PN JUNCTION DIODE CONSTRUCTION AND VI CHARACTERISTICS

PN DIODE CHARACTERISTICS

1. EC 8351 Electronic Devices And Circuits

2. Syllabus UNIT I PN JUNCTION DEVICES PN junction diode –structure, operation and V-I characteristics, diffusion and transient capacitance - Rectifiers – Half Wave and Full Wave Rectifier,– Display devices- LED, Laser diodes- Zener diode characteristics- Zener Reverse characteristics – Zener as regulator UNIT II TRANSISTORS BJT, JFET, MOSFET- structure, operation, characteristics and Biasing UJT, Thyristor and IGBT - Structure and characteristics.

3. UNIT III AMPLIFIERS BJT small signal model – Analysis of CE, CB, CC amplifiers- Gain and frequency response – MOSFET small signal model– Analysis of CS and Source follower – Gain and frequency response- High frequency analysis . UNIT IV MULTISTAGE AMPLIFIERS AND DIFFERENTIAL AMPLIFIER BIMOS cascade amplifier, Differential amplifier – Common mode and Difference mode analysis – FET input stages – Single tuned amplifiers – Gain and frequency response – Neutralization methods, power amplifiers –Types (Qualitative analysis). UNIT V FEEDBACK AMPLIFIERS AND OSCILLATORS Advantages of negative feedback – voltage / current, series , Shunt feedback –positive feedback – Condition for oscillations, phase shift – Wien bridge, Hartley, Colpitts and Crystal oscillators.

4. Need of Electronics Electronics  is an applied form of science that deals with electrons. It handles electric circuits containing  active elements, passive elements and other underlying techniques making it as an important part of engineering. The world is growing at a fast rate and it is relevant for the technology enthusiast to upgrade with latest changes happening in the society.

5. What is Electronics? “ Electronics”, as the name implies  relating to electrons.  The word electronics arrived from electron mechanics ( Behaviour of the electron when it is subjected to externally applied fields). The  definition of electronics  technically says “Electronics is an engineering branch that concerns with the flow of current through semiconductor, gas or any form of matter.

6. Applications of Electronics 1.Consumer Electronics Office Gadgets, Home appliances, Audio and Video Systems, Advanced Consumer Devices, Storage Devices  2.I ndustrial Electronics Industrial automation and motion control, Machine learning, motor drive control, Mechatronics and robotics, Power converting technologies, Photo voltaic systems, Renewable energy applications, Power electronics, and Biomechanics  

7. Medical applications Stethoscope, Glucose meter, Pace Maker,etc . Meteorological and Oceanographic Anemometer, Barometer, Hygrometer  ,etc. Defence and Aerospace Missile Launching systems, Rocket Launchers for space,Aircraft systems, Cockpit controllers, etc. Automotive Most parts of automobiles consists of electronic devices.

8. UNIT I PN JUNCTION DEVICES

9. Types of Materials based on conductivity

10. TYPES OF SEMICONDUCTOR

11. Intrinsic Semiconductor A semiconductor, which is in its extremely pure form, is known as an intrinsic semiconductor. Silicon and germanium are the most widely used intrinsic semiconductors. Both silicon and germanium are tetravalent, i.e. each has four electrons (valence electrons) in their outermost shell. Each atom shares its four valence electrons with its four immediate neighbours, so that each atom is involved in four covalent bonds.

12. Intrinsic Semiconductor s e m i c o n d u ct o r i s l a r g e nu m be r o f When the temperature of an intrinsic increased, beyond room temperature a electron-hole pairs are generated. Since the electron and holes are generated in pairs so, Free electron concentration (n) = concentration of holes (p) = Intrinsic carrier concentration (n i )

13. Extrinsic Semiconductor P ure s e m i c ondu c t o rs h av e ne g l i g i b l e c o ndu ct i v i ty a t ro o m t e m pe r a tur e . To i ncr e a s e t h e c o ndu c t i v i ty o f semiconductor, some impurity is added. The i n t r i ns i c r e s ul t i ng semiconductor is called impure or extrinsic semiconductor. Impurities are added at the rate of ~ one atom per 10 6 to 10 10 semiconductor atoms. The purpose of adding impurity is to increase either the number of free electrons or holes in a semiconductor.

