SEMICONDUCTOR DIODE PDF
SEMICONDUCTORS MODULE 2 PDF. 2. © E. COATES Diodes are made from semiconductor materials, mainly silicon, with various compounds. Chapter1: Semiconductor. Diode. Electronics I Discussion. cittadelmonte.info 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.
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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.
A diode is a two- terminal electronic component that conducts current primarily in one direction asymmetric conductance ; it has low ideally zero resistance in one direction, and high ideally infinite resistance in the other. A diode vacuum tube or thermionic diode is a vacuum tube with two electrodes , a heated cathode and a plate , in which electrons can flow in only one direction, from cathode to plate. A semiconductor diode , the most common type today, is a crystalline piece of semiconductor material with a p—n junction connected to two electrical terminals. The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in Today, most diodes are made of silicon , but other materials such as gallium arsenide and germanium are used.
Any point on the V-I characteristics of the diode, the static resistance is equal to reciprocal of the slope of a line joining the operating point to the origin. The static resistance varies with V and I and is not a useful parameter.
Dynamic resistance: It is defined as the reciprocal of slope of the V-I characteristics of a diode. Law of Junction: This law states that for a forward biased P-N junction diode, the injected hole concentration at the junction increases over thermal equilibrium value.
Diode current equation: Let us derive the expression for the total current as a function of applied voltage assuming that the width of the depletion region is zero. When a forward bias is applied to a P-N junction diode, holes are injected from the P side to N side. Due to this, the concentration of holes in the N side. Substitute this value in equation 2 3 The diffusion hole current in the N side is given by:. The general equation of the P-N junction diode current equation is given by: Temperature dependence of V-I characteristics: Electron hole pairs are generated in semiconductors whenever temperature increases as a result conductivity increases.
Thus, current passing through the diode increases with temperature as given by the diode current equation. The reverse saturation current increases with temperature according to the following equation. Reverse saturation current of the diode at temperature Reverse saturation current of the diode at temperature. Volt-Ampere Characteristics of P-N junction diode: The total current as a function of applied voltage for a P-N junction diode is given by:. The diode is forward biased if V is positive indicating that the P side of the junction is positive with respect to N side.
The symbol is unity for Ge and 2 for Si. The symbol stands for volt equivalent of temperature and is given by:. The V-I characteristics of P-N junction diode is shown below.
When diode is reverse biased, V is negative. In forward biased characteristics, up to some applied voltage, the current passing through P-N junction diode is almost zero. The voltage up to which no current passing through the diode is called Cut-in voltage and is denoted by. In reverse biased characteristics, up to some applied voltage, the current passing through p-N junction diode is almost constant.
Beyond PIV, the junction breaks and enormous current passing through the diode. Explain Transition capacitance and Diffusion capacitances. In the p-n semiconductor diode, there are two capacitive effects to be considered.
In the reverse bias region we have the transition- or depletion-region capacitance CT , while in the forward bias region we have the diffusion CD or storage capacitance. In the reverse bias region there is a depletion region free of carriers that behaves essentially like an insulator between the layers of opposite charge. Since the depletion width d will increase with increased reverse-bias potential, the resulting transition capacitance will decrease.
The fact that the capacitance is dependent on the applied reverse-bias potential has application in a number of electronic systems. The capacitive effects described above are represented by a capacitor in parallel with the ideal diode, as shown below. Temperature effects on p-n diode Exp Q.
Explain temperature effects on p-n diode characteristics Temperature can have a marked effect on the characteristics of a silicon semiconductor diode. It has been found experimentally that the reverse saturation current Io will just about double in magnitude for every 10C increase in temperature.
Typical values of Io for silicon are much lower than that of germanium for similar power and current levels. The result is that even at high temperatures the levels of Io for silicon diodes do not reach the same high levels obtained for germanium.
As the temperature increases the forward characteristics are actually becoming more ideal. Zener Diode Exp Q. Explain break down mechanisms in semiconductor diodes Zener diode is a reverse biased heavily doped whose doping concentration is one part of impurity is added to every parts of pure semiconductor material P-N junction diode.
