Card Set Information
what determines the electrical characteristics of each particular type of atom?
the electrons in the outer shell
aka valence electrons
Two important semiconductor materials
What is the energy level?
the amount of energy required to extract an electron from the atom
how are the energy levels of the orbiting electrons measured?
in electron volts (eV)
the amount of energy required to move one electron through a voltage difference of one volt
What are the 3 energy bands?
energy gap(forbidden gap)
electrons in which band become disconnected from atoms and are drifting around in the material?
what is the distinction between conductors, insulators and semiconductors largely concerned with?
the relative widths of the forbidden gap
When does conduction occur in materials?
when an applied voltage causes electrons in the material to move in a particular direction
free electrons in the conduction band are moved under the influence of the applied electric field
electrons which are still attached to atoms in the valence band
what may be the reason a flow of current occurs?
hole movement or hold transfer
electrons and holes are referred to as
current flow from positive to negative is referred to as
the conventional current direction
electron flow from negative to positive is known as
the direction of electron flow
What is the bonding force that holds atoms together in a conductor is
when an electron fills one of the holes in the valence shell of an adjacent atom
when valence shell electrons are so strongly attached to the atoms that no charge carriers are available for current flow
When atoms give up outer shell electrons which are accepted into the orbit of nearby atoms
insulators have a _________ forbidden gap
Semiconductors have a _______forbidden gap
Conductors have a _____forbidden gap
how does conduction occur in a semiconductor?
by both electron movement in the conduction band and hold transfer in the valence band
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
pure semiconductor material is known as
what must be added to intrinsic material before material can be used in the manufacture of a device to improve its conductivity?
What is the process of adding impurity atoms to intrinsic materials?
two types of doping
What is the material referred to after doping?
type of doping material where impurity atoms have five electrons and three holes in the valence shells
antimony, phosphorus, and arsenic
what are antimony, phosphorus and arsenic referred too as?
type of doping material with 3 electrons and 5 holes
p-type donor material
boron, aluminum, and gallium
which doping material is considered acceptor-doped material
p-type material from semiconductors
term where thermal energy causes electrons to break free and enter the conduction band creating pairs of holes and electrons
hole-electron pair generation
term where thermal energy causes electrons to fall into holes is
what is the majority charge carriers in n-type material
what are the minority carriers in n-type material?
what is the majority charge carriers in p-type material
what is the minority charge carriers in p-type material?
What happens when a conductor is heated?
* atoms vibrate
* movement of surrounding electrons
* reduction in flow
* conductor's resistance increases
resistance that increases with increasing temperature
positive temperature coefficient (PTC)
what temperature coefficient does a conductor have?
at what temp does a semiconductor behave as an insulator?
What is the dominating factor in a semiconductor's current?
thermal generation of electrons
increase in current flow and a decrease in resistance with rising temperature
negative temperature coefficient (NTC)
what causes a semiconductor to behave more like a conductor?
when it's heavily doped
what is a material called that has few free electrons available for conduction when not illuminated?
high dark resistance
what happens when the semiconductor material is illuminated?
comparable to a conductor
when a electron going from negative to positive collides with atoms and rebounds towards the positive terminal due to the electric field
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
which has greater mobility? electrons or holes?
what determines the electron and hole velocities under the influence of an electric field?
what does the initial diffusion of charge carriers in a pn-junction create?
What can the magnitude of the barrier voltage at the pn-junction be calculated with?
* doping densities
* electronic charge
* junction temperature
what does the barrier voltage oppose and assist across the pn-junction?
opposes majority carriers
assists minority carriers
The layer on each side of the junction that is depleted of charge carriers
how is the depletion region created?
by movement of charge carriers across the junction
what is on the n-side of the depletion region?
donor impurity atoms that lost free electrons and have become positively charged
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)
What happens to the depletion region when either side is more heavily doped?
penetrates deeper into the opposite side
a two-electrode, or two-terminal, device
one-way device, offering a low resistance when forward-biased, and behaving almost as an open switch when reverse-biased
what are low-current diodes used for?
what are high-current diodes most often used for?
rectifiers for ac to dc conversion
what is the positive terminal of a diode for forward bias called?
what is the negative terminal of a diode when forward biased?
what can destroy a pn-junction diode?
high level of forward current
large reverse voltage
another name for high-current diodes
what do power diodes generate a lot of?
what are power diodes generated for?
to be connected mechanically to a metal heat sink
can pass forward currents of many amperes and can survive several hundred volts of reverse bias
is largely a minority charge carrier reverse saturation current
what happens if theres a small increase in Ir?
minority charge carriers leak into the junction surface
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
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
in what device is reverse break-down useful
forward voltage drop
reverse saturation current
reverse breakdown voltage
maximum forward current
the constant resistance (or dc resistance) of the diode at a particular constant forward current
the resistance offered to changing levels of forward voltage
The dynamic resistance
reciprocal of the slope of the forward characteristics beyond the knee
incremental resistance or ac resistance
a diode with zero forward resistance and zero forward voltage drop
ideal diode aka perfect diode
the reverse current of a ideal diode
infinitely high reverse resistance resulting in zero reverse current
what is the relationship between the diode forward voltage and current in the circuit defined by?
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
What dictates the slope of the dc load line in a diode series circuit
what determines point A on the load line?
supply voltage E
what will happen if the maximum power dissipation of a diode is exceeded?
overheat and may short-circuit or open-circuit
factor that defines the slope of the power-vs-temperature graph
derating factor (D) can be employed to draw graph
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
depletion layer capacitance aka transition capacitance
the capacitance of a reverse-biased pn-junction
depletion layer capacitance
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
what are the factors to consider with reverse-biased diodes
high reverse resistance (Rr) in parallel with depletion layer capacitance (Cpn)
what are the factors to consider with forward-biased diode
dynamic resistance rd in series with voltage cell representing Vf
the time required for the current to decrease to the reverse saturation current level
reverse recovery time (trr)
Vr or Vrrm
peak reverse voltage (peak inverse voltage and dc blocking voltage)
max reverse voltage that may be applied across the diode
Io or If(av)
steady-state forward current
max current that may be passed continuously through the diode
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
repetitive peak surge current
peak current that may be repeated over and over again during each cycle of a rectified waveform
static forward voltage drop
max forward volt drop for a given forward current and device temp
Continuous power dissipation at 25 C
max power that the device can safely dissipate continuously
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
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
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
cathode bar approximately in the shape of a letter Z
zener breakdown voltage
test current for measuring Vz
reverse current near the knee of the characteristic, minimum reverse current to sustain breakdown
Max zener current, limited by the max power dissipation
the zener diode may be operated at any reverse current level between :
Izk and Izm
what is the diode normally operated at for the greatest voltage stability