Chapter-1

INTRODUCTION

The scope of the study is to analyse and study the I-V characteristics curves of PN junction diode,

Zener diode and LED. Through this project we will know and learn about different aspects and

principles involved in construction, working and behaviour of different elements. We will try to study

the input and output behaviour of these elements and how input fluctuations affect the output.

Figure 1.1 PN junction Apparatus

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Chapter-2

PN JUNCTION DIODE

2.1 INTRODUCTION

Donor impurities (pentavalent) are introduced into one-side and acceptor impurities into the

other side of a single crystal of an intrinsic semiconductor to form a p-n diode with a junction

called depletion region (this region is depleted off the charge carriers). This region gives rise

to a potential barrier Vγ called Cut- in Voltage. This is the voltage across the diode at which

it starts conducting. The P-N junction can conduct beyond this Potential. The P-N junction

supports uni-directional current flow. If +ve terminal of the input supply is connected to

anode (P-side) and –ve terminal of the input supply is connected to cathode (N- side), then

diode is said to be forward biased. In this condition the height of the potential barrier at the

junction is lowered by an amount equal to given forward biasing voltage. Both the holes from

p-side and electrons from n-side cross the junction simultaneously and constitute a forward

current (injected minority current – due to holes crossing the junction and entering N-side

13of the

diode, due to electrons crossing the junction and entering P-side of the diode). Assuming

current flowing through the diode to be very large, the diode can be approximated as short-

circuited switch. If –ve terminal of the input supply is connected to anode (p-side) and +ve

terminal of the input supply is connected to cathode (n-side) then the diode is said to be

reverse biased. In this condition an amount equal to reverse biasing voltage increases the

height of the potential barrier at the junction. Both the holes on p-side and electrons on n-side

tend to move away from the junction thereby increasing the depleted region. However, the

process cannot continue indefinitely, thus a small current called reverse saturation current

continues to flow in the diode. This small current is due to thermally generated carriers.

Assuming current flowing through the diode to be negligible, the diode can be approximated

as an open circuited switch. The volt-ampere characteristics of a diode explained by

following equation:

I = Io(Exp(V/ ηVT)-1)

I=current flowing in the diode

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Io=reverse saturation current

V=voltage applied to the diode

VT=volt-equivalent of temperature=kT/q=T/11,600=26mV(@ room temp).

η=1 (for Ge) and 2 (for Si)

It is observed that Ge diode has smaller cut-in-voltage when compared to Si diode. The

reverse saturation current in Ge diode is larger in magnitude when compared to silicon diode.

2.2 EQUILIBRIUM

In a p–n junction, without an external applied voltage, an equilibrium condition is reached in

which a potential difference is formed across the junction. This potential difference is called

build in potential. 

After joining p-type and n-type semiconductors, electrons from the n region near the p–n

interface tend to diffuse into the p region leaving behind positively charged ions in the n

region and being recombined with holes, forming negatively charged ions in the p region.

Likewise, holes from the p-type region near the p–n interface begin to diffuse into the n-type

region, leaving behind negatively charged ions in the p region and recombining with

electrons, forming positive ions in the n region. The regions near the p–n interface lose their

neutrality and most of their mobile carriers, forming the space charge region or depletion

layer (see figure A).

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Figure 2.1 A p–n junction in thermal equilibrium with zero-bias voltage applied.

Electron and hole concentration are reported with blue and red lines, respectively. Grey

regions are charge-neutral. Light-red zone is positively charged. Light-blue zone is negatively

charged. The electric field is shown on the bottom, the electrostatic force on electrons and

holes and the direction in which the diffusion tends to move electrons and holes. (The log

concentration curves should actually be smoother with slope varying with field strength.)

The electric field created by the space charge region opposes the diffusion process for both

electrons and holes. There are two concurrent phenomena: the diffusion process that tends to

generate more space charge, and the electric field generated by the space charge that tends to

counteract the diffusion. The carrier concentration profile at equilibrium is shown in figure

A with blue and red lines. Also shown are the two counterbalancing phenomena that establish

equilibrium.

