Basic electronic components(diodes)

What is the photoconductive mode of a photodiode?

Photoconductive mode: When a certain reverse potential is applied to the device then it behaves as a photoconductive device. Here, an increase in depletion width is seen with the corresponding change in reverse voltage.

What is the photovoltaic mode of a photodiode?

Photovoltaic mode: It is also known as zero-bias mode because no external reverse potential is provided to the device. However, the flow of minority carrier will take place when the device is exposed to light.

What is a diode?3pts

- special device made from semi-conductor material, e.g. silicon - it is used to regulate the potential difference in circuits - it lets the current flow freely in one direction but not the other as there is a very high resistance in the reverse direction

Where are backward diodes used?3

1. Detector: It can be used as a detector up to the frequency of 40 GHz. It possesses low capacitance thus the problem of charge storage is minimized in these diodes. Besides, it's nonlinear characteristics for small signal makes it appropriate for application of detector. 2. Switch: The low capacitance of these diodes imparts an ability to the diode to switch from On state to off state efficiently. Thus, it is used in switching circuitry. 3. Rectifier: It is used for rectification of signal with small peak voltage i.e. about 0.1 V- 0.7 V. This is all about backward diode. Its ability to possess low capacitance is utilized in switching application. Besides, it also finds significance in rectifier circuits.

What is a PIN photodiode

A PIN photodiode is one of the most widely used forms of photodiode today. Although the PIN or p-i-n photodiode was not the first type of photodiode to be used, it collects the light photons more efficiently than the more standard PN photodiode, and also offers a lower capacitance. A p-i-n or PIN photodiode is a photodiode with an intrinsic (i) (i.e., undoped) region in between the n- and p-doped regions. Most of the photons are absorbed in the intrinsic region, and carriers generated therein can efficiently contribute to the photocurrent

What is a backward diode?

A backward diode (also called back diode[2) is a variation on a Zener diode or tunnel diode having a better conduction for small reverse biases (for example -0.1 to -0.6 V) than for forward bias voltages. The reverse current in such a diode is by tunnelling, which is also known as the tunnel effect. It is designed by providing variation in the design characteristics of Zener diode and tunnel diode. It is unilateral device because its designing mechanism allows it to operate in one direction only. It is designed for specific purpose. It works in the same way in reverse biasing as the conventional diode operates in forward biasing. The negative resistance characteristics of tunnel diode are used in the backward diode.

Explain the current/voltage characteristic of a zener diode?

A graph of current through vs the voltage across the device is called the characteristic of Zener diode. The first quadrant is the forward biased region. Here the Zener diode acts like an ordinary diode. When a forward voltage is applied, current flows through it. But due to higher doping concentration, higher current flows through the Zener diode. In the third quadrant, the magic happens. The graph shows the current vs voltage curve when we apply a reverse bias to the diode. The Zener breakdown voltage is the reverse bias voltage after which a significant amount of current starts flowing through the Zener diode. Here in the diagram, VZ refers to the Zener breakdown voltage. Until the voltage reaches Zener breakdown level, tiny amount of current flows through the diode. Once the reverse bias voltage becomes more than the Zener breakdown voltage, a significant amount of current starts flowing through the diode due to Zener breakdown. The voltage remains at the Zener breakdown voltage value, but the current through the diode increases when the input voltage gets increased. Due to the unique property of Zener diode, the depletion region regains its original position when the reverse voltage gets removed. The Zener diode doesn't get damaged despite this massive amount of current flowing through it. This unique functionality makes it very useful for many applications.

Explain the conduction and valence bands of an unbiased diode?

A p-n junction diode is formed by doping one half of the semiconductor crystal with p-type impurity and the other half with n-type impurity while the crystal is being formed. Unbiased p-n junction Unbiased conditions mean that there is no external energy source (no voltage) In an unbiased diode an electric field is set up across the depletion layer between the n-type and the p-type material. This is caused by the imbalance in free electrons due to the doping.

What is a photodiode?

A photodiode is a p-n junction or pin semiconductor device that consumes light energy to generate electric current. It is also sometimes referred as photo-detector, photo-sensor, or light detector. Photodiodes are specially designed to operate in reverse bias condition. Reverse bias means that the p-side of the photodiode is connected to the negative terminal of the battery and n-side is connected to the positive terminal of the battery. Photodiode is very sensitive to light so when light or photons falls on the photodiode it easily converts light into electric current. Solar cell is also known as large area photodiode because it converts solar energy or light energy into electric energy. However, solar cell works only at bright light.