14. Extrinsic Semiconductor Two types of impurity atoms are added to the semiconductor Atoms containing 5 valance electrons (Pentavalent impurity atoms) e.g. P, As, Sb, Bi Atoms containing 3 valance electrons (Trivalent impurity atoms) e.g. Al, Ga, B, In N-type semiconductor P-type semiconductor

15. Comparison of Intrinsic and Extrinsic Semiconductor

16. PN Junction Formation

17. PN Junction Formation

18. PN Junction Formation

19. PN Junction Formation P-Type semiconductor having excessive holes N-Type semiconductor having excessive free electrons Ju n c t i on Acceptor atoms D o nor atoms

20. Charge Distribution - + - + - + P N Positive and negative ions are created when holes and free electrons cross the junction and move to the other side this charge is called “space charge” Diffusion current flows whenever P and N materials are joined together

21. The P-N Junction When initially joined electrons from the n-type migrate into the p- type – less electron density there When an electron fills a hole – both the electron and hole disappear as the gap in the bond is filled This leaves a region with no free charge carriers – the depletion layer – this layer acts as an insulator Slide 10

22. Barrier Potential P N + + + - - - E Depletion Region Charges of opposite polarities establish “Electric Field” also known as “Barrier Potential”. This field prevents any further diffusion current Barrier potential is also known as “Junction Potential” or “Diffusion Potential”. It is denoted by V o Si -0.7 V Ge-0.3 V

23. DIODE (Formed Using P-N Junction)

24. DIODE A PN Junction is also called DIODE. Term diode from the Greek roots di , meaning 'two', and ode, meaning 'path'. It is used in various electronics application. We will use this diode to form transistor and FET. Same diode are also used to form logic circuit

25. P-N Junction diode

26. DIODE SYMBOL, SIGN

27. https://www.youtube.com/watch?v=ar7xDMR4P_U https://www.youtube.com/watch?v=ar7xDMR4P_U

28. Forward Biased Junction + + + - - - E N P + - Opposing field due to battery Depletion region shrinks and drift current begins to flow

29. Reverse Biased Junction + + + - - - E N P + - Supporting field due to battery Depletion region expands and opposes flow of current

30. DIODE Characteristics

31. Drift and Diffusion currents

32. Drift Current Drift current can be defined as the charge carrier’s moves in a semiconductor because of the electric field. There are two kinds of charge carriers in a semiconductor like holes and electrons. Once the voltage is applied to a semiconductor, then electrons move toward the + Ve terminal of a battery whereas the holes travel toward the – Ve terminal of a battery. Here, holes are positively charged carriers whereas the electrons are negatively charged carriers. Therefore, the electrons attract by the + Ve terminal of  a battery,  whereas the holes attract by the - Ve terminal of a battery.

33. Diffusion Current The diffusion current can be defined as the flow of charge carriers within a semiconductor travels from a higher concentration region to a lower concentration region. A higher concentration region is nothing but where the number of electrons present in the semiconductor. Similarly, a lower concentration region is where the less number of electrons present in the semiconductor.

34. Diode junction capacitances Transition capacitance (C T ) Diffusion capacitance (C D )

35. T ransition capacitance The amount of capacitance changed with increase in voltage is called transition capacitance . The transition capacitance is also known as depletion region capacitance, junction capacitance or barrier capacitance. Transition capacitance is denoted as C T . The change of capacitance at the depletion region can be defined as the change in electric charge per change in voltage.

