vi characteristics of pn junction diode experiment

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V-I Characteristics of p-n-Junction Diode

V-I characteristics of p-n-Junction Diode

Objectives:

• To understand the basic concepts of semiconductors.
• To study p type and n type semiconductor and potential barrier.
• To understand forward and reverse biasing.
• Perform the experiment on bread board and the trainer kit and plot the graph of V-I characteristics of PN junction diode.

Components and equipments required: single strand cable, diode, resistors, bread board, multimeter, connecting wires, CRO, voltage source.

General Instructions: You will plan for Experiment after self study of Theory given below, before entering in the Lab.

PN Junction Diode The effect described in the previous tutorial is achieved without any external voltage being applied to the actual PN junction resulting in the junction being in a state of equilibrium. However, if we were to make electrical connections at the ends of both the N-type and the P-type materials and then connect them to a battery source, an additional energy source now exists to overcome the barrier resulting in free charges being able to cross the depletion region from one side to the other. The behavior of the PN junction with regards to the potential barrier width produces an asymmetrical conducting two terminal device, better known as the Junction Diode.

A diode is one of the simplest semiconductor devices, which has the characteristic of passing current in one direction only. However, unlike a resistor, a diode does not behave linearly with respect to the applied voltage as the diode has an exponential I-V relationship and therefore we cannot described its operation by simply using an equation such as Ohm's law. If a suitable positive voltage (forward bias) is applied between the two ends of the PN junction, it can supply free electrons and holes with the extra energy they require to cross the junction as the width of the depletion layer around the PN junction is decreased. By applying a negative voltage (reverse bias) results in the free charges being pulled away from the junction resulting in the depletion layer width being increased. This has the effect of increasing or decreasing the effective resistance of the junction itself allowing or blocking current flow through the diode.

Then the depletion layer widens with an increase in the application of a reverse voltage and narrows with an increase in the application of a forward voltage. This is due to the differences in the electrical properties on the two sides of the PN junction resulting in physical changes taking place. One of the results produces rectification as seen in the PN junction diodes static I-V (current-voltage) characteristics. Rectification is shown by an asymmetrical current flow when the polarity of bias voltage is altered as shown below.

But before we can use the PN junction as a practical device or as a rectifying device we need to firstly bias the junction, ie connect a voltage potential across it. On the voltage axis above, "Reverse Bias" refers to an external voltage potential which increases the potential barrier. An external voltage which decreases the potential barrier is said to act in the "Forward Bias" direction.

There are two operating regions and three possible "biasing" conditions for the standard Junction Diode and these are:

• Reverse Bias - The voltage potential is connected negative, (-ve) to the P-type material and positive, (+ve) to the N-type material across the diode which has the effect of Increasing the PN-junction width.
• Forward Bias - The voltage potential is connected positive, (+ve) to the P-type material and negative, (-ve) to the N-type material across the diode which has the effect of Decreasing the PN-junction width.

Forward Biased Junction Diode When a diode is connected in a Forward Bias condition, a negative voltage is applied to the N-type material and a positive voltage is applied to the P-type material. If this external voltage becomes greater than the value of the potential barrier, approx. 0.7 volts for silicon and 0.3 volts for germanium, the potential barriers opposition will be overcome and current will start to flow. This is because the negative voltage pushes or repels electrons towards the junction giving them the energy to cross over and combine with the holes being pushed in the opposite direction towards the junction by the positive voltage. This results in a characteristics curve of zero current flowing up to this voltage point, called the "knee" on the static curves and then a high current flow through the diode with little increase in the external voltage as shown below.

The application of a forward biasing voltage on the junction diode results in the depletion layer becoming very thin and narrow which represents a low impedance path through the junction thereby allowing high currents to flow. The point at which this sudden increase in current takes place is represented on the static I-V characteristics curve above as the "knee" point.

This condition represents the low resistance path through the PN junction allowing very large currents to flow through the diode with only a small increase in bias voltage. The actual potential difference across the junction or diode is kept constant by the action of the depletion layer at approximately 0.3v for germanium and approximately 0.7v for silicon junction diodes. Since the diode can conduct "infinite" current above this knee point as it effectively becomes a short circuit, therefore resistors are used in series with the diode to limit its current flow. Exceeding its maximum forward current specification causes the device to dissipate more power in the form of heat than it was designed for resulting in a very quick failure of the device.