Zener Diode operates in the breakdown region.
Types of Diodes
When a Zener Diode is operated in forword biased, its characteristics are same as that of ordinary P-N junction diode. Following are two mechanisms of Zener breakdown. Zener breakdown generally occur in very thin junctions i. When a small reverse bias is applied, a very strong electric field is set up across the junction.
This field is enough to break the covalent bonds. Now large number of free electrons and holes are produced which constitute the reverse saturation current. This type of breakdown occurs when both sides of junction are lightly doped and resultant the depletion layer is large. In this case, the electric field across the junction is not so strong to produce Zener breakdown.
In this case, free electrons acquire sufficient energy from applied potential and collide with the semiconductor atoms in the depletion region. Due to the collision with valance electrons, covalent bonds are broken and electron hole pairs are generated. These new charge carriers again acquire sufficient energy from the applied potential and collide with semiconductor atoms.
In turn produce additional charge carriers. This forms cumulative process called an avalanche multiplication. The breakdown is called avalanche breakdown. In general, at reverse voltages less than 6 volts, Zener breakdown occurs while greater 6 volts, Avalanche breakdown occurs. When the breakdown voltage is reached in Zener diode, the current increases rapidly with small change in voltage. The V-I characteristics of Zener Diode is shown below.
The complete equivalent circuit of the Zener diode in the Zener region includes a small dynamic resistance and dc battery equal to the Zener potential. Tunnel Diode: A Tunnel diode also called Esaki diode is a heavily heavily doped P-N junction diode whose doping concentration is one part in In the case of lightly doped P-N junction diode, the Fermi level lies inside the forbidden energy gap.
But in the case of heavily heavily doped P-N junction diode, the Fermi level lies outside forbidden energy gap. In heavily heavily doped n type material, the Fermi level lies in the conduction band.
In heavily heavily doped P type semiconductor, the Fermi level lies in the valence band. Under open circuit conditions, the energy band diagram of a heavily heavily doped P-N junction diode is shown in the following figure a.
The Fermi level in the P side is at same energy as the Fermi level in the N side. Above the Fermi level in the valence band in P side indicates completely filled with holes.
Below the Fermi level in the conduction band in N side indicates completely filled with free electrons. Reverse Biased Condition: Let us consider that the P type semiconductor is grounded and that a voltage applied across a diode shift the N side with respect to the P side. If a reverse bias voltage is applied across the tunnel diode, the height of barrier is increased above its open circuit value. Hence, electrons will tunnel from the P side to the N side, giving rise to a reverse diode current.
As the magnitude of the reverse bias increases, the reverse current also increases as shown in the following figure c. Forward Bias Condition: If a forward bias voltage is applied across a tunnel diode, the height of barrier is decreased below its open circuit value. Resultant, electrons will tunnel from the N side to the P side, giving rise to a forward diode current as shown below figure C. As the forward bias is increased further, the condition is shown in the following figure E.
Now maximum number of electrons will tunnel from the N side to the P side, giving rise to the peak current. Now number of electrons will tunnel from the N side to the P side decreases. Resultant, the tunnelling current decreases as shown in the following figure C. On further increasing forward bias voltage, the condition.
Now electrons will not tunnel from the N side to the P side, giving rise to zero current as shown in the following figure C. The solid curve gives the tunnelling current which is shown in the following figure C. But in addition to this, the P-N junction diode current also flows and is shown by dotted lines in the following figure c0. The sum these two currents is the tunnel diode current which is shown in the following figure H.
The symbol for tunnel diode is shown in the following figure I. EDC unit-1 semiconductor diode. Flag for inappropriate content. Related titles. Electronic devices and circuits By Salivahanan. ECE High Resolution.
Jump to Page. Search inside document. Explain PN diode characteristics in forward bias and reverse bias regions The P-N junction diode permits the easy flow of current in one direction but restricts the flow current in the opposite direction.
The current passing through a P-N junction diode is given by: The symbol for volt equivalent of temperature and is given by: It is equal to 0. There are two minority currents current in N side and as indicated in the following figure. Consequently in the P side, there must be a second component of current which combining with gives the total current I. Similarly the electron current in the N side is given by: For away from the junction in P side, the current is a drift current of holes.
