Card Set Information

2015-08-29 20:57:40
electrical devices

pn-junctions diodes
Show Answers:

  1. what determines the electrical characteristics of each particular type of atom?
    • the electrons in the outer shell
    • aka valence electrons
  2. Two important semiconductor materials
    • silicon (Si)
    • germanium (Ge)
  3. What is the energy level?
    the amount of energy required to extract an electron from the atom
  4. how are the energy levels of the orbiting electrons measured?
    in electron volts (eV)
  5. the amount of energy required to move one electron through a voltage difference of one volt
    electron volt
  6. What are the 3 energy bands?
    • Valence band
    • energy gap(forbidden gap)
    • conduction band
  7. electrons in which band become disconnected from atoms and are drifting around in the material?
    conduction band
  8. what is the distinction between conductors, insulators and semiconductors largely concerned with?
    the relative widths of the forbidden gap
  9. When does conduction occur in materials?
    when an applied voltage causes electrons in the material to move in a particular direction
  10. free electrons in the conduction band are moved under the influence of the applied electric field
    electron motion
  11. electrons which are still attached to atoms in the valence band
    hole transfer
  12. what may be the reason a flow of current occurs?
    hole movement or hold transfer
  13. electrons and holes are referred to as
    charge carriers
  14. current flow from positive to negative is referred to as
    the conventional current direction
  15. electron flow from negative to positive is known as
    the direction of electron flow
  16. What is the bonding force that holds atoms together in a conductor is
    metallic bonding
  17. when an electron fills one of the holes in the valence shell of an adjacent atom
    covalent bonding
  18. when valence shell electrons are so strongly attached to the atoms that no charge carriers are available for current flow
    insulating materials
  19. When atoms give up outer shell electrons which are accepted into the orbit of nearby atoms
    • ionic bonding
    • very strong
  20. insulators have a _________ forbidden gap
    Semiconductors have a _______forbidden gap
    Conductors have a _____forbidden gap
    • wide
    • narrow
    • no
  21. how does conduction occur in a semiconductor?
    by both electron movement in the conduction band and hold transfer in the valence band
  22. how does conduction occur in a conductor
    with no forbidden gap the valence and conduction band overlaps so very large numbers of electrons are available for conduction
  23. pure semiconductor material is known as
    intrinsic material
  24. what must be added to intrinsic material before material can be used in the manufacture of a device to improve its conductivity?
    impurity atoms
  25. What is the process of adding impurity atoms to intrinsic materials?
  26. two types of doping
    • donor doping
    • acceptor doping
  27. What is the material referred to after doping?
    extrinsic material
  28. type of doping material where impurity atoms have five electrons and three holes in the valence shells
    n-type material
  29. n-type materials
    antimony, phosphorus, and arsenic
  30. what are antimony, phosphorus and arsenic referred too as?
    pentavalent atoms
  31. type of doping material with 3 electrons and 5 holes
    p-type material
  32. p-type donor material
    boron, aluminum, and gallium
  33. which doping material is considered acceptor-doped material
    p-type material from semiconductors
  34. term where thermal energy causes electrons to break free and enter the conduction band creating pairs of holes and electrons
    hole-electron pair generation
  35. term where thermal energy causes electrons to fall into holes is
  36. what is the majority charge carriers in n-type material
  37. what are the minority carriers in n-type material?
  38. what is the majority charge carriers in p-type material
  39. what is the minority charge carriers in p-type material?
  40. What happens when a conductor is heated?
    • * atoms vibrate
    • * movement of surrounding electrons
    • * reduction in flow
    • * conductor's resistance increases
  41. resistance that increases with increasing temperature
    positive temperature coefficient (PTC)
  42. what temperature coefficient does a conductor have?
  43. at what temp does a semiconductor behave as an insulator?
    • -273 C
    • absolute zero
  44. What is the dominating factor in a semiconductor's current?
    thermal generation of electrons
  45. increase in current flow and a decrease in resistance with rising temperature
    negative temperature coefficient (NTC)
  46. what causes a semiconductor to behave more like a conductor?
    when it's heavily doped
  47. what is a material called that has few free electrons available for conduction when not illuminated?
    high dark resistance
  48. what happens when the semiconductor material is illuminated?
    • resistance decreases
    • comparable to a conductor
  49. when a electron going from negative to positive collides with atoms and rebounds towards the positive terminal due to the electric field
    drift current
  50. electrical current that occurs when a concentration of one type of charge carrier is at one end of a semiconductor material causing repulsion towards a low concentration area
    diffusion current
  51. which has greater mobility? electrons or holes?
  52. what determines the electron and hole velocities under the influence of an electric field?
    mobility constants
  53. what does the initial diffusion of charge carriers in a pn-junction create?
    barrier voltage
  54. What can the magnitude of the barrier voltage at the pn-junction be calculated with?
    • * doping densities
    • * electronic charge
    • * junction temperature
  55. what does the barrier voltage oppose and assist across the pn-junction?
    • opposes majority carriers
    • assists minority carriers
  56. The layer on each side of the junction that is depleted of charge carriers
    depletion region
  57. how is the depletion region created?
    by movement of charge carriers across the junction
  58. what is on the n-side of the depletion region?
    donor impurity atoms that lost free electrons and have become positively charged
  59. what is on the p-side of the depletion region?
    acceptor impurity atoms that have become negatively charged by losing the hold associated with them (filled with an electron)
  60. What happens to the depletion region when either side is more heavily doped?
