1. EMT111 CHAPTER 1 Introduction to Semiconductor By Pn
EMT111 CHAPTER 1 Introduction to Semiconductor By Pn. ‘Aini Syuhada Md Zain

2. Introduction to Semiconductor - Chapter Outline :
1.8 Voltage Current Characteristic of a Diode
1.9 Diode Models
1.10 Testing a Diode

3. 1.8 Voltage-Current Characteristic of a Diode ( V-I Characteristic for forward bias)
-When a forward bias voltage is applied – current called forward current,
-In this case with the voltage applied is less than the barrier potential so the diode for all practical purposes is still in a non-conducting state. Current is very small.
-Increase forward bias voltage – current also increase
Fig 1-26a measurements with meters
FIGURE Forward-bias measurements show general changes in VF and IF as VBIAS is increased.

4. 1.8 Voltage-Current Characteristic of a Diode ( V-I Characteristic for forward bias)
-With the applied voltage exceeding the barrier potential (0.7V), forward current begins increasing rapidly.
-But the voltage across the diode increase only above 0.7 V.
Fig. 1-26b measurements with meters
FIGURE Forward-bias measurements show general changes in VF and IF as VBIAS is increased.

5. dynamic resistance r’d decreases as you move up the curve
1.8 Voltage-Current Characteristic of a Diode ( V-I Characteristic for forward bias)
-Plot the result of measurement in Figure 1-26, you get the V-I characteristic curve for a forward bias diode
Increase to the right
increase upward
dynamic resistance r’d decreases as you move up the curve
zero
bias
Fig. 1-26b measurements with meters

6. 1.8 Voltage-Current Characteristic of a Diode ( V-I Characteristic for Reverse bias)
Breakdown voltage
not a normal operation of pn junction devices
the value can be vary for typical Si
Fig. 1-26b measurements with meters
Reverse Current

7. 1.8 Voltage-Current Characteristic of a Diode ( Complete V-I Characteristic curve)
Combine-Forward bias
& Reverse bias  Complete
V-I characteristic curve
Fig. 1-26b measurements with meters

8. 1.8 Voltage-Current Characteristic of a Diode ( Temperature effect on the diode V-I Characteristic)
Forward biased dioed : for a given value of
For a given
Barrier potential decrease as T increase
Reverse current breakdown – small & can be neglected
Fig. 1-26b measurements with meters

9. 1.9 Diode Models ( Diode structure and symbol)
Directional of current
cathode
anod
Fig ideal diode curve

10. 1.9 Diode Models DIODE MODEL The Ideal Diode Model
The Practical Diode Model
DIODE
MODEL
Fig ideal diode curve
The Complete Diode Model

11. 1.9 Diode Models ( The ideal Diode model)
Ideal model of diode- simple switch:
Closed (on) switch -> FB
Open (off) switch -> RB
Assume
Forward current, by Ohm’s law
(1-2)
Fig ideal diode curve

12. 1.9 Diode Models ( The Practical Diode model)
Adds the barrier potential to the ideal switch model
‘ is neglected
From figure (c):
The forward current [by applying Kirchhoff’s voltage low to figure (a)]
Ohm’s Law
Equivalent to close switch in series with a small equivalent voltage source equal to the barrier potential 0.7V
Represent by produced across the pn junction
Same as ideal diode model
Fig ideal diode curve
(1-3)

13. 1.9 Diode Models ( The Complete Diode model)
Complete model of diode consists:
Barrier potential
Dynamic resistance,
Internal reverse resistance,
The forward voltage:
The forward current:
acts as closed switch in series with barrier potential and small
acts as open switch in parallel with the large
(1-4)
Fig ideal diode curve
(1-5)

14. 1.9 Diode Models ( Example)
(1) Determine the forward voltage and forward current [forward bias] for each of the diode model also find the voltage across the limiting resistor in each cases. Assumed rd’ = 10 at the determined value of forward current.
1.0kΩ
Fig ideal diode curve
1.0kΩ 5V
10V

15. 1.9 Diode Models ( Example)
Ideal Model:
Practical Model:
(c) Complete model:
Fig ideal diode curve

16. 1.9 Diode Models ( Typical Diodes)
Diodes come in a variety of sizes and shapes. The design and structure is
determined by what type of circuit they will be used in.
Fig ideal diode curve

17. 1.10 Testing A Diodes ( By Digital multimeter)
Testing a diode is quite simple, particularly if the multimeter used has a diode check function. With the diode check function a specific known voltage is applied from the meter across the diode.
With the diode check function a good diode will show approximately .7 V or .3 V when forward biased.
Fig 1-38 DMM check w/electrode labels
When checking in reverse bias the full applied testing voltage will be seen on the display.
K A
A K

18. 1.10 Testing A Diodes ( By Digital multimeter)
Defective Diode
Fig 1-38 DMM check w/electrode labels

19. 1.10 Testing A Diodes ( By Analog multimeter – ohm function )
Select OHMs range
Good diode:
Forward-bias:
get low resistance reading (10 to 100 ohm)
Reverse-bias:
get high reading (0 or infinity)
Fig 1-38 DMM check w/electrode labels

20. Summary
Diodes, transistors, and integrated circuits are all made of semiconductor material.
P-materials are doped with trivalent impurities
N-materials are doped with pentavalent impurities
P and N type materials are joined together to form a PN junction.
A diode is nothing more than a PN junction.
At the junction a depletion region is formed. This creates barrier which requires approximately .3 V for a Germanium and .7 V for Silicon for conduction to take place.

21. Summary
A diode conducts when forward biased and does not conduct when reverse biased
When reversed biased a diode can only withstand so much applied voltage. The voltage at which avalanche current occurs is called reverse breakdown voltage.
There are three ways of analyzing a diode. These are ideal, practical, and complex. Typically we use a practical diode model.