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Figure 2.2. A p–n junction in thermal equilibrium with zero-bias voltage applied.

Under the junction, plots for the charge density, the electric field, and the voltage are

reported. The space charge region is a zone with a net charge provided by the fixed ions

(donors or acceptors) that have been left uncovered by majority carrier diffusion. When

equilibrium is reached, the charge density is approximated by the displayed step function. In

fact, since the y-axis of figure A is log-scale, the region is almost completely depleted of

majority carriers (leaving a charge density equal to the net doping level), and the edge

between the space charge region and the neutral region is quite sharp (see figure B, Q(x)

graph). The space charge region has the same magnitude of charge on both sides of the p–n

interfaces, thus it extends farther on the less doped side in this example (the n side in figures

A and B).

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2.3 FORWARD BIAS

In forward bias, the p-type is connected with the positive terminal and the n-type is connected

with the negative terminal.

PN junction operation in forward-bias mode, showing reducing depletion width. The panels

show energy band diagram, electric field, and net charge density. Both p and n junctions are

doped at a 1e15/cm3 (0.00016C/cm3) doping level, leading to built-in potential of ~0.59 V.

Reducing depletion width can be inferred from the shrinking charge profile, as fewer dopants

are exposed with increasing forward bias. Observe the different quasi-fermi levels for

conduction band and valence band in n and p regions (red curves)

With a battery connected this way, the holes in the p-type region and the electrons in the n-

type region are pushed toward the junction and start to neutralize the depletion zone, reducing

its width. The positive potential applied to the p-type material repels the holes, while the

negative potential applied to the n-type material repels the electrons. The change

in potential between the p side and the n side decreases or switches sign. With increasing

forward-bias voltage, the depletion zone eventually becomes thin enough that the zone's

electric field cannot counteract charge carrier motion across the p–n junction, which as a

consequence reduces electrical resistance. The electrons that cross the p–n junction into the p-

type material (or holes that cross into the n-type material) will diffuse into the nearby neutral

region. The amount of minority diffusion in the near-neutral zones determines the amount of

current that may flow through the diode.

Only majority carriers (electrons in n-type material or holes in p-type) can flow through a

semiconductor for a macroscopic length. With this in mind, consider the flow of electrons

across the junction. The forward bias causes a force on the electrons pushing them from the N

side toward the P side. With forward bias, the depletion region is narrow enough that

electrons can cross the junction and inject into the p-type material. However, they do not

continue to flow through the p-type material indefinitely, because it is energetically

favourable for them to recombine with holes. The average length an electron travels through

the p-type material before recombining is called the diffusion length, and it is typically on the

order of micrometres.[2]

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Although the electrons penetrate only a short distance into the p-type material, the electric

current continues uninterrupted, because holes (the majority carriers) begin to flow in the

opposite direction. The total current (the sum of the electron and hole currents) is constant in

space, because any variation would cause charge build-up over time (this is Kirchhoff's

current law). The flow of holes from the p-type region into the n-type region is exactly

analogous to the flow of electrons from N to P (electrons and holes swap roles and the signs

of all currents and voltages are reversed).

Therefore, the macroscopic picture of the current flow through the diode involves electrons

flowing through the n-type region toward the junction, holes flowing through the p-type

region in the opposite direction toward the junction, and the two species of carriers constantly

recombining in the vicinity of the junction. The electrons and holes travel in opposite

directions, but they also have opposite charges, so the overall current is in the same direction

on both sides of the diode, as required.

The Shockley diode equation models the forward-bias operational characteristics of a p–n

junction outside the avalanche (reverse-biased conducting) region.

2.4 REVERSE BIAS

Figure2.3 A silicon p–n junction in reverse bias.

Connecting the p-type region to the negative terminal of the battery and the n-type region to

the positive terminal corresponds to reverse bias. If a diode is reverse-biased, the voltage at

the cathode is comparatively higher than at the anode. Therefore, very little current will flow

until the diode breaks down. The connections are illustrated in the adjacent diagram.