36. Transition capacitance CT = dQ / dV Wh e r e CT = Transition capacitance dQ = Change in electric charge, dV = Change in voltage The transition capacitance can be mathematically written as C T = ε A / W, W here ε = Permittivity of the semiconductor A = Area of plates or p-type and n-type regions W = Width of depletion region

37. Diffusion capacitance When the junction is forward biased, a capacitance comes into play , that is known as diffusion capacitance denoted as C D . It is much greater than the transition capacitance. During forward bias, the potential barrier is reduced. The charge carriers moves away from the junction and recombine. The density of the charge carriers is high near the junction and reduces or decays as the distance increases. The change in charge with respect to applied voltage results in capacitance called as diffusion capacitance. Diffusion capacitance is directly proportional to the electric current or applied voltage.

38. Diffusion capacitance C D = τ I D / η V T , where τ is the mean life time of the charge carrier, ID is the diode current and V T is the applied forward voltage, and η is generation recombination factor. The diffusion capacitance is directly proportional to the diode current. In forward biased C D >> C T . And thus C T can be neglected. The diffusion capacitance value will be in the range of nano farads ( nF ) to micro farads ( μF ).

39. DIODE APPLICATION S

40. HALF WAVE RECTIFIER

41. HALFWAVE RECTIFIER WITH FILTER

42. RMS Value

43. 4.Efficiency

44. 5.Ripple Factor

45. 6. Transformer Utilization Factor(TUF)

46. 7 . Peak Inverse Voltage(PIV) Peak Inverse Voltage (PIV) is the maximum voltage that the diode can withstand during reverse bias condition. If a voltage is applied more than the PIV, the diode will be destroyed . For Half wave Rectifier, PIV= Vm

47. FULL WAVE RECTIFIER

48. FULL WAVE RECTIFIER

49. FULL WAVE RECTIFIER

50. Derive the Parameters for Full wave rectifier

51. Efficiency Pdc = Idc2 RL = (2Im / π)2 RL Pac =Irms2 ( rf + RL)       =( Im / √2)2 ( rf + RL) Rectifier Efficiency (η) = Pdc / Pac Put the values of Pdc and Pac from above equations, therefore, η =[ (2Im / π)2 * RL ] / [( Im / √2)2 * ( rf + RL)]    = 0.812 RL / ( rf + RL)   = 0.812 / (1+ rf /RL) If rf is neglected as compared to RL then the efficiency of the rectifier is maximum. Therefore , η max =0.812 = 81.2%

52. BRIDGE RECTIFIER

53. BRIDGE RECTIFIER

54. RECTIFIER COMPARISON

55. Zener Diode

56. Introduction The zener diode is a silicon p-n junction devices that differs from rectifier diodes because it is designed for operation in the reverse-breakdown region .

57. Circuit of Zener One Zener Diode connected with one resist a nce and battery.

58. Characteristics A Zener diode is always reverse connected When forward biased, its characteristics are just like of ordinary diode It has sharp breakdown voltage, called Zener voltage

59. VI characteristics of Zener diode

60. Principle of Zener Diode The Working Principle of zener diode lies in the cause of breakdown for a diode in reverse biased condition. Normally there are two types of breakdown. 1) Zener Breakdown 2) Avalanche Breakdown.

61. Zener Breakdown This type of breakdown occurs for a reverse bias voltage between 2 to 8V . Even at low voltage, the electric field intensity is strong enough to exert a force . The valence electrons of the atom such that they are separated from the nuclei . This type of break down occurs normally for highly doped diode with low breakdown voltage and larger electric field. As temperature increases, the valence electrons gain more energy to disrupt from the covalent bond and the less amount of external voltage is required . Thus zener breakdown voltage decreases with temperature.

62. Avalanche Breakdown This type of breakdown occurs at the reverse bias voltage above 8V and higher. It occurs for lightly doped diode with large breakdown voltage. As minority charge carriers (electrons) flow across the device. They tend to collide with the electrons in the covalent bond and cause the covalent bond to disrupt.

