EC6201_uw

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Where dn/dx – concentration gradient for electrons Dp/dx - concentration gradient for holes D n and D p – diffusion coefficient for electrons and holes Total Current The total current in a semiconductor is the sum of both drift and diffusion currents that is given by Similarly the total current density for an N type semiconductor is given by FORWARD BIAS CONDITION When positive terminal of the battery is connected to the P-type and negative terminal to N-type of the PN junction diode that is known as forward bias condition. Operation The applied potential in external battery acts in opposition to the internal potential barrier which disturbs the equilibrium.
As soon as equilibrium is disturbed by the application of an external voltage, the Fermi level is no longer continuous across the junction. Under the forward bias condition the applied positive potential repels the holes in P type region so that the holes move towards the junction and the applied positive potential repels the electrons in N type region so that the electrons move towards the junction. When the applied potential is more than the internal barrier potential the depletion region and internal potential barrier disappear. V-I Characteristics As the forward voltage increased for V F < Vo, the forward current I F almost zero because the potential barrier prevents the holes from P region and electrons from N region to flow across the depletion region in opposite direction. For V F > Vo, the potential barrier at the junction completely disappears and hence, the holes cross the junction from P to N type and electrons cross the junction to opposite direction, resulting large current flow in external circuit. A feature noted here is the cut in voltage or threshold voltage V F below which the current is very small. At this voltage the potential barrier is overcome and the current through the junction starts to increase rapidly. Cut in voltage is 0.3V for germanium and 0.7 for silicon. UNDER REVERSE BIAS CONDITION When the negative terminal of the battery is connected to the P-type and positive terminal to N-type of the PN junction diode that is known as forward bias condition. Operation
Page 1 and 2: FATIMA MICHAEL COLLEGE OF ENGINEERI
Page 3 and 4: temperature leads to an increase in
Page 5 and 6: THE PN JUNCTION The total charge on
Page 7 and 8: If one side of crystal pure semicon
Page 9 and 10: Forward currents V V P ( 0 ) p ( e
Page 11 and 12: If V >> V T then the term e (-V/ Ƞ
Page 13: (a) Exess hole concentration varyin
Page 17 and 18: Electrons forming covalent bonds of
Page 19 and 20: Forward recovery time is defined is
Page 21 and 22: In clamping networks used as DC Res
Page 23 and 24: Transistor currents - The arrow is
Page 25 and 26: • A very small number of carriers
Page 27 and 28: As the voltages applied to the base
Page 29 and 30: (5) The collector current is theref
Page 31 and 32: In CB configuration a variation of
Page 33 and 34: Input Characteristics It is defined
Page 35 and 36: Transistor parameters in CE configu
Page 37 and 38: To determine input characteristics,
Page 39: Hybrid-Pi Model Bipolar transistors
Page 42: The h-parameter model is defined by
Page 45 and 46: We can also write the emitter curre
Page 47 and 48: Gummel-Poon Model The Gummel-Poon m
Page 49 and 50: Multi Emitter Transistor (Transisto
Page 51 and 52: If the channel is doped with a dono
Page 53 and 54: • With a steady gate-source volta
Page 55 and 56: The metal-oxide semiconductor field
Page 57 and 58: Fig 2. n - channel depletion type M
Page 59 and 60: The SiO 2 layer is still present to
Page 61 and 62: Fig 3. Change in channel and deplet
Page 63 and 64: UNIT IV SPECIAL SEMICONDUCTOR DEVIC
Page 65 and 66:
Zener diode A Zener diode is a type
Page 67 and 68:
VARACTOR DIODE A varactor diode is
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ENERGY BAND DIAGRAM Energy-band dia
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- Hence tunneling current is maximu
Page 73 and 74:
laser (often another diode laser) a
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LDR: A photoresistor or light-depen
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UNIT V POWER DEVICES AND DISPLAY DE
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Silicon Controlled Rectifier (SCR)
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The SCR can be made to conduct heav
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Construction The diac can be constr
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When switch S is closed, the gate c
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There is also the existence of two
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A digit on an LCD display may have
Page 91 and 92:
‣Used for image sensing circuits.
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same figure, a sketch of the photot
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Fig 1. (a) cross section; (b) top v
Page 97 and 98:
phototransistor in the same package
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