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Because the p-type material is now connected to the negative terminal of the power supply,

the 'holes' in the p-type material are pulled away from the junction, leaving behind charged

ions and causing the width of the depletion region to increase. Likewise, because the n-type

region is connected to the positive terminal, the electrons will also be pulled away from the

junction, with similar effect. This increases the voltage barrier causing a high resistance to the

flow of charge carriers, thus allowing minimal electric current to cross the p–n junction. The

increase in resistance of the p–n junction results in the junction behaving as an insulator.

The strength of the depletion zone electric field increases as the reverse-bias voltage

increases. Once the electric field intensity increases beyond a critical level, the p–n junction

depletion zone breaks down and current begins to flow, usually by either the Zener or

the avalanche breakdown processes. Both of these breakdown processes are non-destructive

and are reversible, as long as the amount of current flowing does not reach levels that cause

the semiconductor material to overheat and cause thermal damage.

This effect is used to advantage in Zener diode regulator circuits. Zener diodes have a low

breakdown voltage. A standard value for breakdown voltage is for instance 5.6 V. This

means that the voltage at the cathode cannot be more than about 5.6 V higher than the voltage

at the anode (although there is a slight rise with current), because the diode will break down –

and therefore conduct – if the voltage gets any higher. This in effect limits the voltage over

the diode.

Another application of reverse biasing is Varicap diodes, where the width of the depletion

zone (controlled with the reverse bias voltage) changes the capacitance of the diode

2.5 CURRENT ACROSS DEPLETION REGION

The Shockley ideal diode equation characterizes the current across a p–n junction as a

function of external voltage and ambient conditions (temperature, choice of semiconductor,

etc.). To see how it can be derived, we must examine the various reasons for current. The

convention is that the forward (+) direction be pointed against the diode's built-in potential

gradient at equilibrium.

Forward Current

Diffusion Current  

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Reverse Current

Field Current

Generation Current

2.6 CIRCUIT DIAGRAM

2.6.1 FORWARD BIAS

Figure 2.4 Circuit diagram of forward bias.

2.6.2 REVERSE BIAS

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Figure 2.5 Circuit diagram of reverse bias

2.7 PRECAUTIONS

1. While doing the experiment do not exceed the ratings of the diode. This may lead to

damage of the diode.

2. Connect voltmeter and Ammeter in correct polarities as shown in the circuit diagram.

3. Do not switch ON the power supply unless you have checked the circuit connections as per

the circuit diagram.

2.8 EXPERIMENT

2.8.1 FORWARD BIASED CONDITION

1. Connect the PN Junction diode in forward bias i.e. Anode is connected to positive of the

power supply and cathode is connected to negative of the power supply.

2. Use a Regulated power supply of range (0-30) V and a series resistance of 1kΏ.

3. For various values of forward voltage (Vf) note down the corresponding values of forward

current(If).

2.8.2 REVERSE BIASED CONDITION

1. Connect the PN Junction diode in Reverse bias i.e; anode is connected to negative of the

power supply and cathode is connected to positive of the power supply.

2. For various values of reverse voltage (Vr) note down the corresponding values of reverse

current (Ir).

2.9 GRAPH

1. Take a graph sheet and divide it into 4 equal parts. Mark origin at the centre of the graph

sheet.

2. Now mark +ve x-axis as Vf

-ve x-axis as Vr

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+ve y-axis as If

-ve y-axis as Ir.

3. Mark the readings tabulated for diode forward biased condition in first Quadrant and diode

reverse biased condition in third Quadrant.