As the holes approaching the junction, some of them recombine with electrons which are injected in to the P side from N side. Thus the current decreases towards the junction.
Diode - Wikipedia
The rate of decrease is such that the total current remains constant independent of distance. Hence in a forward biased P-N junction diode, the current enters in to the P side as a hole current and leaves from the N side as an electron current of the same magnitude. Explain static resistance and dynamic resistance DC or Static Resistance: This boundary condition is the law of junction. It is given by: Due to this, the concentration of holes in the N side is increased to thermal equilibrium hole concentration in N side plus injected hole concentration in N side [ ].
At the junction i. But according to law of junction Substitute this value in equation 2 3 The diffusion hole current in the N side is given by: Hence, the temperature increased at constant voltage, current I increases. Where Reverse saturation current of the diode at temperature Reverse saturation current of the diode at temperature Volt-Ampere Characteristics of P-N junction diode: The total current as a function of applied voltage for a P-N junction diode is given by: The symbol stands for volt equivalent of temperature and is given by: The voltage up to which no current passing through the diode is called Cut-in voltage and is denoted by is approximately equal to 0.
Explain Transition capacitance and Diffusion capacitances In the p-n semiconductor diode, there are two capacitive effects to be considered.
Hence N side levels must shift downward with respect to the P side levels as shown in the following figure b.
Hence N side levels must shift upward with respect to the P side levels as shown in the following figure D. Now maximum number of electrons will tunnel from the N side to the P side, giving rise to the peak current as shown in the following figure C.
If still more forward bias voltage is applied, the condition is shown in the following figure F. Syuk Syfar. Pradeep Kumar Sahu. Sakthhi Lakshmi.
Thomas Neumann. Vijayakumar S. Rodolfo Lucena. Http s3. Mohammed UD. Mashgol Karim. Saravana Karthikeyan. More From SaiKrishna. Popular in Electric Current. 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.
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. It is nearly equal to the Shockley diode. As its name indicates it is mainly used for the control purpose when small voltages are applied in the circuit. The symbol of the Silicon Controlled Rectifier is as shown below: Vacuum diodes consist of two electrodes which will acts as an anode and the cathode.
Cathode is made up of tungsten which emits the electrons in the direction of anode. Always electron flow will be from cathode to anode only.
EDC unit-1(semiconductor diode).pdf
So, it acts like a switch. If the cathode is coated with oxide material then the electrons emission capability is high. Anode is a bit long in size and in some cases their surface is rough to reduce the temperatures developing in the diode.
The diode will conduct in only one case that is when the anode is positive regarding to cathode terminal. The symbol is as shown in figure: In PIN diode doping is not necessary. The intrinsic material means the material which has no charge carriers is inserted between the P and N regions which increase the area of depletion layer.
When we apply forward bias voltage the holes and electrons will pushed into the intrinsic layer. At some point due to this high injection level the electric field will conduct through the intrinsic material also. This field made the carriers to flow from two regions. The symbol of PIN diode is as shown below: A gold or tungsten wire is used to act as the point contact to produce a PN junction region by passing a high electric current through it.
A small region of PN junction is produced around the edge of the wire which is connected to the metal plate which is as shown in the figure. In forward direction its operation is quite similar but in reverse bias condition the wire acts like an insulator. Since this insulator is between the plates the diode acts as a capacitor. In general the capacitor blocks the DC currents when the AC currents are flowing in the circuit at high frequencies.
So, these are used to detect the high frequency signals. Gunn diode is fabricated with n-type semiconductor material only. The depletion region of two N-type materials is very thin. When voltage increases in the circuit the current also increases. After certain level of voltage the current will exponentially decrease thus this exhibits the negative differential resistance. It has two electrodes with Gallium Arsenide and Indium Phosphide due to these it has negative differential resistance.
It is also termed as transferred electron device. It can also use as an amplifier. The symbol of Gunn diode is shown below: It is very very important information to learn about different types of semiconductors…….