What is a semi-conductor?

A substance such as silicon or Germanium that can be made to conduct electricity under certain conditions.

How do varactor diodes work?

A varactor diode is designed to store electric charge not to conduct electric current. So varactor diode should always be operated in reverse bias. When a reverse bias voltage is applied, the electrons from n-region and holes from p-region moves away from the junction. As a result, the width of depletion region increases and the capacitance decreases. However, if the applied reverse bias voltage is very low the capacitance will be very large. The capacitance is inversely proportional to the width of the depletion region and directly proportional to the surface area of the p-region and n-region. So the capacitance decreases as the as the width of depletion region increases. If the reverse bias voltage is increased, the width of depletion region further increases and the capacitance further decreases. On the other hand, if the reverse bias voltage is reduced, the width of depletion region decreases and the capacitance increases. Thus, an increase in reverse bias voltage increases the width of the depletion region and decreases the capacitance of a varactor diode. The decrease in capacitance means the decrease in storage charge. So the reverse bias voltage should be kept at a minimum to achieve large storage charge. Thus, capacitance or transition capacitance can be varied by varying the voltage. In a fixed capacitor, the capacitance will not be varied whereas, in variable capacitor, the capacitance is varied.

What are 4 advantages of using backward diodes?

Advantages of Backward Diode 1. Temperature Sensitivity: The temperature sensitivity of Backward Diode is less than the temperature sensitivity of conventional diode. The sensitivity of backward diode is -0.1 mV/0C for both semiconductor material i.e. germanium and silicon. On the other hand, the sensitivity of conventional diode is -2mV/0C. Thus, backward diode is less affected with variation in temperature due to low-temperature sensitivity. 2. Low Break Point: The break point of a backward diode is 0 V, while the break point of a conventional diode is between 0.6 V - 0.7 V. Thus, its low break point is effective for various application because the device can withstand high magnitude of voltage without the breakdown of the device. While the conventional diode break point is not low thus, it cannot withstand high voltage and if the voltage exceeds 0.6 V-0.7 V the diode breaks down. 3. Low Noise Level: The noise level of these diodes is low, thus signal to noise ratio in the case of the diode is far much better than conventional diodes. 4. Efficiency: The efficiency of the diode is also better than a conventional diode, the structural characteristics impart an ability to the diode to improve its performance.

What are the advantages of photodiodes?

Advantages of Photodiode 1. It shows a quick response when exposed to light. 2. Photodiode offers high operational speed. 3. It provides a linear response. 4. It is a low-cost device.

Explain the valence, and conduction band in an insulator?

An insulator has a large gap between the valence band and the conduction band. The valence band is full as no electrons can move up to the conduction band. As a result, the conduction band is empty. Only the electrons in a conduction band can move easily, so because there aren't any electrons in an insulator's conduction band, the material can't conduct.

Explain the characteristic curve of a normal PN junction diode in reverse bias?

Analyzing 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 are the applications of photodiodes?

Applications of Photodiode 1. Photodiodes majorly find its use in counters and switching circuits. 2. Photodiodes are extensively used in an optical communication system. 3. Logic circuits and encoders also make use of photodiode. 4. It is widely used in burglar alarm systems. In such alarm systems, if exposure to radiation runs uninterrupted, the current flows, but as the light energy fails to fall on the device, it sounds the alarm. 5. In case of a typical photodiode, the normal reverse current is in tens of microampere range..

What are tunnel diodes used for?

Applications of Tunnel Diode 1. Tunnel diode can be used as a switch, amplifier, and oscillator. 2. Since it shows a fast response, it is used as high frequency component. 3. Tunnel diode acts as logic memory storage device. 4. They are used in oscillator circuits, and in FM receivers. Since it is a low current device, it is not used more.

Where are varactor diodes used?

Applications of varactor diode Varactor diode is used in frequency multipliers. Varactor diode is used in parametric amplifiers. Varactor diode is used in voltage-controlled oscillators.

What is a schottky photodiode?