Reverse Biased Junction Diode When a diode is connected in a Reverse Bias condition, a positive voltage is applied to the N-type material and a negative voltage is applied to the P-type material. The positive voltage applied to the N-type material attracts electrons towards the positive electrode and away from the junction, while the holes in the P-type end are also attracted away from the junction towards the negative electrode. The net result is that the depletion layer grows wider due to a lack of electrons and holes and presents a high impedance path, almost an insulator. The result is that a high potential barrier is created thus preventing current from flowing through the semiconductor material.

Procedure:-

• Make the connections as shown in fig.:
• Switch on the power supply.
• Now vary in small step the forward bias voltage and current readings on multimeter. Draw the graph between current and voltage.
• Make the connection as shown in fig:

Observation:

Forward biasing

Observation Table

Reverse biasing

Do and Don’ts to be strictly observed during experiment:

Do (also go through the General Instructions):

• Before making the connection, identify the components leads, terminal or pins before making the connections.
• Before connecting the power supply to the circuit, measure voltage by voltmeter/multimeter.
• Use sufficiently long connecting wires, rather than joining two or three small ones.
• The circuit should be switched off before changing any connection.
• Avoid loose connections and short circuits on the bread board.
• Do not exceed the voltage while taking the readings.
• Any live terminal shouldn't be touched while supply is on.

Outputs: Submit the graph as per observation table.

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VI Characteristics of a Diode            

Aim of the experiment.

At the end of the experiment, the student should be able to

• Explain the structure of a P-N junction diode
• Explain the function of a P-N junction diode
• Explain forward and reverse biased characteristics of a Silicon diode
• Explain forward and reverse biased characteristics of a Germanium diode

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VI Characteristics of a P-N Junction Diode

Semiconductors is a kind of material that has resistivity and conductivity in between metals and insulators. On the basis of purity semiconductors are of two types: Intrinsic Semiconductors is a kind of pure semiconductor without any significant dopant (impurities) species present. An intrinsic semiconductor is also called an undoped semiconductor and Extrinsic Semiconductors is a kind of semiconductor they are doped with an impurity, it is known as an extrinsic semiconductor.

p-n Junction Diode

Junction generally means the area or point that bounds two different parts, similarly in diodes junction is a boundary of two semiconductor materials i.e. the p-type and the n-type, semiconductor.

The p-side in the p-n junction has a positive side of the semiconductor and it has an excess of holes whereas the n-side has an excess of electrons, therefore, it is the negative side. The p-n junction in semiconductors is developed by the method of doping. adding impurities in a semiconductor is known as doping.

Formation of p-n Junction

Let us understand for an example, consider a thin p-type silicon semiconductor sheet. If we add a small amount of pentavalent impurity(having valency five) to this, a part of the p-type Si will get converted to n-type silicon. This sheet will now contain both regions i.e. p and n-type region and a junction is created between two regions. 

• There are two types of processes that follow after the formation of a p-n junction – diffusion and drift. As we know, diffusion is the process that follows the flow of particles from higher concentration to lower concentration, due to difference in the concentration of electrons and holes at the two sides of a junction, the electrons from the n-side diffuse to the p-side and the holes from the p-side diffuse to the n-side. this leads to raise in diffusion current.
• Also, there is an ionized donor is left behind on the n-side, which is an immobile charge this develop when an electron diffuses from the n-side to the p-side. As the result of this process, a layer of positive charge is developed on the n-side of the junction. 
• Similarly, An ionized acceptor is left behind in the p-side when a hole goes from the p-side to the n-side, resulting in the formation of a layer of negative charges in the p-side of the junction. This region of negative (-) and positive charge (+) on either side of the junction is termed the depletion region. 
• An electric field direction from a positive charge towards the negative charge is developed, Due to this positive charge region on either side of the junction, Due to this electric field, the flow of electrons and holes takes place. This is termed the drift motion. generally, the direction of the drift current is opposite to that of the diffusion current.

Forward Bias

The forward bias of p-n  junction

In biasing semiconductor is connected to an external source. when the p-type semiconductor is connected to the positive terminal of the source or battery and negative terminal to the n-type, then this type of junction is said to be forward-biased. In forward bias the direction of built-in electric field near the junction and applied electric field are opposite in direction. this means that the resultant electric field has a magnitude lesser than the built-in electric field. due to this there is less resistivity and therefore depletion region is thinner. In silicon, at the voltage of 0.6 V, the resistance of the depletion region becomes completely negligible.

