# data[].attributes.body
conceptual map

# data[].attributes.attachment_link.title
York Associates - Mappa Mentale - Schema

# data[].attributes.attachment_link.description
Polarizzazioni Diodo, Appunti, Caratteristica voltamperometrica, Principali applicazioni, TIPI DI DIODI, Testing con multimetro

# data[].attributes.body
ELECTRICAL4U.COM

# data[].attributes.attachment_link.readable_text
Forward Biased P-N Junction

When we connect p-type region of a junction with the positive terminal of a voltage source and n-type region with the negative terminal of the voltage source, then the junction is said to be forward biased. At this condition, due to the attraction of positive terminal of source, electrons which participated in covalent bond creations in p-type material, will be attracted towards the terminal. As result numbers of covalent bonds are broken and, electrons are shifted towards the positive terminal. As a result, the concentration of electrons in the crystal nearer to the terminal increases and these electrons recombine with holes here. In this way, the number of holes increases in the portion of the p-type region away from the junction, and it is reduced in the portion of p-type region nearer to the terminal. As such holes are shifted from terminal to junction.

Due to the higher concentration of holes adjacent to negative impurity ions layer the electrons of negative ions come out and recombine with those holes and create new holes in the layer. Consequently, the width of this negative ions layer is reduced and finally this layer vanishes.

Similarly due to the negative terminal of source the free electrons in the n-type region will repeal towards junction where they will find the layer of positive impurity ions and start recombine with these ions and generate free electrons inside the layer. Consequently, the width of positive impurity ions is reduced, and finally, it vanishes. In these ways, both layers of ions disappear, and there will be no more depletion layer. After the depletion layer disappeared, free electrons from the n-type region can easily drift to p-type region and holes from p-type region to n-type region in the crystal. Hence, ideally there will be no obstruction of flowing current and the pn junction behaves as the short circuit.

Reverse Biased PN Junction

When positive terminal of a voltage source is connected to the n-type region and the negative terminal of the source is connected to the p-type region then the pn junction is said to be in reverse biased condition. When there is no voltage applied across the p n junction, the potential developed across the junction is 0.3 volts at 25 oC for germanium pn junction and 0.7 volts at 25 o C for silicon p n junction.

The polarity of this potential barrier is same as the polarity of voltage source applied during reverse biased condition. Now if reverse biased voltage across the pn junction is increased the barrier potential developed across the pn junction is also increased. Hence, the pn junction is widened. When positive terminal of the source is connected to the n-type region, the free electrons of that region are attracted towards positive terminal of the source because of that more positive impurity ions are created in the depletion layer which makes the layer of positive impurity ions thicker. At the same time since negative terminal of the source is connected to the p-type region of the junction, electrons are injected in this region. Due to the positive potential of the n-type region the electrons are drifted towards the junction and combine with holes adjacent to the layer of positive impurity ions and create more positive impurity ions in the layer. Hence, the thickness of the layer increases. In this way over all width of the depletion layer increases along with its barrier potential. This increment of the width of depletion layer will continue till the barrier potential reaches to applied reverse biased voltage. Although this increment of barrier potential will continue up to applied reverse biased voltage but if the applied reverse biased voltage is sufficiently high then the depletion layer will disappear due zener breakdown and avalanche breakdowns. It is also to be noted that after completion of reverse biased depletion layer there is no more drift of charge carriers (electrons and holes) through the junction as the potential barrier opposes the applied voltage which has the same value as the potential barrier. Although tiny current flow from n-type region to p-type region due to minority carriers that is thermally generated electrons in p-type semiconductor and holes in n-type semiconductor.

Forward Current in PN Junction

When battery voltage is applied across the junction in the forward bias, a current will flow continuously through this junction.

I S is Saturation Current (10⁻⁹ to 10⁻¹⁸ A) V T is Volt-equivalent temperature (= 26 mV at room temperature) n is Emission coefficient (1 ≤ n ≤ 2 for Si ICs) Actually this expression is approximated.

