Semiconductor diodes

This ppt is about semiconductor diodes.You can get every basic information about PN junction diode and its working and some more information about the semiconductors.

1. OBJECTIVE Energy band and energy band gap Classification of materials on the basis of energy band gap What is Semiconductor Types of semiconductor Extrinsic semiconductor Semiconductor junction Semiconductor device (P-N DIODE) Applications of diode

2. DIFFERENCE BETWEEN CONDUCTORS,INSULATORS,SEMICONDUCTORS Energy band & energy band gap:- Each isolated atom has a discrete energy level. But in general isolated atoms are not exist .they exist in the form of crystal. In that crystal there are nearby atoms ,which also have an energy level nearly equal to the previous energy level. so these “closely spaced energy levels form a band of energy” called energy band. valance band is located blow the conduction band eperated from it by a energy band gap. In conductors C.B. and V.B. are overlapped In insulators energy band gap is 6eV In semiconductors energy band gap is 1eV

3. CLASSIFICATION OF MATERIALS ON THE BASIS OF ENERGY BAND GAP Coductors Insulators Semiconductors

4. SEMICONDUCTOR Semiconductor are those materials which behaves like insulators at 0 degree Celsius and like conductor at room temperature. They have properties between conductors and insulators.

5. Types of semiconductor Intrinsic semiconductors:- Intrinsic semiconductors are pure semiconductors, no impurities are added in these conductors. So the no. of free electrons and holes are equal . Conductivity of these semiconductors is low because of electrons are in perfect covalent bonding. Extrinsic semiconductors

6. INTRINSIC (PURE) SILICON At 0 Kelvin Silicon density is 5*10 ²³ particles/cm ³ Silicon has 4 valence electrons, it covalently bonds with four adjacent atoms in the crystal lattice Higher temperatures create free charge carriers. A “hole” is created in the absence of an electron. At 23C there are 10 ¹º particles/cm ³ of free carriers

7. Extrinsic semiconductors An  extrinsic semiconductor  is a  semiconductor  that has been  doped , that is, into which a  doping agent  has been introduced, giving it different electrical properties than the intrinsic (pure) semiconductor .

8. Doping involves adding dopant atoms to an intrinsic semiconductor, which changes the  electron  and  hole   carrier concentrations  of the semiconductor at  thermal equilibrium . Dominant carrier concentrations in an extrinsic semiconductor classify it as either an n-type or p-type semiconductor. The electrical properties of extrinsic semiconductors make them essential components of many electronic devices.

9. Types of extrinsic semiconductor P type N type

10. P-type n-type When a doped semiconductor contains excess holes it is called P-type semiconductor. Doping is trivalent,B,Ga,In,Al When a dped semiconductor contains excess electrons it is called N-type semiconductor. Doping is pentavalent,As,Bi,Sb,P

11. DOPING The N in N-type stands for negative. A column V ion is inserted. The extra valence electron is free to move about the lattice There are two types of doping N-type and P-type. The P in P-type stands for positive. A column III ion is inserted. Electrons from the surrounding Silicon move to fill the “hole.”

12. Crystalline Nature of Silicon Silicon as utilized in integrated circuits is crystalline in nature As with all crystalline material, silicon consists of a repeating basic unit structure called a unit cell For silicon, the unit cell consists of an atom surrounded by four equidistant nearest neighbors which lie at the corners of the tetrahedron

13. P-N Junction Also known as a diode One of the basics of semiconductor technology - Created by placing n-type and p-type material in close contact Diffusion - mobile charges (holes) in p-type combine with mobile charges (electrons) in n-type

14. P-N Junction Region of charges left behind (dopants fixed in crystal lattice) Group III in p-type (one less proton than Si- negative charge) Group IV in n-type (one more proton than Si - positive charge) Region is totally depleted of mobile charges - “depletion region” Electric field forms due to fixed charges in the depletion region Depletion region has high resistance due to lack of mobile charges

15. THE P-N JUNCTION

16. The Junction  The “potential” or voltage across the silicon changes in the depletion region and goes from + in the n region to – in the p region

17. Biasing the P-N Diode Forward Bias Applies - voltage to the n region and + voltage to the p region CURRENT! Reverse Bias Applies + voltage to n region and – voltage to p region NO CURRENT THINK OF THE DIODE AS A SWITCH

18. P-N Junction – Reverse Bias positive voltage placed on n-type material electrons in n-type move closer to positive terminal, holes in p-type move closer to negative terminal width of depletion region increases allowed current is essentially zero (small “drift” current)

19. P-N Junction – Forward Bias positive voltage placed on p-type material holes in p-type move away from positive terminal, electrons in n-type move further from negative terminal depletion region becomes smaller - resistance of device decreases voltage increased until critical voltage is reached, depletion region disappears, current can flow freely

20. P-N Junction - V-I characteristics Voltage-Current relationship for a p-n junction (diode)

21. Current-Voltage Characteristics THE IDEAL DIODE Positive voltage yields finite current Negative voltage yields zero current REAL DIODE

22. The Ideal Diode Equation

23. Semiconductor diode - opened region The p-side is the cathode, the n-side is the anode The dropped voltage, V D is measured from the cathode to the anode Opened: V D  V F : V D = V F I D = circuit limited, in our model the V D cannot exceed V F

24. Semiconductor diode - cut-off region Cut-off: 0 < V D < V F : I D  mA Semiconductor diode - closed region Closed: V F < V D  0: V D is determined by the circuit, I D = mA Typical values of V F : 0.5 ¸ 0.7 V

25. Zener Effect Zener break down: V D <= V Z : V D = V Z , I D is determined by the circuit. In case of standard diode the typical values of the break down voltage V Z of the Zener effect -20 ... -100 V Zener diode Utilization of the Zener effect Typical break down values of V Z : -4.5 ... -15 V

26. LED Light emitting diode, made from GaAs V F =1.6 V I F >= 6 mA

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