Reverse Bias

The reverse bias of p-n  junction

In the reverse biasing, the n-type is connected to the positive terminal and the p-type is connected to the negative terminal of the battery . In this case, the applied electric field and the built-in electric field are in the same direction and the resultant of electric field has higher magnitude than the built-in electric field creating a more resistive, therefore depletion region is thicker. if the applied voltage becomes larger, then the depletion region becomes more resistive and thicker.

p-n Junction Formula The potential difference created by the electric field in the p-n junction is given by: E o = V T ln [N d N a / n i 2 ]  where E o  junction voltage at no bias, V T is the thermal voltage at room temperature i.e. 26mv, N d and N a are the concentrations of impurity and n i is intrinsic concentration.

V-I Characteristics of p-n Junction Diode

V-I characteristics of p-n junction diode

• In forward bias condition p-type is connected to positive terminal of battery and the n-type to the negative terminal of the battery, there is a reduction in the potential barrier, in this condition. For germanium diodes, when the voltage is 0.3 V, and for silicone diodes, when the voltage is 0.7 V the potential barriers decrease and there is a flow of current.
• When the diode is in forward bias , as the voltage applied to the diode is overcoming the potential barrier, the current increases slowly and the curve obtained is non-linear. Once the potential barrier is crossed by the diode, the diode behaves normally and the curve rises sharply as further external voltage increases and the curve obtained is linear.
• When the PN junction diode is under reverse bias , this results in an increase in the potential barrier and resistance also increases. Minority carriers are present in the junction which creates reverse saturation current flows in the beginning.
• If the applied voltage increases rapidly, there is increased kinetic energy due to minority charge carriers which affect the majority charges. In this stage the diode breaks down. or the voltage is called breakdown voltage, This may also destroy the diode.

Sample Questions

Question 1: When silicon is doped with indium it leads to which type of semiconductor?

As we know, Valency of Indium is 3 therefore it is Trivalent in nature, when it is doped in Silicon it has majority of holes, that’s why it is of p-type semiconductor.

Question 2: A transistor has a current gain of 30 Ampere. If the collector resistance is 6 kΩ, the input resistance is 1 kΩ, calculate its voltage gain.

Given, R in =1 kΩ  and R out = 6k Ω   ∴ R gain =  R out /R in   =  6/1 = 6   Voltage gain = current gain × Resistance gain                        = 30 × 6 =180

Question 3: Write characteristics of holes.

Following are the characteristics of holes: A hole is equivalent to a positive electric charge. The mobility of a hole as compare to that of an electron is less.

Question 4: Name the kind of biasing which leads the following result:

a) Increase in resistance,

b) Decrease in resistance and 

c) Increase in width of the depletion region.

a) In reverse bias resistance increases. b) In forward bias resistance decrease. c) In reverse bias there is increase in the width of depletion region take place.

Question 5: What is the ratio of electrons and holes in the intrinsic semiconductor?

Number of electrons = n e Number of holes = n h In intrinsic semiconductor, n e = n h n e /n h = 1 

Question 6: Define the term breakdown voltage of p-n junction.

In reverse bias condition, when the applied voltage increases gradually at a certain point there is increase in reverse current noticed, this is junction breakdown, corresponding applied voltage is known as breakdown voltage of p-n junction diode.

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V-i characteristics of pn junction diode.

Volt-ampere (V-I) characteristics of a pn junction or semiconductor diode is the curve between voltage across the junction and the current through the circuit.

Normally the voltage is taken along the x-axis and current along y-axis.

The circuit connection for determining the V-I characteristics of a pn junction is shown in the figure below.

Fig.1: Circuit Connection for V-I characteristics of a pn junction

The characteristics can be explained under three cases , such as :

• Forward bias
• Reverse bias

Case-1 : Zero Bias

In zero bias condition , no external voltage is applied to the pn junction i.e the circuit is open at K.

Hence, the potential barrier (ref : pn junction tutorial for better understanding) at the junction does not permit current flow.

Therefore, the circuit current is zero at V=0 V, as indicated by point O in figure below.

Fig.2: V-I Characteristics of pn Junction

Case-2 : Forward Bias

In forward biased condition , p-type of the pn junction is connected to the positive terminal and n-type is connected to the negative terminal of the external voltage.

This results in reduced potential barrier.

At some forward voltage  i.e 0.7 V for Si and 0.3 V for Ge, the potential barrier is almost eliminated and the current starts flowing in the circuit.

Form this instant, the current increases with the increase in forward voltage. Hence.  a curve OB is obtained with forward bias as shown in figure above.

From the forward characteristics, it can be noted that at first i.e. region OA , the current increases very slowly and the curve is non-linear. It is because in this region the external voltage applied to the pn junction is used in overcoming the potential barrier.