Reverse Current in PN Junction

When a p-n junction is connected across a battery in such a manner that its n-type region is connected to the positive potency of the battery and the p-type region is connected to the negative potency of the battery the p n junction is said to be in reverse biased condition and ideally there is no current flowing through the junction. But practically there will be a tiny reverse bias current i D which is expressed as. i D drops to zero value or very small value. i D can be written as i ₀.

I S is Saturation Current (10⁻⁹ to 10⁻¹⁸ A) V T is Volt-equivalent temperature (= 26 mV at room temperature) n is Emission coefficient (1 ≤ n ≤ 2 for Si ICs) Actually this expression is approximated.

General Specification of PN Junction

A p-n junction is specified in four manners.

1. Forward Voltage Drop (VF): Is the forward biasing junction level voltage (0.3V for Germanium and 0.7V for Silicon Diode )

2. Average Forward Current (IF): It is the forward biased current due to the drift electron flow or the majority carriers. If the average forward current exceeds its value the diode gets over heated and may be damaged.

3. Peak Reverse Voltage (VR): It is the maximum reverse voltage across the diode at it reverse biased condition. Over this reverse voltage diode will go for breakdown due to its minority carriers.

4. Maximum Power Dissipation (P): It is the product of the forward current and the forward voltage.

V-I Characteristics of A PN Junction

In the forward bias, the operational region is in the first quadrant. The threshold voltage for Germanium is 0.3 V and for Silicon is 0.7 V. Beyond this threshold voltage the graph goes upward in a non linear manner. This graph is for the dynamic Resistance of the junction in the forward bias.

In the reverse bias the voltage increases in the reverse direction across the p-n junction, but no current due to the majority carriers, only a very small leakage current flows. But at a certain reverse voltage p-n junction breaks in conduction. It is only due to the minority carriers. This amount of voltage is sufficient for these minority carriers to break the depletion region. At this situation sharp current will flow through this junction. This breakdown of voltage is of two types.

Avalanche Breakdown: it is not properly sharp, rather inclined linear graph i.e. after break down small increase in reverse voltage causes more sharp current gradually.

Zener Breakdown: This breakdown is sharp and no need to increase reverse bias voltage to get more current, because current flows sharply.

Resistances of p-n Junction

Dynamic Resistance of p-n Junction

From V-I characteristics of a p-n junction, it is clear that graph is not linear. The forward biased p-n junction resistance is r d ohm it is called AC resistance or dynamic resistance. It is equivalent to slope of voltage-current of the PN junction.

Average AC Resistance of p-n Junction

Average AC resistance is determined by the straight line that is drawn linking the intersection of the minimum and maximum values of external input voltage.

Some important terms related to p-n Junction

Transition Capacitance of p-n Junction

When depletion region exist in the common junction around, the diode acts as a capacitor. Here the depletion region is the dielectric and two regions (p-type and n-type) at both ends act as the charged plates of a capacitor. As the depletion layer decreases the capacitance value goes down.

Diffusion Capacitance of p-n Junction

It the capacitance of the diode in forward biased condition and it is defined as the ratio of transiting charge created to the differential change in voltage. When the current through the junction increases the diffusion capacitance also increases. Along with this increase in current, the forward biased resistance also decreases. This diffusion capacitance is somewhat greater than the Transition capacitance.

Storage Time of PN Junction

It is the time taken by the electrons to move from n-type region to p-type region and p-type region to n-type region by applying simultaneous forward and reverse bias voltage during switching.

Transition Time of p-n Junction

It is the time taken by the current to decrease to reverse leakage current. This transition time can be determined by geometry of P-N junction and concentration of the doping level.

Reverse Recovery Time of P-N Junction

It is sum of the storage time and transition time. It is the time for diode to raise applied current to get 10% of the constant state value from the reverse leakage current.

# data[].attributes.attachment_link.title
Forward and Reverse Bias of P N Junction

# data[].attributes.attachment_link.description
When we connect p-type region of a junction with the positive terminal of a voltage source and n-type region with the negative terminal of the voltage source, then the junction is said to be forward biased. At this condition, due to the attraction of positive terminal of source, electrons which participated in covalent bond creations in p-type material, will be attracted towards the terminal.