As the name indicates, Schottky photodiode technology is based upon the Schottky diode. In view of the small diode capacitance it offers a very high speed capability and is used in high bandwidth communication systems.

What is the avalanche breakdown?

Avalanche Breakdown The avalanche breakdown is observed in the Zener Diodes having Vz having than 8 V. In the reverse biased condition, the conduction will take place only due to the minority carriers. As we increase the reverse voltage applied to the Zener diode, these minority carriers tend to accelerate. Therefore, the kinetic energy associated with them increases. While travelling, these accelerated minority carriers will collide with the stationary atoms and impart some of the kinetic energy to the valence electrons present in the covalent bonds. Due to this additionally acquired energy, these valence electrons will break their covalent bonds and jump into the conduction bond to become free conduction. Now these newly generated free electrons will get accelerated. They will knock out some more valence electrons by means of collision. This phenomenon is called as carrier multiplication.

What is an avalange photodiode?

Avalanche photodiode technology is used in areas of low light. The avalanche photodiode offers very high levels of gain, but against this it has high levels of noise. Accordingly this photodiode technology is not suitable for all applications and it tends to be used .

Explain the current/voltage characteristics of a backward diode?

Characteristics of Backward Diode The reverse characteristics are similar to the characteristics of the Zener diode. The forward characteristics can be understood with the help of the below diagram. Initially, current increases with an increase in voltage, but after a particular time, the magnitude of current becomes constant. It does not show a significant increase even if the variation in voltage is large.

how does the n-type of semiconductor work

Conduction Through n-Type Semiconductor In the n-type semiconductor, a large number of free electrons are available in the conduction band which are donated by the impurity atoms. The figure below shows the conduction process of an n-type semiconductor. When a potential difference is applied across this type of semiconductor, the free electrons are directed towards the positive terminals. It carries an electric current. As the flow of current through the crystal is constituted by free electrons which are carriers of negative charge, therefore, this type of conductivity is known as negative or n-type conductivity. The electron-hole pairs are formed at room temperature. These holes which are available in small quantity in valence band also consists of a small amount of current. For practical purposes, this current is neglected.

how does the p-type semiconductor work?

Conduction in P-Type Semiconductor When the external supply of voltage is given to the p-type semiconductor there majority carriers present in valence band tends to move towards the negative terminal of the supply and the minority carriers that are electrons present in the conduction band move towards the positive terminal. Conduction in P-Type Semiconductor However, the concentration of electrons is less in the conduction band and the majority of holes are present in the valence band. Hence the current in the p-type is because of majority carriers in valence band a little amount of current is in conduction band because of few electrons that are their minority carriers.

Explain the valence, and conduction band in a conductor?

Conductors In a conductor there are no band gaps between the valence and conduction bands. In some metals the conduction and valence bands partially overlap. This means that electrons can move freely between the valence band and the conduction band. The conduction band is only partially filled. This means there are spaces for electrons to move into. When electrons for the valence band move into the conduction band they are free to move. This allows conduction.

What are the disadvantages of photodiodes?

Disadvantages of Photodiode 1. It is a temperature-dependent device. And shows poor temperature stability. 2. When low illumination is provided, then amplification is necessary.

Explain the energy diagram of a p-type semi-conductor?

Energy Band Diagram of p-Type Semiconductor The energy band diagram of a p-Type Semiconductor is shown below. A large number of holes or vacant space in the covalent bond is created in the crystal with the addition of the trivalent impurity. A small or minute quantity of free electrons is also available in the conduction band.

explain the energy diagram of n-type semi-conductor?

Energy Diagram of n-Type Semiconductor The Energy diagram of the n-type semiconductor is shown in the figure below. A large number of free electrons are available in the conduction band because of the addition of the Pentavalent impurity. These electrons are free electrons which did not fit in the covalent bonds of the crystal. However, a minute quantity of free electrons is available in the conduction band forming hole- electron pairs.

How does a basic pn junction semi conductor diode work at forward bias?

Forward Biased PN 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.

Explain the conduction and valence bands of an forward biased diode?

