PDF | Electronic devices are components for controlling the flow of electrical currents for the purpose of information processing and system. Semiconductor Diode and. Its Applications. Objectives. After studying this unit you should be able to: • Explain how barrier potential is set up in a p-n junction. Semiconductors & Diodes. Jaesung Jang. Semiconductors. PN Junction. Rectifier Diodes. DC Power Supply. Ref: Sedra/Smith, Microelectronic Circuits, 3rd ed.
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SEMICONDUCTORS MODULE 2 PDF. 2. © E. COATES Diodes are made from semiconductor materials, mainly silicon, with various compounds. Chapter1: Semiconductor. Diode. Electronics I Discussion. smeltitherabpigs.ml Salah The semiconductor diode is formed by doping P-type impurity in one side and. Small-Signal Diodes. Diode: a semiconductor device, which conduct the current in one direction only. Two terminals: anode and cathode. When the positive.
Therefore, a complete connection is not possible, giving the semiconductor material an abundance of positively charged carriers known as holes in the structure of the crystal where electrons are effectively missing. As there is now a hole in the silicon crystal, a neighbouring electron is attracted to it and will try to move into the hole to fill it. However, the electron filling the hole leaves another hole behind it as it moves. This in turn attracts another electron which in turn creates another hole behind it, and so forth giving the appearance that the holes are moving as a positive charge through the crystal structure conventional current flow.
This movement of holes results in a shortage of electrons in the silicon turning the entire doped crystal into a positive pole. Boron symbol B is commonly used as a trivalent additive as it has only five electrons arranged in three shells around its nucleus with the outermost orbital having only three electrons.
Then a semiconductor basics material is classed as P-type when its acceptor density is greater than its donor density. Therefore, a P-type semiconductor has more holes than electrons. Boron Atom and Doping The diagram above shows the structure and lattice of the acceptor impurity atom Boron. Semiconductor Summary N-type e. The Donors are positively charged. There are a large number of free electrons. A small number of holes in relation to the number of free electrons. Doping gives: o positively charged donors.
Supply of energy gives: o negatively charged free electrons. P-type e.
The Acceptors are negatively charged. There are a large number of holes. A small number of free electrons in relation to the number of holes. Doping gives: o negatively charged acceptors. Supply of energy gives: o positively charged holes.
Antimony Sb and Boron B are two of the most commonly used doping agents as they are more feely available compared to other types of materials. However, the periodic table groups together a number of other different chemical elements all with either three, or five electrons in their outermost orbital shell making them suitable as a doping material. These other chemical elements can also be used as doping agents to a base material of either Silicon S or Germanium Ge to produce different types of basic semiconductor materials for use in electronic semiconductor components, microprocessor and solar cell applications.
These additional semiconductor materials are given below. 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 potential barrier.
The effect of adding this additional energy source results in the free electrons being able to cross the depletion region from one side to the other. A PN Junction Diode is one of the simplest Semiconductor Devices around, and which has the characteristic of passing current in only one direction only.
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.
Journal of the Optical Society of America B
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 firstlybias the junction, ie connect a voltage potential across it.
Zero Bias — No external voltage potential is applied to the PN junction diode. 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 transfer of electrons and holes back and forth across the R PN junction is known as diffusion, as shown below. Zero Biased PN Junction Diode 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.
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.
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.
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. 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.
Reverse Characteristics Curve for a Junction Diode Sometimes this avalanche effect has practical applications in voltage stabilising circuits where a series limiting resistor is used with the diode to limit this reverse breakdown current to a preset maximum value thereby producing a fixed voltage output across the diode.
These types of diodes are commonly known as Zener Diodes and are discussed in a later tutorial. 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.
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. Forward Characteristics Curve for a Junction Diode 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.
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.
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. Either way we can model these D D current-voltage characteristics for both an ideal diode and for a real diode.
Junction Diode Ideal and Real Characteristics In the next tutorial about diodes, we will look at the small signal diode sometimes called a switching diode which is used in general electronic circuits. As its name implies, the signal diode is designed for low-voltage or high frequency signal applications such as in radio or digital switching circuits.
Signal diodes, such as the 1N only pass very small electrical currents as opposed to the high-current mains rectification diodes in which silicon diodes are usually used. Also in the next tutorial we will examine the Signal Diode static current-voltage characteristics curve and parameters. The Zener diode is like a general-purpose signal diode consisting of a silicon PN junction.