# data[].attributes.body
911ELECTRONIC.COM

# data[].attributes.attachment_link.readable_text
Semiconductor diode definition - type of diode, which contains "p-n junction" made of semiconductor materials. It's double-ended, nonlinear element where the end attached to the " p" layer (+) is called anode and " n" layer ( -) - cathode.
Semiconductor diode symbol
The main advantage of this electronic component is current flowing only in one direction (from anode to the cathode) after forward-biasing the "p-n junction". However, in the opposite direction (reverse bias) current doesn't flow and we could call this as the electric valve. Diode is constructed from two semiconductors, which were doped in different proportions - "p" and "n" types. They together form the p-n junction. The "n" layer with donor dopants has excess of electrons where the "p" layer (acceptor dopants) - have deficiency of them. After combining these on semiconductor diode together, a proportional distribution of electrons begins. Electrons, which previously lacked in "p" layer are transferred there from "n" layer. In this way region called depletion region that prevents the electric flow is formed. With passing time, technological requirements were increasing what resulted in formation of new types of diodes.

When semiconductor is combined with the corresponding metal, we acquire MS junction (metal-semiconductor), which also possesses rectifying properties (current conduction in one direction) - it is used for example in Schottky diode. MS junctions can have one of two current-voltage characteristics:
Illustration of differently biased P-N junctions: How to determine where is the anode and where is the cathode?
MS junction properties depends mainly on the surface state of semiconductor and on the output work difference of electrons from metal and semiconductor itself. Schottky diode is mainly used in systems that require short switching time (small junction capacitance Cj of diode has decisive impact) with frequencies up to several tens of GHz.

Simple multimeter can be used to determine the polarity of a diode. There are at least three ways to do this but I will show two most popular that can be used with cheap multimeters ( Get INNOVA 3320 Auto-Ranging Digital Multimeter ):

a) Using ohmmeter (2kΩ range):

You can also use "diode check" function (diode symbol on the multimeter) but the result will be the same as the above with using ohmmeter.
Experiment for self execution:
b) Using VDC measurement function:
Items needed:
This experiment will allow you to visualize the principle of operation of a semiconductor diode, whether current conducts or not. Because you will do it by yourself, you will better remember this lesson.

We will be using two schemes you've seen earlier:

Below you can see pictures showing the circuit mounted on the breadboard and visualization in two opposite positions of the LED diode (reverse polarity).

On the first picture, the LED was put into conducting state. Voltage on her anode was higher (+) than at the cathode (-), so the flow of current was possible. In our experiment we used a 9V battery, so the current flowing through the diode will be about 9mA (from Ohm's law).

On the second picture, the diode was inserted in the opposite way (the voltage at the cathode was higher (+) than at the anode (-)), so the diode entered a blocking state, which prevented flow of the current - LED isn't lit.

Common types of semiconductor diodes (and their main functions):

# data[].attributes.attachment_link.title
Semiconductor Diode - Definition, Structure, Characteristic

# data[].attributes.attachment_link.description
Semiconductor diode definition - type of diode, which contains "p-n junction" made of semiconductor materials. It's double-ended, nonlinear element where the end attached to the " p" layer (+) is called anode and " n" layer ( -) - cathode.

# data[].attributes.headline
How to determine where is the anode and where is the cathode?

# data[].attributes.subject
How to determine where is the anode and where is the cathode?

# data[].attributes.body
Simple multimeter can be used to determine the polarity of a diode. There are at least four ways to do this but I will show two most popular that can be used with cheap multimeters.

Without measurement instrument:

You can determinate where is the cathode  identifying  a gray or black score on electrical component.