63. Avalanche Breakdown As voltage increases, the kinetic energy (velocity) of the electrons also increases. The covalent bonds are more easily disrupted, causing an increase in electron hole pairs. The avalanche breakdown voltage increases with temperature.

64. As Voltage Regulator

65. As Voltage Regulator In a DC circuit, Zener diode can be used as a voltage regulator or to provide voltage reference. The main use of zener diode lies in the fact that the voltage across a Zener diode remains constant for a larger change in current. This makes it possible to use a Zener diode as a constant voltage device or a voltage regulator. In any power supply circuit, a regulator is used to provide a constant output (load) voltage.

66. While designing a voltage regulator using zener diode The latter is chosen with respect to its maximum power rating. The maximum current through the device should be:- Imax = Power/Zener Voltage Since the input voltage and the required output voltage is known. It is easier to choose a zener diode with a voltage approximately equal to the load voltage, i.e. Vz ~=Vo.

67. The value of the series resistor is chosen to be R =(Vin – Vz)/(Izmin + IL), where IL = Load Voltage/Load resistance. It is advisable to use a forward biased diode in series with the Zener diode. This is because the Zener diode at higher voltage follows the avalanche breakdown principle, having a positive temperature of coefficient. Hence a negative temperature coefficient diode is used for compensation.

68. 1 L ight E mitting D iodes

69. Introduct ion Construction of LED Working Colors & Materials Types Comparison Applications Advantages & Disadvantages L ight E mitting D iodes 2

70. LED is an acronym for Light Emitting Diode. A Light Emitting Diode(LED) is a two LED semiconductor light source. It is a P N Junction diode Which emits light when activated by a suitable voltage is applied to the leads. I n t r oduction 3

71. The LED consist s of a chip of semiconductor material doped with impurities to create a P N junction. The chips are mounted in a reflecting tray order to increase the light output. The contacts are made on the cathode side by means of conductive adhesive and on the anode side via gold wire to the lead frame. The plastic case encloses the chip area of the lead frame. Construction of LED 7

72. W orking W h en the negative end of a circuit is hooked up to the N-type layer and the positive end is hooked up with P-type layer than electron and holes start moving. If you try to run current the other way, with the P-type side connected to the negative end of the circuit and the N-type side connected to the positive end, current will not flow. No current flows across the junction because the holes and the electrons are each moving in the wrong direction. 10

73. When current flows across a diode Negative electrons move one way and positive holes move the other way LED: How It Works 11

74. The holes exist at a lower energy level than the free electrons . Therefore when a free electron falls , it loses energy . LED: How It Works 12

75. This energy is emitted in a form of a photon, which causes light The color of the light is determined by the fall of the electron and hence energy level of the photon LED: How It Works 13

76. Colors Colors Name Wavelength Range(nm) Typical Efficiency(lm/W) Red 620 - 645 72 Red –Orange 610 - 620 98 Green 520 - 550 93 Cyan 490 - 520 75 Blue 460 - 490 37 Efficiency & Operational Parameter 14

77. LEDs are produced in a variety of shapes and sizes. The color of the plastic lens is often the same as th e actual color of light emitted. Types of LEDs 15

78. Traditional Inorganic LEDs Multi Color LED Bi-color Try-color Organic LED Miniature High power Different size of LEDs : 8 mm, 5 mm and 3 mm, Modern high-power LEDs such as those used for lighting and backlighting are generally found in Surface Mount Technology (SMT ) (not shown here) Some main types is given below; Types of LEDs 16

79. This type of LEDs manufactured from inorganic materials. Some of the more widely used are compound semiconductor such as Aluminum Gallium Arsenide(AlGaAr), Gallium Arsenide Phosphide(GaArP) , and many more. Traditional Inorganic LEDs 17

80. Two different LED emitters in one case. There are two types of these. One type consists of two dies connected to the same two color types of light. Current flow in one direction emits one color, and current in the opposite direction emits the other color. Multi Color LED 18 Bi - color