Forward biased diode A diode will only allow current to flow in one direction. In forward bias electrons in the conduction band of the n-type to move towards the conduction band of the p-type. Electrons drop from the conduction band to valence band of the p-type semiconductor. Energy is released due to the change in energy level causing a normal pn junction diode to heat up when conducting. Depending on the impurity and semiconductor used, the difference in energy level between conduction and valence bands can be large enough to emit the energy as a photon of light. This is a light emitting diode, or LED. Diodes can also be made so that the junction will absorb photons of light. A photon of light will cause an electron from the valence band of the p type to be promoted to the n type conduction band in the junction allowing the diode to generate an EMF. This is a photo diode or photo voltaic cell.

Explain the current/illumination curve of the photodiode?

From the above curve it can be seen that current proportionally increases with the luminous flux.

Explain the operation of a tunnel diode with a further increased voltage applied?

Further Increased Voltage Applied to the Tunnel Diode A further increase in the applied voltage will cause a slight misalignment of the conduction band and valence band. Still there will be an overlap between conduction band and valence band. The electrons move from conduction band to valence band of p region. Therefore, this causes small current to flow. Hence, tunnel current starts decreasing.

Explain the voltage/current characteristic of the photodiode?

Here, the vertical line represents the reverse current flowing through the device and the horizontal line represents the reverse-biased potential. The first curve represents the dark current that generates due to minority carriers in the absence of light. As we can see in the above figure that all the curve shows almost equal spacing in between them. This is so because current proportionally increases with the luminous flux. It is noteworthy here that, the reverse current does not show a significant increase with the increase in the reverse potential.

What is p-type semi conductor?

If the intrinsic semiconductor is doped with an electron acceptor in order to make it as a p-type semiconductor. The electron acceptor is responsible for the formation of a hole by accepting an electron from the lattice. As a result, majority carriers in the p-type semiconductor formed are holes. In this way, a p-type semiconductor is defined based on its electron acceptor capability.

Explain the valence, and conduction band in a semi conductor?

In a semiconductor, the gap between the valence band and conduction band is smaller. At room temperature there is sufficient energy available to move some electrons from the valence band into the conduction band. This allows some conduction to take place. An increase in temperature increases the conductivity of a semiconductor because more electrons will have enough energy to move into the conduction band.

Explain the diagram of a tunnel diode?

In a tunnel diode the p-type and n-type semiconductor is heavily doped so there is a greater number of impurities. Heavy doping results in a narrow depletion region. When compared to a normal p-n junction diode, tunnel diode has a narrow depletion width. Therefore, when small amount of voltage is applied, it produces enough electric current in the tunnel diode.

How is P-type silicon semi-conductor made?

In order to form a p-type semiconductor the basic step is to dope intrinsic semiconductor with trivalent impurity. In this type, the valence shell consists of three electrons requires further one more electron. This is possible by sharing the electron. As it is accepting electrons it is generally referred to as acceptor. The acceptor impurities are Boron, indium, gallium. Once these are added to either silicon or germanium p-type semiconductors are formed. Trivalent impurities such as boron or gallium are commonly used in silicon as doping impurity. Then silicon doped with boron or gallium is a perfect example for a p-type semiconductor. Whether silicon is doped with gallium or indium the process is also can be represented by utilizing the same concept of boron and silicon. Silicon Doped with Boron

Explain the diagram and characteristic curve of a basic pn junction semi conductor diode work at reverse bias?

Increase in the Depletion Layer due to Reverse Bias This condition represents a high resistance value to the PN junction and practically zero current flows through the junction diode with an increase in bias voltage. However, a very small leakage current does flow through the junction which can be measured in micro-amperes, ( μA ). One final point, if the reverse bias voltage Vr applied to the diode is increased to a sufficiently high enough value, it will cause the diode's PN junction to overheat and fail due to the avalanche effect around the junction. This may cause the diode to become shorted and will result in the flow of maximum circuit current, and this shown as a step downward slope in the reverse static characteristics curve below.

Explain the operation of a tunnel diode with an increased voltage applied?

Increased Voltage Applied to the Tunnel Diode When the amount of voltage applied is increased, the number of free electrons generated at n side and holes at p side is also increased. Due to voltage increase, overlapping between the bands are also increased. Maximum tunnel current flows when the energy level of n-side conduction band and the energy level of a p-side valence band becomes equal.

Explain the characteristic curve of a normal PN junction diode in forward bias?

Its from the "characteristics graph" seen above, conclusions can be made about the behavior of pn junction diode. The first thing that can be noticed is about "barrier potential". From the graph, it can be observed 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. 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).