` Figure 2.6 Graph of forward & reverse biased condition

2.10 CALCULATION FROM GRAPH

Static forward Resistance Rdc = Vf/If Ω

Dynamic forward Resistance rac = ΔVf/ΔIf Ω

Static Reverse Resistance Rdc =Vr/Ir Ω

Dynamic Reverse Resistance rac = ΔVr/ΔIr Ω

2.11 APPLICATION OF PN JUNCTION DIODE

1.PN junction in reverse biased configuration is sensitive (generates an electron-hole pair) to

light from 400-1000nm which includes VISIBLE Light (400nm to 700nm). So all/most of the

sensors involving capturing light information will use a photodiode.  PN junction in reverse

biased configuration is the most widely used sensor compared to any other sensor. For

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example, all the digital cameras use an array of photodiodes to capture light and produce an

image & Solar Cells

2. PN junction (which has direct energy bandgap) in forward biased condition produces light

when biased with a current. All LED lighting uses a PN junction diode. Voltage across PN

junction biased at a constant current has a negative temperature coefficient. Difference

between the PN junction voltages of two differently biased diodes has a positive temperature

coefficient. These properties are used to create Temperature Sensors, Reference voltages

(Bandgap). Various circuits like Rectifiers, Reactors for Voltage Controlled Oscillators

(VCO) etc.

Chapter-3

ZENER DIODE

The diode is one of the basic components in electronic circuits. When you want to know

about voltage considerations you should know about the diodes. The diode is basically made

up of semiconductors which have two characteristics, ‘P’ type and ‘N’ type. The ‘P’type and

‘N’ type semiconductors represent positive and negative type semiconductors.‘P’type

semiconductor will have excess amount of holes in configuration and ‘N’ type semiconductor

will have excess amount of electrons. If both types of characteristics present in a single

crystal, then it can be termed as a diode. The positive terminal of the battery connects with

the ‘P’ side and the negative side is connected with the ‘N’ side. Let’s discuss about Zener

diode working, it is nothing but a simple diode connecting in reverse bias.

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Figure 3.1 Symbol of Zener diode

It is mainly a special property of the diode rather than any special type of equipment. The

person named Clearance Zener invented this property of the diode that’s why it is named

after him as a remembrance. The special property of the diode is that there will be

a breakdown in the circuit if the voltage applied across a reversely biased circuit. This does

not allow the current to flow across it. When the voltage across the diode is increased,

temperature also increases and the crystal ions vibrate with greater amplitude and all these

leads to the breakdown of the depletion layer. The layer at the junction of ‘P’ type and ‘N’

type. When the applied voltage exceeds an specific amount Zener breakdown takes place.

Figure 3.2 Zener diode & its characteristics

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Zener diode is nothing but a single diode connected in a reverse bias mode and Zener diode

can be connected in reverse bias positive in a circuit as shown as picture. We can connect it

for different applications.

3.1 UNBIASED SEMICONDUCTOR DIODE

In normal conditions, holes from the p side tend to diffuse to a low concentration region and

the same thing happens for electrons from n-side. Thus the holes diffuse to the n-side and the

electrons diffuse to the p-side. This results in accumulation of charges around the junction,

forming a depletion region.

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Figure 3.3 Characteristics of unbiased semiconductor diode

An electric polarity or electric dipole is formed across the junction, causing flow of flux from

n side to p side. This results in varying negative electric field intensity, generating an electric

potential across the junction. This electric potential is actually the threshold voltage of the

diode and is around 0.6V for silicon and 0.2V for Germanium. This acts as a potential barrier

for flow of majority charge carriers and the device does not conduct.

Now when a normal diode is biased such that a negative voltage is applied to the n side and

positive voltage to the p side, the diode is said to be in forward biasing condition. This

applied voltage tends to decrease the potential barrier after it goes beyond the threshold

voltage.

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At this point and afterwards, the majority carriers cross the potential barrier and the device

starts conducting with flow of current through it.

When the diode is biased in reverse condition to above, the applied voltage is such that it

adds to the potential barrier and hinders the flow of majority carriers. However, it does allow

the flow of minority carriers (holes in n type and electrons in p type). As this reverse bias

voltage increases, the reverse current tends to increase gradually.