However, once the external voltage exceeds the potential barrier voltage, the  potential barrier is eliminated and the pn junction behaves as an ordinary conductor. Hence , the curve AB  rises very sharply with the increase in external voltage and the curve is almost linear.

Case-3 : Reverse Bias

In reverse bias condition , the p-type of the pn junction is connected to the negative terminal and n-type is connected to the positive terminal of the external voltage.

This results in increased potential barrier at the junction.

Hence, the junction resistance becomes very high and as a result practically no current flows through the circuit.

However, a very small current of the order of μA , flows through the circuit in practice. This is knows as reverse saturation current(I S ) and it is due to the minority carriers in the junction.

As we already know, there are few free electrons in p-type material and few holes in n-type material. These free electrons in p-type and holes in n-type are called minority carriers .

The reverse bias applied to the pn junction acts as forward bias to there minority carriers and hence, small current flows in the reverse direction.

If the applied reverse voltage is increased continuously, the kinetic energy of the minority carriers may become high enough to knock out electrons from the semiconductor atom.

At this stage breakdown of the junction may occur. This is characterized by a sudden increase of reverse current and a sudden fall of the resistance of barrier region. This may destroy the junction permanently.

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Class 12 Physics (India)

Course: class 12 physics (india)   >   unit 14.

• Forward biasing a PN junction
• Reverse biasing a PN junction
• Forward and reverse current mechanism

PN diode characteristics

• PN breakdown and avalanche

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Video transcript

PN Junction Diode Characteristics – Explained in Detail with Graphs

In this article, we learn about PN junction diode characteristics in detail – like how to bias a PN junction (Forward & Reverse bias methods), behavior of PN junction during forward & reverse bias setups, how to plot the VI characteristics, what is reverse breakdown and many other essential concepts regarding a PN junction diode. So let’s begin.

In chapter 1 – Understanding the PN junction , we have seen how a PN junction is formed from a p-type and n-type semiconductor. We have also learned about diffusion current, depletion region, drift current and barrier potential. If you find these terms foreign, just read the chapter about “ understanding the pn junction ” once more. Lets just make some questions. What is the use of a PN junction? Why have scientists created a pn junction device? What kind of problem it solves ? Learning anything is really fun when we question it. So these are our questions. Why there exists a pn junction in this world! ?;)

To get an answer to all these questions, lets first try to understand the characteristics of a PN junction. We know a pn junction has a “barrier potential”. Only if we overcome this “barrier potential” by applying an external voltage to the pn junction, we would be able to make it conducting. This simply means, current will pass through the pn junction only if we apply an external voltage higher than the “barrier potential” of pn junction. In chapter 1, we have seen that  net current inside a pn junction is zero. Inorder to understand the behavior of a pn junction we need to make it conducting by applying an external voltage over a range (say from 0 volts 5 or 10 volts ), and then we study how the current passed through the pn junction varies with increasing voltage levels. To apply an external voltage, we usually connect 2 metallic contacts at the two ends of the pn junction ( known as terminals ); one on the p-side and other on the n-side. A PN junction with two metallic contacts is known as a pn junction diode or a semiconductor diode. 

Note:- I have written an interesting article which tells the story behind invention & discovery of PN Junction diode. If you like to read the story, follow here:- Story behind Invention & Discovery of PN Junction

PN junction diode is symbolically represented as shown in picture. The direction of arrow is the direction of conventional current flow (under forward bias). Now lets try applying an external voltage to the pn junction diode. The process of applying an external voltage is called as “biasing” . There are two ways in which we can bias a pn junction diode.

1) Forward bias and 2) Reverse bias  

The basic difference between a forward bias and reverse bias is in the direction of applying external voltage. The direction of external voltage applied in reverse bias is opposite to that of  external voltage applied in forward bias.

Forward biasing a PN Junction diode

Forward biasing a pn junction diode is very simple. You just need to take a battery whose values can be varied from (o to V volts), connect its positive terminal to the p-side of pn junction diode and then connect the negative terminal of battery to the n-side of the pn junction diode. If you have done upto this, the forward bias circuit of pn junction diode is complete. Now all we need to do is understand how the pn junction diode behaves when we increase the voltage levels from 0 to say 10 volts or 100 volts. We have learned that if we apply an external voltage higher than the barrier potential of pn junction diode, it will start conducting, which means it will start passing current through it. So how we are going to study the behavior of pn junction diode under forward biased condition? Lets get a voltmeter and ammeter and connect it to the forward biased circuit of pn junction diode.A simple circuit diagram is shown below, which has a pn junction diode, a battery (in picture it is not shown as variable. keep in mind we are talking about a variable power source), an ammeter (in milli ampere range) and a voltmeter.