Explain the operation of a tunnel diode with a largely increased voltage applied?

Largely Increased Voltage Applied to the Tunnel Diode The tunneling current will be zero when applied voltage is increased more to the maximum. At this voltage levels, the valence band and the conduction band does not overlap. This makes tunnel diode to operate same as a PN junction diode. When applied voltage is more than the built-in potential of the depletion layer the forward current starts flowing through the tunnel diode. In this condition, current portion in the curve decreases when the voltage increases and this is the negative resistance of tunnel diode. Such diodes operating in negative resistance region is used as amplifier or oscillator.

What is a n-type semi-conductor?

N-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material (e.g. phosphorus in silicon). This creates an excess of negative (n-type) electron charge carriers.

What is zener breakdown?

Normal diodes comprise a P-N junction that conducts in the forward direction, but blocks any reverse voltage applied across it. If this reverse voltage exceeds a certain value, the junction breaks down, usually failing permanently in the process. However, some devices, known as Zener diodes, exhibit a Zener effect; they can tolerate a reverse voltage, and start conducting reliably once this reaches a critical level, without ill effect.

what is an extrinsic semi-conductor?

Once the impurity is added to the semiconductor then its purity gets affected and also there is the increment in the charge carriers. These types of semiconductors are known as extrinsic semiconductors. Further, this is classified into two types' p-type and n-type. In these types, the numbers of electrons are more in n-type whereas the number of holes in p-type.

Explain the diagram and characteristic curve of a basic pn junction semi conductor diode work in forward bias?

Reduction in the Depletion Layer due to Forward Bias 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.

How does a basic pn junction semi conductor diode work at reverse bias?

Reverse Biased PN 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.

Explain the conduction and valence bands of an reverse biased diode?

Reverse biased diode In reverse bias the diode is connected with the p-type connected to the negative supply terminal and the n-type connected to the positive. The electric field across the depletion layer increases. This acts as a barrier that stops electron flow. The valence band energy level in the p-type material is raised above the free electrons of the conduction band of the n-type. This is due to the combination of doping and electric field across the junction.

What is reverse current?

Reverse current is the current through the diode in reverse bias conditions.

What is the zener effect?

The Zener effect is a type of electrical breakdown that occurs in a reverse-biased PN junction when the electric field enables tunneling of electrons from the valence to the conduction band of a semiconductor, leading to a large number of free minority carriers which suddenly increase the reverse current. The Zener effect is best-known for its use in the appropriately-named Zener diode.

How is the backward diode structured?

The construction of backward diode is similar to that of the tunnel diode. One side of the junction is lightly doped and another side of the junction is heavily doped. The characteristics so generated resembles the characteristics of the tunnel diode. The operation of the diode takes place in reverse biasing mode thus, it is called backward diode.

What is the structure of a backward diode?

The construction of backward diode is similar to that of the tunnel diode. One side of the junction is lightly doped and another side of the junction is heavily doped. The characteristics so generated resembles the characteristics of the tunnel diode. The operation of the diode takes place in reverse biasing mode thus, it is called backward diode.

What causes differences in the valence band of semi conductors?

The difference between insulators and semiconductors is due to a small amount of impurity added to a semiconductor which affects the energy bands. This process is called doping.

Explain the diagram and characteristic curve of a basic pn junction semi conductor diode work at zero bias?

The potential barrier that now exists discourages the diffusion of any more majority carriers across the junction. However, the potential barrier helps minority carriers (few free electrons in the P-region and few holes in the N-region) to drift across the junction. Then an "Equilibrium" or balance will be established when the majority carriers are equal and both moving in opposite directions, so that the net result is zero current flowing in the circuit. When this occurs the junction is said to be in a state of "Dynamic Equilibrium". The minority carriers are constantly generated due to thermal energy so this state of equilibrium can be broken by raising the temperature of the PN junction causing an increase in the generation of minority carriers, thereby resulting in an increase in leakage current but an electric current cannot flow since no circuit has been connected to the PN junction.

what is an intrinsic semi-conductor?

The semiconductor in its pure form is termed an intrinsic semiconductor. It is also related to its energy gaps for the silicon in its pure form the energy gap will be 1.1 electron volts and for germanium, it is 0.72 electron volts. In this type semiconductor at room temperature, the number of carriers and number of holes is equal to each other indicating the neutral condition.

