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  1. DMT 121ELECTRONIC 1 PN. SITI NOR DIANA BT ISMAIL Rumah PLV, KKF Taman Kuala Perlis Emel : H/P : 012-3272514

  2. Schedules • Lectures - Monday(8.00 – 9.00 am), BKS 1 - Wednesday(2.00 – 3.00 pm), BKS 1 • Laboratories - Thursday (8.00 am – 9.00 am), MMES - Friday (8.00 am – 9.00 am), MMES

  3. Topics 1. Introduction to Semiconductor 2. Diode Applications 3. Bipolar Junction Transistors (BJTs) 4. DC BJT Biasing 5. Field – Effects Transistors (FETs) Reference book : Electronic Devices 8th Edition By Thomas L. Floyd

  4. Laboratory sessions Lab 1 : Introduction to Basic Laboratory Equipment Lab 2 : Introduction to Diode Lab 3 : Diode as Rectifiers Lab 4 : Limiter and Clamper Circuit Lab 5 : Current & Voltage Characteristics of BJT Lab 6 : Voltage Divider Biasing Lab 7 : JFET Characteristics

  5. Evaluation Contribution Final Examination : 50 % Course Works : 50 % Details of course work contribution • Lab works : 25 % • Test : 10 % • Lab Test : 10 % • Assignment : 5%

  6. Semiconductor Materials • Definition: Semiconductors are a special class of elements having a conductivity between that of a good conductor and that of an insulator

  7. Semiconductor Materials • Single crystal – Germanium (Ge) and Silicon (Si) • Compound Semiconductor – Gallium Arsenide (GaAs), Cadmium Sulfide (CdS), Gallium Nitride (GaN) and Gallium Arsenide phosphide (GaAsP). • Mostly used : Ge, Si and GaAs

  8. Semiconductor Materials • Ge – First discovered. Used as Diode in 1939, transistor in 1947. Sensitive to changes in temperature – suffer reliability problem. • Si – Introduced in 1954 (as transistor), less sensitive to temperature. Abundant materials on earth. Over the time – its sensitive to issue of speed. • GaAs– in 1970 (transistor), 5x speed faster than Si. Problem – difficult to manufacture, expensive, had little design support at the early stage.

  9. • Columns: Similar Valence Structure 1e 2e inert gases give up accept 2e accept 1e Metal 3e give up Nonmetal H He give up Intermediate Li N e Be O F Mg Na Ar S Cl K Ca Sc Kr Se Br Sr Y Rb Xe Te I Cs Ba Po At Rn Fr Ra Electropositive elements: Readily give up electrons to become + ions. Electronegative elements: Readily acquire electrons to become - ions. Periodic Table

  10. Electropositive elements: Readily give up electrons to become + ions. Electronegative elements: Readily acquire electrons to become - ions.

  11. Semiconductors, Conductors & Insulators Conductors • Material that easily conducts electrical current. • The best conductors are single-element material (e.g copper,silver,gold,aluminum,ect.) • One valence electron very loosely bound to the atom- free electron Insulators • Material that does not conduct electric current under normal conditions. • Valence electron are tightly bound to the atom – less free electron Semiconductors • Material between conductors and insulators in its ability to conduct electric current • in its pure (intrinsic) state is neither a good conductor nor a good insulator • most commonly use semiconductor- silicon(Si), germanium(Ge), and carbon(C). • contains four valence electrons

  12. Neutrons (uncharged) Protons (positive charge) Electrons (negative charge) Nucleus (core of atom) ATOM Covalent Bonding & Intrinsic Materials • Atom = electron + proton + neutron • Nucleus = neutrons + protons

  13. Atomic Structure No. of electron in each shell Ne = 2(n)2 n = no of shell.

  14. Covalent Bonding Covalent bonding of the Silicon atom Covalent bonding of the GaAs crystal

  15. Intrinsic Carrier • Intrinsic (pure) carriers – The free electrons in a material due to only external causes • Ge has the highest number of carriers and GaAs has the lowest intrinsic carriers. • The term intrinsic (pure) is applied to any semiconductor material that has carefully refined to reduce the number of impurities to a very low level – essentially as pure as can be made available through modern technology

  16. Relative Mobility Factor µn • Relative mobility – the ability of the free carriers to move throughout the material. • GaAs has 5X the mobility of free carriers compared to Si, a factor that results in response times using GaAs electronic devices is 5X those of the same device made from Si. • Ge has more than twice the mobility of electrons in Si, a factor that results in the continued of Ge in high-speed radio frequency applications.