At a certain point, this voltage is such that it causes breakdown of the depletion region,

causing a massive increase in the flow of current. This is where the Zener diode working

comes into play.

3.2 PRINCIPLE & WORKING OPERATION

3.2.1 ZENER BRAEKDOWN

This type of breakdown occurs for a reverse bias voltage between 2 to 8V.  Even at this low

voltage, the electric field intensity is strong enough to exert a force on the valence electrons

of the atom such that they are separated from the nuclei. This results in formation of mobile

electron hole pairs, increasing the flow of current across the device.  Approximate value of

this field is about 2*10^7 V/m.

This type of break down occurs normally for highly doped diode with low breakdown voltage

and larger electric field. As temperature increases, the valence electrons gain more energy to

disrupt from the covalent bond and less amount of external voltage is required. Thus Zener

breakdown voltage decreases with temperature.

As stated above the basic principle behind the working of a Zener diode lies in the cause of

breakdown for a diode in reverse biased condition. Normally there are two types of

breakdown- Zener and Avalanche.

 

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Figure 3.4 Working &Operation of Zener diode

3.3 EXPERIMENT

3.3.1 FORWARD BIASED CONDITION

1. Connect the Zener diode in forward bias i.e; anode is connected to positive of the power

supply and cathode is connected to negative of the power supply as in circuit

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2. Use a Regulated power supply of range (0-30) V and a series resistance of 1kΏ.

3. For various values of forward voltage (Vf) note down the corresponding values of forward

current(If).

3.3.2 CIRCUIT DIAGRAM

Forward Bias

Figure 3.5 Forward bias of Zener diode

3.3. REVERSE BIAS CONDITION

1. Connect the Zener diode in Reverse bias i.e; anode is connected to negative of the power

supply and cathode is connected to positive of the power supply as in circuit.

2. For various values of reverse voltage (Vr) note down the corresponding values of reverse

current (Ir).

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Figure 3.6 Reverse bias of Zener diode

3.4 CHARACTERISTICS MODEL

Figure 3.7 Characteristics Model

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Calculations from graph

Cut in voltage = ---------- (v)

Break down voltage = ------------(v)

3.5 APPLICATION OF ZENER DIODE

3.5.1 ZENER DIODE AS A VOLTAGE

In a DC circuit, Zener diode can be used as a voltage regulator or to provide voltage

reference. The main use of Zener diode lies in the fact that the voltage across a Zener diode

remains constant for a larger change in current. This makes it possible to use a Zener diode as

a constant voltage device or a voltage regulator.

In any power supply circuit, a regulator is used to provide a constant output (load) voltage

irrespective of variation in input voltage or variation in load current. The variation in input

voltage is called line regulation, whereas the variation in load current is called load

regulation.

Figure 3.8 Zener Diode as voltage regulator

A simple circuit involving Zener diode as a regulator requires a resistor of low value

connected in series with the input voltage source. The low value is required so as to allow the

maximum flow of current through the diode, connected in parallel. However, the only

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constraint being, the current through Zener diode should not be less than minimum Zener

diode current. Simply put, for a minimum input voltage and a maximum load current, the

Zener diode current should always be Izmin.

While designing a voltage regulator using Zener diode, the latter is chosen with respect to its

maximum power rating. In other words, the maximum current through the device should be: -

Imax = Power/Zener Voltage

Since the input voltage and the required output voltage is known, it is easier to choose a

Zener diode with a voltage approximately equal to the load voltage, i.e. Vz ~=Vo.

The value of the series resistor is chosen to be

R =(Vin – Vz)/(Izmin + IL), where IL  = Load Voltage/Load resistance.

Note that for load voltages up to 8V, a single Zener diode can be used. However, for load

voltages beyond 8V, requiring Zener voltages of higher voltage value, it is advisable to use a

forward biased diode in series with the Zener diode. This is because the Zener diode at higher

voltage follows the avalanche breakdown principle, having a positive temperature of

coefficient.