How does a backward diode work?

The working principle of the backward diode is similar to that of the tunnel diode, the mechanism of quantum tunnelling plays a crucial role to conduct current in reverse biasing operation. The working of the backward diode can be understood in detail with the help of energy band diagram of the backward diode. The energy band of the semiconductor under no biased condition can be seen in the above diagram. The band which is at higher energy level is called conduction band and the band which is at lower energy level is called valence band. When external energy is supplied to electrons they attain the excited state of energy and enter conduction band. When electrons leave from valence band to conduction band they leave holes behind them in the valence band. Under the no-biased condition, the filled valence band is opposite to filled conduction band. But when reverse biasing is applied to the semiconductor the P-region moves up with respect to N-region. The filled band in P-side is just opposite to empty band at N-side. Thus, the electrons start tunnelling from the filled band in P-region to empty band in N-region. Thus, the current flows even in reversed biased condition. When forward biasing is applied, the N-side moves up with respect to P-side. Thus, the filled valence band of the N-type semiconductor will be just opposite to empty conduction band of P-type. Thus, the electrons flow from N-type to P-type. The Backward Diode is operated in a reverse biased mode. The negative resistance region is created and this region is utilized for the operation of the diode.

What is a tunnel diode?

Tunnel diode definition A Tunnel diode is a heavily doped p-n junction diode in which the electric current decreases as the voltage increases. In tunnel diodes, electric current is caused by "Tunneling". The tunnel diode is used as a very fast switching device in computers. It is also used in high-frequency oscillators and amplifiers.

What is the tunnel effect?

Tunneling Effect In electronics, Tunneling is known as a direct flow of electrons across the small depletion region from n-side conduction band into the p-side valence band. In a p-n junction diode, both positive and negative ions form the depletion region. Due to these ions, in-built electric potential or electric field is present in the depletion region. This electric field gives an electric force to the opposite direction of externally applied voltage. As the width of the depletion layer reduces, charge carriers can easily cross the junction. Charge carriers do not need any form of kinetic energy to move across the junction. Instead, carriers punch through junction. This effect is called Tunneling and hence the diode is called Tunnel Diode.

Explain the operation of an unbiased tunnel diode?

Unbiased Tunnel Diode In an unbiased tunnel diode, no voltage will be applied to the tunnel diode. Here, due to heavy doping conduction band of n - type semiconductor overlaps with valence band of p - type material. Electrons from n side and holes from p side overlap with each other and they will be at same energy level. Some electrons tunnel from the conduction band of n-region to the valence band of p-region when temperature increases. Similarly, holes will move from valence band of p-region to the conduction band of n-region. Finally, the net current will be zero since equal numbers of electrons are holes flow in opposite direction.

Explain the current/voltage characteristic of the tunnel diode?

V-I Characteristics of Tunnel Diode Due to forward biasing, because of heavy doping conduction happens in the diode. The maximum current that a diode reaches is Ip and voltage applied is Vp. The current value decreases, when more amount of voltage is applied. Current keeps decreasing until it reaches a minimal value. The small minimal value of current is Iv. From the above graph, it is seen that from point A to B current reduces when voltage increases. That is the negative resistance region of diode. In this region, tunnel diode produces power instead of absorbing it.

What is a varactor diode?

Varactor diode The term varactor is originated from a variable capacitor. Varactor diode operates only in reverse bias.The varactor diode acts like a variable capacitor under reverse bias. Varactor diode is also sometimes referred to as varicap diode, tuning diode, variable reactance diode, or variable capacitance diode.

What is reverse breakdown voltage?

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.

What is a zener diode?

What is Zener Diode? Working Principle of Zener Diode Zener diode is basically like an ordinary PN junction diode but normally operated in reverse biased condition. But ordinary PN junction diode connected in reverse biased condition is not used as Zener diode practically. A Zener diode is a specially designed, highly doped PN junction diode.

how is n type semi conductor made?

