semiconductor diodes ch: 2 Flashcards
Explain working of p-n junction diode
p-type has holes majority carriers & n-type has electrons majority carriers. At the junction the holes and electrons are close to each so electrons get attracted towards holes & vise versa.
When atom gains an extra electron from outside it’ll become -ion, so each electron that has crossed the junction from the n-side will become -charged. When atom loses an electron from outside it’ll become +ion, so each hole that has crossed the junction from the p-side will become +charged.
what is P-N junction?
A region where p-type and n-type semiconductors are joined
Explain working of forward bias
The holes are repelled by the +terminal & the electrons are repelled by the -terminal. So the electrons & holes move towards the junction and fill in the the depletion region as well as barrier potential. At a particular voltage the depletion region breaks & a large amount of current flows
Explain working of reverse bias
The electrons are attracted towards +terminal & holes are attracted towards -terminal, this increases the depletion region & barrier potential, but a small amount of carriers manage to cross the junction & a small amount of current flows in reverse biased condition.
What is Biasing?
The process of applying external energy to a diode.
Reverse saturation current
current that flows due to minority carriers in reverse biased condition.
V-I forward characteristics
+terminal to anode & - to cathode. When voltage is applied initially negligible or no current flows through the diode(becuz of barrier potential). When the external voltage increases due to barrier potential a large amount of current starts flowing & the diode is said to be conducting.
Knee voltage
voltage at which diode conducts
V-I reverse characteristics
-terminal to anode & + to cathode. When the voltage is applied initially the current is small and constant , as voltage is increased reverse saturated current increases & damages the diode.
breakdown voltage
the voltage at which reverse saturated current increases & damages the diode.
What is Avalanche breakdown?
When high electric field is applied to the reverse biased condition the electrons gain kinetic energy & break other covalent bonds & create more hole-electron pairs, these pairs cross the depletion region.
What is Zener breakdown?
The p-n junction is is heavily doped so that the electrons in valence bond on p region can jump off to conduction band of n region.
Characteristics of zener diode
*it’s forward characteristics are similar to that of a normal p-n junction diode.
*initially a small amount of current flows, if the voltage increases above the zener voltage there’s a sharp increase in the current, now dure to this there is only change in current & the voltage remains the same
Applications of p-n junction & zener diode
p-n junction: *wave shaping circuits *used as switch *communication circuits *rectifier diode in power supply.
zener diode: *voltage regulator *wave shaping circuits *protection circuits *fixed reference voltage
What is LED
p-n junction that emits light when in forward bias LED(light emitting diode)
working of LED
*consists of 3 layers p-type semiconductor, n-type semiconductor & active region.
*works on the concept of electroluminescence
*When external voltage is applied the valence electrons break bonds with the parent atom and enter conduction band ,the conduction band has a higher energy level so the electrons are free to move, but eventually their energy level lowers and releases energy in form of photons.
What is Varactor diode
A diode whose internal capacitance changes with change in voltage (reverse biased condition)
Explain the working of varactor diode?
*when the p-n junction diode is connected in reverse biased condition then the depletion layer acts as dielectric of capacitor and the P and P region acts as capacitor plates.
*When the voltage increases the depletion region widens & the distance b/w 2 plates is increased & capacitance in reduced.
*When the voltage decreases thn the depletion layer narrows down & this reduces the distance b/w 2 plates & capacitance increases.
Characteristics of Varactor diode?
*low cost
*small and light weight
*doesn’t work in forward biased condition
*produces less noise
Applications of LED and Varactor diode?
LED: *traffic signal lights *remote controllers *decoration lights *alarms
Varactor diode: *low noise parametric amplifiers *automatic frequency control device *self balancing bridge circuits *radio &television
What is a tunnel diode?
when the impurity atoms is increased in a normal diode it becomes tunnel diode.
V-I characteristics of of tunnel diode
Initially if the forward voltage is increased current increases rapidly till it reaches its max value called peak current (Ip) and the corresponding voltage peak voltage(Vp).
If the voltage is increased even more current decreases, till it reaches its minimum value known as valley current (Iv).
If the voltage is increased further, then the current acquires the normal
PN junction diode value.
The region between the peak point (A) and the valley point (B) is negative resistance region because the current decreases with an increase in voltage. The current which increases rapidly when small increased in voltage is
known as Tunneling current.
What is a Photo diode?
2 terminal P-N junction device which operates in reverse biased condition.
has a small transparent window which allows the light to strike p-n junction
reverse current increases with increase in light intensity.
no incident light, the reverse current is minimum, and is known as Dark current.
light intensity increases, the value of reverse current increases.
Characteristics of Photo-diode
vertical line represents the
reverse current flowing through the device
and the horizontal line represents the
reverse-biased potential.
The first curve represents the dark current
that generates due to minority carriers in
the absence of light.
curve shows almost equal spacing in
between them. This is so because current
proportionally increases with the luminous
flux.
