Semiconductors

Chapters

19 20 22

Tubes

Semiconductors

Silicon Atom

Germanium Atom(Less abundant than Silicon!!)

Intrinsic Material

• Pure Substance

• No Impurities!

Silicon

• Low Temperature – Poor Conductor

• High Temperature – Good Conductor

Negative Temperature CoefficientTemperature Increases – Resistance Decreases

Silicon

Si

Si

Si

Si

Si

Si

Si

Si

Si

Si

Si

Si

CovalentBond

Share 2e-

Doped Material – N-Type(electrons – majority carrier)

Si

Si

As Si

Si

Si

Si

Si

Si

SiAs

As

e-

e-

e-

Doped Material – P-Type (holes – majority carrier)

Si

Si

Si

Si

Si

Si

Si

Si

Si

Ga

Ga

Ga+

+

+

HOLE

HOLE

HOLE

N - Material

e-e-e-e-

e-e- e-

e-

e-

e-

e-

P Material

e-

e-e-

e-

e-

e-

++

+

+++ +

+

P – N Type Material

N Type: Negative Charge (-)

P Type: Positive Charge (+)

Advantagesof Semiconductors

• Smaller• Low Power• Cheaper• High Efficiency• Great Reliability• Runs Cooler• More Rugged

• Long Life• Hazardous

Environment• Economic Production• Less Noisy• Made Part of an I.C. (Integrated Circuit)

Disadvantagesof Semiconductors

• Susceptible to Temperature Changes.

• Extra components for Stabilization.

• Easily Damaged• Exceeding Power Limits

• Reversing Polarity

• Excess Heat when Soldering

The PN Junction

P-N Junction

P N

Depletion RegionAn area that has no majority carriers.

{e-

e-

e- e-

e-e-

++

+++

++

e-

P-N Junction

e-e-

e- e-

e-e-

+P N

+

+++

++

e-

Barrier VoltageBuild up of charge for each side.Must be overcome to conduct.

{

Diode Operation

e- +- +e-e-e- e-

e-e-e-+

+

+++

Reversed Bias(No Current Flow)

Bias Voltage

There is a small Leakage Current that can flow!!!

e-e-

Diode Operation

e-e-e-

e-

e-e-

e- e-e-+ +

+

+++ ++ +

e-+ e--

Forward Bias(Current Flows)

+

Once the barrier voltage is exceeded!!

Forward Biased Diode

• EF is the Forward Voltage on the Diode

• EF for Germanium is 0.3V

• EF for Silicon is 0.7V

e-+++++ e-

e-

e-

e-

e-

Example: What is the Forward Biased Current (IF)? Germanium Diode

R = 10kΩ

Es= 9V

EF= 0.3V

IF=ER

R

ES - EF

R=

9V - 0.3V

10kΩ= 0.87mA=

Manufacturers Specifications

Maximum Forward Current

Maximum Reverse Voltage

One Directions!!!

Diode Symbol

P N

CathodeAnode

Diode Identification

CathodeAnode

White or Silver Line on Anode

Diode Construction

•Grown Junction

•Alloyed Junction

•Diffused Junction•(Most Common)

Diode Testing

Low Resistance High

Resistance

LED – Light Emitting Diodes

LED – Light Emitting Diodes

LED – Light Emitting Diodes

+Hole

Low Energy

e-

ElectronHigh Energy

LED – Light Emitting Diodes

+

e-Electron and Hole

CombineLight

Zener Diode

• Made to operate at a voltage greater than normal breakdown voltage.

• Manufacture with a specific voltage in mind.

• Voltage is determined by the resistance.

Zener DiodeSymbol

Temperature Coefficient

• Positive – Breakdown voltage increases with Temperature.

• Operate in the 4 – 5 volt range

• Negative – Breakdown voltage Decreases with Temperature.

• Operate at less than 4 volts.

Silicon Controlled Rectifier (SCR)

Gate

Cathode Anode

Silicon Controlled Rectifier (SCR)

I

I

Turn on GateDiode Works!!!!

Tra

nsis

tor

Transistor

• Bipolar or Junction Transistor.

• Three layer device.

• Amplification

• Switch

N-P-N Transistor

Base

Collector

Emitter

N

NP

P-N-P Transistor

Base

Collector

Emitter

P

P

N

Transistor Use

• Type• NPN• PNP

• Material• Germanium• Silicon

• Major Use• High or Low power• Switching• High Frequency

Transistor Packaging

Transistor Packaging

PartNumber

Transistor

Operation

Base

Collector

Emitter

N-P-N Transistor

++++e- e-e- e-e-e-

e-e-e-e-e-e-e- e-

B

C

E

IB

IC

IE

DiodeTurnsOn!!!

+

P-N-P Transistor

+e-

B

C

E

IB

IC

IE

DiodeTurnsOn!!!

e-e-e-e-++

++

++

++

Transistor Testing - Resistance

Forward – Low Resistance

Reverse – Low High Resistance

B

C

E

Transistor Testing