Using ohmmeter (2kΩ range):

Forward-bias: Ohmmeter will indicate approximate forward voltage of the diode (near 0,7V)

Reverse-bias: Ohmmeter indicates “1” what means very high resistance

Using VDC measurement function:

Forward-bias: Multimeter should indicate voltage drop of approximately 0,7V for silicon diodes

Reverse-bias: Multimeter will indicate the approximate full voltage of the supply

Diode check:

# data[].attributes.body
In the forward bias, the operational region is in the first quadrant. The threshold voltage for Germanium is 0.3 V and for Silicon is 0.7 V. Beyond this threshold voltage the graph goes upward in a non linear manner. This graph is for the dynamic Resistance of the junction in the forward bias.

In the reverse bias the voltage increases in the reverse direction across the p-n junction, but no current due to the majority carriers, only a very small leakage current flows. But at a certain reverse voltage p-n junction breaks in conduction. It is only due to the minority carriers. This amount of voltage is sufficient for these minority carriers to break the depletion region. At this situation sharp current will flow through this junction. This breakdown of voltage is of two types.

Avalanche Breakdown: it is not properly sharp, rather inclined linear graph i.e. after break down small increase in reverse voltage causes more sharp current gradually.

Zener Breakdown: This breakdown is sharp and no need to increase reverse bias voltage to get more current, because current flows sharply.

# data[].attributes.body
Structure and Doping of Device

# data[].attributes.body
Structure - Electic Symbol - Device

# data[].attributes.body
When positive terminal of a voltage source is connected to the n-type region and the negative terminal of the source is connected to the p-type region then the pn junction is said to be in reverse biased condition. When there is no voltage applied across the p n junction, the potential developed across the junction is 0.3 volts at 25oC for germanium pn junction and 0.7 volts at 25oC for silicon p n junction.

The polarity of this potential barrier is same as the polarity of voltage source applied during reverse biased condition. Now if reverse biased voltage across the pn junction is increased the barrier potential developed across the pn junction is also increased. Hence, the pn junction is widened. When positive terminal of the source is connected to the n-type region, the free electrons of that region are attracted towards positive terminal of the source because of that more positive impurity ions are created in the depletion layer which makes the layer of positive impurity ions thicker. At the same time since negative terminal of the source is connected to the p-type region of the junction, electrons are injected in this region. Due to the positive potential of the n-type region the electrons are drifted towards the junction and combine with holes adjacent to the layer of positive impurity ions and create more positive impurity ions in the layer. Hence, the thickness of the layer increases.

# data[].attributes.body
When we connect p-type region of a junction with the positive terminal of a voltage source and n-type region with the negative terminal of the voltage source, then the junction is said to be forward biased. At this condition, due to the attraction of positive terminal of source, electrons which participated in covalent bond creations in p-type material, will be attracted towards the terminal. As result numbers of covalent bonds are broken and, electrons are shifted towards the positive terminal. As a result, the concentration of electrons in the crystal nearer to the terminal increases and these electrons recombine with holes here. In this way, the number of holes increases in the portion of the p-type region away from the junction, and it is reduced in the portion of p-type region nearer to the terminal. As such holes are shifted from terminal to junction. Due to the higher concentration of holes adjacent to negative impurity ions layer the electrons of negative ions come out and recombine with those holes and create new holes in the layer. Consequently, the width of this negative ions layer is reduced and finally this layer vanishes.

# data[].attributes.body
However, in the opposite direction (reverse bias) current doesn’t flow and we could call this as the electric valve. Diode is constructed from two semiconductors, which were doped in different proportions – “p” and “n” types. They together form the p-n junction. The “n” layer with donor dopants has excess of electrons where the “p” layer (acceptor dopants) – have deficiency of them. After combining these on semiconductor diode together, a proportional distribution of electrons begins. Electrons, which previously lacked in “p” layer are transferred there from “n” layer. In this way region calleddepletion region that prevents the electric flow is formed. With passing time, technological requirements were increasing what resulted in formation of new types of diodes.

# data[].attributes.body
Type of diode, which contains “p-n junction” made of semiconductor materials. It’s double-ended, nonlinear element where the end attached to the “p” layer (+) is called anode and “n” layer (–) – cathode. The main advantage of this electronic component is current flowing only in one direction (from anode to the cathode) after forward-biasing the “p-n junction”.