Semiconductor Electronics Flashcards
What happens to covalent bond when temp is high?
Bond breaks, & e’ go to conduction band
What happens to intrinsic semiconductor at 0K?
It behaves as insulator
What is intrinsically created e’s?
e’s due to breaking of covalent bond
Types of extrinsic semiconductors
p & n type
When is a semiconductor extrinsic?
When impurities are added and conductivity is increased
n type of impurities
pentavalent
pentavalent is also called
donors
p type of impurities
trivalent
metal have _____ resistivity
low
semiconductors have _____ resistivity
intermediate to metals & insulators
Elemental semiconductors
Silicon & Germanium
Valence band
Band which includes the energy levels of the valence electrons
conduction band
Band above valence band
In intrinsic semiconductors, the number of free
electrons, ne is __________ the number of holes, nh
equal to
Doping
Addition of impurities
Dopants
Impurity atoms
2 things before formation of P N junc diode?
Diffusion & drifting
In diffusion, e’ moves from
n to p
In drifting, e’s move from
p to n
Diffusion current & drifting current are always
opposite
Depletion region?
Space-charge region on either side of the junction together
What happens due to +ve space-charge region on n side and -ve space-charge on p-side?
electric field directed from positive charge towards negative charge develops
What is drifting?
The motion of minority charge
carriers due to the electric field
As the diffusion process continues, the space-charge regions on either side
increases
When space charge region increase, EF & drift current
increases
In a p-n junction under equilibrium there
is _____ net current
no
Barrier potential
Potential that tends to prevent the movement of
e’ from the n to p
In forward bias, as applied voltage increases
depletion width and effective barrier decreases
When applied voltage is less, barrier potential and current
reduces slightly below eq. level; will be less
Minority carrier injection
e’ from n-side cross depletion region reach p side where they are minority
In reverse bias, barrier potential & effective barrier value
increases
In reverse bias, diffusion current
decreases
Diode reverse current is not very much dependent on
applied voltage
threshold voltage
Voltage at which current starts increases
threshold voltage for Si
0.7V
threshold voltage for Ge
0.2V
Reverse saturation current
Current which remains const with change in bias
Rectification?
Conversion of AC to DC
Types of rectifiers
Full & half wave recifiers
When only will a diode conduct?
In forward bias
Why can’t Ge & Si be used to make LEDs
Their energy gap is very less
Colour of LED is due to
energy gap
2 Types of transistors
npn & pnp
BJT full form
Bipolar Junction Transistor
Which is an efficient circuit for getting rectified voltage?
full wave rectifier
Rectified voltage is _____ direcitonal
Uni
How to get a steady DC output?
Capacitor/Inductor is connected across the output terminals || to load
What are filters?
Those filter out the ac ripple and give a pure dc voltage
What happens when voltage across capacitor increases?
Rectifier gets charged
Why should large capacitors be used?
To make the time constant large, value of
C should be large
What is used to make LEDs?
GaAs
Use of LEDs?
Remote controls, burglar alarm systems,
optical communication
LED vs incandescent low power lamps:
Low operational voltage & less power.
Fast action and no warm-up time required
Long life and ruggedness
Fast on-off switching capability
