DOPING

“DONATION”

DOPANTS

N type P type(donor impurities) (acceptor

impurities)-antimony -aluminum-arsenic -boron-bismuth -gallium-phosporus -indium

MAJORITY and MINORITY CHARGE CARRIERS

Charge carriers are those that inhibits current conduction in a semiconductor which are either electrons (-) or holes (+).

The dominating charge carriers , whether holes or electrons, are the majority carriers.

The less abundant ones are the minority carriers.

ELECTRON FLOW

In a N type semiconductor, most of the current flows as “electrons” passing from atom to atom. This defines an electron flow.

HOLE FLOW

In a P type semiconductor, most of the current flows as an “electron absence”. The absences, called “holes”, move in a direction opposite to that of the electrons. This defines the hole flow.

BEHAVIOR of a P-N Junction

A resistor must be included in a circuit to prevent destruction of the diode by the excessive current.

FORWARD BREAKOVER VOLTAGE

This is essential for conduction to occur, wherein, it varies from about 0.3V to 1V. Its application can be useful in amplitude limiters, waveform clippers and treshold detectors.

How does junction works?Forward bias

Reverse bias

JUNCTION CAPACITANCE

Some P-N junctions can alternate between conduction (in forward bias) and nonconduction (in reverse bias) millions or billions of times per second. Other junctions are slower.

The capacitance is the main limitting factor at the P-N junction during conditions of reverse bias.

The amount of capacitance depends on several factors:

Operating voltage

Type of semiconductor material

Cross-sectional area of the P-N junction

Junction capacitance can be varied by changing the reverse-bias voltage, because the voltage affects the width of the depletion region.

AVALANCE EFFECT

“If the reverse bias goes past teh critical value of depletion, the voltage overcomes the ability of the junction to prevent the flow of current, and the junction conducts as if it were forward biased.”

Some components are designed to take advantage of the avalanche effect. In other cases, avalanche effect limits the performance of a circuit.