When biased in the forward direction it behaves just like a normal signal diode passing the rated current, but as soon as a reverse voltage applied across the Zener Diode exceeds the rated voltage of the device, the diodes breakdown voltage is reached at which point a process called Avalanche Breakdown occurs in the semiconductor depletion layer and a current starts to flow through the diode to limit this increase in voltage. The current now flowing through the zener diode increases dramatically to the maximum circuit value which is usually limited by a series resistor and once achieved this reverse saturation current remains fairly constant over a wide range of applied voltages.
This zener breakdown voltage on the I-V curve is almost a vertical straight line. From the I-V characteristics curve above, we can see that the zener diode has a region in its reverse bias characteristics of almost a constant negative voltage regardless of the value of the current flowing through the diode and remains nearly constant even with large changes in current as long as the zener diodes current remains between the breakdown currentIZ min and the maximum current rating IZ max.
This ability to control itself can be used to great effect to regulate or stabilise a voltage source against supply or load variations. The fact that the voltage across the diode in the breakdown region is almost constant turns out to be an important application of the zener diode as a voltage regulator. The function of a regulator is to provide a constant output voltage to a load connected in parallel with it in spite of the ripples in the supply voltage or the variation in the load current and the zener diode will continue to regulate the voltage until the diodes current falls below the minimum IZ min value in the reverse breakdown region.
The Zener Diode Regulator Zener Diodes can be used to produce a stabilised voltage output with low ripple under varying load current conditions. By passing a small current through the diode from a voltage source, via a suitable current limiting resistor RS , the zener diode will conduct sufficient current to maintain a voltage drop of Vout.
We remember from the previous tutorials that the DC output voltage from the half or full-wave rectifiers contains ripple superimposed onto the DC voltage and that as the load value changes so to does the average output voltage. By connecting a simple zener stabiliser circuit as shown below across the output of the rectifier, a more stable output voltage can be produced.
Zener Diode Regulator The resistor, RS is connected in series with the zener diode to limit the current flow through the diode with the voltage source, VS being connected across the combination.
The stabilised output voltageVout is taken from across the zener diode. The zener diode is connected with its cathode terminal connected to the positive rail of the DC supply so it is reverse biased and will be operating in its breakdown condition.
Resistor RS is selected so to limit the maximum current flowing in the circuit.
ELECTRONIC DEVICES AND CIRCUITS
There is a minimum zener current for which the stabilization of the voltage is effective and the zener current must stay above this value operating under load within its breakdown region at all times. The upper limit of current is of course dependant upon the power rating of the device. The supply voltage VS must be greater than VZ.
One small problem with zener diode stabiliser circuits is that the diode can sometimes generate electrical noise on top of the DC supply as it tries to stabilise the voltage. Then to summarise a little.
A zener diode is always operated in its reverse biased condition. A voltage regulator circuit can be designed using a zener diode to maintain a constant DC output voltage across the load in spite of variations in the input voltage or changes in the load current. The zener voltage regulator consists of a current limiting resistor RS connected in series with the input voltage VS with the zener diode connected in parallel with the load RL in this reverse biased condition. The stabilized output voltage is always selected to be the same as the breakdown voltage VZ of the diode.
Zener Diode Example No1 A 5. The maximum power rating PZ of the zener diode is 2W. Using the zener regulator circuit above calculate: a.
The maximum current flowing through the zener diode. The minimum value of the series resistor, RS c.
The zener current IZ at full load. Zener Diode Voltages As well as producing a single stabilised voltage output, zener diodes can also be connected together in series along with normal silicon signal diodes to produce a variety of different reference voltage output values as shown below. Zener Diodes Connected in Series The values of the individual Zener diodes can be chosen to suit the application while the silicon diode will always drop about 0.
The supply voltage, Vin must of course be higher than the largest output reference voltage and in our example above this is 19v. A typical zener diode for general electronic circuits is the mW, BZX55 series or the larger 1. The mW series of zener diodes are available from about 2. Diode clipping and clamping circuits are circuits that are used to shape or modify an input AC waveform or any sinusoid producing a differently shape output waveform depending on the circuit arrangement.
Diode clipper circuits are also called limiters because they limit or clip-off the positive or negative part of an input AC signal. As zener clipper circuits limit or cut-off part of the waveform across them, they are mainly used for circuit protection or in waveform shaping circuits.
If the output waveform tries to exceed the 7. Note that in the forward bias condition a zener diode is still a diode and when the AC waveform output goes negative below In other words a peak-to-peak voltage of This type of clipper configuration is fairly common for protecting an electronic circuit from over voltage.