Note:- Assume that the pn junction diode is made from Silicon. The reason is difference in barrier potential for a diode made from Germanium and Silicon. (For a silicon diode – barrier potential is 0.7 volts where as for a Germanium diode barrier potential is low ~ 0.3 volts)

How to plot the characteristics of a pn junction ?

What we are going to do is, vary the voltage across diode by adjusting the battery. We start from o volts, then slowly move 0.1 volts, 0.2 volts and so on till 10 volts. Lets just note the readings  of voltmeter and ammeter each time we adjust the battery (in steps of 0.1 volts). Finally after taking the readings, just plot a graph with voltmeter readings on X-axis and corresponding Ammeter readings on Y axis. Join all the dots in graph paper and you will see a graphical representation as shown below. Now this is what we call “characteristics of a pn junction diode” or the “behavior of diode under forward bias” 

How to analyse the characteristics of a pn junction diode ?

Its from the “characteristics graph ” we have just drawn, we are going to make conclusions about the behavior of pn junction diode. The first thing that we shall be interested in is about “barrier potential” . We talked a lot about barrier potential but did we ever mention its value ? From the graph, we observe that the diode does not conduct at all in the initial stages. From 0 volts to 0.7 volts, we are seeing the ammeter reading as zero! This means the diode has not started conducting current through it. From 0.7 volts and up, the diode start conducting and the current through diode increases linearly with increase in voltage of battery. From this data what you can infer ? The barrier potential of silicon diode is 0.7 volts 😉  What else ? The diode starts conducting at 0.7 volts and current through the diode increases linearly with increase in voltage. So that’s the forward bias characteristics of a pn junction diode. It conducts current linearly with increase in voltage applied across the 2 terminals (provided the applied voltage crosses barrier potential).

What happens inside the pn junction diode when we apply forward bias ?

We have seen the characteristics of pn junction diode through its graph. What really happens inside the diode during the forward bias ? We know a diode has a depletion region with a fixed barrier potential. This depletion region has a predefined width, say W . This width will vary for a Silicon diode and a Germanium diode. The width highly depends on the type of semiconductor used to make pn junction, the level of doping etc. When we apply voltage to the terminals of diode, the width of depletion region slowly starts decreasing. The reason for this is, in forward bias we apply voltage in a direction opposite to that of barrier potential. We know the p-side of diode is connected to positive terminal and n-side of diode is connected to negative terminal of battery. So the electrons in n-side gets pushed towards the junction (by force of repulsion) and the holes in p-side gets pushed towards the junction. As the applied voltage increases from 0 volts to 0.7 volts, the depletion region width reduces from ‘ W’ to zero. This means depletion region vanishes at 0.7 volts of applied voltage.  This results in increased diffusion of electrons from n-side to p-side region and the increased diffusion of holes from p-side to n-side region. In other words, “ minority carrier ” injection happens on both p-side (in a normal diode (without bias) electrons are a minority on p-side) and n-side (holes are a minority on n-side) of the diode.

How current flow takes place in a pn junction diode ?

This is another interesting factor, to explain. As the voltage level increases, the electrons from n-side gets pushed towards the p-side junction. Similarly holes from p-side gets pushed towards the n-side junction. Now there arises a concentration gradient between the number of electrons at the p-side junction region and the number of electrons at the region towards the p-side terminal. A similar concentration gradient develops between the number of holes at the n-side junction region and the number of holes at region near the n-side terminal. This results in movement of charge carriers (electrons and holes) from region of higher concentration to region of lower concentration. This movement of charge carriers inside pn junction gives rise to current through the circuit.

Reverse biasing a PN junction diode

Why should we reverse bias a pn diode ? The reason is, we want to learn its characteristics under different circumstances. By reverse biasing, we mean, applying an external voltage which is opposite in direction to forward bias. So here we connect positive terminal of battery to n-side of the diode and negative terminal of the battery to p-side of the diode. This completes the reverse bias circuit for pn junction diode. Now to study its characteristics (change in current with applied voltage), we need to repeat all those steps again. Connect voltmeter, ammeter, vary the battery voltage, note the readings etc etc. Finally we will get a graph as shown.