Hence a negative temperature coefficient diode is used for compensation.  Of course, these

days, practical temperature compensated Zener diodes are used.

3.5.2. ZENER DIODE AS A REFERENCE VOLTAGE 

Figure 3.9 Zener diode as voltage reference

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In power supplies and many other circuits, Zener diode finds its application as a constant

voltage provider or a voltage reference.  The only conditions are that the input voltage should

be greater than Zener voltage and the series resistor should have a minimum value such that

the maximum current flows through the device.

3.5.3. ZENER DIODE AS A VOLTAGE CLAMPER 

In a circuit involving AC input source, different from the normal PN diode clamping circuit,

a Zener diode can also be used. The diode can be used to limit the peak of the output voltage

to Zener voltage at one side and to about 0V at other side of the sinusoidal waveform.

Figure 3.10 Zener diode as voltage clamper

In the above circuit, during positive half cycle, once the input voltage is such that the Zener

diode is reverse biased, the output voltage is constant for a certain amount of time till the

voltage starts decreasing.

Now during the negative half cycle, the Zener diode is in forward biased connection. As the

negative voltage increases till forward threshold voltage, the diode starts conducting and the

negative side of the output voltage is limited to the threshold voltage.

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Chapter-4

LED

4.1 INTRODUCTION

Figure 4.1 Structure of LED

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator

lamps in many devices and are increasingly used for other lighting. Introduced as a practical

electronic component in 1962, early LEDs emitted low-intensity red light, but modern

versions are available across the visible, ultraviolet and infrared wavelengths, with very high

brightness.

The LED consists of a chip of semiconducting material doped with impurities to create a p-n

junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or

cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the

junction from electrodes with different voltages. When an electron meets a hole, it falls into a

lower energy level, and releases energy in the form of a photon.

The wavelength of the light emitted, and thus its colour depends on the band gap energy of

the materials forming the p-n junction. In silicon or germanium diodes, the electrons and

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holes recombine by a non-radiative transition which produces no optical emission, because

these are indirect band gap materials. The materials used for the LED have a direct band gap

with energies corresponding to near-infrared, visible or near-ultraviolet light.

LED development began with infrared and red devices made with gallium arsenide.

Advances in materials science have enabled making devices with ever-shorter wavelengths,

emitting light in a variety of colours. LEDs are usually built on an n-type substrate, with an

electrode attached to the p-type layer deposited on its surface. P-type substrates, while less

common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire

substrate.

Most materials used for LED production have very high refractive indices. This means that

much light will be reflected back into the material at the material/air surface interface. Thus,

light extraction in LEDs is an important aspect of LED production, subject to much research

and development.

4.2 WORKING PRINCIPLE

To understand the working principle of light emitting diode, we first have to understand a

basic of quantum theory. According to this theory, when an electron comes down from its

higher energy level to lower energy level, it emits energy in form of a photon. The energy of

this photon is equal to the energy gap between these two energy levels. When a pn junction

diode is forward biased, current flows through the diode. Flow of current through the

semiconductor is caused by both flow of free electrons in opposite direction of current and

flow of holes in the direction of current. Hence during flow of these charge carriers, there will

be recombination’s. Recombination mean electrons in condition band jump down to the

valence band. During this jump electron will emit electromagnetic energy in form of photons

whose energy is equal to forbidden energy gap E.g. Again according to quantum theory,

energy of a photon is the product of frequency of electromagnetic radiation and Planck

constant. Where h is Planck constant. Again velocity of electromagnetic radiation is fixed and

it is equal to the speed of light i.e. c. The frequency of radiation f is related to velocity of light

as f = c / λ. Where λ is wavelength of the electromagnetic radiation. Hence from equation (1)

So we have seen that wavelength of electromagnetic radiation is inversely proportional to the

forbidden energy gap. In normal silicon, germanium semiconductor this forbidden energy

gaps between condition and valence band are such that entire radiation of electromagnetic

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wave during recombination is in the form of inferred radiation. The wavelengths of the

inferred are out of our visible range so we cannot see it. Inferred electromagnetic radiation is

nothing but heat. This is because, silicon and germanium semiconductor are not direct gap

semiconductor rather these are indirect gap semiconductor. In indirect gap semiconductor the

maximum energy level of valence band and minimum energy level of conduction band do not

occur at same momenta of electrons. Hence during recombination’s of electrons and holes

that is migration of electrons from conduction band to valence band the momentum of

electrons would be changed.