81. The OLED mostly used display technology computer monitors, television , mobile phone Screen etc. Organic Light Emitting Diode(OLED) 19

82. Organic Light Emitting Diode(OLED) The semiconductor in an OLED is organic which means it contains carbon. The OLED uses one of two polymer or small molecule. 20

83. 1.9 to 2.1V for Red, Orange & Yellow. 3.0 to 3.4V for Green & Blue. 2.9 to 4.2V for Violet, Pink, Purple & White. Miniature Miniature surface mount LEDs in most common sizes. They can much smaller than a traditional 5mm lamp Type LED. 21

84. High power 22 For example, the CREE XP-G series LED achieved 105 lm/W in 2009, while Nichia released the 19 series with a typical efficacy of 140 lm/W in 2010.

85. Comparison 24

86. LED uses fall into Three main categories Indicators and signals Lighting Data communication and other signaling Appli c a tions 25

87. The low energy consumption , low maintenance and small size of LEDs has LED to uses as status indicators and displays on a variety of equipment and installations. the are used as stadium airports and railway stations, trains, buses, trams, and ferries etc. Indicators and signals 26

88. LEDs are now used commonly in all market areas from commercial to home use: standard lighting, stage, theatrical, architectural, and public installations, and wherever artificial light is used. Lighting 27

89. Light can be used to transmit data and analog signals. Listening device in many theaters and similar spaces use arrays of infrared LEDs to send sound to listeners receivers. Light-emitting diodes are used to send data over many types of fiber optics cable, from digital audio the very high bandwidth fiber links that form the internet backbone. Data communication and other signaling 29

90. Efficiency: LEDs emit more lumens per watt than incandescent light bulbs. The efficiency of LED lighting fixtures is not affected by shape and size, unlike fluorescent light bulbs or tubes. Color: LEDs can emit light of an intended color without using any color filters as traditional lighting methods need. Easily available many colors. Size: LEDs can be very small smaller than 2 mm Ad v a n t a g es 30

91. On/Off time: LEDs light up very quickly. A typical red indicator LED will achieve full brightness in under a microsecond Cycling : LEDs are ideal for uses subject to frequent on-off cycling, unlike incandescent and fluorescent lamps that fail faster when High- intensity discharge lamps that require a long time before restarting. Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer. Focus: The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner. Ad v a n t a g es 31

92. High initial price : LEDs are currently more expensive, price per lumen. Light Quality: Most cool-white LEDs have spectra that differ significant from a black body radiator like the sun or an incident light. Temperature dependence: Driving the LED hard in high ambient temperatures may result to overheating of the led package ,eventually leading to device failure. Voltage sensitivity Non reparation Disadvantages 32

93. LASER DIODE

94. Introduction to Laser Diode  LASER stands for Light Amplification by Stimulated Emission of Radiation.  A laser diode is an electronic device, which converts electrical energy into light energy to produce high-intensity coherent light.  Laser diode is very small in size and appearance.  It is similar to a transistor and has operation like LED but it emit coherent light.  The material which often used in Laser diode is the gallium Arsenide (GaAs).  It is also called injection laser diode.  It work s on forward biasing.

95. Symbo l :

96. Laser diode construction The laser diode is made of two doped gallium arsenide layers. One doped gallium arsenide layer will produce an n-type semiconductor whereas another doped gallium arsenide layer will produce a p-type semiconductor. In laser diodes, selenium, aluminum, and silicon are used as doping agents. P-N junction When a p-type layer is joined with the n-type layer, a p-n junction is formed. The point at which the p-type and n-type layers are joined is called p-n junction. The p-n junction separates the p-type and n-type semiconductors.

97. Main steps required for producing a coherent beam of light in laser diodes Absorption of energy :  Absorption of energy is the process of absorbing energy from the external energy sources.  In laser diodes, electrical energy or DC voltage is used as the external energy source. When the DC voltage or electrical energy supplies enough energy to the valence electrons or valence band electrons, they break bonding with the parent atom and jumps into the higher energy level (conduction band). The electrons in the conduction band are known as free electrons.