Analysing the revere bias characteristics

Here the interesting thing to note is that, diode does not conduct with change in applied voltage. The current remains constant at a negligibly small value (in the range of micro amps) for a long range of change in applied voltage. When the voltage is raised above a particular point, say 80 volts, the current suddenly shoots (increases suddenly). This is called as “ reverse current ” and this particular value of applied voltage, where reverse current through diode increases suddenly is known as “ break down voltage “.

What happens inside the diode ?

We connected p-side of diode to negative terminal of battery and n-side of diode to positive terminal of battery. So one thing is clear, we are applying external voltage in the same direction of barrier potential. If applied external voltage is V and barrier potential is Vx , then total voltage across the pn junction will be V+Vx . The electrons at n-side will get pulled from junction region to the terminal region of n-side and similarly the holes at p-side junction will get pulled towards the terminal region of p-side.  This results in increasing the depletion region width from its initial length, say ‘W’ to some ‘W+x’. As width of depletion region increases, it results in increasing the electric field strength.

How reverse saturation current occurs and why it exists ?

The reverse saturation current is the negligibly small current (in the range of micro amperes) shown in graph, from 0 volts to break down voltage. It remains almost constant (negligible increase do exist) in the range of 0 volts to reverse breakdown voltage. How it occurs ? We know, as electrons and holes are pulled away from junction, they dont get diffused each other across the junction. So the net “ diffusion current ” is zero! What remains is the drift due to electric field. This reverse saturation current is the result of drifting of charge carriers from the junction region to terminal region. This drift is caused by the electric field generated by depletion region.

What happens at reverse breakdown ?

At breakdown voltage, the current through diode shoots rapidly. Even for a small change in applied voltage, there is a high increase in net current through the diode. For each pn junction diode, there will be a maximum net current that it can withstand. If the reverse current exceeds this maximum rating, the diode will get damaged.

Conclusion about PN junction characteristics

To conclude about pn junction characteristics, we need to get an answer to the first question we have raised – What is the use of pn junction? From the analysis of both forward bias and reverse bias, we can arrive at one fact – a pn junction diode conducts current only in one direction – i.e during forward bias. During forward bias, the diode conducts current with increase in voltage. During reverse bias, the diode does not conduct with increase in voltage (break down usually results in damage of diode). Where can we put this characteristics of diode into use ? Hope you got the answer! Its in conversion of alternating current to direct current (AC to DC). So the practical application of pn junction diode is rectification!

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Hey! That’s so helpful

Thickness of diplition layer depend on which factor?

DESC: Diode forward biased 24VDC QTY: 20pcs

DESC: Diode Reverse biased 24VDC QTY: 20pcs

Faith N. Dolorito Procurement Specialist MANILA OVERSEAS INC. TEL:6328004227 FAX:6328004172

thank you so very much…. I am clearly understood to read it……. ……..

As width of depletion region increases, it results in increasing the electric field strength.Why?

What is zener effect and avalanche effect.?

Utmost/extremly thanks ….. For this crystal clear explanation….. I really got something from it…. But sir what is Zener effect.and avalenche effect.?

Why internal electric field generate after diffusion process in pn junction

i hve a question. why the arrow in pn junction thicker????

explain the working of PN junction diode in forward and reverse biasing configuration please ?

why the battery in reverse bias is greater than in forward bias

I think I missed something. You say that the PN junction only starts to conduct current after the voltage aplied on the diode (Vd) reaches 0.7V, the barrier potential as you call it, but all the graphics and equations shows us that there is current through the diode for values of Vd smaller than 0,7V. I mean, even considering the current for Vd near zero negligible, with Vd~0.60V there is current.

As I see it, we just consider 0.7V as a practival value for a conducting diode, where any variation of the current will cause a small variation on Vd, keeping it around the same 0.7V. It would me consistent with the diode current equation Id=Is(exp(Vd/nVt)-1), cause in 0.7V for a regular diode, de slope in the curve is too large to see any change in Vd as the current varies.

I don’t know if I made myself clear, but thats a point that is not really clear in many books about semiconductors physics and it’s annoying me. If you could clarify that for me I would be glad.

Why the forward voltage values are almost constant for source voltage from 5V to 1V during forward-biased?

what is the difference between the connections of forwardbias and reverse bias in pn junction…?

in forward biasis -VE terminal of battery is connected to pentavelent group N and +ve is connected to trivalent group P but in reverse biasis the connection is opposite …

can I get a pdf of this chapter??

very clear presantation if you were around i would offer you a cup of tea or coffee good work

why is the voltmeter connected across the ammeter and reverse biased diode..?