In the next tutorial about diodes, we will look at using the forward biased PN junction of a diode to produce light. We know from the previous tutorials that when charge carriers move across the junction, electrons combine with holes and energy is lost in the form of heat, but also some of this energy is dissipated as photons but we can not see them. If we place a translucent lens around the junction, visible light will be produced and the diode becomes a light source.
This effect produces another type of diode known commonly as the Light Emitting Diode which takes advantage of this light producing characteristic to emit light photons in a variety of colours and wavelengths. Diode Clipping Circuits The Diode Clipper, also known as a Diode Limiter, is a wave shaping circuit that takes an input waveform and clips or cuts off its top half, bottom half or both halves together to produce an output waveform that resembles a flattened version of the input.
For example, the half-wave rectifier is a clipper circuit, since all voltages below zero are eliminated. But Diode Clipping Circuits can be used a variety of applications to modify an input waveform using signal and Schottky diodes or to provide over-voltage protection using Zener Diodes to ensure that the output voltage never exceeds a certain level protecting the circuit from high voltage spikes.
Then diode clipping circuits can be used in voltage limiting applications. We saw in the Signal Diodes tutorial that when a diode is forward biased it allows current to pass through itself clamping the voltage. When the diode is reverse biased, no current flows through it and the voltage across its terminals is unaffected, and this is the basic operation of the diode clipping circuit.
Although the input voltage to diode clipping circuits can have any waveform shape, we will assume here that the input voltage is sinusoidal. Consider the circuits below. Positive Diode Clipping Circuits In this diode clipping circuit, the diode is forward biased anode more positive than cathode during the positive half cycle of the sinusoidal input waveform.
When this happens the diodes begins to conduct and holds the voltage across itself constant at 0. Thus the output voltage which is taken across the diode can never exceed 0.
During the negative half cycle, the diode is reverse biased cathode more positive than anode blocking current flow through itself and as a result has no effect on the negative half of the sinusoidal voltage which passes to the load unaltered. Then the diode limits the positive half of the input waveform and is known as a positive clipper circuit.
Negative Diode Clipping Circuits Here the reverse is true. The diode is forward biased during the negative half cycle of the sinusoidal waveform and limits or clips it to As the diode limits the negative half cycle of the input voltage it is therefore called a negative clipper circuit. Clipping of Both Half Cycles If we connected two diodes in inverse parallel as shown, then both the positive and negative half cycles would be clipped as diode D1 clips the positive half cycle of the sinusoidal input waveform while diode D2 clips the negative half cycle.
Then diode clipping circuits can be used to clip the positive half cycle, the negative half cycle or both. For ideal diodes the output waveform above would be zero. Biased Diode Clipping Circuits To produce diode clipping circuits for voltage waveforms at different levels, a bias voltage, VBIAS is added in series with the diode as shown.
Any anode voltage levels above this bias point are clipped off. Positive Bias Diode Clipping Likewise, by reversing the diode and the battery bias voltage, when a diode conducts the negative half cycle of the output waveform is held to a level -VBIAS - 0. Negative Bias Diode Clipping A variable diode clipping or diode limiting level can be achieved by varying the bias voltage of the diodes.
If both the positive and the negative half cycles are to be clipped, then two biased clipping diodes are used. But for both positive and negative diode clipping, the bias voltage need not be the same. The positive bias voltage could be at one level, for example 4 volts, and the negative bias voltage at another, for example 6 volts as shown. Diode D2 does not conduct until the voltage reaches —6. The function of the diode is regulating the voltage at a particular current.
It functions as a two terminal current limiter. In this JFET acts as current limiter to achieve high output impedance. The constant current diode symbol is shown below.
semiconductor diode characteristics .pdf - Electronics...
In this type of diode the junction is formed by contacting the semiconductor material with metal. Due to this the forward voltage drop is decreased to min. The semiconductor material is N-type silicon which acts as an anode and the metal acts as a cathode whose materials are chromium, platinum, tungsten etc. Due to the metal junction these diodes have high current conducting capability thus the switching time reduces. So, Schottky has greater use in switching applications.
Mainly because of the metal- semiconductor junction the voltage drop is low which in turn increase the diode performance and reduces power loss. So, these are used in high frequency rectifier applications. The symbol of Schottky diode is as shown below.
