1. Electronics Chapter Three
Seventh, ninth weeks
/ 2/ 1439 هـ
أ / سمر السلمي

2. Time of Periodic Exams The third homework
The first periodic exam in / 2/ 1439 هـ 20
The third homework
I put the second homework in my website in the university homework Due Monday 2 / 3/ 1439 H in my mailbox in Faculty of Physics Department , I will not accept any homework after that , but if you could not come to university you should sent it to me by in the same day

3. Chapter Three: Transistor
Brief its history
The discovery of the transistor in year 1947 in Bell Lab’s in United States of America. Since then, this discovery is one of the most important discoveries and that the performance of a global revolution in technology.
the first transistor in Now

4. Transistor Transistor mission
In the second chapter we studied and we focused on two types of contacts :
PN Junction: ( semiconductor of n-type & p-type ) which enters in the structure of bipolar junction transistor (BJT) and Junction gate field-effect transistor (JFET)
MOS contact: (Metal, Oxide, Semiconductor of n-type or p-type) which enters in the structure of metal–oxide–semiconductor field-effect transistor (MOSFET)
Concept of transistor
It is a piece of three parts and as PN Junction this parts contain extrinsic semiconductor N-type & p-type
Transistor mission
1. Works as amplifier in electrical signals 2. works as switch in integrated circuits =

5. Transistor’s types Bipolar junction transistor (BJT):
The most important types of transistor two types are:
Bipolar junction transistor (BJT):
Will be studied in detail in this chapter (Chapter There)
Field-effect transistor (FET) :
Will be studied in detail in (Chapter four)
Diffusion transistor
Unijunction transistors
Single-electron transistors
Nanofluidic transistor,

6. Transistor’s types
There are special types classified within provirus types which
Within bipolar junction transistor
Heterojunction bipolar transistor Schottky transistor
Avalanche transistor Darlington transistors.
Insulated-gate bipolar Photo transistor
Multiple-emitter transistor Multiple-base transistor
Within field effect transistor
Carbon nanotube field-effect transistor (CNFET)
Junction gate field-effect transistor (JFET)
metal–semiconductor field-effect transistor (MESFET (
metal–oxide–semiconductor field-effect transistor (MOSFET)
metal–Insulator–semiconductor field-effect transistor (MISFET)
Organic field-effect transistor
Ballistic transistor
Floating-gate transistor etc… =

7. Bipolar junction transistor
BJT structure
The Bipolar junction transistor contains
of npn or pnp
Which is distributed in three parts
Emitter, Base & Collector
emitter and collector contain from the
same semiconductor type either n-type
or p-type; but often emitter has more
Impurities than base and collector.
Therefore n+p n or p+n p =

8. Bipolar junction transistor
BJT structure =

9. Bipolar junction transistor
BJT structure =

10. Contact methods for BJT’s Circuits
The electronic circuits often have a signal or voltage inside and another outside, and here in a BJT part of the three parts involved in each of the entrance and exit thus
common emitter configuration
base common configuration
common collector configuration
The figure for (npn) type, however for the other type (pnp) just reverse the arrow =

11. Currents and voltage and symbols in circles BJT
IB Base current IE Emitter current IC Collector current
Always gather those three by relationship IE = IB + IC
VBE voltage between base & emitter VBC voltage between base & collector
VCE voltage between emitter & collector
Distribution in the two types npn & pnp
W The length of the first depletion region between base and emitter
W2 The length of the second depletion region between base and collector
WB The length of the base region =

12. Currents and voltage and symbols in circles BJT
IB Base current IE Emitter current IC Collector current
Always gather those three by relationship IE = IB + IC
VBE voltage between base & emitter VBC voltage between base & collector
VCE voltage between emitter & collector
Distribution in the two types npn و pnp
In electronic circuits for system method for contact transistor we need to know
Vin Input voltage Vout Output voltage
Rin Input resistance Rout Output resistance (often called load resistance RL ) =

13. Band Energy Description of BJT at equilibrium Conditions to npn & pnp
In the first figure
in equilibrium condition for npn,
the second figure for pnp
In two figures, we notice
Fermi level stability along
across emitter, base &
collector.
It must be recalled that the contact
potential between emitter and base junction higher than the contact
potential between , base and
collector junction . This is because impurities in emitter higher than impurities in base
and collector. = E C B P n+ n Ec Ef Ev P+ P n

