Question: Why Is Emitter Heavily Doped?

Why collector is lightly doped?

Base is lightly doped because we want that the base current should be small.

Now the collector is moderately doped may be because we dont want a crowd of electrons in the collector otherwise the electrons coming from the Emitter-Base path may repelled and collector current may decrease..

What is the cause of Zener breakdown?

The main cause of zener breakdown is high doping concentrations. The breakdown is a condition when upon increasing the voltage in small amounts; we experience a massive current flow in the device. Zener breakdown occurs when we apply reverse bias to a heavily doped diode.

Why is base width small in BJT?

Because of this reason base is lightly doped. Thus, more current passing to the collector side or an output side. … The base region is lightly doped so that width of the base is less. Collector region of a transistor is highly doped so collector region has more width than other two.

Which is heavily doped?

In most transistors, emitter is heavily doped. Its job is to emit or inject electrons into the base. These bases are lightly doped and very thin, it passes most of the emitter-injected electrons on to the collector.

Why do we use zener diode?

Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits. The load voltage equals breakdown voltage VZ of the diode. The series resistor limits the current through the diode and drops the excess voltage when the diode is conducting.

Why is emitter always forward biased?

Emitter is always forward biased w.r.t base so as to supply majority charge carriers to the base.

What do you mean by reverse active?

Just as saturation is the opposite of cutoff, reverse active mode is the opposite of active mode. A transistor in reverse active mode conducts, even amplifies, but current flows in the opposite direction, from emitter to collector.

Which method of biasing is used for operating transistor as an amplifier?

Base Biasing a Common Emitter Amplifier. One of the most frequently used biasing circuits for a transistor circuit is with the self-biasing of the emitter-bias circuit were one or more biasing resistors are used to set up the initial DC values for the three transistor currents, ( IB ), ( IC ) and ( IE ).

Why zener diode is reverse biased?

When connected in parallel with a variable voltage source so that it is reverse biased, a Zener diode conducts when the voltage reaches the diode’s reverse breakdown voltage. From that point on, the low impedance of the diode keeps the voltage across the diode at that value.

Which one is lightly doped?

In most transistors, emitter is heavily doped. Its job is to emit or inject electrons into the base. These bases are lightly doped and very thin, it passes most of the emitter-injected electrons on to the collector. The collector is so named because it collects electrons from base.

Which region is heavily doped in Zener diode?

Explanation: Zener diode is heavily doped than the normal p-n junction diode. Hence, it has very thin depletion region.

Why collector current is less than emitter current?

Some of the electrons combine with the majority charge carrier holes present in the base and most of the electrons reach the collector, crossing the collector-base junction. This implies that collector current is always less than the emitter current due to the reason (b).

What is the need of biasing in transistor?

Biasing is the process of providing DC voltage which helps in the functioning of the circuit. A transistor is based in order to make the emitter base junction forward biased and collector base junction reverse biased, so that it maintains in active region, to work as an amplifier.

Is photodiode reverse biased?

The photodiode is reverse biased for operating in the photoconductive mode. As the photodiode is in reverse bias the width of the depletion layer increases. This reduces the junction capacitance and thereby the response time. In effect, the reverse bias causes faster response times for the photodiode.

Why collector region is moderately doped?

Base is lightly doped because we want that the base current should be small. Now the collector is moderately doped may be because we dont want a crowd of electrons in the collector otherwise the electrons coming from the Emitter-Base path may repelled and collector current may decrease.

Why base is lightly doped?

The base region in a transistor is doped lightly so that the number density of majority carriers (electrons in p-n and holes in n-p-n transistor) is low. When emitter is forward biased, the majority carriers move from emitter to collector through base.

Why is the emitter the base and the collector of a BJT doped differently?

To improve the emitter efficiency and the common-base current gain (a), it can be shown that the emitter should be much heavily doped than the base. Also, the base width is a function of the base-collector voltage. … The base doping is less than the emitter doping but greater than the collector doping.

Is photodiode heavily doped?

The p-type and n-type semiconductors are heavily doped. Therefore, the p region and n region of the PIN photodiode has large number of charge carriers to carry electric current. … Therefore, majority carriers will not carry electric current under reverse bias condition.

Why is zener diode heavily doped?

The Zener diode, however, is heavily doped, as a result, they have a thin depletion region. Zener diode, under forward bias condition, conducts like a normal diode and if the applied voltage is higher than the reverse voltage then it conducts in the reverse bias condition too.

Why BJT is called bipolar?

device is often called the bipolar junction transistor because its operation requires that the negatively charged electrons and their positively charged counterparts (the holes corresponding to an absence of electrons in the crystal lattice) coexist briefly in the presence of one another.

Is led heavily doped?

The light emitting diode (LED) is a heavily doped p-n junction with forward bias. … It is a specially designed forward-biased p-n junction diode which emits light spontaneously when energised.