It was the invention of first semiconductor devices it has four layers. It is equal to a thyristor without a gate terminal which means the gate terminal is disconnected. As there is no trigger inputs the only way the diode can conduct is by providing forward voltage. The diode has two operating states conducting and non-conducting. In non-conducting state the diode conducts with less voltage. It is also called as snap-off diode or charge-storage diode.
These are the special type of diodes which stores the charge from positive pulse and uses in the negative pulse of the sinusoidal signals. The rise time of the current pulse is equal to the snap time. Due to this phenomenon it has speed recovery pulses. The applications of these diodes are in higher order multipliers and in pulse shaper circuits.
The cut-off frequency of these diodes is very high which are nearly at Giga hertz order. As multiplier this diode has the cut-off frequency range of to GHz.
In the operations which are performing at 10 GHz range these diodes plays a vital role. The efficiency is high for lower order multipliers. The symbol for this diode is as shown below. It is used as high speed switch, of order nano-seconds. Due to tunneling effect it has very fast operation in microwave frequency region.
It is a two terminal device in which concentration of dopants is too high. The transient response is being limited by junction capacitance plus stray wiring capacitance. Mostly used in microwave oscillators and amplifiers. It acts as most negative conductance device. Tunnel diodes can be tuned in both mechanically and electrically. The symbol of tunnel diode is as shown below. These are also known as Varicap diodes. It acts like the variable capacitor. Operations are performed mainly at reverse bias state only.
These diodes are very famous due to its capability of changing the capacitance ranges within the circuit in the presence of constant voltage flow.
They can able to vary capacitance up to high values. In varactor diode by changing the reverse bias voltage we can decrease or increase the depletion layer. These diodes have many applications as voltage controlled oscillator for cell phones, satellite pre-filters etc. The symbol of varactor diode is given below. Similar to LED in which active region is formed by p-n junction. Electrically laser diode is p-i-n diode in which the active region is in intrinsic region.
In semiconductor devices due to the sudden change in the state voltage transients will occur. They will damage the device output response. To overcome this problem voltage suppression diode diodes are used.
1. Semiconductor Diode.pdf
The operation of voltage suppression diode is similar to Zener diode operation. The operation of these diodes is normal as p-n junction diodes but at the time of transient voltage its operation changes. In normal condition the impedance of the diode is high. When any transient voltage occurs in the circuit the diode enters in to the avalanche breakdown region in which the low impedance is provided.
It is spontaneously very fast because the avalanche breakdown duration ranges in Pico seconds. Transient voltage suppression diode will clamp the voltage to the fixed levels, mostly its clamping voltage is in minimum range. These are having applications in the telecommunication fields, medical, microprocessors and signal processing.
It responds to over voltages faster than varistors or gas discharge tubes. The symbol for Transient voltage suppression diode is as shown below. In these diodes gold is used as a dopant. These diodes are faster than other diodes. In these diodes the leakage current in reverse bias condition also less. Even at the higher voltage drop it allows the diode to operate in signal frequencies.
In these diodes gold helps for the faster recombination of minority carriers. It is a rectifier diode having low forward voltage drop as schottky diode with surge handling capability and low reverse leakage current as p-n junction diode. It was designed for high power, fast switching and low-loss applications.
Super barrier rectifiers are the next generation rectifiers with low forward voltage than schottky diode. In this type of diode, at the two material junction of a semiconductor it generates a heat which flows from one terminal to another terminal. This flow is done in only single direction that is as equal to the direction of current flow.
This heat is produced due to electric charge produced by the recombination of minority charge carriers. This is mainly used in cooling and heating applications. This type of diodes used as sensor and heat engine for thermo electric cooling.
Its operation depends on the pressure of contact between semiconductor crystal and point. In this a metal wire is present which is pressed against the semiconductor crystal. In this the semiconductor crystal acts as cathode and metal wire acts as anode.
These diodes are obsolete in nature. Mainly used in microwave receivers and detectors. This is passive element works under principle of avalanche breakdown. It works in reverse bias condition. It results large currents due to the ionisation produced by p-n junction during reverse bias condition. These diodes are specially designed to undergo breakdown at specific reverse voltage to prevent the damage.
The symbol of the avalanche diode is as shown below: It consists of three terminals they are anode, cathode and a gate.The total current as a function of applied voltage for a P-N junction diode is given by: Most diodes have a 1-prefix designation e. Doping gives: o negatively charged acceptors. This is called the reverse bias phenomenon. The boundary between these two regions, called a p—n junction , is where the action of the diode takes place.
However the flow of minority charge carriers remains uninfluenced by the increased barrier potential.