98. Cont…  When the valence electron leaves the valence shell, an empty space is created at the point from which electron left. This empty space in the valence shell is called a hole.  Thus, both free electrons and holes are generated as a pair because of the absorption of energy from the external DC source.

99. Spontaneous emission:  Spontaneous emission is the process of emitting light or photons naturally while electrons falling to the lower energy state.  In laser diodes, the valence band electrons or valence electrons are in the lower energy state. Therefore, the holes generated after the valence electrons left are also in the lower energy state.  On the other hand, the conduction band electrons or free electrons are in the higher energy state. In simple words, free electrons have more energy than holes.  The free electrons in the conduction band need to lose their extra energy inorder to recombine with the holes in the valence band.  The free electrons in the conduction band will not stay for long period. After a short period, the free electrons recombine with the lower energy holes by releasing energy in the form of photons.

100. Cont…

101. Stimulated emission:  Stimulated emission is the process by which excited electrons or free electrons are stimulated to fall into the lower energy state by releasing energy in the form of light. The stimulated emission is an artificial process.  In stimulated emission, the excited electrons or free electrons need not wait for the completion of their lifetime. Before the completion of their lifetime, the incident or external photons will force the free electrons to recombine with the holes. In stimulated emission, each incident photon will generate two photons.  All the photons generated due to the stimulated emission will travel in the same direction. As a result, a narrow beam of high-intensity laser light is produced.

102. Cont…

103. How laser diode works?  When DC voltage is applied across the laser diode, the free electrons move across the junction region from the n-type material to the p-type material. In this process, some electrons will directly interact with the valence electrons and excites them to the higher energy level whereas some other electrons will recombine with the holes in the p-type semiconductor and releases energy in the form of light. This process of emission is called spontaneous emission.  The photons generated due to spontaneous emission will travel through the junction region and stimulate the excited electrons (free electrons). As a result, more photons are released. This process of light or photons emission is called stimulated emission. The light generated due to stimulated emission will moves parallel to the junction.

104. Cont…  The two ends of the laser diode structure are optically reflective. One end is fully reflective whereas another end is partially reflective. The fully reflective end will reflect the light completely whereas the partially reflective end will reflect most part of the light but allows a small amount of light.  The light generated due to the stimulated emission is escaped through the partially reflective end of the laser diode to produce a narrow beam laser light.  All the photons generated due to the stimulated emission will travel in the same direction. Therefore, this light will travel to long distance without spreading in the space.

105. Working Di a gr a m

106. Advantages of laser diodes  Simple construction  Lightweight  Very cheap  Small size  Highly reliable compared to other types of lasers.  Longer operating life  High efficiency  Mirrors are not required in the semiconductor lasers.  Low power consumption

107. Disadvantages of laser diodes  Not suitable for the applications where high powers are required.  Semiconductor lasers are highly dependent on temperature.

108. Applications of laser diodes  Laser diodes are used in laser pointers.  Laser diodes are used in fiber optic communications.  Laser diodes are used in barcode readers.  Laser diodes are used in laser printing.  Laser diodes are used in laser scanning.  Laser diodes are used in range finder

109. PROBLEMS 1. An a.c . supply of 230 V is applied to a half-wave rectifier circuit through a transformer of turn ratio 10 : 1. Find ( i ) the output d.c. voltage and (ii) the peak inverse voltage. Assume the diode to be ideal.

110. 2. A crystal diode having internal resistance r f   = 20 Ω is used for half-wave rectification. If the applied voltage v = 50 sin ω t and load resistance R L = 800 Ω, find : ( i ) Im , Idc , Irms (ii) a.c . power input and d.c. power output (iii) d.c. output voltage (iv) efficiency of rectification.