692
24 Transistors
(a)
(b)
emitter
base
collector
Fig. 24.1 a Schematic image of a vacuum triode. The electron current flows from the heated cathode to the anode when
the latter is at a positive potential. The flow of electrons is controlled with the grid voltage. b Bell Laboratories’ first
(experimental) transistor, 1947
(a)
(b)
Fig. 24.2 a First commercial, developmental (point contact) transistor from BTL (Bell Telephone Laboratories) with
access holes for adjustment of the whiskers pressing on a piece of Ge, diameter 7/32"=5 mm, 1948. b First highperformance silicon transistor (npn mesa technology), model 2N697 from Fairchild Semiconductor, 1958 (at $200, in
1960 $28.50). The product number is still in use (now $ 0.95)
(a)
p
++
n
+
p
I E
I C
I B
emitter
collector
base
(b)
n
++
p
+
n
I E
I C
I B
emitter
collector
base
Fig. 24.3 Schematic structure and circuit symbol for a pnp and b npn transistors
important point is that the base is sufficiently thin (in relation to its minority carrier diffusion length)
and carriers from the emitter (which are minority carriers in the base) can dominantly reach the collector
by diffusion.
In Fig. 24.4, the three basic circuits with a transistor are shown. They are classified by the common
contact for the input and output circuit. The space charges and band diagram for a pnp transistor in the
base circuit configuration are depicted in Fig. 24.5. The emitter–base diode is switched in the forward
direction to inject electrons into the base. The base–collector diode is switched in the reverse direction.
The electrons that diffuse through the base and reach the neutral region of the collector were transported
by the high drift field away from the base.
24 Transistors
(a)
(b)
emitter
base
collector
Fig. 24.1 a Schematic image of a vacuum triode. The electron current flows from the heated cathode to the anode when
the latter is at a positive potential. The flow of electrons is controlled with the grid voltage. b Bell Laboratories’ first
(experimental) transistor, 1947
(a)
(b)
Fig. 24.2 a First commercial, developmental (point contact) transistor from BTL (Bell Telephone Laboratories) with
access holes for adjustment of the whiskers pressing on a piece of Ge, diameter 7/32"=5 mm, 1948. b First highperformance silicon transistor (npn mesa technology), model 2N697 from Fairchild Semiconductor, 1958 (at $200, in
1960 $28.50). The product number is still in use (now $ 0.95)
(a)
p
++
n
+
p
I E
I C
I B
emitter
collector
base
(b)
n
++
p
+
n
I E
I C
I B
emitter
collector
base
Fig. 24.3 Schematic structure and circuit symbol for a pnp and b npn transistors
important point is that the base is sufficiently thin (in relation to its minority carrier diffusion length)
and carriers from the emitter (which are minority carriers in the base) can dominantly reach the collector
by diffusion.
In Fig. 24.4, the three basic circuits with a transistor are shown. They are classified by the common
contact for the input and output circuit. The space charges and band diagram for a pnp transistor in the
base circuit configuration are depicted in Fig. 24.5. The emitter–base diode is switched in the forward
direction to inject electrons into the base. The base–collector diode is switched in the reverse direction.
The electrons that diffuse through the base and reach the neutral region of the collector were transported
by the high drift field away from the base.