3 Semikonduktor Dan Diode.ppt

Semikonduktor dan Diode

Jenis Bahan Berdasar daya hantar listrik dibagi menjadi: • Konduktor • Isolator • Semikonduktor Pembedanya adalah jumlah elektron bebas yang dimiliki.

Konduktor  Logam

In metals, the atom-to-atom interactions free up one electron from each atom. The metal crystals have as many free electrons as they do atoms.

Atom concentration N ~ 1023 atoms per 1 cm3. Free electron concentration, n ~ 1023 cm-3 The metal conductivity is very high.

Atom Model • Recall that atoms are really tiny • With a golf ball size nucleus, the atom is 2.5 miles in diameter, so it is mostly empty space

Free Electrons in Semiconductors Silicon (Si) is the most important semiconductor material

• Silicon atom. There are 14 Protons in the nucleus, and 14 electrons orbiting. An electron can exist in any of these orbits, but not outside their confines. • The furthest 4 are known as Valence electrons. • No free electrons: the electrons in the isolated Si atom cannot leave the atom

Doped Semiconductors: Donor Impurities (Tipe N)

A silicon lattice with a single impurity atom (Phosphorus, P) added. As compared to Si, the Phosphorus has one extra valence electron which, after all bonds are made, has very weak bonding. Very small energy is required to create a free electron from an impurity atom. This type of impurity is called donor. Note, that there is no hole created when a free electron comes from the impurity atom.

Doped Semiconductors: Acceptor Impurities (Tipe P)

A silicon lattice with a single impurity atom (Boron, B) added. Boron has only three valence electrons, one electron less than the Si atom. Having only three valence electrons - not enough to fill all four bonds - it creates an excess hole that can be used in conduction. This type of impurity is called acceptor.

There is no corresponding free electron created from acceptor impurity

p-n junction formation

p-type material

n-type material

Semiconductor material doped with acceptors.

Semiconductor material doped with donors.

Material has high hole concentration

Material has high concentration of free electrons.

Concentration of free electrons in p-type material is very low.

Concentration of holes in n-type material is very low.

Contains NEGATIVELY charged acceptors (immovable) and POSITIVELY charged holes (free).

Contains POSITIVELY charged donors (immovable) and NEGATIVELY charged free electrons.

Total charge = 0

Total charge = 0

p- n junction formation What happens if n- and p-type materials are in close contact?

Being free particles, electrons start diffusing from n-type material into p-material

Being free particles, holes, too, start diffusing from p-type material into n-material

Have they been NEUTRAL particles, eventually all the free electrons and holes had uniformly distributed over the entire compound crystal. However, every electrons transfers a negative charge (-q) onto the p-side and also leaves an uncompensated (+q) charge of the donor on the n-side. Every hole creates one positive charge (q) on the n-side and (-q) on the p-side

DIODA

DIODES • • • •

Ideal Diode Diode Circuits Zener Diodes Rectifier Circuits

anoda

katoda

• A diode can be considered to be an electrical oneway valve. • They are made from a large variety of materials including silicon, germanium, gallium arsenide, silicon carbide …

Diodes • Conduct electricity in one direction • Two terminal electronics devices

• Circuit symbol

– n-type and p-type side

• Primarily made of silicon Doping The adding of impurities

p-type n-type

• n-type crystal – e.g. Silicon doped with Phosphorous – negative charge carriers • electrons

• p-type crystal – e.g. Silicon doped with Aluminum – positive charge carriers • vacancy or hole

The PN-Junction One of the simplest bipolar devices, important for the understanding of more complex devices (bipolar = both electrons and holes contribute to device characteristics).

No Voltage holes

- +

electrons

N-doped P-doped (DEPLETION LAYER)

At the junction, free electrons from the N-type material fill holes from the P-type material. This creates an insulating layer in the middle of the diode called the depletion zone.

+

holes

Forward bias

Reverse bias

current

“no” current

-+

electrons

-

-

holes

-

+

electrons

+

How do you convert AC to DC? AC Input

Diode Rectifier

Smoothing Capacitor

DC Output

Voltage Regulator

Voltage Regulators remove the ripple.

RECTIFIERS Original input

Half wave rectified output

Full wave rectified output

Electrical Devices • Rectifier – Converts AC DC – Designed to have small resistance to current flow in one direction & large resistance in opposite direction – Typically called a diode or rectifier

Effect of a p-n junction on alternating voltage.

Half - Wave Rectifier 1:1 R1

VIN

IR1

VOUT

T1 Positive half-cycle the diode is Forward Bias (FB), negative half-cycle the diode is Reverse Bias (RB).

VDC = VPK X .318

Where: VDC = Average DC voltage VPK = Peak input voltage .318 = Constant

Full - Wave Rectifier •

Positive half-cycle, 1 diode is FB, negative half-cycle the other diode is FB. IR1 1:1 VIN

R1 IR2

VOUT

T1

VDC = VPK X .637

Where: VDC = Average DC voltage VPK = Peak input voltage .637 = Constant

Full – Wave Bridge Rectifier 1:1 IR2

IR1

VIN

IR4

IR3

T1 R1

VOUT

Filter Configuration •

Capacitor Input Filter Schematic Diagram C1 VIN

VOUT RB

• LC Choke Filter Schematic Diagram L1

VIN

C1

VOUT RB