    penetrates deeper into the opposite side
  61. a two-electrode, or two-terminal, device
  62. one-way device, offering a low resistance when forward-biased, and behaving almost as an open switch when reverse-biased
  63. what are low-current diodes used for?
    switching circuits
  64. what are high-current diodes most often used for?
    rectifiers for ac to dc conversion
  65. what is the positive terminal of a diode for forward bias called?
  66. what is the negative terminal of a diode when forward biased?
  67. what can destroy a pn-junction diode?
    • high level of forward current
    • large reverse voltage
  68. another name for high-current diodes
    power diodes
  69. what do power diodes generate a lot of?
  70. what are power diodes generated for?
    to be connected mechanically to a metal heat sink
  71. can pass forward currents of many amperes and can survive several hundred volts of reverse bias
    power diodes
  72. is largely a minority charge carrier reverse saturation current
  73. what happens if theres a small increase in Ir?
    minority charge carriers leak into the junction surface
  74. why is it that a reverse-biased diode may be treated almost as an open switch?
    because the reverse current is 1/10000 of the lowest normal forward current level
  75. what happens when diode reverse voltage  (Vr) is sufficiently increased?
    goes into reverse breakdown which can destroy a diode unless current is limited by suitable series-connect resistor
  76. in what device is reverse break-down useful
    Zener diodes
  77. Vf
    forward voltage drop
  78. Ir
    reverse saturation current
  79. Vbr
    reverse breakdown voltage
  80. rd
    dynamic resistance
  81. If(max)
    maximum forward current
  82. the constant resistance (or dc resistance) of the diode at a particular constant forward current
    static quantity
  83. the resistance offered to changing levels of forward voltage
  84. The dynamic resistance
  85. reciprocal of the slope of the forward characteristics beyond the knee
    incremental resistance or ac resistance
  86. a diode with zero forward resistance and zero forward voltage drop
    ideal diode aka perfect diode
  87. the reverse current of a ideal diode
    infinitely high reverse resistance resulting in zero reverse current
  88. what is the relationship between the diode forward voltage and current in the circuit defined by?
    device characterisitics
  89. what is the point on the dc load line where the diode voltage and current are compatible with the circuit conditions
    point Q or quiescent point or dc bias point
  90. What dictates the slope of the dc load line in a diode series circuit
    R1 resistor
  91. what determines point A on the load line?
    supply voltage E
  92. what will happen if the maximum power dissipation of a diode is exceeded?
    overheat and may short-circuit or open-circuit
  93. factor that defines the slope of the power-vs-temperature graph
    derating factor (D) can be employed to draw graph
  94. depletion region is layer depleted of charge carriers situated between two blocks of low-resistance material refers to what two different devices?
    pn-junction and capacitor
  95. Cpn
    depletion layer capacitance aka transition capacitance
  96. the capacitance of a reverse-biased pn-junction
    depletion layer capacitance
  97. what is the process of diffusion capacitance Cd
    • E is reversed
    • If ceases immediately
    • majority charge carriers in depletion region
    • depletion region widened
    • creates a large reverse current at first 
    • current decreases to level of reverse saturation current
  98. what are the factors to consider with reverse-biased diodes
    high reverse resistance (Rr) in parallel with depletion layer capacitance (Cpn)
  99. what are the factors to consider with forward-biased diode
    dynamic resistance rd in series with voltage cell representing Vf
  100. the time required for the current to decrease to the reverse saturation current level
    reverse recovery time (trr)
  101. Vr or Vrrm
    • peak reverse voltage (peak inverse voltage and dc blocking voltage)
    • max reverse voltage that may be applied across the diode
  102. Io or If(av)
    • steady-state forward current
    • max current that may be passed continuously through the diode
  103. Ifsm
    • Non-repetitive peak surge current
    • A one time current that is very much higher than the normal max
    • may be passed for a specified time or flow briefly when a circuit is first switched on
  104. Ifrm
    • repetitive peak surge current
    • peak current that may be repeated over and over again during each cycle of a rectified waveform
  105. Vf
    • static forward voltage drop
    • max forward volt drop for a given forward current and device temp
  106. P
    • Continuous power dissipation at 25 C
    • max power that the device can safely dissipate continuously
  107. how can you get a diode to operate continuously in reverse device
    • reverse voltage is sufficiently increased
    • junction breaks down
    • large reverse current flow
    • reverse current limited by a suitable series-connected resistor
    • Ir returns to its normal level when the voltage is reduced below the reverse breakdown level
  108. name and process of a reverse biased pn-junction (breakdown diodes) with a very narrow depletion region
    • ionization by electric field aka Zener breakdown
    • electric field strength (volts/width) can be very high
    • high-intensity electric field causes electrons to break away from atoms
    • converting depletion region from insulating into conduction
  109. name and process of a reverse biased pn-junction (breakdown diodes) with a very wide depletion region
    • ionization by collision-avalanche breakdown
    • electrons in the reverse saturation current can be given sufficient energy
    • electrons to break free when they strike atoms in depletion region
    • collide with other atoms
    • produces more free electrons
    • avalanche effect
  110. Z
    • Zener diode
    • cathode bar approximately in the shape of a letter Z
  111. Vz
    zener breakdown voltage
  112. Izt
    test current for measuring Vz
  113. Izk
    reverse current near the knee of the characteristic, minimum reverse current to sustain breakdown
  114. Izm
    Max zener current, limited by the max power dissipation
  115. Zz
    dynamic impedance
  116. the zener diode may be operated at any reverse current level between :
    Izk and Izm
  117. what is the diode normally operated at for the greatest voltage stability
    • Izt
    • test current