Can a diode work on ac voltage or not

@Anuj – A diode is basically a PN Junction. It is used to convert AC to DC.

diode worked on ac voltage but it will give output is DC why because ac has two half cycles in that case,it will conduct only positive half cycle….do not allow -ve cycles…

it’s working on ac voltage

The junction information is clearly understand so nice of it thanx

for eachelectron hole combination that take place near the junction a covalent bond breaks in the p section near the +ve pole of the battery how it is formed?

it is so helpful and it clears all the confusion…….plz answer meone question thatis why in CB mode the emitter current increases with increase of V(CB)

this is a exellent article……….sir plz letme know about base width modulation

It is very short notes It is very useful i am very happy after read that notes thank u very much

thanks 4 the good explanation. will you please show the one connected image source circuit of both forward and reverse biased a pn-junction

Please see Fig.10

wow it is very much helpful to me. Thanks the author

yes, its very great answer that i want. Thanks.

I really appreciate. Got a clearer explanation that i did in class… Kudos. Thanks Admin

a great work with full clearification. thanx !

Really interesting and clear clarification of every aspect of a junction diode characteristics.Very nice

Brilliant! Very helpful article. It’s clearly explaind and easy to understand. Bravo for the person who has put so much work to make it!!

Thanq So Much 🙂 this helped me a lot 🙂 Is there explanation for Transistor as a Switch and Amplifier?

explanation is little bit invalid

thaks very much for the good explanation.can you describe the current voltage characteristics of a photodiode when light is incident on it?

veryyyy goood explanation, i got it perfectly, please tell me about bridge wave rectifier, we connect 4 diodes in bridge but when the d1 and d2 are forward biased then haw the d3 and d4 are reversr biased

@Nayan – Read this article:- https://www.circuitstoday.com/full-wave-bridge-rectifier

It will help you understand bridge rectifier perfectly.

when we talk about reverse bias ,thn the width of depletion layer increases thn after more reverse voltage(greater than reverse breakdown voltage) how current flow through dide?

At break down, what happens really is that the diode gets damaged. It loses its junction & characteristics associated with the junction. The “diode” almost behaves like a shorted wire & hence current flows through it easily. Theoretically, internal resistance of a diode at breakdown is zero. But in practice, there exists a small internal resistance and hence the current increases with a deviation factor (and not a perpendicular graph).

Hope this helps!

Really helpfull , Thanks sir..

good explanation with neat a diagrams

its very simple to understand ……i like to read a lot in webpage…thank u to author who wrote this.

well explained. really enyoyed.

sir please add the curve charcterstic found when we use ge semiconductor as pn junction diode due to the this experiment

it was very useful and was written in a readble mannar

I like this and I enjoy

its a rely nuc explanation abt pn junctoin m a net qualified scientist

Thank you Pintu 🙂 It was very nice words 🙂

the difference between depletion barrier’s height and width . i mean why they are different and what they indicate?

If depletion region’s width indicates the area covered by defused electrons/holes then read further.

In forward bias condition external electric field ( produced by battery) will be opposite to the internal electric field ( produced depletion barrier ). in this case the external electric field will cancel the internal electric field and more electron will flow from n type to p type material(assumed external voltage is greater than depletion barrier) which increases the depletion region but in real, in forward bias condition the depletion region’s width decreases. And in reverse bias condition the depletion region increases instead of decreasing. (I am familiar with the increase/decrease of potential of depletion barrier and agree with the books)

I am very confused with this question. so please help me. Thank you

What really matters is the “barrier potential” of a diode. In a Silicon diode, the “barrier width” is higher than a Germanium diode. So “barrier potential” of a Silicon diode is higher than Germanium diode. I hope you understood.

cool great approach. hoping that 2 give more information about electronics

Please help me out.. In forward bias if battery voltage is 2v , drop across si diode cant be more than 1v i.e. Vd<1v… So now my qusetion is where this remaining 1v of battery is if no resistor is in series with diode?

In that case, 1 volt will be dropped across the wires with the help of a very large current.

Awesome explanation.thank you

Crystal Clear approach, awesome!!

it’s very useful thank you

Really amazing! I have never seen a website this successful in explanation! You can’t imagine how much this helped me! Thanks

Keep adding more and more info….

owsam… PERFECT …!!

Thanks so much. That was a comprehensive expose. Keep keeping

oh thank u..i am very confused to read my text book but now every thing is clear….thank you very much ..