  17. Difference between Conductors & Semiconductors • Conductors – Resistance increases with the increase in heat, because their vibration pattern about relatively fixed location makes it increasingly difficult for a sustained flow of carriers through the material – positive temperature coefficient. • Semiconductors – Exhibit an increased level of conductivity with the application of heat. As the temperature rises, an increasing number of valence electron absorb sufficient thermal energy to break the covalent bond and contribute to the number of free carriers – negative temperature effects

  18. Energy Level Figure: Energy levels: conduction and valence bands of an insulator, a semiconductor, and a conductor.

  19. Extrinsic Materials : n-Type and P-Type Materials • The characteristics of a semiconductor material can be altered significantly by the addition of a specific purity atoms to relatively pure semiconductor materials – this process is known as doping process • A semiconductor that has been subjected to the doping process is called an extrinsic materials. • Extrinsic Materials are n-type material [five valence electrons (pentavalent)] and p-type material [three valence electrons atom (trivalent)]

  20. N-Type Materials • n-Type material is created by introducing the impurity (bendasing) elements that have five valence electrons (pentavalent). • There are antimony (Sb), Arsenic (As) and phosphorous (P). Diffused impurities with five valence electrons are called donor atoms Figure: Antimony impurity in n-type material

  21. N-Type Materials • The effect of this doping cause the energy level (called the donor level) appears in the forbidden band with Eg significantly less than intrinsic material. • This cause less thermal energy to move free electron (due to added impurity) into conduction band at room temperature. Figure: Effect of donor impurities on the energy band structure

  22. N-Type Material • Pentavalent atoms is an n-type semiconductor (n stands for the negative charge on electrons). • The electrons are called the majority carrier in n-type materials. • In n-type material there are also a few holes that are created when electrons-holes pairs are thermally generated • Holes in n-type materials are called minority carrier.

  23. Diffused impurities with three valence electrons are called acceptor atoms Figure: Boron impurity in p-type material. P-Type Material • Si or Ge doped with impurities atoms having three valence electrons. • Mostly used are boron (B), gallium (Ga) and indium (In). • The void (vacancy) is called ‘hole’ represented by small circle or a ‘+’ sign.

  24. P-Type Material • In p-type materials the hole is the majority carrier and the electron is the minority carrier. • Holes can be thought as +ve charges because the absence of electron leaves a net +ve charge on the atom.

  25. Electron vs Hole Flow • With sufficient kinetic energy to break its covalent bond, the electron will fills the void created by a hole, then a vacancy or hole, will be created in the covalent bond that released the electron.

  26. Assignment 1 • What is an ATOM? • What is maximum no of electron that can exist in the 3rd shell of an atom? Prove it. • ________ has four electron valences. • Give 3 differences between n – types and p – types Submit tomorrow morning during lab session(8-9,MMES)

  27. Semiconductor Diode Diode • Simple construction of electronic device • It is a joining between n-type and p-type material (joining one with majority carrier of electron to one with a majority carrier of holes)

  28. Diode @ No Bias (VD=0V)

  29. Forward Bias (VD > 0 V) Figure: Forward-biased p–n junction. (a) Internal distribution of charge under forward-bias conditions; (b) forward-bias polarity and direction of resulting current.

  30. Reverse Bias (VD < 0 V) Figure: Reverse-biased p–n junction. (a) Internal distribution of charge under reverse-bias conditions; (b) reverse-bias polarity and direction of reverse saturation current.

  31. Diode Characteristics Curve Figure: Silicon semiconductor diode characteristics.

  32. Ge, Si and GaAs Figure: Comparison of Ge, Si, and GaAs diodes.

  33. Temperature Effects Figure: Variation in Si diode characteristics with temperature change.

  34. Ideal Vs Practical • Semiconductor diode behaves in a manner similar to mechanical switch that can control the current flow between it’s two terminal • However, semiconductor diode different from a mechanical switch in the sense that it permit the current flow in one direction

  35. Ideal Vs Practical Figure: Ideal semiconductor diode:(a) forward-biased (b) reverse-biased. Figure: Ideal versus actual semiconductor characteristics. (Short circuit equivalent –fwd bias, actual case R ≠ 0) (Open circuit equivalent – Reverse bias, actual case saturation current Is ≠ 0)

  36. Approximate Diode

  37. Resistance Levels DC or Static Response • Application of dc voltage will result in an operating point on the characteristic curve will not change with time. In general, the higher the current through a diode, thelower is the dc resistance level. Figure: Determining the dc resistance of a diode at a particular operating point.

  38. Resistance Levels • Average AC Response Figure: Determining the average ac resistance between indicated limits.

  39. Diode Equivalent Model

  40. Example 1 Determine the forward voltage (VF) and forward current [IF]. Also find the voltage across the limiting resistor. Assumed rd’ = 10 at the determined value of forward.

  41. Example 2 Determine the Reverse voltage (VR). Also find the voltage across the limiting resistor. Assumed IR = 1 µA. Answer: VRLIMIT =1mV VR=4.999V

  42. Diode Testing • Analog MM (or Ohm meter testing) Figure: Checking a diode with an ohmmeter.

  43. Diode Testing – Defective diode • Digital MM (Testing Defective Diode) Diode is shorted: get 0 V reading in both forward and reverse bias test. Diode failed open: get open circuit reading (2.6 V) or ‘OL’

  44. Diode Notation

  45. Zener Diode Figure: Conduction direction: (a) Zener diode (b) semiconductor diode (c) resistive element. Figure: Characteristics of Zener region.

  46. Zener Region • The Zener region is in the diode’s reverse-bias region. • At some point the reverse bias voltage is so large the diode breaks down and the reverse current increases dramatically. • This maximum voltage is called avalanche (runtuhan) breakdown voltage • The current is called avalanche current.