When a small amount of Pentavalent impurity is added to a pure semiconductor providing a large number of free electrons in it, the extrinsic semiconductor thus formed is known as n-Type Semiconductor. The conduction in the n-type semiconductor is because of the free electrons denoted by the pentavalent impurity atoms. These electrons are the excess free electrons with regards to the number of free electrons required to fill the covalent bonds in the semiconductors. The addition of Pentavalent impurities such as arsenic and antimony provides a large number of free electrons in the semiconductor crystal. Such impurities which produce n-type semiconductors are known as Donor Impurities. They are called a donor impurity because each atom of them donates one free electron crystal. When a few Pentavalent impurities such as Arsenic whose atomic number is 33, which is categorised as 2, 8, 15 and 5. It has five valence electrons, which is added to germanium crystal. Each atom of the impurity fits in four germanium atoms as shown in the figure above. Hence, each Arsenic atom provides one free electron in the Germanium crystal. Since an extremely small amount of arsenic, impurity has a large number of atoms; it provides millions of free electrons for conduction.

Explain the operation of a tunnel diode with a small voltage applied?

When a small voltage, that has lesser value than the built-in voltage of the depletion layer, is applied to the tunnel diode, there is no flow of forward current through the junction. Nevertheless, a minimal number of electrons from the conduction band of n region will start tunneling to valence band in p region. Therefore, this movement creates a small forward biased tunnel current. When a small voltage is applied, tunnel current starts to flow.

What is special about the width of the depletion region in the tunnel diode?

Width of the Depletion Region in Tunnel Diode When mobile charge carriers both free electrons and holes are missing, the region in a p-n junction has a region called Depletion region. To stop the flow of electrons from the n-type semiconductor and holes from the p-type semiconductor, depletion region acts as a barrier. Depending on the number of impurities added, width of depletion region varies. To increase electrical conductivity of the p-type and n-type semiconductor impurities are added. A wide and big depletion region is formed when a smaller number of impurities is added to p-n junction diode. At the same time, when a greater number of impurities is added, narrow depletion region occurs.

What are zener diodes used for?

Zener diode applications Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits.

What are some common zener diode specifications?9

Zener diode specifications 1. zener diodes vary in specifications such as nominal working voltage, power dissipation, maximum reverse current, and packaging. Some commonly used specifications include: 2. Voltage Vz: The Zener voltage refers to the reverse breakdown voltage—2.4 V to about 200 V; can go up to 1 kV while the maximum for the surface-mounted device (SMD) is about 47 V). 3. Current Iz (max.): Maximum current at the rated Zener voltage Vz—200 uA to 200 A). 4. Current Iz (min.): Minimum current required for the diode to break down—5 mA and 10 mA. 5. Power rating: The maximum power the Zener diode can dissipate; given by the product of voltage across the diode and the current flowing through. Typical values are 400 mW, 500 mW, 1 W, and 5 W; for surface mounted, 200 mW, 350 mW, 500 mW, and 1 W are typical. 6. Voltage tolerance: Typically ±5%. 7. Temperature stability: Diodes around 5 V have the best stability. 8. Package: Leaded devices and the surface mount either as discrete devices or within integrated circuits. 9. Zener resistance (Rz): The diode exhibits some resistance as evident from the IV characteristics.

how does a zener diode work?

Zener diodes are operated in reverse biased conditions, and this diode does not get damaged even when the voltage across this exceeds the reverse breakdown voltage. Let us learn about this exciting and unique kind of diode. Zener diodes are heavily doped than ordinary diodes. They have extra thin depletion region. When we apply a voltage more than the Zener breakdown voltage (can range from 1.2 volts to 200 volts), the depletion region vanishes, and large current starts to flow through the junction. There is a crucial difference between an ordinary diode and a Zener diode. The depletion region regains its original position after removal of the reverse voltage in Zener diode whereas in regular diodes, they don't, and hence they get destroyed.

How does a basic pn junction semi conductor diode work at zero bias?

Zero Biased Junction Diode When a diode is connected in a Zero Bias condition, no external potential energy is applied to the PN junction. However if the diodes terminals are shorted together, a few holes (majority carriers) in the P-type material with enough energy to overcome the potential barrier will move across the junction against this barrier potential. This is known as the "Forward Current" and is referenced as IF Likewise, holes generated in the N-type material (minority carriers), find this situation favourable and move across the junction in the opposite direction. This is known as the "Reverse Current" and is referenced as IR. This transfer of electrons and holes back and forth across the PN junction is known as diffusion, as shown below.