14. forward bias reverse bias
Band Energy Description of BJT at non equilibrium Conditions to npn & pnp
In the first figure in non
equilibrium condition
for npn, the second
figure for pnp
In two figures, we notice
Fermi level variable along
across emitter, base &
Collector duo to forward
and reverse bias.
We will see in detail what is
happening in the diffusion of electrons
and holes and also the recombination
process in BJT in the next topics. = Ec Ev E C B P n+ n Ef
forward bias reverse bias P P+ n

15. Modes of Operation for BJT
We saw that in equilibrium condition there will be two case of the forward and reverse bias. thus there will be four modes of operation BJT (we will only mention now)
Active mode :
The forward bias in base & emitter junction. The reverse bias in base & collector junction.( which often we will take about)
Saturation mode :
The forward bias in two junctions. the transistor in this case be a maximum connection status and operates as if it is closed switch in a circle
Cut – off mode :
The reverse bias in two junctions. the transistor in this case only leaking current passes in circle and operates as if it is open switch in a circle
Inverted mode :
The reverse bias in base & emitter junction. The forward bias in base & collector junction

16. Bipolar junction transistor
What happens inside transistor
At the beginning, we deal with Active mode and base common configuration to npn. We notice that in forward bias between base & emitter junction, the length of the depletion region W1 is small unlike the length of the depletion region between base & collector junction W2 is big. Also, we care about the thickness of base WB is small.
At base & emitter junction (np), the diffusion of electrons from emitter to base and opposite for the diffusion of hole from base to emitter. If the thickness of base WB is small, the diffusion of electrons from emitter to base complete its way to collector = - + W1 W2

17. What happens inside transistor
At the beginning ,electrons inject in emitter then diffuse to base and part of electrons recombine with holes. In return, holes inject in base then diffuse to emitter which know base current. However, we must remember that the emitter and base junction n+p has more impurities in emitter therefore most junction current in forward bias will be from electrons (electronic current). As we mentioned earlier, if the thickness of base is small, electronic current will not be able to recombine with all majority carrier (holes) in base. =

18. What happens inside transistor
Thus, most electronic current will withdraw or diffused to base and collector junction pn (also, reverse voltage effects in diffusion process which lead to the fall of electrons in energy well). This is followed by the appearance of equivalent region inside base as we move away from two junctions region toward the center, if concentration of impurities’ injection regular, the base region will be free of electronic field and charge carrier will be driven by diffusion power.
Also, base current IB creates from recombination some of electrons which inject with holes in base region (IB considers of most important current). In addition, there are small weak currents such as reverse leakage current Icp of thoes in base and collector junction . =

19. what happen inside transistor
Also, from the figure we should know
IEn Total electronic current emit from emitter
ICn Residual part of total electronic current emit from emitter and collect in collector
IEn - Icn Residual part of total electronic current emit from emitter and flow in base as recombination current
IEp hole current at base current and it creates from holes inject in base to emitter
Icp hole current as reverse leakage current direction from collector to base =

20. Transistor parameters
Previously we mentioned that WB the thickness of base plays very important role in efficiency transistor ( two possibilities)
1- WB ≈ Ln or Lp (The diffusion length of electron and hole depending on the type of transistor npn or pnp, respectively ) is small, as we mentioned early, so a few amount of charge carrier recombine with other type of carrier . Thus, efficiency transistor increases, in addition to injection of emitter from a number of charge carrier to base so it requires(high doping of emitter as n+ or p+ ) =

21. Transistor parameters
2 - WB >>Ln or Lp (The diffusion length of electron and hole depending on the type of transistor npn or pnp, respectively ), the thickness of base is big.
Therefore, any charge carrier which inject from emitter to base will recombine with other type of carrier in base before going to collector . Thus, the only current in base and collector junction is reverse leakage current or reverse saturation current ICBO and no passing of other current in base and collector junction and become two open circles

22. How amplification occurs in the transistor
Here also, we deal with npn type and active mode but we now use emitter common configuration . When hole current enters from base, potential reduce between emitter and base (forward bias). If WB the thickness of base is small, we will assume that % 1 of electronic current recombine with hole current in base and 99% of electronic current go toward collector
Therefore, output current from collector IC
almost 99% higher from base current IB
Thus, we can say when a small amount of
current enters of IB , it will create high
current of IE also of IC because most
electronic current go from emitter to
collector. We can say IE ≈ IC =