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• CBSE Class 12
• CBSE Class 12 Physics Practical
• To Draw The I V Characteristic Curve For P N Junction In Forward And Reverse Bias

To Draw The I-V Characteristic Curve of a P-N Junction In Forward Bias and Reverse Bias

In a standard diode, forward bias and reverse bias takes place. Let us know how to draw the I-V characteristic curve of a P-N junction in forward bias and reverse bias.

To draw the I-V characteristic curve of a P-N junction in forward bias and reverse bias.

Materials Required

• A P-N junction diode
• A 3-volt battery
• A 50-volt battery
• A high resistance rheostat
• One 0-3 volt voltmeter
• One 0-50 volt voltmeter
• One 0-100 mA ammeter
• One 0-100 μA ammeter
• One way key
• Connecting wires
• Piece of sandpaper

Forward bias characteristics

The junction is said to be forward-biased when the p-section of the diode is connected to the positive terminal of the battery and the n-section of the diode is connected to the negative terminal of the battery. With an increase in the voltage, the current also increases. For Si diode, at 0.7 V the current increases suddenly.

Reverse bias characteristics

The junction is said to be reverse-biased when the p-section of the diode is connected to the negative terminal of the battery and the n-section of the diode is connected to the positive terminal of the battery. With an increase in the voltage, there is a small change in the current but the reverse current increases to a higher value with an increase in the voltage.

For forward bias

• The circuit connections should be as shown in the diagram.
• All the connections should be neat, clean and tight.
• For voltmeter (V) and milli-ammeter (mA), the least count and zero error should be noted.
• To get the zero reading from the voltmeter and milli-ammeter, rheostat should be brought near the negative end by inserting the key K.
• To apply the forward bias voltage (V F ) of 0.1V, the contact should be moved towards the positive end. The current remains zero.
• Keeping current zero, increase the forward bias voltage up to 0.3 V for Ge diode.
• To record a small current using milli-ammeter, increase the V F to 0.4 V.
• Increase the V F by 0.2 V and record the corresponding current. When the V F becomes 0.7 V, the current will increase rapidly.
• When V F = 0.72 V, the current increases suddenly and this is known as forward breakdown stage.
• Take out the key if the forward current won’t change as V F increased beyond forward breakdown.
• Record the observations.

For reverse bias

• Note the least count and zero error of voltmeter (V) and micro-ammeter (μA).
• To get zero reading from the voltmeter V and micro-ammeter μA, insert the key K and bring the rheostat near the positive end.
• To apply reverse bias voltage (V R ) of 0.5 V, move the rheostat to the negative end so as to flow the reverse current.
• Increase V R by 0.2 V and record the corresponding current. When V R becomes 20 V, the current will increase rapidly.
• When V R = 25 V, the current increases suddenly and this is known as reverse breakdown stage. Record the current reading and take off the key.

Observations

Range of voltmeter = …….V

Least count of the voltmeter = …….V

Zero error of voltmeter = ……..V

Range of milli-ammeter = …….mA

Least count of milli-ammeter = …….mA

Zero error of milli-ammeter = ……..mA

Table for forward bias voltage and forward current

Range of micro-ammeter = …….μA

Least count of micro-ammeter = …….μA

Zero error of micro-ammeter = ……..μA

Table for reverse bias voltage and reverse current

Plotting of Graphs

Plot a graph between V F and I F taking V F on the x-axis and I F on the y-axis. The graph obtained is known as forward bias characteristic curve.

Plot a graph between V R and I R taking V R on the negative x-axis and negative I R on the y-axis. The graph obtained is known as reverse bias characteristic curve.

Junction resistance for forward bias = …… ohms

Junction resistance for reverse bias = ……… ohms.

Precautions

• The connections should be neat, clean and tight.
• Key should be used when the circuit is being used.
• Beyond breakdown, forward bias voltage should not be applied.
• Beyond breakdown, reverse bias voltage should not be applied.

Sources Of Error

Faulty junction diode might be supplied.

Q1. Define the energy level in an atom.

Ans: Energy level in an atom is defined as the energy value of an electron in the subshell of an atom.

Q2. What are the different types of energy bands?

Ans: Following are the different types of energy bands:

• Conduction band (C)
• Valence band (V)
• Forbidden band (F)

Q3. What are the different types of substances?

Ans: Following are the different types of substances:

• Semiconductors

Q4. What is the SI unit of conductance?

Ans: SI unit of conductance is siemens (S).

Q5. Name the different types of biasing.

Ans: Following are the different types of biasing:

• Forward biasing
• Reverse biasing

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