Doping is the addition of minute amounts of specific impurities to extremely pure semiconductor materials to build in a number of available carriers. In materials that are called p-type trivalent atoms like boron have been added to create holes. Whereas, introducing a pentavalent impurity like phosphorus produces n-type material with a background level of conduction electrons. It should be noted that the material is still electrically neutral. The name n or p type describes the type of free carrier that predominates in the material (called the majority carrier). In general both electrons and holes are present. Further information regarding doped semiconductors and device fabrication may be found in Pulfrey and Tarr (1989).

REFERENCES

Streetman, B. G. (1990) Solid State Electronic Devices, 3rd edn., Prentice Hall International.

Pulfrey, D. L. and Tarr, N. G. (1989) Introduction to Microelectronic Devices, Prentice Hall-International.

References

  1. Streetman, B. G. (1990) Solid State Electronic Devices, 3rd edn., Prentice Hall International.
  2. Pulfrey, D. L. and Tarr, N. G. (1989) Introduction to Microelectronic Devices, Prentice Hall-International.

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