23. Calculation gain coefficient β and α
Gain coefficient α when base common configuration & gain coefficient β when common emitter configuration .
We start with gain coefficient β when common emitter configuration , so when we discussed about amplification in this configuration, we mentioned how base current effect on emitter current. thus, gain coefficient β is ratio between collector current &base current
When we assume that few recombination in base duo to its small thickness so IE ≈ IC
Here emitter current proportional with emitter doping and base current proportional with base doping. therefore, gain coefficient β equal to is ratio between collector doping & base doping
Here also efficiency transistor depend on gain coefficient , so when gain coefficient is big , the efficiency transistor is increases

24. Calculation gain coefficient β and α
Gain coefficient α when base common configuration & gain coefficient β when common emitter configuration.
However, the Gain coefficient α when base common configuration equal to is ratio between collector current & emitter current
We can find relation between gain coefficient β & gain coefficient α Or

25. Calculation gain coefficient β
In the diode, we derive diffusion current density for excess of minority - carriers of electrons and holes
Since transistor is as two diodes, diode’s calculation will be the same for transistor’s calculation . current density equal to current per area (the area is the same for 3 part) therefore, for npn
And when assume base thickness is small (WB ≈ Ln ) also from previously relation
By substitute in gain coefficient
this relation is approximately =

26. Calculation gain coefficient β
Final approximately relation for gain coefficient β in npn is
Where is time of minority – carriers life in base
And is time of transit electrons to base =

27. Calculation Emitter Efficiency coefficient γ
It know as ratio between electronic current (npn) which injection from emitter and total current
Since total current is , therefore:
In transistor of n+p n type , so IEp < IEn . therefore =

28. The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits
Previously, we discussed about gain coefficient α and β to two of common base configuration & common emitter configuration , respectively. In two cases the equation was
Here, we will calculate voltage, current and power gains Av , Ai & Ap respectively for the three common configurations in addition to the characteristics of their circuits.
In the three circuits, we will focus at active mode . Aslo, we must remember the equation
IE = IB + IC =

29. emitter common configuration
The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits
emitter common configuration
This circuit is the most important and used in
amplifiers for transistor
input current is base current & output
current is collector current
input voltage is Vin & output voltage is Vout .
the output signal opposite to input signal ,mean Out of phase with 180o , so it is Inverting Amplifier circuit
input resistance Rin is lower duo to forward bias & output resistance RL is higher duo to reverse bias
Current gain is
Voltage gain is
The gain in this circuit less than base common configuration
power gain is

30. base common configuration
The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits
base common configuration
input current is emitter current & output
current is collector current
input voltage is Vin & output voltage is Vout .
the output signal the same to input signal ,mean In of phase , so it is non inverting Amplifier circuit
the ratio between output resistance RL &input resistance Rin is higher
Current gain is
In most case approximate value is one and IB is small, thus IE ≈ IC
Voltage gain is
power gain is

31. collector common configuration
The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits
collector common configuration
input current is base current & output
current is emitter current
input voltage is Vin & output voltage is Vout .
the output signal the same to input signal ,mean In of phase , so it is non inverting Amplifier circuit
input resistance Rin is higher & output resistance RL is lower
in the circuit input voltage contact direct to base while output voltage is taken from load resistance
Current gain is
Voltage gain is
Always is less than one duo to
power gain is

32. The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits
Characteristic
Common
Base
Emitter
Collector
Input Impedance
Low
Medium
High
Output Impedance
Very High
Phase Angle 0o
180o
Voltage Gain
Current Gain
Power Gain

33. I – V Characteristic of BJT
In chapter two, we study I – V Characteristic of diode in lecture and Lab, so we know about proportional relation in addition to load line. Also, in this chapter we will study I – V Characteristic of BJT and its calculation and duo to different contact methods, there will be different curves , however, the relation always proportional
I – V Characteristic emitter common I – V Characteristic base common

34. I – V Characteristic of BJT in emitter common configuration and load line
we will deal with emitter common configuration to see
relation between IC & VCE
1- we notice that IC increases rapidly by change VCE
at beginning in region called Saturation Region. Than,
The increase becomes very slow unnoticed which
consider as constant in region called
Amplification Region or Active Region.
2- when we change IB , IC will also change
duo to input voltage (means that IC
control by IB)
3- the third region called Cut Off Region
which is region under current value IB =0

