semiconductors chapters 19 20 22. tubes semiconductors
TRANSCRIPT
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