The photons originated from these electrons will be mostly utilized for the electron

momentum. In direct gap semiconductor the maximum of valence band and minimum of

conduction band occur at same electron momenta. Hence, there will be no change of

momentum of electrons during migration from conduction band to valence band so the

photons originated due that migration have not to provide momentum to electrons. As a

result, the photons are emitted from the surface of semiconductor crystal. There is some

special type of specially alloyed direct energy gap semiconductors whose energy gap between

condition and valence band are such that the electromagnetic radiation emitted during

recombination’s has wavelengths within our visible range. That means in these special

semiconductors when recombination’s between electrons and holes occur, there will be

emissions of light. This is how a light emitting diode works.

The wave length of output optical signals depends upon the band gap energy. The output

wave length can be engineered within certain limits by using compound semiconductors, so

that a particular colour can be observed, provided the output is in visible range.

Application of LED or Light Emitting Diode

Today almost everywhere LEDs lights are used and the application of LED is huge. First we

are going to see through the list, then we will categorize the application of these.

In motorcycle and bicycle lights.

In traffic lights and signals.

In message displaying boards.

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In light bulbs and many more.

Figure 4.2 Energy diagram of LED

Now, practically if we sit to list all the applications it will be a non-ending list. So, here we

are classifying the use in to some parts.

Indicators and Signs: - These are mainly used in traffic signals, exit signs, light weight

message, displaying box etc.

Lighting: - Light Emitting Diode lamps have become highly popular and as the energy

consumption is very low for them, they are also being made by LED s. In 2001, the Italian

village Tarrasa was the first place to convert all its lighting to LED. In television and

computer/laptop displaying, LEDs are used.

Non Visual Application:- Communication, sensor are the main area of non-visual application

of LEDs.

4.3 CIRCUIT DIAGRAM

Forward Bias

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Figure 4.3 Circuit diagram of forward bias

REVERSE BIAS

Figure 4.4 Circuit diagram of reverse bias

4.4 EXPERIMENTAL PROCEDURE

1. Give the connection as per the circuit diagram.

2. Vary the input voltages at the RPS and note down the corresponding current for the voltages.

3. Repeat the procedure for reverse bias condition and tabulate the corresponding voltages and currents.

4. Plot the graph between voltage and current for forward bias and reverse bias.

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4.5 CHARACTERISTICS CURVE OF LED

Figure 4.5 Characteristics of LED

4.6 APPLICATIONS OF LED

Today almost everywhere LEDs lights are used and the application of LED is huge. First we are going to see through the list, then we will categorize the application of these.

In motorcycle and bicycle lights.In traffic lights and signals.In message displaying boards.In light bulbs and many more.

Now, practically if we sit to list all the applications it will be a non-ending list. So, here we are classifying the use in to some parts.

1. Indicators and Signs: - These are mainly used in traffic signals, exit signs, light weight message, displaying box etc.

2. Lighting: - Light Emitting Diode lamps have become highly popular and as the energy consumption is very low for them, they are also being made by LED s. In 2001, the Italian Village Terrace was the first place to convert all its lighting to LED. In television and computer/laptop displaying, LEDs are used.

3. Non Visual Application:- Communication, sensor are the main area of non-visual application of LEDs.

CONCIUSION

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In the experiment, the main objective was fulfilled i.e. obtain the IV characteristics of P-N junction diode for forward bias and reverse bias circuit. Two graphs were made i.e. I versus for verification purpose, In the end, IV characteristics of P-N Junction were discussed.

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