35. I – V Characteristic of BJT in emitter common configuration and load line
4 - load line will cut y- axis at Saturation point (S –point) and x- axis at cut off point (C –point)
5- at operation point (Q- point) cut of load line with I – V Characteristic
load line equation
6- from equation and figure, we notice
cut off point when IB =0 & IC =0 thus
VCE = VCC
Saturation point when VCE =0 thus
The mean operation point is )

36. I – V Characteristic of BJT and his job as Switch
we can describe job’s BJT as switch
1- Saturation Region:
which represent an close switch (Fully-ON)
input voltage and base contact with VCC
VBE > 0.7V
the maxim value of collector current
The two junction at forward bias
ideal Saturation at VCE =0

37. I – V Characteristic of BJT and his job as Switch
we can describe job’s BJT as switch
2- Cut Off Region :
which represent an open switch (Fully-OFF)
input voltage and base contact with
grounded 0V
VBE < 0.7V
The two junction at reverse bias
There no current flow to collector
IC = 0

38. Finding minority carrier distributions & terminal currents in BJT
we deal with active mode and base common configuration to npn . At the beginning and to make calculation ease, we assume the following :
1- the thickness of base WB is small, therefore, the diffusion here for electronic current from emitter to collector . In addition, we neglects drift current at base.
2- emitter efficiency γ ≈ 1 because emitter current is only electronic current
3- reverse leakage current or reverse saturation current is neglected
4- the action part in base and two
junctions have regular section area
and electronic current move in one
direction or one dimension which is x
5- all currents and voltages are stable A
VEB
VCB WB xp n p
ΔnE
ΔnC

39. First: the solution of diffusion equation in the base region in BJT
we deal with active mode and base common configuration to npn . Previously, we study about a excess of minority -carriers of electrons concentration in p-type in base region.
Electronic current enter to base from emitter, also come out from base to collector.
To calculate excess of electrons to two end-sides of base at two depletion regions from emitter side and collector side to obtain :
excess of electrons concentration from
end-side depletion regions of emitter
end-side depletion regions of collector A
VEB
VCB WB xp n p
ΔnE
ΔnC

40. First: the solution of diffusion equation in the base region in BJT
If we assume that emitter & base junction has strong forward bias which means
and base & collector junction has strong reverse bias which means
, we will obtain
We mentioned before of minority carrier diffusion equations which is quadratic equation, hence the solution are
Where Ln the diffusion length of minority
carrier electron . We must remember that
thickness of base is small which means that
WB ≤ Ln to move all electronic current from
emitter to collector. A
VEB
VCB WB xp n p
ΔnE
ΔnC

41. First: the solution of diffusion equation in the base region in BJT
Finding constants C with boundary conditions at the two end-sides of base
When multiply the first equation with , we obtain
And collected with second equation to obtain C1
by substituting in the first equation to obtain C2

42. First: the solution of diffusion equation in the base region in BJT
by substituting with constants C in
we mentioned that high reverse voltage to obtain
We can write equation in this from
where

43. First: the solution of diffusion equation in the base region in BJT
the figure shows the distribution of minority carriers in the base also in the emitter and collector
where δn
ΔnE
M1ΔnE
M2ΔnE

44. Second: Evaluation Values of Terminal Currents in BJT
We will find current by known current density to two end-sides of base
At driven excess of electron in base reign in p-type respect of xp
This driven at borders of depletion region from emitter
Therefore, electronic emitter current
by substituting in constants
since the
So emitter current

45. Second: Evaluation Values of Terminal Currents in BJT
This derivation at the borders of the depletion region from collector side
Therefore, collector current is
By substituting in constants

46. Second: Evaluation Values of Terminal Currents in BJT
Finally, we can find base current from emitter and collector currents
When taking into consideration , we obtain threse approximate value

47. minority carrier distributions for modes of operation for BJT for npn
Active mode: the figure shows the distribution of minority carriers in the base also in the emitter and collector in active mode

48. minority carrier distributions for modes of operation for BJT for npn
Saturation mode: the figure shows the distribution of minority carriers in the base also in the emitter and collector in saturation mode

49. minority carrier distributions for modes of operation for BJT for npn
Cut - off mode the figure shows the distribution of minority carriers in the base also in the emitter and collector in cut off mode

50. minority carrier distributions for modes of operation for BJT for npn
Inverted mode :the figure shows the distribution of minority carriers in the base also in the emitter and collector in inverted mode